SEWAGE SLUDGE 2/1/02 17:27 Pagina 3

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European Commission 4KH-17-01-003-EN-N 14

Disposal and recycling routes for sewage sludge Part 3 – Scientific and technical report

OFFICE FOR OFFICIAL PUBLICATIONS OF THE EUROPEAN COMMUNITIES

L-2985 Luxembourg ISBN 92-894-1800-1

See our publications catalogue at: http://europa.eu.int/comm/environment/pubs/home.htm

Compuesta A great deal of additional information on the European Union is available on the Internet. It can be accessed through the Europa server (http://europa.eu.int).

Luxembourg: Office for Official Publications of the European Communities, 2001

ISBN 92-894-1800-1

© European Communities, 2001 Reproduction is authorised provided the source is acknowledged. (QYLURQPHQW

'LVSRVDODQG5HF\FOLQJ5RXWHV IRU6HZDJH6OXGJH Scientific and technical sub-component report 23 October, 2001

European Commission DG Environment – B/2  7DEOHRI&RQWHQWV /,672)7$%/(6  /,672)),*85(6   (;(&87,9(6800$5<   2%-(&7,9(62)7+(6&,(17,),&$1'7(&+1,&$/3$57   :+$7,66/8'*("   :KDWLVVOXGJH"   6OXGJHW\SHV  3.2.1 Pre-treatment 20 3.2.2 Primary sludge 20 3.2.3 Secondary sludge 20 3.2.4 Mixed sludge 21 3.2.5 Tertiary sludge 21 3.2.6 Digested sludge 21  ,QIOXHQFHRIWKHZDWHUWUHDWPHQWRQWKHFRPSRVLWLRQRIWKHVOXGJH   &RPSRVLWLRQ  3.4.1 Organic matter 23 3.4.2 Nitrogen and phosphorus content 24 3.4.3 Calcium enrichment 26 3.4.4 Other compounds of agricultural value 26 3.4.5 Heavy metals 26 3.4.6 Organic pollutants 27 3.4.7 Pathogens 28  ,QGXVWULDOVOXGJH  3.5.1 Pulp and paper industry 28 3.5.2 Tannery Sludge 29  6/8'*(75($70(17352&(66(6   &RQGLWLRQLQJ   7KLFNHQLQJ   'HZDWHULQJ   'U\LQJ   6WDELOLVDWLRQDQGGLVLQIHFWLRQ   5(&<&/,1*$1'',6326$/5287(6)256(:$*(6/8'*(   /DQGVSUHDGLQJ  5.1.1 Technical description 47 5.1.2 Impacts and benefits 48  ,QFLQHUDWLRQ  5.2.1 Technical description 49 5.2.2 Impacts and benefits 51  /DQGILOOLQJ  5.3.1 Technical description 54 5.3.2 Impacts and benefits 55  2WKHUURXWHV  5.4.1 Use in forestry and silviculture 57 5.4.2 Land reclamation and revegetation 60  'HYHORSLQJWHFKQRORJLHV  5.5.1 Wet oxidation 61 5.5.2 Pyrolysis 63

 5.5.3 Gasification 65  /LWHUDWXUHUHYLHZ  5.6.1 LCA for the ARA Region Bern, Switzerland 66 5.6.2 LCA for the City of Bremen, Germany 66 5.6.3 LCA for the French Water Agencies, France 67  75$16)(5352&(66(6   +HDY\PHWDOV  6.1.1 Behaviour in soil 71 6.1.2 Transfer to water 76 6.1.3 Uptake by plants 77 6.1.4 Uptake by livestock 82 6.1.5 Human exposure 84 6.1.6 Conclusion on heavy metals transfers in food chain 86  2UJDQLFSROOXWDQWV  6.2.1 Behaviour in soil 88 6.2.2 Transfer to water 92 6.2.3 Uptake by plants 93 6.2.4 Uptake by livestock 93 6.2.5 Conclusion and human exposure 94  3DWKRJHQV  6.3.1 Origin in sludge 95 6.3.2 Behaviour in soil 96 6.3.3 Water contamination 98 6.3.4 Survival on plants 98 6.3.5 Pathogens transfers to animals and to natural ecosystems 99 6.3.6 Human exposure 99 6.3.7 Conclusion 100  6SHFLILFHPLVVLRQVIURPLQFLQHUDWLRQDQGODQGILOOLQJ  6.4.1 Halogens and derived acids 102 6.4.2 SO2 102 6.4.3 NOx 103 6.4.4 Particulate matter 103 6.4.5 Other Gases 104  02'(//,1*2)32//87$1775$16)(56   2EMHFWLYHVRIWKHPRGHO   0RGHOSUHVHQWDWLRQ  7.2.1 Assumptions made 108 7.2.2 Equations used 110  5HVXOWVDQGGLVFXVVLRQ  7.3.1 Results 113 7.3.2 Influence of sludge composition and transfer phenomena 119 7.3.3 Limits and evolution of the model 121 7.3.4 Sensitivity analysis 121  *$36,1.12:/('*($1'*22'35$&7,&(6   *DSVLQNQRZOHGJH   *RRGSUDFWLFHV  */266$5<  $33(1',; 

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2EMHFWLYHRIWKHUHSRUW This report aims to describe sewage sludge production, composition, treatment and disposal or recycling, as well as to review scientific evidence regarding the migration and accumulation of substances and elements contained in sludge into the environment and the food chain, and to identify the associated risks. It focuses in particular on the recycling routes.

6OXGJHFRPSRVLWLRQDQGWUHDWPHQW Sludge is composed of by-products collected at different stages of the wastewater treatment process. It contains both compounds of agricultural value (including organic matter, nitrogen, phosphorus and potassium, and to a lesser extent, calcium, sulphur and magnesium), and pollutants which usually consist of heavy metals, organic pollutants and pathogens. The characteristics of sludge depend on the original pollution load of the treated water, and also on the technical characteristics of the waste water and sludge treatments carried out. Sludge is usually treated before disposal or recycling in order to reduce its water content, its fermentation propensity or the presence of pathogens. Several treatment processes exist, such as thickening, dewatering, stabilisation and disinfection, and thermal drying. The sludge may undergo one or several treatments.

6OXGJHUHF\FOLQJRUGLVSRVDOURXWHV Once treated, sludge can be recycled or disposed of using three main routes: recycling to agriculture (landspreading), incineration or landfilling. Other, less developped outlets exist, such as silviculture, land reclamation, and other developing combustion technologies including wet oxidation, pyrolysis and gasification. Each recycling or disposal route has specific inputs, outputs and impacts.

Landspreading Landspreading of sludge or sludge-derived material partially replaces the use of conventional fertilisers, since it contains compounds of agricultural value. It also contains organic matter, although under a form and at a level below that which would have a significant positive impact on soil physical properties. Composted sludge however presents a more stable organic matter due to the addition of a vegetal co-product during the process. However, landspreading also involves the application of the pollutants contained in sludge to the soil. These pollutants undergo different transformations or transfer processes. These processes include leaching to groundwater, runoff, microbial transformation, plant uptake and volatilisation and enable transfer of the compounds into the air and water, and their subsequent introduction into the food chain. Therefore outputs of sludge recycling consist of yield improvement, but also of emissions of pollution into the soil, and indirect emissions into air and water. Other emissions into the air include exhaust gases from transportation and application vehicles.

 Incineration Incineration is a combustion reaction. Different techniques are currently performed, classified between mono-incineration when sludge is incinerated in dedicated incineration plants, incineration with other wastes, or co-incineration when sludge is used as fuel in energy or material production. Other technologies are also being developed such as wet oxidation or pyrolysis. Outputs are flue gases, ashes, and wastewater, as well as the production of energy. Therefore incineration generates emissions into the air (particles, acid gases, greenhouse gases, heavy metals, volatile organic compounds, etc.), soil (disposal of ashes and flue gas treatment residues to landfill, atmospheric deposition of air emissions) and water (flue gas treatment wet processes). Emissions into the air may be reduced thanks to flue gas treatment. Emissions depend on the process, but are also influenced by the sludge type. Energy production generally counterbalances the energy needs for sludge drying. Operation of an incineration plant may also produce noise, dust, odour and visual pollution.

Landfilling There are two possibilities in terms of sludge landfilling: mono-deposits, where only sludge is disposed of, and mixed-deposits (most commonly observed), when the landfill is also used for municipal wastes. The inputs of landfilling are the waste and additional resources required for the operation of the landfill site, such as fuel for vehicles, electricity, and additional materials when leachate is treated on-site. Outputs consist of leachate, landfill gas and energy production when the gas is recovered. Landfill operation therefore generates emissions into the air (mainly greenhouse gases like methane and carbon dioxide, reduced when biogases are collected and burnt), and into the soil and water at dumpsites (various compounds such as ions, heavy metals, organic compounds and micro- organisms in leachate). The operation of a landfill also generates other impacts in terms of noise and dust from the delivery vehicles, as well as odours, land use, disturbance of vegetation and the landscape.

Other routes Other sewage sludge recycling routes presently used in Europe include the use of sludge in forestry and silviculture or in land reclamation. )RUHVWU\DQGVLOYLFXOWXUH refer to different kinds of tree plantation and use. The term forestry is mainly used when considering amenity forests, or mature forest exploitation. On the contrary, silviculture is more specifically used when referring to intensive production. From the agricultural and environmental point of view, differences exist in terms of the impact of landspreading as compared to the use of sludge in forestry, relating to such factors as the plant species grown, the fauna and flora involved, and the soil types. Agronomic benefits are increased tree growth and the provision of nutrients to the soil. However, competition with weeds, especially in young plantations may be observed. Excessive rates of sludge application may also lead to degradation of the upper layer of the soil and the humus, as well as nitrogen leaching to groundwater. The use of sludge in a forest environment may cause an alteration in the characteristics of the ecosystem and, in the case of a mature forest where there is no need to have an additional input of nutrients, may disturb the natural biotopes. More research is however needed on this issue. When considering the risks to humans associated with the presence of heavy metals in sludge, it is assumed that these are lower than those associated with spreading on agricultural land, as forest products represent only a very small part of the human diet. However, some risks may still exist due to the transfer of heavy metals to game or edible mushroom species, and in a general manner to wild fauna and flora.

 After identifying gaps in knowledge, some recommendations are given in this report concerning sludge application in forest or tree plantations. Use of sewage sludge in ODQG UHFODPDWLRQ DQG UHYHJHWDWLRQ aims to restore derelict land or protect soil from erosion through soil provision and increased vegetal covering. In the case of industrial sites, topsoil may often be absent or if present, damaged by storage or handling. Soil or soil forming materials on site may be deficient in nutrients and organic matter. Other problems may exist, such as toxicity, or adverse pH levels. All these problems create a hostile environment for the development of vegetation. Possible solutions include the use of inorganic fertilisers or imported topsoil, which can be very expensive depending on location and availability. An alternative solution is the use of organic wastes such as sewage sludge, which is already performed in Sweden, Finland, Germany and the United Kingdom. Sludge application takes place using the same machinery as in recycling to agriculture. Some specific machinery for sludge projection may be needed when applying sludge in areas where access is difficult. It was assumed that risks are lower than in the case of spreading on agricultural land, when its use is not related to food production. However, no data is available concerning the potential impacts on wild fauna and flora. Moreover, the amount of sludge applied as well as the application of sludge to sloping land to reduce erosion go against current regulatory prescriptions for the use of sludge in agriculture, inducing risks in terms of pollutants application.

Developing technologies Several technologies presenting an alternative to conventional combustion processes are currently being developed or introduced onto the market. These technologies mainly include by the wet oxidation process, pyrolysis, and the gasification process. Other technologies may be found, which are most often combinations of these three main processes. These technologies present advantages in terms of flue gas and ash treatment. Moreover, they also seem to have reduced impacts on the environment compared to conventional combustion processes.

3ROOXWDQWVWUDQVIHU A review of current scientific knowledge concerning pollutants transfer mechanisms in the different environment media and the food chain has been carried out in order to assess the possible impacts on the environment and human health. Each route has specific transfer processes, but transfers relating to landspreading covers most of the significant transfers relating to the other routes, with the exception of air emissions.

Heavy metals The presence of numerous metals in soil and sludge has been reported in the literature. Once applied to the VRLOtheyare distributed between the different soil media. Scientific evidence shows that they accumulate in the upper layers of the soil, due to binding to the different existing organic or mineral particles. Their mobility and biovailability to plants and micro-organisms may be influenced by several factors of which the pH level of the soil is the most important. Heavy metals are naturally present in soil at varying levels, and may originate from several anthropogenic sources such as fertilisers, animal manure, sludge, or atmospheric deposition. However, variety in the metal levels in European soils may also be due to the diversity of the extracting methods used rather than differences in the field. In order to ensure the quality of the comparisons, a harmonisation of the sampling and measurement methods would be required.

 Micro-organisms species present in the soil are numerous. Some of them are important for soil fertility and therefore for agricultural production. Concern has been expressed about the consequences of metal provision to the soil on the micro-organisms population and biodiversity. Available scientific literature shows contradictory results, depending on the species taken into consideration, the local conditions of the experiments, and the confusion of short-term laboratory experiments with long-term field trials. Some authors mentioned the ability of microbial populations to adapt to changing conditions, which may be considered a result of negative pressure on the population. On the basis of long-term field trials, some studies concluded that soil micro- organisms’ diversity and population could be negatively affected by sludge-borne metals in the long-term, and by metal levels in soil which were in some cases below current regulatory prescriptions. It must also be stressed that microbial activity indicators must not be used as the only indicators of microbial reaction to metal application, as they do not reflect changes in population structure. /HDFKLQJWRJURXQGZDWHUappears to be a negligible phenomenon. On the contrary, UXQRII, when it occurs, may play a significant role in metal transfer. Its importance depends greatly on the local situation, and the fate of metals needs to be further documented. 3ODQWXSWDNHoccurs for all heavy metals and is described by transfer factors. Some metals (e.g. copper and zinc) are of biological importance for the plant. It has been observed that heavy metals are concentrated in the roots and vegetative parts of plants and are less present in the generative parts such as wheat grain. Uptake will increase with increasing metal levels in soil, but only applies to the bioavailable part of the metals present in soil. However there may be no direct relation between total metal concentration and bioavailable metals in soil. pH is the most important factor influencing metal uptake. In particular, a decrease in the pH value in soil in the range of pH 7 to pH 4 causes an increase in the uptake of Cd, Ni and Zn. The same effect is observed for Cu, but is less marked. Lastly, when considering usual acidity levels in agricultural soils, a pH decrease had no observed effect on Pb and Cr uptake. This information supports the setting of different limit values for Cd, Ni and Zn, and possibly for Cu, for soil with pH values of between 5 and 7 as well as for soil with pH values of higher than 7. Sludge spreading should also be avoided on soil with a pH value below 5 and limit values should refer to the bioavailable part of metals in soil rather than to the total concentration, although it is not possible at the moment to define for all heavy metals what is the bioavailable fraction. 8SWDNH of metals by animals occurs through contaminated plant consumption or soil ingestion. However little information is available concerning metal quantities ingested and absorbed and their subsequent toxicity levels to animals. Metals do not seem to accumulate in meat. More focus is needed concerning possible Pb and Cd transfer to offal, as in some cases this could lead to levels nearing acceptable limits in foodstuffs. Transfer of Pb and Cd across the placenta and into the milk was observed during indoor feeding trials, but there are likely to be few practical consequences for finished animals. Concentration of Cu in the milk was not influenced by the ingestion of sludge- amended soil. A quantitative assessment of this contamination pathway is not available at the present time. In a general manner, KXPDQH[SRVXUHWRKHDY\PHWDOVmay be attributed to several sources and depends on many factors such as diet, actual absorption, and food processing. Consumption of contaminated crops appears to be the main means of exposure to sludge-borne metals. It is assumed that the specific contribution of sludge-borne metals to the human diet is very low, when taking into account the observed level of metals present in soil, and considering the surface area over which sludge spreading takes place.

Organic pollutants Numerous organic compounds are present in sludge. Once applied to the land, they are distributed throughout all soil media and undergo several retention and transport processes. They are

 physically, chemically and biologically transformed in other intermediary compounds during their mineralisation, for which no data is presently available. The degradation pathway of the organic compounds and thus the duration before reaching negligible concentration in soils may greatly depend on the aerobic or anaerobic degradation conditions. /HDFKLQJ RI RUJDQLF SROOXWDQWV to ground water appears to be insignificant but, unlike metals, cannot be neglected in some cases. The importance of this mechanism depends on the properties of the compounds and the soil. It appears on the one hand that many compounds present short half-life values, reducing the risk of leaching to groundwater. On the other hand, persistent compounds such as PCDD/Fs or PCBs show an affinity with soil particles and will therefore bind to soil rather than leach to ground water. 5XQRII, when it occurs, may play an important role in the transfer of organic compounds. Even if definitive evidence is lacking, it appears that soil PLFURRUJDQLVPV are not affected by sludge-borne organic pollutants in most cases and that they are able to adapt to changing conditions. Most organic pollutants are QRWWDNHQXSE\ SODQWV. However, a risk of contamination of the food chain exists when spreading sludge directly onto crops, especially on plants which are to be consumed raw or semi-cooked. Soil and sludge ingestion on land used for grazing is the main route for DQLPDO contamination. Accumulation of bioaccumulative compounds such as PCDD/Fs, PCBs or PAHs may occur in meat and milk. However, it is presently not possible to assess the quantities and fates of organic compounds ingested by animals. It appears that the consumption of animal products is the major source of KXPDQ exposure to sludge-borne organic pollutants, due to the ingestion of soil by livestock. As in the case of heavy metals, it is assumed that the specific contribution of sludge-borne organic pollutants to the human diet is very low, when considering the reduced proportion of the utilised agricultural area onto which sludge spreading takes place. Lastly, it should be noted that at the present time no universally accepted and validated analytical method exists for analysing most organic compounds. There is also a lack of data concerning levels of organic pollutants in European sewage sludge as no regular survey has been performed in the past. Therefore, considering presently available knowledge on organic compounds, it appears at the present time, that: - transfer to water is low, micro-organisms adapt to changing conditions in soil, and numerous organic compounds are rapidly degraded in soil. Attention should therefore mainly be given to compounds with higher half-life time values, - from the point of view of crop protection, no limit value seems to be necessary as transfers to plant do not occur for most organic compounds, - restrictions should focus on bio-accumulative compounds spread on grazing land such as PCBs and PCDD/Fs. In this case deep injection of sludge could reduce the risk of livestock contamination by organic pollutants, - a survey of organic pollutant levels in sludge should be performed by sludge producers, focusing on the specific organic pollutants identified within the waste water catchment area of the WWTP.

Pathogens There are five main types of pathogens observed in sludge: bacteria, viruses, fungi and yeast, parasitic worms, and protozoa. Humans and animals are sensitive to some of these organisms, which may cause numerous pathologies ranging from simple digestion troubles to lethal infections.

 Sludge-borne pathogens are mainly present on the VRLO surface or at shallow depths where sludge has been ploughed into the soil. Pathogen penetration depends on the effective depth of the soil, its texture (particularly its clay content), its organic matter content and also on possible cracks, prolonged drought, faults or absence of vegetation. Survival of pathogens in soil depends on numerous direct or indirect factors. Indirect factors are climatic factors such as sunlight, temperature, desiccation or pH, characteristics of the soil (texture, moisture etc.), quantity of sludge spread, the pathogen content of the sludge, its organic content and the eventual presence of competing organisms. Direct factors are related to the biological characteristics of the pathogen, and especially to the form under which it may survive. Parasites’ eggs or cysts are the longest survivors – one to two years in certain favourable circumstances. Depending on the conditions and the organisms themselves, survival periods may vary from a few days to several years. The pathogenic agent population decreases faster when the sludge is spread on the soil surface rather than when it is ploughed into it. Transfer to JURXQGZDWHU is only assumed to occur in some particular cases, while VXUIDFHZDWHU contamination is more likely to occur when runoff water transports pathogens which are bound to soil particles. Survival on SODQWV is shorter than in soil, due to the effects of desiccation and sunlight. Transmission to grazing GRPHVWLF DQG IDUP DQLPDOV takes place via ingestion of contaminated feed and soil. +XPDQV can mainly be affected by consuming raw or semi-cooked contaminated vegetables or meat. Therefore the risks of sewage sludge application onto the land – that may be addressed by good practices – have to be taken into account as pathogens are present in sludge and may have significant impacts on humans and animals. In general, deep injection or ploughing down may be recommended during or after sludge application. Although those practices reduce the deleterious effect of weather on micro-organisms, contact with animals, wildlife and humans as well as dissemination into the environment will be reduced. Sewage sludge may also contain plant pathogens, as well as weed seeds. They mainly originate from washing of vegetable and fruit, or from road or roof runoff after aerial deposition. Plant pathogens have in general low optimum growth temperature, so that disinfection will be achieved at a lower temperature than for mammalian pathogens.

3ROOXWDQWVWUDQVIHUPRGHOOLQJ Based on the description of the transfer mechanisms of different sludge-borne pollutants in the environment, a PRGHO was developed in order to assess: - the transfer of pollutants in soil (in particular due to runoff and leaching), - the transfer of pollutants to plants in order to make a comparison with limit values in foodstuffs, - the accumulation of pollutants in the soil, - the time before reaching a given limit value of pollutants in soil. 2QO\KHDY\PHWDOVDUHWDNHQLQWRFRQVLGHUDWLRQ. Knowledge concerning organic pollutants does not enable accurate calculations to be made as very little is known about their behaviour and degradation pathways in soils (moreover, it appears that organic pollutant transfer to plants is negligible and that this particular route should not involve a significant human health risk). It is not relevant to apply such calculations to pathogens. 7ZR VFHQDULRV DUH H[DPLQHG ZKLFK UHSUHVHQW WZR H[WUHPH VLWXDWLRQV RI ORZ DQG KLJK DFFXPXODWLRQ. Several assumptions were necessary in order to perform the calculation. 7KHUHIRUH

 WKH UHVXOWV DUH LQGLFDWLYH YDOXHV DQG DUH QRW VXSSRVHG WR EH XVHG QHLWKHU LQGLYLGXDOO\ RU ZLWKRXWLQGLFDWLQJWKHK\SRWKHVHVXVHG The main results can be summarised as follows: - on a one-year basis, it must be observed that pollutants brought to soil by sludge application represent a very low proportion of the amount of metals present in soil before sludge application; - plant uptake of sludge-borne metals may vary, but always represents a minor part of the amount of sludge-borne metals contained in soil; in the long-term, plant uptake will increase with increasing soil concentration ; - runoff is the main parameter in the model influencing the heavy metal accumulation in soil ; - global plant uptake of metals present in soil always remains below the limit values for foodstuffs. However, in the worst case, it may reach a significant proportion of these limit values; - on the contrary, uptake of metals originating only from sewage sludge application is very low, and reaches, in the worse case of our modelling, 1 % of the limit value for foodstuffs ; - an equilibrium may be reached after several years between plant uptake and sludge application, indicating that, in some cases, a limit value for metal levels in soil would never be reached ; - the number of years required before a limit value is reached for metal accumulation in soil would vary greatly between the two extreme cases considered herein: figures range from around 4,500 years to over 34,000 years in the case of low accumulation, and from 20 years to around 140 years in the high accumulation scenario.

*DSVLQNQRZOHGJH Today, many uncertainties remain concerning the transfer of pollutants (especially organic pollutants) to the environmental media and the food chain. Several issues would need to be more accurately documented. Amongst these issues, the following may be mentioned: - The importance of the runoff process in the pollutants’ transfer should be assessed. Mechanisms need to be understood, as well as quantities of pollutants concerned, and their fate. - An issue of concern is the degradation pathway of the organic compounds in soil. Compounds may be degraded into intermediary chemicals before total mineralisation. The toxicity and leaching potential of these metabolites is not well known. Lysimeter and field studies should be carried out. - Long-term impacts of heavy metals and organic pollutants, in particular on soil micro- organisms and fertility, are not well documented. - More data is needed concerning the ingestion and absorption levels of organic compounds and, to some extent, heavy metals by animals. - There is also a lack of knowledge concerning the specific contribution of sewage sludge to pollutants’ transfers. - A survey of the organic pollutants’ levels in sewage sludge should be performed in the Member States in order to gain an accurate appreciation of their occurrence. This may only be possible if standard analytical methods are set and broadly accepted. - Available literature does not always enable a comparison between the different countries, as no common research protocol and no trans-national study has been carried out. - More information is also needed concerning other routes for sludge recycling, such as land reclamation or use in forestry and silviculture. Research should be carried out to precisely identify the agricultural benefits of sewage sludge spreading and its environmental and sanitary

 impacts (especially concerning organic pollutants for which no data is currently available). Moreover, currently available information does not enable an assessment and comparison of the benefits and risk as regard the diversity of European forests. - Lastly, some interesting new technologies such as wet oxidation, pyrolysis or gasification have been developed. More information concerning their environmental impact and their application is needed. Tests have not always been carried out on sludge, and this issue requires further documentation.

  2EMHFWLYHVRIWKHVFLHQWLILFDQGWHFKQLFDOSDUW

The objective of this intermediary report is to review scientific evidence on the migration and accumulation of substances and elements contained in sludge into the environment and the food chain, and identify the associated risks. The present report aims to: - present the main waste water treatment technologies and their impact on sludge composition; - present the sewage sludge treatment processes and the different substances and elements present in sewage sludge; - identify the main routes for sludge disposal and recycling and describe their technological characteristics; - review current scientific knowledge on the main biophysical processes involved, flows of different elements of the sludge through the environmental media and the associated risks; - develop a simple model describing the flows and accumulations of pollutants in the environment. $V WKH WHFKQLFDO GHVFULSWLRQ RI LQFLQHUDWLRQ DQG ODQGILOOLQJ RI ZDVWHV DV ZHOO DV WKHLU HQYLURQPHQWDO DQG VDQLWDU\ LPSDFWV KDYH DOUHDG\ EHHQ H[WHQVLYHO\ GRFXPHQWHG HOVHZKHUH WKLVUHSRUWZLOOPDLQO\VXPPDULVHWKHDYDLODEOHFRQFOXVLRQVIRUWKRVHURXWHVDQGDGGUHVVWKH VSHFLILFLWLHVIRUVOXGJHLQFLQHUDWLRQDQGODQGILOOLQJLIDYDLODEOH2QWKHFRQWUDU\SDUWLFXODU DWWHQWLRQ KDV EHHQ JLYHQ WR WKH GHVFULSWLRQ RI WKH EHQHILWV DQG LPSDFWV RI VOXGJH XVH LQ DJULFXOWXUHDQGWKLVUHSRUWIRFXVHVHVSHFLDOO\RQWKHVHLVVXHV The different steps covered in this report are presented below:

Sludge Wastewater Water Sludge recycling Impacts collection treatment treatment and disposal

   :KDWLVVOXGJH"

 :KDWLVVOXGJH" Sludge is a by-product of the water clean up process. There are three main categories of sludge:

- sludge originating from the treatment of urban wastewater, consisting in domestic waste water or in the mixture of domestic waste water with industrial waste water and/or run-off rain water.

- sludge originating from the treatment of industrial wastewater, i.e. water used in industrial processes.

- sludge from drinking water treatment. Water has to be treated before its consumption. The amount of sludge generated from drinking water treatment is significantly lower than that generated from wastewater treatment.

The characteristics of sludge depend on the original pollution load of the treated water, and also on the technical characteristics of the treatment carried out. Water treatment concentrates the pollution present in water and therefore sludge contains a wide variety of matter, suspended or dissolved. Some compounds may be usefully reused (organic matter, nitrogen, phosphorus, potassium, calcium, etc.) whereas other compounds are pollutants (such as heavy metals, organic pollutants, and pathogens).

 6OXGJHW\SHV

Sludge Wastewater Water Sludge recycling Impacts collection treatment treatment and disposal

Sludge from conventional wastewater treatment plants (WWTP) is derived from primary, secondary and tertiary treatment processes. Most often, the sludge produced has a concentration of a few grams per litre, and is highly biodegradable. Each process has a different impact on the water pollution load. These are presented below.

 3K\VLFDOÃDQGÃ %LRORJLFDOÃ 3ÃÉÃ1Ã 3UHWUHDWPHQW FKHPLFDOÃ 3ULPDU\ÃVHWWOHPHQW 6HFRQGDU\ÃVHWWOHPHQW WUHDWPHQW 5HPRYDO WUHDWPHQWV

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)LJXUH wastewater treatment and sludge generation More information on the European wastewater treatment system is provided in box 1 at the end of this chapter.

3.2.1 Pre-treatment Pre-treatment consists of various physical and mechanical operations, such as screening, sieving, blast cleaning, oil separation and fat extraction. Pre-treatment allows the removal of voluminous items, sands and grease. The residues from pre- treatments are not considered to be sludge. They are disposed of in landfills.

3.2.2 Primary sludge Primary sludge is produced following primary treatment. This step consists of physical or chemical treatments to remove matter in suspension (e.g. solids, grease and scum). The most common physical treatment is sedimentation. Sedimentation is the removal of suspended solids from liquids by gravitational settling. Sedimentation is usually considered first because it is a simple and cost-effective method. Another physical treatment is flotation. Air is introduced into the wastewater in the form of fine bubbles, which attach themselves to the particles to be removed. The particles then rise to the surface and are removed by skimming.

In the mechanical stage, 50 to 70 % of the suspended solids and 25 to 40 % of the BOD5 can be removed [Werther and Ogada 1999]. Chemical treatments are coagulation and flocculation. Coagulation and flocculation are used to separate suspended solids when their normal sedimentation rates are too slow to provide effective clarification. Coagulation is the addition and rapid mixing of a coagulant to neutralise charges and collapse the colloidal particles so they can agglomerate and settle. The flocculation is the agglomeration of the colloidal particles that have been subjected to coagulation treatment.

3.2.3 Secondary sludge Secondary sludge is generated from the use of specially provided decomposers to break down remaining organic materials in wastewater after primary treatment. The active agents in these systems are micro-organisms, mostly bacteria, which need the available organic matter to grow. There are various techniques such as lagooning, bacterial beds, activated sludge as well as filtration or biofiltration processes.

 The lagooning technique uses the development of a bacterial population in a lagoon, which converts organic matter into CO2 and biomass. Oxygen is fed into the system via the photosynthetic activity of microphytes (unicellular algae) or macrophytes (plants), although an alternative technique consists of artificial aeration of the lagoon. Practically water is passed through several lagoons, each reaching a higher level of de-pollution. This technique is suitable for WWTPs with large site areas. In bacterial beds, the effluent is in contact with bacteria, which are attached to a support. In activated sludge, bacteria are kept in suspension in the vessel in aerobic conditions. At the end of the process, the treated water has to be decanted off in order to separate the cleaner water from the activated sludge. This treatment generates another type of sludge, called surplus activated sludge.

3.2.4 Mixed sludge The primary and secondary sludge described above can be mixed together generating a type of sludge referred to as mixed sludge.

3.2.5 Tertiary sludge Tertiary sludge is generated when carrying out tertiary treatment. It is an additional process to secondary treatment and is designed to remove remaining unwanted nutrients (mainly nitrogen and phosphorus) through high performance bacterial or chemical processes. These treatments are necessary when a high level of depollution is required, for example in sensitive areas identified in the Member States. Nitrogen consumes oxygen when a nitrification reaction takes place in the natural environment. It is toxic under its ammoniac or nitrate phase, and is responsible of eutrophication. The removal of nitrogen is a biological process leading to the production of N2. Each step is carried out by specific bacteria, which need different conditions to grow. The removal of phosphorus may be performed using chemical processes or biological treatments. Chemical processes consist of chemical precipitation using additives followed by sedimentation. Physical-chemical removal of phosphorus increases the quantity of sludge produced by an activated sludge plant by about 30 %. Biological treatments employ specific micro-organisms, which are able to store phosphorus. It accumulates within the bacteria enabling its removal with the rest of the sludge.

3.2.6 Digested sludge After water treatment, additional treatments need to be performed RQVOXGJH, in order to: - reduce its water content, - stabilise its organic matter and reduce the generation of odours - reduce its pathogen load, - reduce its volume and global mass. Several treatments can be applied to sludge to achieve this. These are described in a following part of this report. One of those transforms the sludge in a way that it is considered as a new type of sludge usually referred to as “digested sludge”. This so-called digestion process is described further in the following part.

  ,QIOXHQFHRIWKHZDWHUWUHDWPHQWRQWKHFRPSRVLWLRQRIWKHVOXGJH Each kind of treatment has a specific impact on the composition of sewage sludge. We can define four types of sludge: - A : primary sludge, primary sludge with physical/chemical treatment or high pollution load1 - B1 : biological sludge (low load) - B2 : biological sludge from clarified water (low and middle load) - C : mixed sludge (mix of A and B2 types) - D : digested sludge

Composition of each kind of sludge is provided below:

$ % % & ' 'U\PDWWHU '0 J/ 12 9 7 10 30 9RODWLOHPDWWHU 90 '0 65 67 77 72 50 S+ 6 7 7 6,5 7 & 90 51,5 52,5 53 51 49 + 90 7 6 6,7 7,4 7,7 2 90 35,5 33 33 33 35 1 90 4,5 7,5 6,3 7,1 6,2 6 90 1,5 1 1 1,5 2,1 &1  11,4 7 8,7 7,2 7,9 3 '0 22222 &O '0 0,8 0,8 0,8 0,8 0,8 . '0 0,3 0,3 0,3 0,3 0,3 $O '0 0,2 0,2 0,2 0,2 0,2 &D '0 10 10 10 10 10 )H '0 22222 0J '0 0,6 0,6 0,6 0,6 0,6 )DW '0 18 8 10 14 10 3URWHLQ '0 24 36 34 30 18 )LEUHV '0 16 7 10 13 10 &DORULILFYDOXH N:KW'0 4 200 4 100 4 800 4 600 3 000

7DEOH impact of treatments on the sewage sludge composition and properties [OTV 1997]

 &RPSRVLWLRQ Sewage sludge contains both compounds of agricultural value and pollutants. Compounds of agricultural value include organic matter, nitrogen, phosphorus and potassium, and to a lesser extent, calcium, sulphur and magnesium. Pollutants are usually divided between heavy metals, organic pollutants and pathogens. A table summarising the average composition of sewage sludge in the Member States is provided in the appendix. However, this data has to be taken carefully, as years and time series are different. The figures provided are mean values, and do not take into account differences between small and larger WWTP. In addition, we are not always confident that it accurately represents the situation of each country, especially in the Accession Countries and in some EU countries where no comprehensive survey has been performed.

1 The load (Cm) is defined as the ratio between the daily mass of pollution to be removed and the mass of bacteria used for depollution. Usually the following levels are defined:

- high load: Cm>0,5 kg BOD5/kg sludge/day - middle load: 0,2

 In order to perform comparisons, typical composition of animal manure and slurry is also provided in appendix.

3.4.1 Organic matter Organic matter is mainly used for soil improvement. Known benefits of organic matter application to soil are the improvement of the physical properties of soil such as structure or improvement of the retention capacity of minerals and water. Other benefits of sludge application may be the improvement of the soil bearing strength, or the reduction of the potential for surface runoff and water erosion [ADAS 2000]. Degradation of the organic matter can also increase the soil content in compounds of agricultural value (such as N, S, Mg etc.), which are slower released than in the case of mineral fertilisers and therefore available for a longer period to crop [ADAS 2000]. Organic matter is lastly an energy source for micro-organisms living in soil. Therefore sludge spreading may induce an increase of the soil population and activity, and of its mineralisation capacity. Sludge organic matter is mostly constituted of soluble matter, such as hydrocarbons, amino-acids, small proteins or lipids. Its content in urban sewage sludge is high (usually more than 50 % of the dry matter) but varies according to the treatment and conditioning2 carried out on sludge. Content level may be reduced due to dilution after incorporation of lime or salts for instance. The table below compares the content of organic matter of urban sewage sludge against other urban wastes and animal manure.

2UJDQLF0DWWHUFRQWHQW RI'0 8UEDQVOXGJH Aerobic digestion 60 - 70 Anaerobic digestion 40 - 50 Thermal treatment < 40 Lime treatment < 40 Composting 50 – 85 8UEDQFRPSRVW 40 – 60 *UHHQZDVWHVFRPSRVWLQJ 30 – 60 $QLPDOPDQXUH 45 – 85 7DEOH content of organic matter in sludge after different treatments and in other urban waste and animal manure [Lineres 2000]

However, a recent UKWIR funded literature review indicated that the minimum threshold level for detectable effects of sludge additions on soil physical properties was c. 5 tonnes organic matter/ha, i.e. about 10 t dry solids/ha. Considering current quantity limitations for agricultural use of sludge implemented in the Member States, those benefits do not occur [Lineres 2000]. Improvement of soil physical properties may however be observed when using sludge for land reclamation (provided that limit values for pollutants applied are respected), as amounts of sludge used may be very important. Moreover sludge organic matter is mostly constituted of soluble matter, such as hydrocarbons, amino-acids, small proteins or lipids. There is only a small amount of lignin or cellulose entering in its composition. Therefore, sewage sludge’s organic matter mineralises fast, and its rapid degradation could generate a peak in the nitrate and pollutant levels in soil It may be observed that the specific case of composting induces the addition of stable organic matter to the sludge, originating from the co-product. In this case, organic matter mineralises slower, and nutrients are slower released, reducing the potential risk of nitrogen leaching to

2 for a description of the different types of treatments, see section 4

 groundwater. ADEME [2001] observes that the rapidity of the compost mineralisation depends on the type of compost, as well as from its maturity, and that compost decomposition may continue several years following its application on soil. It is also assumed that composted sludge could have a more significant impact on soil structure than non-composted sludge. However no information is available in the literature concerning a lower threshold level for detectable effects of sludge additions on soil physical properties.

3.4.2 Nitrogen and phosphorus content The table provided in appendix shows the content of nitrogen and phosphorus in sludge in the Member States. The ranges are between 20 and 80 000 mg/kg DM for Nitrogen and 10 and 90 000 mg/kg DM for Phosphorus. The proportion of phosphorus and nitrogen in sewage sludge is comparable to the one of animal manure.

7RWDO1 1±1+ 3 (% of DM) (% of N total) (% of DM) 8UEDQVOXGJH 0,9 – 5,2 Liquid 1 – 7 2 - 70 Semi-solid 2 – 5 < 10 Solid 1 – 3,5 < 10 Composted 1,5 – 3 10 – 20 0,2 – 1,5 8UEDQ&RPSRVW 0,96 0,39 &RPSRVWHGJUHHQZDVWH 1,0 – 2,4 0,04 – 0,44 /LWWHU 2,2 – 4,4 10 0,61 – 1, 61 0DQXUH 4 – 7 50 – 70 0,91 – 3,3 7DEOH content of nitrogen and phosphorus in sludge after different treatments and in other urban waste and animal manure [Lineres 2000]

1LWURJHQ Nitrogen is mostly found under organic form in sludge, and to a lesser extent under ammoniac form. Other mineral forms of nitrogen are only found as traces. Treatments carried out on sludge can greatly influence their content of nitrogen and phosphorus, as shown in the table below. For instance, as most of the ammoniac is located in the liquid phase of sludge, an important part of it will be removed during the thickening and dewatering steps. The nitrogen content is also influenced by the operation of the WWTP, and the sludge storage conditions: in some cases a reduction of the nitrogen content in stored liquid sludge by 30 % after 4 months has been reported [ADEME 1996].

  7\SHRIWUHDWPHQW 7RWDO1 11+ (% of DM) (% of total N)

/LTXLGVOXGJH aerobic digestion, gravity thickening 5 – 7 5 – 10 aerobic digestion, mechanical thickening 4 – 7 2 – 8 anaerobic digestion 1 – 7 20 – 70 lagooning 1 – 2 N/A

6HPLVROLGVOXGJH aerobic digestion, mechanical dewatering 3 – 5.5 < 5 anaerobic digestion, mechanical dewatering 1.5 – 3 < 5 lime treatment 3.4 – 5 < 10

6ROLGVOXGJH aerobic digestion, lime treatment (press filter) 2.5 < 10 composted 1.5 – 3 10 – 20 aerobic, dewatered on drying beds 2 – 3.5 < 10 anaerobic, dewatered on drying beds 1.5 – 2.5 < 10

'ULHGVOXGJH 3.5 – 6 10 – 15 7DEOH influence of treatment on the nitrogen content of some sewage sludge [ADEME 1996]

As plants can assimilate only mineral nitrogen, the agricultural value of the sludge is also determined by the aptitude of its organic N to be mineralised. The nitrogen availability depends on the type of sludge. It varies between 4 and 60 %, but within one type of sludge, great variations have been reported (see table below). The nitrogen availability may be classified as follows: composted sludge < anaerobic digested sludge < aerobic digested sludge. The different treatments carried out on sludge may also greatly influence the availability of the nitrogen in sludge, without knowing the influence of each one of them [ADEME 1996]. Other factors influencing the availability of the nitrogen are extrinsic factors: temperature, humidity, pH and texture of the soil, and condition of landspreading. Loss of nitrogen can also occur if volatilisation of the ammoniac takes place, or if nitrates are leached. This may represent a possible risk of groundwater pollution. It may happen if the amount of sludge applied does not correspond to plant needs in nutrients or because of the fast degradation of sludge-borne organic matter which could give rise to a peak of nutrient in soil.

6OXGJHW\SH $YDLODELOLW\  Aerobic digested sludge 24-61 % Anaerobic digested sludge 4-48 % Digested composted sludge 7 % Composted raw sludge 4 % Thermally dried sludge 7-34 % 7DEOH nitrogen availability according to laboratory results [ADEME 1996]

3KRVSKRUXV Phosphorus is used by the plant for its growth, the rigidity of its cell walls, and for the development of its root system. Sludge-borne phosphorus is of particular interest as phosphorus is a limited natural resource. Phosphorus in sludge is mostly present under mineral form: mineral phosphorus can represent between 30 and 98 % of the total phosphorus, according to the type of sludge. As in the case of

 nitrogen, the amount of phosphorus available in sludge depends on the treatments carried out, and is not proportional to the amount of total phosphorus. Variations in composition are illustrated in the table below. Of course, the amount of phosphorus in sludge is much higher when a specific tertiary waste water treatment for phosphorus removal is carried out. It has also been observed that composted sludge has a lower phosphorus content than non-composted sludge, due to the low phosphorus content of the co-products used during the composting process. Contrary to nitrogen, phosphorus content in sewage sludge is not significantly reduced after storage.

7\SHRIWUHDWPHQW 32 3 (% of DM) (% of DM) Liquid sludge ;anaerobic digestion 4.9 – 6.9 2.1 – 3 Aerobic digestion 2.5 – 12.65 1.1 – 5.5 Primary sludge, lime treated 2.5 – 12 1.1 – 5.2 7DEOH influence of treatment on the phosphorus content of some sewage sludge [ADEME 1996]

3.4.3 Calcium enrichment Lime addition to sewage sludge is performed in order to stabilise the sludge (see chapter 4). To reach a good level of stabilisation, it is recommended to add about 30 % of lime to the dry matter. Lime treatment of sludge therefore generates a product with a useful content in CaO that could be of interest on certain soils. However, as the calcium content may be highly variable in lime treated sludge, it is generally necessary to analyse sludge before use. Field studies have shown that lime treated sewage sludge has positive impacts on the pH, structure and permeability of the soil [Lineres 2000]. Calcium is also a useful element for the plant as it strengthens its cell walls. Calcium supply to the soil may in some cases correct a deficiency of this element.

3.4.4 Other compounds of agricultural value Other compounds present in sludge such as potassium, sulphur, magnesium, sodium and oligo- elements (e.g. boron, cobalt, selenium, iodine) may be of interest in crop production, each of them being useful for the plant development and growth. However, they may appear in sludge under various forms (for instance magnesium sulphate or magnesium oxide), and their efficiency will depend on their availability. It has been mentioned in the UK literature that, as atmospheric sulphur deposition continues to fall, sulphur fertiliser additions are increasingly generating yield responses. Biosolids applications typically supply between 140 and 200 kg/ha total SO3, making a valuable contribution to crop requirements [Chambers HWDO. 2000]. However, the agricultural value of those compounds related to their level in sludge is not extensively documented in literature.

3.4.5 Heavy metals Numerous heavy metals are present in sludge. Heavy metals may affect plant health and growth, soil properties and micro-organisms, livestock and human health, and accumulate in the environment. Their impacts are more accurately described in chapter 6. On certain soils however, for example on copper deficient soils, the heavy metals content of sewage sludge can correct trace element deficiency.

 The average content of 7 heavy metals in the Member States is presented below. Data refers to the information collected in the Member States for this study, which are summarised in appendix.

'LUHFWLYH 5DQJHLQWKH ((& 0HPEHU6WDWHV mg/kg DM mg/kg DM

&G 20 – 40 0.4 – 3.8 &U 1000 – 1750 16 - 275 &X 1000 – 1750 39 - 641 +J 16 – 25 0.3 - 3 1L 300 – 400 9 - 90 3E 750 – 1200 13 - 221 =Q 2500 – 4000 142 - 2000 7DEOH average content in sewage sludge of 7 heavy metals in the Member States

In all countries, the average values of composition are clearly under the limits of the 86/278/EEC directive. In most cases, the values given in this table are also below the national limit values set in the regulations of each country. For some compounds, such as cadmium and mercury, the values are quite homogeneous: between 0.5 and 3.8 mg/kg DM. For other compounds however, there are great differences among European countries. This may be due to the industrial context of each country. Concerning the Accession Countries, we have collected data from Cyprus, the Czech Republic, Estonia, Latvia, Lithuania, Slovakia and Slovenia. The situation is heterogeneous. Compared with the values in the Member States, Latvia has sludge of worst quality. The sludge of other countries presents levels of contaminants, which are comparable or slightly higher than in the Member States (Cd, Pb, Cr in Estonia, for instance) or much higher (Hg, Ni). However, those values are all below the actual limits of the 86/278/EEC directive. In Slovakia, only one WWTP, representing 3,3% of the total sludge production, produces a sludge, which can not be applied on land (higher Cr content due to tannery effluent treatment). There are three main origins for heavy metals in sewage sludge: domestic effluents, road runoff, and industry. For each metal, the proportion of each origin may be very different, and the importance of heavy metals originating from the industry depends greatly from the industrial situation of each country. As a comparison, typical heavy metal levels in animal manure and slurry is provided in appendix.

3.4.6 Organic pollutants A wide variety of organic chemicals with diverse physical and chemical properties may be found in sludge. They also may affect soils, plant, animals and human health, and have impacts on the environment, which are described in chapter 5 and 6 of this report. In this study we especially take into consideration the compounds to which it is most often referred, but many others are present as traces. The considered compounds are: - PAH : Polynuclear aromatic hydrocarbons - PCB : Polychlorinated biphenyls - PCDD/F : Polychlorodibenzodioxins/furans

 - AOX : Sum of organohalogenous compounds - LAS : Linear alkylbenzenesulphonates - NPE : Nonylphenol and Nonylphenolethoxylates - DEHP : Di(2-ethylexyl)phtalate A description of each of them is provided in appendix. So far, we have not received satisfactory data from the Member States concerning those compounds. As they are often not mentioned in the national regulations, no survey has been regularly performed describing the organic pollutant content in sewage sludge. To compensate the missing information, the concentrations given have been collected from various documentary sources. Therefore, those figures must be considered only as indicative values. Concerning PCDD/F, data have been taken from the &RPSLODWLRQ RI (8 'LR[LQ H[SRVXUH DQG KHDOWK GDWD [AEA Technology 1999]. It shows that average concentrations of dioxins are quite similar among Member States, between 15 and 40 ng I-TEQ/kg DM. According to the study, this would indicate that the sources of contamination in the Member States are similar. Industrial inputs can also cause important contamination in sludge. In some cases, more than 1 000 I-TEQ/kg DM have been reported. Data available concerning other organic pollutant levels in sludge are not consistent and reliable enough to draw any conclusion.

3.4.7 Pathogens Sewage sludge contains various micro-organisms, especially when biological treatments are carried out. Only some of them have health-related impacts. Sludge may also contain plant pathogens. As for organic compounds, no satisfactory data could be found for the Member States and the Accession Countries concerning their content in sludge. Presence of pathogens in sludge is related to the sanitary level of the population, and the type of industry in the region. The types of pathogens usually considered are viruses, bacteria, protozoa, and helminths. Their load in sludge varies along time. More information concerning treatments that may be performed in order to reduce or destroy pathogens present in sludge is given in part 4.5, and the fate of pathogens in the environment and their sanitary impact is summarised in part 6.3.

 ,QGXVWULDOVOXGJH Data provided above refers mainly to urban sewage sludge. As a comparison, table 8 describes the composition of some types of industrial sludge, namely pulp and paper, and tannery sludge. More information is available in the WRc report, “Survey of wastes spread on land” [2001].

3.5.1 Pulp and paper industry Composition of pulp and paper industry sludge depends on the paper production process. Using virgin wood fibre generates a liquid effluent mainly loaded with lignin and cellulose, therefore containing a higher level of stable organic matter. On the contrary, recycling of waste paper induces additional steps such as de-inking and bleaching, and therefore generates a so-called de- inking sludge, containing colouring agents and chemicals. Reusing waste paper usually generates a greater amount of sludge than when using virgin wood fibres. Pulp and paper sludge is therefore a mixture of cellulose fibres, ink and mineral components. Inks used to be produced by using heavy metals. Their usage has however been greatly reduced in the last 20 years, therefore reducing their level in sludge. The higher content of cellulose fibres makes the nitrogen availability lower than in the case of urban sludge. As a consequence, nitrogen is released more slowly into the soil after application, reducing the risk of leaching to groundwater.

 3.5.2 Tannery Sludge Leather manufacturing generates liquid and solid wastes originating from the different steps in the transformation of the mammalian skin into leather, performed by using several reactive products. Liquid effluents contain collagen fixed to tanning agents and heavy metals originating from the reactive products used during the tanning process. Sludge composition varies according to the specific process performed on site. As tannery wastewater is rich in proteins, nitrogen content in the sludge is higher than in the case of urban sludge, and therefore of interest for landspreading. However, heavy metal (especially chromium) content may prevent their use in agriculture.

3XOSDQGSDSHULQGXVWU\VOXGJH 7DQQHU\VOXGJH 'LUHFWLYH

(/(0(176 0LQ 0D[ 0HDQ 0LQ 0D[ 0HDQ 'U\VROLGV  1,7 65 31,60 4,10 13,21 7,38 &15DWLR 12,5 200 77,80 ZDWHUS+ 4,5 9,4 7,30 6,7 7,20 6,86 $JULFXOWXUDOYDOXH '0 2UJDQLFPDWWHU 19,1 90,4 63,90 47,61 68,87 54,15 17RWDO 0,4 4,9 1,31 3,59 5,60 5,05 11+ 0 0,3 0,02 &D2 0,52 19,9 12,50 13,35 21,41 16,02 0J2 0,02 6,5 0,86 0,30 0,51 0,38 32 0,19 8 0,68 0,40 0,88 0,62 .2 0,06 0,79 0,180 0,12 0,92 0,65 62 1,270 +HDY\PHWDOV SSP PJNJ'0 &DGPLXP±&G 0,2 4,4 0,98 0,15 0,07 0,17 20 – 40 &KURPLXP±&U < 1 44,5 34,10 92,00 162,50 127,60 - &RSSHU±&X 2 349 61,20 8,50 12,80 9,90 1000 – 1750 0HUFXU\±+J < 0,01 1,4 0,240 0,03 0,04 0,03 16 – 25 1LFNHO±1L < 1 32 12,40 1,10 2,07 1,53 300 – 400 /HDG±3E < 1 83 13,10 2,25 5,15 3,67 750 – 1 200 =LQF±=Q 1,3 330 135,10 20,40 30,60 26,80 2500 – 4000 $UVHQLF±$V <8 2UJDQLFFRPSRXQGV SSP PJNJ'0 )OXRUDQWKHQH 0,01 <0,1 <0,055 %HQ]R E IOXRUDQWKHQH <0,005 0,04 <0,022 %HQ]R D S\UHQH <0,005 0,03 <0,017 6XPRI3&% 0,002 <1 <0,5 7DEOH composition of some industrial sludge types [WRc 2001] (*: PAH compounds)

 %R[  :DVWHZDWHU WUHDWPHQW V\VWHP LQ WKH (XURSHDQ 8QLRQ DQGWKH$FFHVVLRQ&RXQWULHV Tables below summarise the level of the wastewater treatment in the Member States and the Accession Countries. In some countries however, such as Finland, access to sewerage may be replaced by the use of septic tanks.

2&'('DWD (XURVWDW'DWD 1RDFFHVV $FFHVVWRSXEOLFVHZHUDJH $FFHVVWR WR 1R &RXQWU\ 3 36 367 7RWDO VHZHUDJH VHZHUDJH WUHDWPHQW

7DEOH sewerage access and wastewater treatment in the Member States [OECD 1999 and Eurostat 1998-2000; Italy : Cecchi HWDO. 1996] ; P: primary treatment ; S: Secondary treatment; T: Tertiary treatment

(($ HDUO\¶V 1RDFFHVV $FFHVVWRVHZHUDJH &RXQWU\ WR 1R 3 36 367 7RWDO VHZHUDJH WUHDWPHQW % of population Bulgaria  35 0 34 0  Czech Rep.  17 4 52 0  Estonia  9271522 Hungary  12 5 22 6  Latvia  12 10 51 0  Lithuania  12 32 29 0  Poland  23 10 28 4  Romania  12 6 29 0  Slovenia  85450 Slovakia  13 16 15 0  Total AC  18 8 31 2  7DEOH sewerage access and wastewater treatment in the Accession countries [EEA 1999] ; P: primary treatment ; S: Secondary treatment; T: Tertiary treatment

 %R[6OXGJHTXDOLW\LPSURYHPHQW During the last 20 years, sludge quality has considerably improved. Some examples are provided in figures 2 and 3 and table 11 for heavy metals and organic pollutants. Other examples may be found in WRc [1993] and ADEME [1999] reports. The data provided in figure 2 stems from the state of Upper Austria and concerns 80 up to 140 rural, urban and industrial plants, of which capacities vary between <1000 and 500 0000 Inhabitants equivalent.

3500

3000 Zn 2500 Cr 0 ' Ã 2000 Ni (x10) J N J 1500 Pb (x10) P Cu (x10) 1000 Cd (x100) 500

0 1980 1985 1990 1995 2000

)LJXUH decrease of heavy metals content in sewage sludge in Upper Austria, 1980 – 2000 [Aichberger, 2000]

3500

3000 Zn 2500 Cr 0 Ã'2000 Ni (x10) J N Pb (x10) J1500 P Cu 1000 Cd (x100) Hg (x100) 500

0 1977 1982 1987 1992

)LJXUH decrease of heavy metals content in sewage sludge in Germany, 1977 – 1992/93 [ATV 1996] Eljarrat HW DO (1999) also analysed the dioxin content of sewage sludge from 19 WWTP in Catalonia (Spain), and compared the results with figures from archived sewage sludge originating from 15 WWTP, stored between 1979 end 1987. The most recent samples indicated values ranging from 7 to 160 pg/g, with a mean value of 55 pg/g and a median value of 42 pg/g, whereas archived samples indicated levels between 29 and 8300 pg/g, with a mean value of 620 pg/g and a median value of 110 pg/g. This study showed a reduction in the dioxin amount in sewage sludge. According to the authors, there could also have been a change in the sources to the environment over time.

   $2; mg/kg DM 250 – 350 140 – 280 3&% mg/kg DM < 0,1 0,01 – 0,04 3$+ mg/kg DM 0,25 – 0,75 0,1 – 0,6 '(+3 mg/kg DM 50 - 130 20 - 60 1RQ\OSKHQRO mg/kg DM 60 – 120 - 3&'') ng TE / kg DM < 50 15 - 45

7DEOH average contents of organic micro-pollutants in sewage sludge in 1988/89 compared with data from German publications till 1996 [Leschber 2000] Those figures show that after a significant improvement, the level of pollutants is nearing a base level. These improvements result from reducing the sources of the pollution, mostly point sources such as industrial discharge.

 %R[  6OXGJH SURGXFWLRQ LQ 0HPEHU 6WDWHV DQG $FFHVVLRQ &RXQWULHV

6OXGJHSURGXFWLRQLQ0HPEHU6WDWHV The amount of sludge produced in each Member State is presented in figure 4.

2 500 000

2 000 000

01 500 000 ' WÃ 1 000 000

500 000

0

n d ny ce ly ds ia a UK n ium urg an Ita str g elan b rm r Spain u el Ir e F Swede A Finland Greece G Portugal Denmark B Netherla Luxem

3 )LJXUH sludge production in Member States (t DM) The total amount of sludge produced in the 15 European Union countries is about 7 million tons of dry matter (t DM). As shown in the figure 4, Germany is the first sludge producer, followed by the United Kingdom, France, Italy and Spain, all producing more than 500 000 t DM in a year. These 5 countries generate altogether nearly 75 % of the European sewage sludge. All other countries produce less than 250 000 t DM each. This situation roughly reflects the demography of each country. The amount of sludge is usually presented in tons of dry matter that should be multiplied tenfold4 to obtain the amount of raw sludge produced. The total amount of raw sludge produced in the EU should be around 70 million tons. However, it is only a theoretical figure, as the original water content of the sludge depends on its type and the treatment applied. Figure 5 presents the sludge production in the European Union per inhabitant and per day. According to this data, Greece produces the lowest amount of sludge per inhabitant (15,4 g DM/inhabitant/day), whereas Denmark is the most important producer with 78 g.

90,00 80,00 \ 70,00 D G 60,00  K 50,00 LQ  40,00 0 Ã'30,00 J 20,00 10,00 0,00

l a ia ds nd m ce den UK urg n la iu tug str b Italy e g ee rmany we r u Spain rla Ir l FinlandS A Francee Gr DenmarkGe Po Be Luxem Neth

)LJXUH sludge production in Member States (g DM/inh./day)

3 Source: report of the European Commission on the implementation of the European legislation concerning wastes for the period 1995-1997. Missing data completed from the study on the situation of the agricultural use of sewage sludge in the European Union [ADEME, 1999]. 4 10 % corresponding to an average dry matter content of sewage sludge.

 These differences reflect the diversity of national wastewater treatment systems, including the connection rate of each country. It is also directly linked to the quality, availability, and type of sludge taken into consideration in the statistical data.

6OXGJHSURGXFWLRQLQ$FFHVVLRQ&RXQWULHV In the Accession Countries, the production level is more difficult to assess because of heterogeneous statistical systems, and the low reliability of the data. However, the production is directly linked to the national equipment level. Figure 6 shows the amount of sludge produced in the Accession Countries, when data is available. The values are between 400 tons in Malta and 330 000 tons in Poland (assuming a dry matter level of 10 %), which is the country with the largest population.

350 000 300 000 250 000 0 '200 000 WÃ 150 000 100 000 50 000 0

d c ia ia ry ta li kia nia n a rus lan b o g u va ua Latvia Mal Po loven lo it Cyp Rep S S Est L Hun h ec Cz

5 )LJXUH sludge produced in the Accession Countries (t DM)

The sludge production per inhabitant is presented in Figure 7, showing great differences between countries. Indeed, there is no correlation between the amount of sludge produced and the population. An explanation of such diversity is to be found in the differences in equipment level and connection rate to water treatment, but also to the relatively low reliability of the statistical data. For instance, there is presently no common classification of waste in the Accession Countries.

160,00 140,00 \ D 120,00 G K100,00 Q L 80,00 0 60,00 Ã' J 40,00 20,00 0,00

lic a a akia land ary tonia yprus Latvi Malt Es C ov ituania Po ung Slovenia Repub Sl L H h zec C sludge production in the Accession Countries (g DM/inh./day)

5 Data source: screening realised by the European Commission or data collected for this study. No data were available from Bulgaria and Romania.

 %R[&RPSDULVRQRIVOXGJHVSUHDGLQJZLWKRWKHUIHUWLOLVDWLRQ SURFHVVHV Various fertilisation media in the Member States have been compared and are presented below. The amount of nitrogen and phosphorus brought by the animal manure has been calculated using the Eurostat figures for animal manure production in the Member States, and applying a coefficient to assess N and P content. This coefficient can differ among countries in the European Union, and a study is currently being carried out by Eurostat to compare those figures. However, the results of this study were not available when this report has been written. Therefore, we used coefficients from the French CORPEN (Committee for the reduction of the water pollution by nitrates and phosphorus). We have established an extreme scenario by assuming that all sludge produced in a country would be used in agriculture, although the disposal and recycling routes can greatly differ among the Member States. It must also be reminded that the amount of mineral fertiliser used may sometimes be higher than what it is needed. If only “best practices” would have been considered, this amount would certainly be reduced.

100%

80% N A nimal manure N Sludge 60% N Mineral Fertilizer

40%

20%

0% UK Italy Spain Ireland Finland France Austria Greece Portugal Sweden Denmark Germany Belgium & Belgium Netherlands

)LJXUH sources of nitrogen fertilisation in the Member States In all Member States, sludge fertilisation is the least used media. In the case of nitrogen fertilisation, the amount due to sludge use in agriculture is between 0,1 % in Greece and 2,4 % in Germany. However, considering the low figures, there is no strong difference across Member States. Regarding phosphorus, the part of fertilisation from sewage sludge is between 0,2 % in Greece and 10% in Germany. Unlike nitrogen, there is an important heterogeneity between Member States, as the amount of phosphorus brought by mineral fertilisation is between 25 and 65 %. Phosphorus is a critical factor in fertilisation, and sludge utilisation in agriculture occurs on the basis of their phosphorus content in several countries.

100%

80% P Animal Manure 60% P Sludge P Mineral Fertilizer 40%

20%

0%

n k nd al K ia a U r any Italy pai tug ands reece nl S reland ust rm l G Fi France or I A e P Sweden G Denmar Nether

Belgium & Luxembourg

)LJXUH sources of phosphorus fertilisation in the Member States

   6OXGJHWUHDWPHQWSURFHVVHV Sludge Wastewater Water Sludge recycling Impacts collection treatment treatment and disposal

Sludge produced by wastewater treatment plants is usually processed to reduce the water content of the sludge, its fermentation propensity and pathogens content. The different steps of the sludge treatment are described in the table 12. The different treatments, which will be performed on sludge will depend on its further disposal or recycling.

6WHSV 7\SHVRISURFHVVHV 2EMHFWLYHV &RQGLWLRQLQJ Chemical conditioning - Sludge structure modification Thermal conditioning - Improvement of further treatment

7KLFNHQLQJ Gravity thickening - Obtain sufficient density, strength and Gravity belt thickener solids content to permit hauling for Dissolved air flotation further disposal process - Reduce the water content of the sludge

'HZDWHULQJ Drying beds - Reduce the water content of the sludge Centrifuging Filter belt Filter press

6WDELOLVDWLRQ Biological processes: - Reduce the odour generation DQGRU $QDHURELFGLJHVWLRQ - Reduce the pathogen content of the GLVLQIHFWLRQ $HURELFGLJHVWLRQ sludge /RQJWHUPOLTXLGVWRUDJH &RPSRVWLQJ

Chemical processes: /LPHWUHDWPHQW 1LWULWHWUHDWPHQW

Physical processes: 7KHUPDOGU\LQJ 3DVWHXULVDWLRQ 7KHUPDOGU\LQJ Direct - Highly reduce the water content Indirect 7DEOH the different steps of sludge treatment

A short description of existing treatment processes usually performed in Member States and Accession Countries is provided below. For each of them, a classification is possible between batch and continuous processes. Batch processes necessitate reaching a given quantity of sludge before performing the treatment. On the contrary, continuous processes allow uninterrupted operation.

  &RQGLWLRQLQJ A preliminary phase of chemical or thermal conditioning may be conducted to improve further sludge thickening or dewatering. Chemical conditioning is realised by using mineral agents such as salts or lime, or organic compounds (polymers). Thermal conditioning consists of heating sludge to 150-200 °C for 30 to 60 minutes. Heat changes the physical structure of the sludge, helping further dewatering. However, as part of the organic matter may be hydrolysed during the process, it could trigger offensive smells and high polluted filtration or centrifugation water during the dewatering steps. It is possible to perform partial thermal conditioning by heating at a temperature of 40 to 50 °C. This solution reduces the contamination of centrifugation and filtration water. The advantages and disadvantages of each of those possibilities are summarised in the table below.

&RQGLWLRQLQJ $GYDQWDJHV 'LVDGYDQWDJHV &KHPLFDO - Improvement of the cohesion - Increase in sludge amount PLQHUDODJHQWV and the density of the sludge - Reduction of the organic matter content - Slow reaction &KHPLFDO - Reduction of the mass of sludge, - Costs of the products RUJDQLFDJHQWV - No modification of the agricultural value - Lower quantities to be used - Easy to handle and transport 7KHUPDO - May be applied to all sludge - Energy consumption - Efficient and stable process - Odours - Stabilisation and disinfection - Increase in the pollution load of - Lower sludge amount the filtrate 7DEOH comparison of the different conditioning processes

 7KLFNHQLQJ Thickening is a first step to reduce sludge water content. Sludge reaches 10 to 30 % dryness, and can still be pumped. Various existing techniques are presented below.

*UDYLW\WKLFNHQLQJ Gravity thickening is a widespread technique, performed in tanks usually fitted with a rotating ploughing system. The gravitational forces bring the thickened sludge at the base of the tank from where it is extracted. Water is collected at the top. The process is capable of thickening the sludge by 2 to 8 times, bringing it from a few grams/litre to a few tens of grams/litre. Performing costs are relatively low, as only an electricity supply is needed to operate the harrow and the pumps. The energy consumed is about 5 kWh/t DM.

*UDYLW\EHOWWKLFNHQLQJ The gravity belt thickener consists of an endless filter belt on which thickening takes place in three phases: conditioning, gravity drainage and compression. Flocculated sludge is fed onto the belt and, as it moves along, water passes through the weave of the belt. At the discharge end of the machine, the sludge is further thickened by the compression caused by it being turned over onto itself. A high-pressure wash station continuously washes the belt. Sludge thickening with a gravity belt thickener is made possible by the addition of polyelectrolyte to the sludge.

 Gravity belt thickeners are used for all types of sewage sludge, although they are at their most economical when handling sludge of less than 1 % DM feed and thickening to 6 % DM. Primary sludge can be thickened to 10 % DM at which point it is difficult to process further without expensive pumping systems. Activated sludge is normally thickened to 5 % DM. Performing a gravity belt thickening requires about 50 kWh/t DM and water.

'LVVROYHGDLUIORWDWLRQ The technique of air flotation can be used when the solid particles have a low rate of settlement, and in sewage sludge treatment the process is used to thicken surplus activated sludge. The specific gravity of fine suspended solids is lowered by the attachment of micro-bubbles and brought to the surface, where the thickened sludge is removed by a scraper. Its application in sewage sludge treatment involves dissolving air under pressure and subsequently releasing the pressure in the flotation vessel. Adding a polymer is sometimes needed, when it is necessary to reduce the matter in suspension. The performance of this process is higher than the one of the gravity thickening. However, the energy costs are also higher: 100 to 130 kWh/t DM.

&RPSDULVRQRIWKHGLIIHUHQWWKLFNHQLQJSURFHVVHV The different thickening systems are compared below

$GYDQWDJHV 'LVDGYDQWDJHV *UDYLW\WKLFNHQLQJ - Easy to perform - Needs important room - Low energy consumption - Low performance on - Low investment costs biological sludge *UDYLW\EHOWWKLFNHQLQJ - Easy to perform - Work force need - Compact - Cleaning water consumption - Polymer use compulsory 'LVVROYHGDLUIORWDWLRQ - Easy to perform - Not adapted to variable - Little room needed regimes - Little H2S emission - High energy consumption 7DEOH comparison of the different thickening processes

 'HZDWHULQJ Dewatering is the following step after thickening, and allows further reduction of the sludge water content. Dewatered sludge has a dry matter content of up to 30 %.

'U\LQJEHGV One of the simplest techniques for dewatering sewage sludge is the open air drying bed. This technique is used mainly on small WWTPs whenever sufficient inexpensive land is available and the local climate is favourable for year-round operation of the beds. This technique may be less efficient in cold climates. It consists of a sand and gravel area about 0.3 m thick on which sludge is spread. The water is drained and sent to the head of the plant. The sludge is then atmospherically dried. This process allows a DM content of 40 to 50 % to be reached in some countries, depending on the duration of the drying. This level is reduced to 10% in Nordic countries. It offers the potential of lower operating costs and minimal maintenance requirements, which may offset the disadvantage of high land requirements, weather dependency, and potential odours. However, this technique is relatively labour intensive.

 &HQWULIXJLQJ Centrifuging is a mechanical process that uses centrifugal forces to separate the thickened sludge from the centrifugate. Centrifuges are used in dewatering applications because they are compact, have high throughput capacity, and are simple to operate. Solid-bowl and basket centrifuges are the most commonly types used. It is possible to use centrifuging either as a thickening process or as a dewatering process. The process can produce increases in the dry matter of up to 15 to 25 %. It is also possible to use a high performance centrifuge, gaining an additional 5 %. However, the energy needs of this process are significant: from 25 to 80 kWh/t DM, and it is also necessary to add a polymer to the sludge.

)LOWHUEHOW In the filter belt process, the sludge, mixed with a polymer, is dewatered on the same principle as gravity belt thickening. It is then pressed between two belts. There are different kinds of machines available, depending on the level of pressure applied to the sludge (low, middle or high pressure, respectively about 4, 5 and 7 bars). The process may be combined with a gravity belt thickening. It is possible to increase the level of dry matter by 10 to 20 %, depending on the type of sludge and the pressure applied. To perform this process, costs include polymer, water and energy (about 35 kWh/t DM).

)LOWHUSUHVV It is possible by using this technique to reach a high dewatering level, between 30 to 45 % generally. The investment costs however are quite high, especially for high capacities. Plate and frame filter presses are commonly used to dewater sludge. Conventional filter presses consist of rows of vertical plates between which sludge is injected under pressure. The filtrate is collected before separating the plates. The sludge cakes then fall and are collected. In some cases, membranes are placed between the plates, which can be filled with water in order to improve the dewatering rate. In this case however operating costs are significantly higher. A preliminary conditioning is usually required either with salts or lime. Electricity needs are about 30-40 kWh/t DM. Investment costs are reduced with increasing capacities.

&RPSDULVRQRIWKHGLIIHUHQWGHZDWHULQJSURFHVVHV The different dewatering processes are compared below.

 $GYDQWDJHV 'LVDGYDQWDJHV 'U\LQJEHGV - Easy to operate - Land requirement - Adapted to small WWTP - Weather dependency - Functions throughout the - Risk of odours year - Workforce requirements - Low operation costs - High DM content reached &HQWULIXJLQJ - Continuous operation - Specialised maintenance - Compact - Sludge texture - Possible automation - Noise - High energy consumption - High investment costs )LOWHUEHOW - Continuous operation - Limited water content - Easy to perform reduction - Moderate investment costs - Cleaning water consumption - Supervision necessary )LOWHUSUHVV - High water content reduction - Discontinuous operation - Structure of the sludge - Low productivity - Possible automation - Consumption of mineral conditioner - Supervision necessary - High investment cost 7DEOH comparison of the different dewatering processes

 'U\LQJ The drying of sludge allows: - the elimination of the interstitial water, to reduce the volume of the sludge, - stabilisation, and disinfection when DM exceeds 90 %, It is also done in order to: - increase the calorific value of the sludge, before thermal oxidation, - allow spreading using techniques similar to those used for mineral fertilisers, - reduce the transportation costs. Drying is a thermal treatment. Heat can be transferred either directly or indirectly to the sludge. In the first case, it requires an intensive contact between gas and sludge material. The most important types of dryers are the revolving drum dryer and the fluidised bed dryer. In the second case, heat is transferred to the material to be dried via heat conduction through a heat transfer surface. Thus, the heating medium is not in contact with the sludge. The drying takes place at different temperatures. However, at higher temperatures (> 300 °C), it must be carefully controlled to ensure that there is no formation of dioxin and furan compounds. The level of DM reached is between 35 and 90 %. Partial drying enables a DM content of 30 to 45 % to be reached at which percentage it is possible auto-combust the sludge. Those processes inhibit the re-growth of bacteria, mainly because of the reduced moisture level which may be reached. Energy requirements for drying are much higher than dewatering when comparing volume of extracted water (tEW). Therefore in most cases, drying takes place after a dewatering phase. Energy needs for electricity or gas are shown in the table below:

 3DUWLDOGU\LQJ '0 7RWDOGU\LQJ '0 )XHO /W'0 120 300 (OHFWULFLW\ N:KW'0 30 50 7DEOH energy needs of the drying treatments [OTV 1997]

Energy requirements are important, but may be strongly reduced if an energy source is available on site (biogas or steam).

 6WDELOLVDWLRQDQGGLVLQIHFWLRQ The stabilisation aims at reducing the fermentation of the putrescible matter contained in the sludge and the emission of odours. Disinfection consists of eliminating pathogens.

$QDHURELFGLJHVWLRQ Applied to thickened sludge, anaerobic digestion (also referred to as methanisation) aims at reducing, stabilising, and partially disinfecting the treated volume of sludge. It consists of confining the sludge in a vessel at a temperature of about 35 °C. The anaerobic digestion is divided in three main phases: - hydrolysis of the macromolecules in smaller components - production of acidic compounds from those smaller compounds - gasification, generating carbon dioxide and methane. The table below shows the input and performance parameters of the anaerobic digestion.

3DUDPHWHU 7\SLFDOYDOXH Volumetric (d) 15-18 Volatile solids loading (kg VS/m3.d) 0.8-1.6 Solids loading (kg SS/m3.d) 1.0-2.0 Operating temperature (°C) 30-37 pH 6.6-7.5 Feed sludge concentration (%DS) 3-8 Total solids destruction (% input load) 30-35 Feed sludge volatile compounds (% of solid input) 70-80 Volatile solids destruction (% of VS input) 40-50 Gas production (m3 /kg VS destroyed) 0.8-1.2 7DEOH input and performance parameters of the anaerobic digestion [CIWEM 1996]

The biogas produced is often reused in boilers, to maintain a temperature around 35 °C. It may also be used to produce electricity on the plant. It is usually recommended to have the sludge remaining in the digester for more than 20 days, to guarantee a good stabilisation and disinfection. Other techniques based on the same process exist. Differences consist in the medium or high temperature used for operation.

 $HURELFGLJHVWLRQ Sludge is placed in a vessel with aerobic micro-organisms. Heat is generated when these bacteria degrade organic matter. In adequate conditions, the temperature can rise to over 70 °C. By subjecting sludge to these high temperatures for a particular period of time, most harmful organisms are destroyed. It is usual to subject the sludge to a temperature of 50 to 65 °C. for 5 to 6 days. In these conditions, volatile matter is reduced by about 40 %. The process is simple in design but has a high energy cost: 5 to 10 times more than anaerobic digestion. The influence of the process on the sludge composition has been given in chapter 3 (table 4).

/RQJWHUPOLTXLGVWRUDJH Storage of sludge has two essential purposes: regulating the flows of sludge to agriculture and homogenising its composition. Odours may arise, and an increase of the dry matter and a reduction of the organic matter have been observed. A reduction of the nitrogen content also takes place: nitrogen is converted into ammonium and to ammoniac in a gaseous form, resulting in decreasing the agricultural value of the sludge. Long-term storage of sewage sludge has a disinfecting property, reducing the amount of viruses and bacteria in sludge. Its efficiency depends on the duration of the storage. However parasites are the most resistant pathogens and it has been reported that long term storage would not affect their infectious potential. In cold climates, this process does not enable to reach a sufficient level of disinfection.

&RPSRVWLQJ Composting is an aerobic process consisting of aerating sludge mixed with a co-product such as sawdust or animal manure. Composting produces excess heat, which can be used to raise the temperature of the composting mass. The mix then evolves for several weeks. There are three types of processes: - Windrow: the sludge cake is mixed with a bulking agent and set out in piles. The composting material is turned mechanically to introduce air and prevent excessive temperatures. This system requires a large land area. - Aerated static piles: the sludge is mixed with a bulking agent and laid over perforated pipes, or on a floor through which air is blown. - Vessel systems: after mixing with a bulking agent, sludge is injected at the top of a vessel, where a harrow permits an equal repartition. In the lower part, air is injected, and the end product is extracted at the base of the vessel. The composting process is used to several purposes. Composted sludge presents a higher agricultural value (see chapter 3), reaches a good level of disinfection, and is stabilised, reducing therefore the arising of odours. It also has a humus-like aspect, which, together with the reduction of odours, makes the acceptance of its use easier. Lastly, composting is used to reduce the water content of the product, as it may reach over 60 % of dry matter, making also its handling easier.

/LPHWUHDWPHQW Lime treatment consists of the addition of lime to sludge, in order to raise its pH to 12, thus destroying or inhibiting the biomass responsible for the degradation of the organic compounds. The treatment helps also disinfecting sludge, increasing its dry matter content and making handling easier. The dry mass increase depends on the initial dry matter content and the amount of lime supplied. It is usually recommended to add 30% of lime to the dry mass of sludge, otherwise the treatment would not avoid fermentation in the long term.

 Lime treatment is not recommended when sludge is incinerated in a fluidised bed incinerator, as it may disturb its good operation. The necessary energy to perform this treatment is about 5 kWh/t DM, used for pumping and mixing.

1LWULWHWUHDWPHQW Nitrite treatment consists of maintaining sludge in an acid environment (about pH 2 or 3 according to the level of treatment expected) for 30 minutes where it undergoes the action of nitrite ion. This treatment is an efficient stabilisation process. Sludge may be stored for several months without generating odours. Concerning disinfection, two levels may be reached: partial disinfection (pH 3; bacteria are eliminated) or advanced disinfection (pH 2; spores are eliminated as well). This treatment is performed on thickened sludge. Its impact on the sludge structure facilitates further dewatering. Nitrite treatment is adapted - to small WWTP, where lime treatment could be expensive, - when lime treatment is not possible before land spreading, - before incineration as it improves its auto-combustibility.

3DVWHXULVDWLRQ Pasteurisation consists of heating the sludge to a temperature of 70 to 80 °C for a short period (about 30 minutes). This treatment allows reduction of the amount of pathogens in the sludge, but can not be considered as a stabilisation process in itself.

0DLQIDFWRUVGXULQJWKHGLIIHUHQWVWDELOLVDWLRQDQGGLVLQIHFWLRQWUHDWPHQWV Generally speaking, the decrease in the micro-organism population follows an exponential kinetic. This kinetic depends on a specific decay rate, which depends on the type of micro-organism, and exogenic factors, including temperature, moisture, duration and pH. The table below (grey areas) indicates the main factors to be controlled when performing the different kinds of stabilisation and disinfection treatments.

GXUDWLRQ WHPSHUDWXUH S+ $QDHURELFGLJHVWLRQ $HURELFGLJHVWLRQ /RQJWHUPOLTXLGVWRUDJH &RPSRVWLQJ 3DVWHXULVDWLRQ /LPHWUHDWPHQW 1LWULWHWUHDWPHQW 7DEOH deciding factors of the stabilisation and disinfection treatments

 (IILFLHQF\RIWKHWUHDWPHQWV Stabilisation and disinfecting treatments described above do not have similar effects on micro- organisms and pathogens. The table below gives a summary and their best conditions of practice.

7UHDWPHQW &RQGLWLRQV

9HU\HIIHFWLYHWUHDWPHQWV Thermophilic anaerobic digestion 55 °C ; 10 days Thermophilic aerobic digestion 55 °C ; 10 days Composting 50 – 60 °C ; 15 – 30 days Pasteurisation 70 – 80 °C ; 30 min Lime treatment pH 12, 10 days, (30 % addition to DM)

/HVVRUORZHIIHFWLYHQHVVWUHDWPHQWV Psychrophilic anaerobic digestion 20 °C ; 30 days Psychrophilic aerobic digestion 20 °C ; 30 days Chemical conditioning and mechanical dewatering - 6 7DEOH effectiveness of the stabilisation and disinfection treatments

When assessing the quality of sludge after treatment, difficulties arise relating to the facts that: - it is not possible to test all pathogens, as there may be a wide range of micro-organisms present in sludge, - tests are in some cases expensive, - results may not be available before one day, or in some cases several weeks. Therefore, monitoring indicators are being developed, which have to safely describe the level of disinfection reached in the sludge after treatment. Indirect parameters may be used, depending on the disinfection treatment used. These may be the temperature, pH, reaction time, moisture level, number of turnings etc. This enables a reduction in the pathogen analysis. The literature also suggests favoring the analysis of certain micro-organisms, thus determining: - the level of some micro-organisms which behave in the same way as pathogens, are consistently present in sludge, and are easy to cultivate and identify - the level of some particular pathogens, based on the assumption that if the most resistant pathogens are destroyed, the less resistant will be destroyed as well. WRc [2001] suggested using (FROL or &ORVWULGLXPSHUIULQJHQV for this purpose.

6 Source: ADEME 1994

 %R[6OXGJHWUHDWPHQWVLQWKH0HPEHU6WDWHV According to the information provided by the Member States to the Commission7, • In Germany, many different techniques are used, but no information was given about the prevailing processes. • In Luxembourg, sludge is digested and then conditioned with lime or iron salts. Mechanical processes are used for dewatering. Polyelectrolytes are added to sludge which are not conditioned in order to facilitate dewatering. • In the Walloon region of Belgium, sludge is digested, aerobically stabilised, mechanically or thermally dried, or conditioned with lime or polyelectrolytes. No information was available from the Flemish region. • In the United Kingdom, used methods are mesophilic anaerobic digestion, composting, lime stabilisation, liquid storage, dewatering and thermal drying. • In Denmark, sludge is digested in a heat digestion chamber or in a bioreactor, stabilised by aeration, composted (in controlled conditions during two weeks at a temperature of 55°C), conditioned with lime or pasteurised at a temperature of 70°C during one hour. • In France, sludge is subject to prolonged aeration, aerobic or anaerobic stabilisation, lime conditioning, thermal drying or composting. • In Finland, sludge is anaerobically digested, or composted. Other methods such as aerobic or lime stabilisation are of decreasing importance. • In Sweden, sludge undergoes following techniques: thickening (gravity thickening or flotation) stabilisation (aerobic, anaerobic, lime), conditioning, dewatering (centrifuge, filter belt press, air drying), thermal drying and composting. • In Ireland, sludge is dewatered (filter belt or centrifugation) before landfilling, or undergoes anaerobic digestion. Over 60% of the sludge used in agriculture originates from the Dublin WWTP, where sludge is dewatered (centrifuge) and thermally dried. • In Portugal, the technologies employed are drying beds (drainage on sand bed and evaporation of humidity), thickening, mechanical dewatering (band filters, filter presses, vacuum filters or centrifuge) and various stabilisation processes. No additional data is currently available about treatments carried out before stabilisation and disinfection (dewatering, and thickening). No data is available in the report mentioned above concerning sludge treatments in Greece. However Tsagarakis HWDO. [1999] documented the management of sewage sludge from WWTP in Greece. It appears that sewage sludge mainly undergoes gravity thickening and dewatering through drying beds or mechanical dewatering with bed filters. Digestion is employed mainly in large conventional activated sludge plants. Composting is only performed in one WWTP in Greece.

7 European Commission; 1999; Report from the Commission, Implementation of Council Directive 91/271/EEC of 21 May 1991 concerning urban wastewater treatment, as amended by Commission Directive 98/15/EC of February 1998; COM(98)775, http://www.europarl.eu.int/basicdoc/basicdoc-en.htm

  5HF\FOLQJDQGGLVSRVDOURXWHVIRUVHZDJHVOXGJH

Sludge Wastewater Water Sludge recycling Impacts collection treatment treatment and disposal

In this part, the operation of the different recycling and disposal routes for sewage sludge is described, before summarising the inputs, outputs and impacts of each of them.

 /DQGVSUHDGLQJ

5.1.1 Technical description Landspreading is a way for recycling the compounds of agricultural value present in sludge to land. All sludge types (liquid, semi-solid, solid or dried sludge) can be spread on land. However, the use of each of them induces practical constraints on storage, transport and spreading itself. The sludge production from a given WWTP is more or less constant throughout the year, but the use on farmland is seasonal. Therefore, storage capacity must be available on the WWTP or on the farm, either separately or in combination with animal slurry when allowed by the national regulations. Average storage duration is about 6 months. Storage on fields may also be practically observed. This however should only be performed shortly before spreading, and with solid and stabilised sludge in order to reduce risks of leaching. Liquid sludge may be stored in concrete tanks (mostly for small WWTP) or lagoons. It can be pumped to be transported. Semi–solid sludge may be stored on a platform, which must be waterproof, or in tanks. Sludge pits may also be found. As in most cases this type of sludge cannot be pumped, sludge has to be conveyed by using specific hauling equipment such as grabs. Odours may arise when sludge is handled to be conveyed. The structure of solid sludge enables storage on piles. Handling implies the use of a crane or a tractor. Dried sludge does not present any specific constraint. If sludge however is pulverulent, storage must be monitored in order to prevent any explosion and emission of particles to air. Transportation is the most expensive aspect of this route. It is possible to use tankers for liquid sludge or articulated lorries for other sludge types. Sludge can be applied to the fields by using trailer tank or umbilical delivery system and may be applied by surface spreading (it is however of importance to reduce the formation of aerosols to reduce the risk of odour nuisance) or directly injected into the soil. Dried sludge may be supplied by using the same equipment as for solid mineral fertilisers. The spreading equipment has also to be adapted to the type of sludge. Culture types, soil occupation, accessibility of the field, meteorological conditions influence landspreading. Mostly, the practice can be performed at two times in the year: at the end of summer, after harvesting, or in spring, before ploughing and sowing. As already stated, sewage sludge contains compounds of agricultural significance such as nitrogen, phosphorus, potassium, organic matter or calcium, making its use relevant as an organic fertiliser. Moreover, the cost of this route may be cheaper than other disposal routes. However, the presence of pollutants in sludge implies that the practice should be carefully done and monitored. To this purpose, in some countries, codes of practice and spreading schemes have been established, summarising the regulatory obligations. Periods for spreading, types of culture, adequate record keeping are described in order to manage the sanitary and environmental risks.

 5.1.2 Impacts and benefits Inputs of landspreading are sludge and additional resources such as petrol for transportation and application, and room for storage. Outputs consist of yield improvement and fertiliser substitution, but also emission of pollutants to soil, and indirect emissions to air and water. Other emissions to air are exhaust gases from transportation and application vehicles. Dried sludge may also be emitted to the air during transportation when trucks are not covered.

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(PLVVLRQÃRIÃDQ SDWKRJHQVÃ SROOXWDQWVÃWRÃ (PLVVLRQÃRIÃ )HUWLOLVHUÃ VXUIDFHÃZDWHU SROOXWDQWVÃDQGÃ VXEVWLWXWLRQ SDWKRJHQVÃWRÃVRLO 6XUIDFHÃ ZDWHU 6RLO

(PLVVLRQÃRIÃ *URXQGZDWHU SROOXWDQWVÃ LQFOÃÃ QLWUDWH ÃWRÃ JURXQGZDWHU

)LJXUH representation of the inputs and outputs for landspreading

(PLVVLRQVWRVRLOZDWHUDQGDLU As already stated in part 3, sludge contains compounds of agricultural significance such as nitrogen, phosphorus, potassium and eventually calcium. Sludge application therefore replaces conventional fertiliser application. It also contains organic matter, but usual application rate is below that which would have a significant positive impact on soil structure. Landspreading also involves the application to soil of the pollutants contained in sludge. Those pollutants undergo different transformations and transfer processes, which are more precisely described in chapter 6. Among those processes, leaching, runoff, volatilisation could enable the transfer of the compounds into the air and water, and their introduction into the food chain.

2WKHULPSDFWV Disamenities may take place because of landspreading operation odour. Operation accidents can also happen, generating an increase in the emissions to soil and a possible reduction of agricultural yields.

  ,QFLQHUDWLRQ

5.2.1 Technical description Incineration is a combustion reaction. Different types of incineration may be considered, separated in the following categories, according to the draft directive on the incineration of wastes: - mono-incineration when sludge is incinerated in dedicated incineration plants, - incineration with other wastes, mainly household wastes, - co-incineration when sludge is used as a fuel in plants whose purpose is the generation of energy or production of material products such as coal power plants or cement plants, Other processes such as wet oxidation or pyrolysis are developing technologies involving thermal oxidation, and are described in a following part of this report. Figure below summarises all possible thermal oxidation routes for sewage sludge.

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Dewatering

Drying

,QFLQHUDWLRQÃDQGÃ 0RQRLQFLQHUDWLRQ FRLQFLQHUDWLRQ $OWHUQDWLYHÃSURFHVVHV

- Multiple Hearth Furnace - With municipal solid waste - Wet oxidation - Fluidised Bed - With coal in power plants - Pyrolysis - Combined MHF-FBC - With other fuels - Gasification - Cyclone Furnace - In other processes: - Pyrolysis-gasification - Smelting Furnace - In cement production - Pyrolysis- combustion - Rotary Furnace - In brick making - In asphalt works

)LJXUH different routes and related technologies of thermal processing of sludge [after Werther and Ogada 1999]

0RQRLQFLQHUDWLRQ As described in the preceding figure, several types of furnaces may be used for sludge mono- incineration. It is however increasingly performed in fluidised bed incinerators. This is mainly due to the fact that: - this process permits virtually complete combustion at relatively low temperatures, - the amount of inert bed material prevents sudden temperature changes in the furnace, - intermittent operation is possible, - maintenance costs are low [Werther and Ogada 1999]. Moreover Mininni [2000] described the partitioning of Cr, , Pb, Sn and Zn during sludge incineration. Cd, Pb, Sn, and Zn showed enrichment factors from 4 to 26 in the fly ash produced in rotary kiln furnace tests, in contrast with negligible enrichment factors measured in fluidised bed tests. Therefore, since metal emissions into the atmosphere are strictly related to the enrichment factors in the fly ash, those test suggest that, from the environmental point of view, sludge incineration with fluidised bed furnaces is safer than rotary kiln furnaces. The fluidised bed system consists of a combustion chamber lined with a refractory material at the base of which a bed of sand is brought to a high temperature and held in suspension by hot air.

 Sludge is introduced inside or above the bed of sand and burnt at a temperature of 900 °C, for a few seconds. The process is described in the figure below.

 1 Sludge feed 2 Supplementary combustible 3 Combustion gas 4 Flue gas 5 Fluidised bed 6 Combustion chamber 7 Air admission chamber 8 Window 9 Heat exchanger 10 Flue gas treatment

)LJXUH operation of a fluidised bed incinerator [source: mg engineering, Lurgi Envirotherm] In order to reduce the consumption of extra-combustibles, a heat recovery system is generally installed. It warms the air that is injected into the combustion chamber. For the incinerator to operate adequately, it is necessary to have sludge with a dry matter content of 30 to 45 %. These kinds of incinerators can operate 24 hours a day, without specific supervision. Designated incinerators may be installed on site in a WWTP, when handled capacities justify such a cost intensive technique. However, designated incinerators may be shared, and therefore burn sludge from different origins. This practice is more or less widespread in Europe and depends on the country8. Flue gas has to be treated, to remove acid gases, heavy metals under gaseous and particulate form, and dust. Different treatments are possible for flue gas, such as electrostatic precipitators and bag filters to remove particulate matter, scrubbers and wet processes for acid gases. They may be combined. It is interesting to observe that sludge quality and the fluidised bed incineration technology often do not imply a specific treatment of nitrous oxides and dioxins [OTV 1997]. The choice of system depends on the emission limits, which have to be reached, and the possible recycling of the ashes.

,QFLQHUDWLRQ Incineration consists of using already existing installations, usually the ones designed for municipal waste incineration, limiting additional investment. The technique is especially attractive if the incinerator is settled near the WWTP. If the calorific value of the sludge is similar to that of municipal wastes (about 60-65 % DM [OTV 1997]), sludge can easily be added to the waste. When sludge is dry, it must be carefully mixed to

8 Source : OTV and EEA

 the waste, to avoid accidents during combustion, such as explosions. It is also possible to introduce thickened sludge, reducing the treatment costs (dewatering and/or drying costs). In this case however, a reduced calorific value implies to restrain the proportion to waste (about 20 % of the tonnage). There are different techniques for injecting the sludge: sludge can be mixed before the combustion with the waste, injected under pressure in the furnace or at the exit of the combustion chamber. The investment costs are much lower than in the case of mono-incineration, as the process only necessitates a modification of an existing installation (sludge injection system, eventually sludge treatment on site).

&RLQFLQHUDWLRQ Other possibilities of incineration of sewage sludge are the use as fuel in coal-fired power plants and cement kilns. The main interest of sludge in cement production is its calorific value. When using sludge as a fuel in cement production plants, the maximal sewage sludge feed rate should not be more than 5% of the clinker production capacity. Consequently, for a 2000 t/day cement kiln, a maximum of 100 t/day dry sludge might be used, without worsening the clinker quality [Werther and Ogada 1999]. Other sources9 however recommend that cement quality should be controlled to ensure that the sludge does not impact the mechanical properties of the product. Gas and effluents of the plants have also to be monitored. Full-scale tests have been performed in power plants in Germany, Netherlands and Belgium. The tests showed that co-combustion had little effect on the emission of gases; a slight increase in the heavy metals content of the ash has been reported. Examples of the emissions from the Franken II power plant near Erlangen in Germany are shown in the table below.  8QLW 0HDVXUHGYDOXHV /LPLWYDOXHV 3 7RWDOGXVW mg/m 2.0 30 3 12[DV12 mg/m 195.0 300 3 62[DV62 mg/m 64.0 200 3 +&O mg/m 6.0 - 3 +) mg/m 1.2 - 3 7RWDO& mg/m < 3.0 - 3 &2 mg/m 18.0 - 3 7O&G mg/m 0.002 0.05 3 +J mg/m 0.002 0.05 3 6E$V3E&U&2 mg/m < 0.05 0.5 &X0Q1L96Q 3 3&'') ngTE/m < 0.0004 0.1 7DEOH emission values of the Franken II power plant near Erlangen (220 MWh), Germany [VDI 2000]

5.2.2 Impacts and benefits

,QSXWVRXWSXWV In order to operate an incineration plant, necessary inputs are wastes and/or sewage sludge. The water content of sewage sludge may be variable. Additional resources are needed, which are mainly: - water, which does not need to be of primary quality,

9 CEN TC 308, Recommendations to preserve and extend sludge utilisation and disposal routes. 10 Directive 2000/76/EC of the European Parliament and of the Council of 4 December 2000 on the incineration of waste.

 - fuels used for starting up the facility - auxiliary materials such as calcium carbonate, especially for flue gas treatment. Outputs are the possible energy recovery, flue gases, ashes, and wastewater. Therefore incineration generates emissions to air, soil and water, mainly located at the incineration site or at the landfill where ashes are disposed of. Emissions depend on the process, but also on the sludge type. In order to reduce those emissions, treatments have to be performed on flue gas and water (see previous part). In most cases, the energy recovery will be counterbalanced by the energy used for reducing the water content of sludge. Indeed, considering the water content of sludge, - either dewatered sludge is burnt, and in this case the energy generated during combustion will contribute to removing the remaining water contained in sludge. In some cases of mono- incineration additional fuel may even be needed, - or, sludge may be dried before incineration, and in this case the energy recovered will counterbalance the energy used for the purpose of drying.

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)LJXUH representation of inputs and outputs to an incineration plant [after COWI 2000]

(PLVVLRQVWRDLU Following pollutants are found in the flue gas, i.e. before any treatment: particulates and fly ash, dioxins, heavy metals bound to particles or under gaseous form (mainly Hg, but also Cd), acid gases (SO2, HCl, HF), nitrogen oxides (NOX), carbon dioxide (CO2) and organic compounds bound to particles and volatile organic compounds (VOC). Flue gas treatment is performed in order to reduce their content in the fumes emitted to the air. At sludge incineration temperature, dioxins and furans are completely destroyed, so that in the incinerator they are present in negligible concentrations. However, in the flue gas cleaning stages, where the gas temperature is below 450 °C, new formations of dioxins and furans may take place [Werther and Ogada 1999]. It has to be observed that in the case of mono-incineration, the amount of dioxins and NOX present in the raw flue gas is low enough to avoid the implementation of a specific gas treatment process for these compounds [OTV 1997]. This is confirmed by Werther and Ogada [1999], who observed that sewage sludge combustion is characterised by low net emissions of NOx with the conversion ratio of fuel N to NOx being less than 5%. Average composition of the flue gas is given in the table below:

  &RPSRVLWLRQRI /LPLWYDOXHV 3 WKHIOXHJDV mg/Nm mg/Nm3 Daily average values 62 300 to 3 500 50 +&O 50 to 400 10 &2 5 to 50 50 12; 50 to 200 200/400 'XVW 25 000 to 65 000 10 +) 0 to 6 1 3 'LR[LQV N/A 0.1 ng/m 7DEOH composition of the flue gas of an incinerator (at the exit of the combustion chamber and before any flue gas treatment) [OTV 1997]

Once emitted into the air, pollutants are dispersed in the atmosphere. Their concentration depends on several factors, depending on the local conditions (climatic conditions, wind direction, wind speed, distance from the incineration plant) or the physical and chemical properties of the compounds. Atmospheric deposition to the soil can also take place. Lastly, emissions to air may be due to handling of ashes and combustion residues.

Emissions to air and especially dust, dioxins, heavy metals, VOC, NOx, CO and SO2 may have adverse health effects. Those pollutants as well as CO2 can also have impacts on ecosystems and climate change. Damages to buildings may also occur, particularly due to particulate matter, NOX and SO2.

(PLVVLRQVWRZDWHU Water emissions occur due to flue gas treatment, when a wet process is performed. However, water treatment reduces the pollutant content of this wastewater. The pollutants present in this wastewater are mostly the same as those released to the atmosphere with the fumes. Emissions to water may also be caused by leaching of ashes disposed of to landfills. Groundwater as well as surface water are concerned by those emissions, which can give rise to adverse health effects and ecotoxicity.

(PLVVLRQVWRVRLO Emissions to soil are due to the disposal of ashes or the flue gas treatment residues to landfill, or the use of ashes in road construction. Bottom or grate ash are largely reused, whilst fly ash and residues from the flue gas cleaning system are generally placed in hazardous waste landfills. They are also the consequence of the atmospheric deposition of the pollutants emitted to the atmosphere. It must be observed that flue gas treatment residues contain much more pollutants than ash. The composition of the ashes of a sewage sludge incinerator is given in table 22.

11 Directive 2000/76/EC of the European Parliament and of the Council of 4 December 2000 on the incineration of waste

 &RPSRVLWLRQRIDVKIURPDIOXLGLVHG EHGVOXGJHLQFLQHUDWRU proportion of dry weight %

6L2 54.9 $O2 18.4 32 6.9 )H2 5.8 &D2 5.4 .2 1.9 0J2 1.3 7L2 1.1 2WKHUPLQHUDOV 2.1 +HDY\PHWDOV 0.1 2UJDQLFDQGYRODWLOHPDWWHU 1.9 7DEOH composition of ashes of a sewage sludge incinerator [Hudson HWDO. 1992 in CIWEM 1995]

2WKHULPSDFWV Disamenities may take place because of the operation of an incineration plant. Among those, noise, dust, odour and visual pollution may be evoked. Operation accidents can also happen, generating an increase in the emissions to air, reducing the energy recovery, and leading also to health impacts on operating personal.

 /DQGILOOLQJ

5.3.1 Technical description So far, landfilling has been a major route for sludge disposal. However, it should be a limited outlet in the future, because of the European legislation on the landfilling of waste which states that “Member States shall set up a national strategy for the implementation of the reduction of biodegradable waste going to landfills”12 no later than 16.07.2003. This solution is being chosen when no other way exists, that is: - when concentration of contaminants makes it unsuitable for land spreading or other method of recycling, - when farmland, forestry or land reclamation are not feasible owing to location or topography or when the total costs would be uneconomic, - if no incineration capacity is available on or near the site. There are two possibilities for landfilling sludge: mono-deposits, where the landfill is only used for sludge, and mixed-deposits, when the landfill is used for municipal wastes as well. There is no specific technical constraint in the conception of the landfill for the disposal of sludge. However, the conditions for disposal of sludge are set out in regulations in each country. Waste deposit in landfill undergoes the following steps:

12 Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste

 - initial aerobic phase: the degradation first occurs under aerobic conditions, during which aerobic micro-organisms consume the available oxygen in the deposit. This step is rather short (about 14 days). The organic content of the leachate increases. - Acetogenesis: as the level of oxygen decreases, acetogenic and fermentative bacteria decompose the easily degradable material of the waste. The pH value decreases in the deposit, increasing consequently the solubility of inorganic substances such as heavy metals. High organic pollution of the leachate is observed. - Anaerobic methanogenesis: methanogenic bacteria proliferate during this phase, increasing the production of methane. The pH value increases, and the organic content of the leachate decreases. The gas production then reaches a stable composition. Little is known concerning the evolution of the deposit in the long term, that is more than 30 years. When processing a mono-deposit, the compacted structure of the deposit in the cell is not favourable for gas formation. However, should this happen, its composition would not be very different from usual municipal wastes deposit: 50 to 60 % methane, 40 to 50 % carbon dioxide, plus trace elements. In mixed deposit with municipal solid wastes, sludge is not the principal ingredient: its proportion reaches usually 20 to 25 % of the total deposit. Technically, disposing to landfill in mixed deposit does not represent the same constraints (especially on water content) as in mono deposit. It is also to be observed that thanks to the physical structure of the deposit, the gas formation is enhanced, and the heavy metals content in leachate is reduced. Sludge can usefully be disposed of before closure of the cell, in order to gain space.

5.3.2 Impacts and benefits The inputs of landfilling are municipal solid wastes and sewage sludge, and additional resources needed for the operation of the landfill site, such as fuel for vehicles, electricity, and additional materials when leachate is treated on site. Outputs consist of leachate, landfill gas and energy production when the gas is recovered. Landfill operation generates therefore emissions to the air, soil and water.

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)LJXUH representation of inputs and outputs to a landfill site [after COWI 2000].

 (PLVVLRQVWRDLU Emissions to air are the release of landfill gas, when this is not recovered on site for energy generation, and dust released during the handling of waste. Other emissions originate from the exhaust gas of the engines used on site. The generation of landfill gas is of about 10 m3 per ton of deposited waste per annum, but may change according to the dimension of the landfill, the input rate, the age of waste, and the physical and chemical characteristics of the deposit. The main components of the landfill gas are methane (between 50 and 60 %) and carbon dioxide (between 40 and 50 %). Many other VOC13s have been reported as traces, accounting in general for less than 1 % of the volume of gas generated. The EEA [2000] reported the presence of 12 halogenated hydrocarbons and about 30 hydrocarbons in landfill gas, with levels ranging from 0,02 mg/m3 to over 600 mg/m3. The amount of VOCs released to the atmosphere is lower when landfill gas is used or flared. In this case however, dioxins may be generated. Volatile substances migrate between the landfill and the atmosphere due to diffusion and pressure difference. VOCs originate from the waste, but new substances are also generated by the chemical and biochemical transformations occurring in the deposit. Carbon dioxide and methane have impacts on the climate, and trace compounds may be toxic and/or carcinogenic, with varying threshold values. An issue of concern is the impact of landfills on the health of people leaving in the neighbourhood of such an installation. Several studies have been conducted, not permitting to identify any exposure pathway or causal link.

(PLVVLRQVWRZDWHUDQGVRLO Leachate generated within a landfill is emitted to soil and water, and the amount generated depends on the climatic conditions and landfill cover. The composition of the leachate varies over time. It 2+ + + + 2- 2- - contains several compounds such as ions (Ca , K , Na , NH4 , CO3 , SO4 , Cl ), heavy metals, organic compounds (chlorinated organics, phenol, benzene, pesticides) and micro-organisms. It can also contain dissolved methane, which is present in the landfill gas. Emissions may be reduced when leachate is collected on site and treated. Otherwise, leachate may leach through the soil to the water table, or be directly released in surface water, and have impacts on human health and ecosystems. Leaching depends on the physical and chemical properties of the compound, but also on the soil properties and environmental factors.

2WKHULPSDFWV Operation of a landfill generates other impacts in terms of - noise and dust from the delivery vehicles - odours - vermin, rats and birds - land use, disturbance of vegetation and landscape - in some cases, bad operation of a landfill can also cause fires, explosion, and accidental emission of leachate or landfill gas.

13 Volatile Organic Compounds

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5.4.1 Use in forestry and silviculture Forestry and silviculture refer to different kinds of tree plantation and use. The term forestry is mainly used when considering amenity forests, or mature forest exploitation. On the contrary, silviculture is more specifically used when referring to intensive production, such as energy coppices or poplar plantation. These definitions are used in this chapter. Use of sewage sludge in forestry and silviculture appears to be an alternative to the recycling of sludge to agricultural land. Relatively small areas could permit the spreading of an important part of the sludge production in Europe. For instance, 50% of the French sludge production could be spread on 1% of the forest area when considering a rate of application of 3 tDM/ha/year [INRA 1999]. From an economical point of view, this route is of interest if areas are available for spreading in the neighbourhood of the WWTP, in order to reduce transportation costs and related pollution. From the agricultural and environmental point of view, even if similarities between landspreading and use in forestry may be observed concerning environmental impacts, great differences exist due, amongst other factors, to the specificity of the species grown, the fauna and flora involved, and the soil types. The issue of sludge recycling to forestry and silviculture has not been addressed to the same extent as its recycling to agricultural land, and much less information is available in the literature concerning this outlet. Some conclusions can however be drawn about agricultural advantages and constraints as well as about environmental and sanitary impacts. Good practices corresponding to the state of the actual knowledge may also be found in scientific literature.

$JULFXOWXUDOLQWHUHVWDQGFRQVWUDLQWV 6OXGJH DSSOLFDWLRQPD\ EH SHUIRUPHG DW GLIIHUHQW WLPHV GXULQJ WUHH JURZWK. Landspreading may be done before plantation, when considering re-afforestation or implantation of an intensive culture. In silviculture, sludge application may also be performed just after sowing or after each cut. In forests, sludge application could occur practically all year round, in accordance with good practices and local conditions. $\LHOGLPSURYHPHQW following sewage sludge application on forest soils has been reported in the literature. In general, an LQFUHDVHLQKHLJKWGLDPHWHUDQGVXUIDFHDUHDFRYHUDJH of the trees have been observed. However, results depend upon the species, in some cases even on the individual, and on the local conditions [INRA 1999]. Yields are further improved when considering young plantations. It must be observed that results refer to tests mainly performed with a single sludge application, at very high rate of application [UBA 1998]. Another benefit which has been reported in the literature is the LPSURYHPHQW RI WKH VRLO FRPSRVLWLRQLQWHUPVRIDJURQRPLFYDOXH (especially Ca, Mg, S and trace elements), which is of particular interest compared to sludge spreading in agriculture, as forest soils are often particularly poor in such compounds [INRA 1999]. Sewage sludge also contains organic matter, which may act as a soil improver (see part 3.4.1). The chemical nature of the sludge organic matter (mainly easily degradable organic compounds) induces a fast mineralisation in soil. Therefore, VHZDJHVOXGJHSUHVHQWVDORZKXPLFYDOXH [INRA 1999]. Moreover, as already mentioned above, it has been reported that the minimum threshold level for the detectable effects of sludge additions on the physical properties of agricultural soil was c. 5 tonnes of organic matter per ha, i.e. about 10 t dry solids/ha. Below this level of application, those benefits are not expected to occur. However, these statements concern agricultural soils, and more information is needed concerning the specific impact of sewage sludge organic matter on the physical properties of forest soil. It may be assumed that the main benefit of sewage sludge organic matter would be its use by the micro-organisms present in the upper soil layer and humus and the release of compounds of agricultural value during its degradation.

 Sludge spreading in forestry and silviculture however also presents disadvantages, mainly related to the high level of application mentioned in field tests. For instance, excess rates of liquid sludge application could lead to the formation of dense, macropore-free barrier layers creating anaerobic conditions in humus and soil. As a consequence, KXPXVDQGXSSHUVRLOOD\HUGHJUDGDWLRQPD\ EHREVHUYHG as well as GHVWUXFWLRQRIKDELWDWV for soil biota and reduced microbial activity [UBA 1998]. When sludge is spread on young plantations, it has been reported that FRPSHWLWLRQ with other vegetal species may occur, reducing the intake of compounds of agricultural value by young trees. Sludge spreading also induces an LQFUHDVHLQWKHSUROLIHUDWLRQRIZHHGV [INRA 1999]. Regarding practical constraints, application of liquid sludge in forested areas may be done by using the same spreading machinery as for landspreading (see figure 15). On the contrary, when spreading other sludge types, either specific spreading machinery is necessary or the machinery used for spreading on agricultural land needs to be adapted, due to the presence of the trees, and in order to avoid any degradation. Moreover, sludge application in timber or mature forest is only possible on forest paths, inducing an uneven repartition of the nutrients.

)LJXUH sludge spreading in forest (France)

(QYLURQPHQWDODQGVDQLWDU\LPSDFWV In a general manner, emissions to soil, air and water, as well as other environmental impacts are similar to those concerning agricultural landspreading. However, some differences have been reported in the scientific literature. As for sludge use in agriculture, DFFXPXODWLRQRIKHDY\PHWDOVLQWKHXSSHUOD\HUVRIWKHVRLO (mainly up to 10 cm) may be observed. Forest soils are often acidic and may therefore induce an increased circulation of metals. The Austrian UBA [1998] reported that no leaching of heavy metals to groundwater has been observed in experimental studies but also that more research is needed on this issue, especially concerning sandy or macroporous soils. An issue of concern when spreading sludge in forests is QLWUDWH OHDFKLQJ: the Austrian UBA reported that nitrogen loads which exceeded the forest stand’s capacity led to strongly increased nitrification and to increased leaching of nitrate together with potassium, magnesium and calcium. This could occur especially when sludge is applied all at once at high levels. Some LQGLUHFWLPSDFWVRQZLOGOLIHHFRORJ\ have also been reported, since sludge application and related yield improvement increased the availability of food resources for numerous animal species such as deer, small mammals and birds. Selective browsing of forest trees has been observed by

 animals trying to reach the nutrient-richer foliage, inducing injuries to mature trees and destruction of young plantations, as well as a related increased susceptibility to pests and pathogenic fungi. Overall, the number of species did not seem to be affected by sludge application [UBA 1998]. Sanitary impacts of sludge application are not well enough documented to draw any conclusions. 7KHULVNDQDO\VLVVKRXOGLQDQ\FDVHGLVWLQJXLVKIRUHVWDUHDVDFFRUGLQJWRWKHLUXVH: forests opened to the public present higher risks than those used for silviculture. In order to reduce the risk of the exposition to pathogens, recommendations usually include a restricted access to the area on which sludge has been spread during 3 to 12 months following its application [INRA 1999]. When considering the risk linked to the presence of heavy metals in sludge, LWKDVEHHQDVVXPHGWKDW ULVNV DUH ORZHU WKDQ WKRVH LQGXFHG E\ VSUHDGLQJ RQ DJULFXOWXUDO ODQG DV IRUHVW SURGXFWV UHSUHVHQWRQO\DVPDOOSDUWRIWKHKXPDQGLHW [INRA 1999]. However, some risk may exist due to the transfer of heavy metals to game species, or to some edible mushroom species which are known to accumulate heavy metals.

*DSVLQNQRZOHGJH Results mentioned above rely on experimental studies. However, these concern very different conditions and species, making comparisons and extrapolation (especially extrapolation to the variety of forests which may be found in the different Member States of the EU) difficult. It must moreover be stressed that most of the experiments concern a XQLTXHDSSOLFDWLRQRIVOXGJHDWKLJK UDWHRIDSSOLFDWLRQ [UBA 1998]. More information is therefore needed concerning repeated sludge spreading at lower rates, especially in terms of yield response, and environmental and sanitary impacts. Moreover, experiments reported in the literature cover a maximum of 13-18 years, to be compared with an average timber rotation of 120 years in forests. There is therefore no data available in the long-term effects, and relevant experiments should be performed. Most of the experiments have been performed with OLTXLGVOXGJH, making it necessary to improve the knowledge concerning this route when using other sludge types. Lastly, more research should be carried out regarding the environmental and sanitary impacts of sludge spreading in forests and silviculture, especially concerning the transfer of heavy metals to game species as well to some edible mushrooms which are known to accumulate heavy metals, and concerning organic pollutants for which no specific data is presently available.

*RRGSUDFWLFHV If sludge spreading is to be performed on forests or in silviculture, some good practices and recommendations may be found in the literature which are summarised below. First of all, spreading should be avoided in forests to which the public may have access, in order to avoid any contact with the sludge. Game or mushroom supply areas should also be excluded from the spreading perimeter. If spreading is to be performed in forests to which the public could have access, - sludge should be disinfected or access should at least be prohibited to areas on which sludge would have been spread during 3 to 12 months [INRA 1999], - the public should be informed, - sludge should be stabilised in order to avoid odour problems, and thereby facilitating the acceptance of sludge spreading. Sludge spreading could be privileged in silviculture, that is on intensive tree production, such as energy coppices. Poplar production should however be excluded, as it is most often performed in wet areas, in which water contamination could occur. In a general manner, sludge spreading should be avoided on sloping land, in areas adjacent to potable water reservoirs, on sandy soils, and in wet areas. An agreement at local level should be reached before sludge spreading is performed. Moreover, the public should be informed of the practice.

 Lastly, recommendations regarding application rates may be found in the literature, relying on the comparison of the results of several field tests. The Austrian UBA recommended a rate of application between 100 and 200 m3/ha/year of liquid sludge, i.e. 5 to 10 tDM per hectare, assuming a dry matter content of 5%. CIWEM [1996] also recommends an application of 200 m3/ha/year, introducing the following restrictions: - The maximum application rate of nitrogen during the pole stage should be 1000 kg N/ha, - The application rate of sludge should be reduced to 100 m3/ha on wet soils, - The application rate of liquid sludge should be reduced to 100 m3/ha on slopes of 15-25 degrees, and further reduced to 50 m3/ha on slopes of 15-25 degrees with sparse vegetation, - The application rate should be increased to 100 t DM/ha during pre-planting and early establishment.

5.4.2 Land reclamation and revegetation Use of sewage sludge in land reclamation and revegetation aims to restore derelict land or protect the soil from erosion, depending on the previous use of the site. In the case of industrial sites, topsoil may often be absent or if present, damaged by storage or handling. Soil or soil forming materials on site may be deficient in nutrients and organic matter. Other problems may exist, such as toxicity or adverse pH. All these problems create a hostile environment for the development of vegetation [WRc 1999]. Possible solutions include the use inorganic fertilisers or imported topsoil, which can be very expensive depending on location and availability. An alternative solution is the use of organic wastes such as sewage sludge, which is already used in Sweden, Finland or the United Kingdom. According to the site use, several situations may arise, for which the provision of sludge could be useful. They are summarised in the following table. In the case of industrial sites, the benefits of sludge application also include the improvement of nutrient status, the addition of organic matter, and control of acid generation.

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$PHQLW\DUHDV XX X VNLUXQVJROIFRXUVHV 7DEOH objectives of the sludge spreading in land reclamation

Sludge application is performed by using the same machinery as in the case of recycling to agriculture. Some specific machinery for sludge projection may be needed when applying sludge on areas to which access is difficult. When aiming to increase soil quantity on the site, two techniques are observed in the field: sludge may be either directly applied before mixing with the soil present on the site or mixed with soil before application. The amount of sludge usually applied is much higher than in the case of landspreading. As an example, some experiments were made to develop ski runs in La Plagne (France). To reach a soil thickness of 5 cm, it was necessary to use about 100 to 150 tons per

 hectare [ADEME 1999]. WRc [1999] also indicates some typical application rates for different reclamation sites which are summarised in the table below

7\SLFDODSSOLFDWLRQUDWHV 7\SHRIODQG 5HDVRQRIDSSOLFDWLRQ Cake (t DM/ha) Liquid (m3/ha) Low maintenance amenity Nutrient status improvement 50 100 Disturbed agricultural soils Nutrient status improvement 100 - Sites lacking top-soil Organic matter addition 100-500 - Acidic colliery spoil Acid generation control > 500 - 7DEOH summary of typical sludge application rates for different reclamation sites

Information is needed to assess the risk of this practice as no sufficient data is available concerning environmental and sanitary impacts. It was assumed that risks are lower than in the case of spreading on agricultural land, when considering that its use is not related to food production. In the case of ski run development, sludge is usually applied in September, ensuring a sufficient time period before the use of the land for grazing. However, no data is available concerning the potential impacts on wild fauna and flora. Moreover, the amount of sludge applied as well as the use of sludge on sloping land for erosion reduction go against actual regulatory prescriptions for the use of sludge in agriculture. A risk may therefore arise because of the amount of pollutants or nitrogen applied to land. WRc [1999] recommends that sludge should be sampled and analysed for heavy metals on a regular basis to ensure that, at the application rates required for land-reclamation, heavy metals additions are well within acceptable limits. In any case, sludge used for land reclamation and revegetation in field experiments is always treated sludge, in order to ensure sufficient disinfection and to reduce the presence of odours.

 'HYHORSLQJWHFKQRORJLHV Several technologies presenting an alternative to conventional combustion processes are currently being developed or introduced into the market. These technologies are mainly represented by the wet oxidation process, pyrolysis, and the gasification process, which are described below. Other technologies may be found, which are most often combinations of these three main processes. As mentioned by Werther and Ogada [1999], co- and mono-combustion of sewage sludge will still play an important role in the future, since alternative technologies are just introduced into the market and therefore do not benefit from the same experience. However, those technologies present advantages in terms of flue gas and ash treatment. Moreover, they also seem to have reduced impacts on the environment compared to conventional combustion processes.

5.5.1 Wet oxidation Liquid sludge is set in contact with an oxidative gas such as oxygen in a wet environment, at a temperature of around 250 °C and under high pressure (70 to 150 bars) in a continuous process. Temperature and pressure levels, the use of catalyser, and the gas used (oxygen or air) differentiate the existing processes. Sludge is changed in three main products: - a liquid phase containing easily degradable organic matter, which is easily treated when sent back at the head of the station

 - clean combustion gases, which do not have to be treated, as the relatively low temperature of the process avoids generation of compounds such as PCDD/F or NOx. Moreover, as the reaction takes place in a wet environment, no dust is released to the atmosphere - mineral residues in a liquid phase which has to be treated. The process is presented in the figure below:

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Organic pollutants are broken down, and heavy metals concentrate in the solid residue, except for mercury which is found in the gas (see table 25).

(mg/kg DM) &RQWHQW &RQFHQWUDWLRQ 5DZVOXGJH 6ROLGUHVLGXH IDFWRU &DGPLXP 10 35 3.5 7RWDO&KURPLXP 40 130 3.2 &RSSHU 376 1300 3.4 0HUFXU\ 5 2 0.4 1LFNHO 32 110 3.4 /HDG 145 528 3.6 =LQF 820 2750 3.3 7DEOH fate of heavy metals in the wet oxidation process [OTV]

No important preliminary treatment is required before performing wet oxidation: in most cases thickening is sufficient. However, the mineral residues and the liquid phase have to be separated after oxidation. In some cases, the mineral residuals may be treated in the same way as incineration ashes.

 Data are available concerning the ATHOS process developed by OTV. Its characteristics are described below:

(QWHULQJVOXGJH DM content g/L 40 VM/DM % 70 COD g/L 40 N-NH4 g/L 0.2 N-NTK g/L 2

%\SURGXFWV 5HDFWLRQ*DV CO2 % vol 53 H2O % vol 38 N2 % vol 3 O2 % vol 6 $TXHRXVVROXWLRQ COD g/L <10 N-NH4 g/L 0.7 AcOH or equiv. g/L 7 – 9 SM g/L <0.8

6ROLGUHVLGXH DM content % 50 TOC % <3 7DEOH characteristics of the ATHOS wet oxidation process [OTV] (*after catalytic treatment)

For the time being, the technique is not widespread enough to assess costs. However it seems to be competitive in terms of investment and operation costs for WWTP up to 200 000 equivalent inhabitants in comparison with incineration on site [OTV 1997]. Wet oxidation also allows reducing the dewatering/drying stages.

5.5.2 Pyrolysis Pyrolysis is a thermal process treatment in absence of oxygen. Waste is not burnt, but brought to a temperature of 300 to 900 °C. The process produces two kinds of residues: solids containing mineral matter and carbon, and hot gases. The process is presented in figure 17, and the matter balance (in the case of household wastes) is detailed in table 27.

Temperature (450 to 750 °C) Absence of air

Hot gases

Sludge Pyrolysis

Solid residue

)LJXUH presentation of the pyrolysis process

 WRQRIZDVWH 'U\LQJNJZDWHU &DUERQDWHGVROLGV NJ +RWJDV NJ Mineral residues : 95 kg Metals : 50 kg Inert, glass, stones : 45 kg Carbonated residue : 210 kg

8OWLPDWHUHVLGXHDVKHVNJ 7DEOH matter balance of household waste pyrolysis [Free University of Brussels]

As the products of the process have a calorific value, pyrolysis is considered as a pre-treatment, requiring further valorisation of the solids and gases. Analyses of the composition of the gaseous product of the pyrolysis of sludge have shown that generally H2, CO, CO2 and hydrocarbons are the main compounds found in the gas. The proportions however depend of the sludge type. CO is the dominant compound, with hydrocarbons representing in some cases an important part of the gas. Composition of the gas also depends on the temperature of the pyrolysis, as described in the table below [Werther and Ogada, 1999]. The composition of gases implies their treatment and use on site. They can also be cracked, as it facilitates their further use.

7HPSHUDWXUH ƒ&     + ZW 2.5 2.59 3.2 4.62 &2 ZW 24.4 18.32 15.39 7.25 &2 ZW 28.63 34.62 43.43 66.17 +\GURFDUERQV ZW 33.54 36.04 31.12 16.45 7DEOH pyrolysis gas composition at different temperatures (in Werther and Ogada [1999])

Solids can be considered as low-quality coal. They have the advantage of easy storage. When considering units of small capacity (10.000 t/year up to 50.000 t/year), this valorisation may take place later, and in another place. The solid residue is then dechlorinated, minerals such as metals are separated, and it may for instance be considered as a substitution fuel in power or cement plants. On the contrary, for units with a capacity set between 25.000 and 500.000t/year, valorisation is possible on site, and the process is then considered as an integrated process. During an integrated process, a gasification step of the solid may be added, or gases and solid residue may be directly burnt, and fumes generated have to be treated to comply with emission limits. In some cases, when the pyrolysis and the energetic valorisation of the by-products are separated, a dechlorination of the solid is possible, and a separation of the minerals (especially metals) may take place. Pyrolysis presents the following advantages: - a reduced gas emission in comparison with incineration (by about 30%), - reduced or no emission of PCDD/F, due to the low temperature of the process, - a possible separation and valorisation of the materials. Besides, the reduced size of the plant and the lower temperature enable to reduce the investment costs. This may offset the technical constraint of building an airtight enclosure.

 There are presently different available techniques, developed by German (PKA, Siemens, Thermoselect) or French (Nexus, Thide, Traidec) firms. About 15 plants in Europe and Japan have been built for waste treatment, some of which still being pilot plants, for capacities ranging from 0,5 to 25 tons per hour.

,QWHJUDWHGS\URO\VLV 3\URO\VLV 3\URO\VLV 3\URO\VLV *DVLILFDWLRQ &RPEXVWLRQ 1XPEHURISODQWV 466 7RWDOWUHDWPHQWFDSDFLW\ 11 t/h 28,5 t/h 38 t/h 7DEOH state of the development of pyrolysis [after Fontana 1999]

On the basis of experiments, the table below establishes the matter balance of processing pyrolysis on sludge in comparison with municipal waste:

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*DV NJW 480 660

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7DEOH residues of the pyrolysis process [Free University of Brussels]

Municipal waste pyrolysis seems to be worthwhile in terms of costs, in comparison with incineration when considering small capacities (below 200 000 t/year) and scattered habitats. It has not been confirmed whether a similar conclusion could be applied to sewage sludge.

5.5.3 Gasification Gasification is a thermal process during which a combustible material is converted with air or oxygen to an inflammable gas and an inert residue. It has been used for a long time to produce gas with coal. This kind of process is performed at a high temperature: between 900 °C and 1100 °C with air, or between 1000 °C and 1400 °C with oxygen. Gasification with oxygen, which is the most often performed one, generates a gas containing 55 to 60 % N2, with a calorific value of 4 to 7 MJ/Nm3. The gasification process enables the flue gas volume to be drastically reduced since carbon dioxide and water, internally formed, participate in the reaction and the unwanted N2 may be avoided by supplying pure oxygen. Comparisons given in literature indicate that whereas during mono- and co- combustion of sewage sludge, 24-30 m3 per kg of dry sludge of flue gas are formed, gasification with pure oxygen generates only 1.7 m3 [Werther and Ogada 1999]. Pyrolysis can also be considered as a gasification process, but performed in absence of oxygen. Both processes may also be performed together: gasification can be applied to the solid residue of the pyrolysis.

 It is a new method when applied to sludge, and therefore not very well documented. The input is either digested or undigested mechanically dewatered sludge [EEA 1998].

 /LWHUDWXUHUHYLHZ In order to compare the environmental impacts of the different recycling routes, Life Cycle Assessment (LCA) methodology may be applied to sewage sludge. Some studies are available in the literature describing LCA studies carried out mainly in Germany, France and Switzerland. Main findings are presented below whilst more information on the applied methodology, especially on the impact weighting methods used, is given in each publication.

5.6.1 LCA for the ARA Region Bern, Switzerland14 A LCA has been performed for the Canton of Bern, Switzerland. The study aimed at comparing six routes. Three of them addressed the recycling of sludge in agriculture whilst the other three focused on the disposal of sludge respectively in an incinerator, in a cement plant and in a plant using a pyrolysis followed by a combustion process. The impact assessment phase did not take organic pollutants in consideration and was performed by using five weighting methods, which each have a different approach for comparing the impacts of the routes considered. As for any LCA analysis, conclusions are valid within the assumptions made for this study, especially concerning the impacts taken into consideration. It was concluded that there was no global difference in the results obtained between the different landspreading disposal routes. Differences appear however when considering each environmental impact independently. Therefore the choice of one specific route to reduce one impact would be made against another environmental impact. An important conclusion was also the substantial contribution of transport to the overall pollution. By comparing the incineration routes, the incineration in cement kilns represented the best option, while the two other options could not be easily differentiated. The global comparison could not definitely distinguish between the various solutions: the incineration routes have a big advantage on the soil pollution avoidance (this study only considered heavy metals, and did not take into consideration atmospheric deposition of metals, but impacts of ashes disposed of in landfills), while the landspreading routes present an advantage concerning the eutrophication of waters. In conclusion, the study suggested a compromise between the various solutions, and the need to define and differentiate “good” and “bad” sludge.

5.6.2 LCA for the City of Bremen, Germany15 The study carried out in Bremen compared the landspreading route with two other possibilities: co- incineration in a coal-fired power plant, and gasification. The impact on the environment was assessed using local demographic values, by comparison with German mean values. No difference could be found between the different options, as it would have been necessary to classify the related environmental impacts. Each option may have a good impact on one specific indicator and a bad one on another: it is therefore necessary to decide which one has priority. ,QDQ\FDVHWKHQHJDWLYHLPSDFWRIWKH

14 CHASSOT G. M.; CANDIDAS T.; 1997; Ökologische Beurteilung vershiedener Entsorgungsvarianten für den Klärschlamm der ARA Region Bern, Bericht 15 FRANKE B.; HÖPER G.; 1995; Ökobilanz zur Klärschlammentsorgung in Bremen : Landwirtschaft, Mitverbrennung, Flugstromvergasung; Korrespondenz Abwasser 9/95 pp. 1529-1541

 WUDQVSRUWKDVEHHQVWUHVVHG. It was therefore decided by the city to give a financial advantage to landspreading near the city.

5.6.3 LCA for the French Water Agencies, France16 The study aimed at comparing ten routes: six of them related to sludge use in agriculture (including spreading of composted sludge), two to co-incineration with household waste, one to dedicated incineration, one to disposal to landfill. Each route was specific to a WWTP size. The weighting method used for this study was the Environmental themes method. Within the assumptions made for this study, there was no global difference in the results obtained between the various landspreading routes, with a small disadvantage however to routes with intensive drying (more energy consumption). A global comparison could not definitely distinguish between solutions: the landspreading routes presents a disadvantage on soil pollution, while incineration and landfilling routes present a disadvantage on air pollution. $QLPSRUWDQWFRQFOXVLRQZDVDJDLQWKHKLJKLPSDFWRIWUDQVSRUWRQWKHSROOXWLRQJHQHUDWLRQ, and also the necessity to take into account benefits of substituting sludge to mineral fertilisers.

16 Agence de l’Eau Rhin Meuse - Arthur Andersen; 1999; Audit environnemental et économique des filières d'élimination des boues d'épuration, http://www.eaufrance.tm.fr/francais/etudes/modele.asp?fiche_id=54

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0HPEHU6WDWHVFXUUHQWVLWXDWLRQ Figure 18 summarises the disposal routes for sewage sludge in the Member States. The data refers to the years 1996, 1997 or 1998 depending on the country.

100% 90% 80% Other 70% Disposal to sea 60% Vegetalisation 50% Landfilling 40% 30% Incineration 20% Agricultural Use 10% 0%

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)LJXUH sludge routes in the Member States; time series from 1996 to 1998 according to the country [ADEME 1999] Agricultural use is at the present time the principal outlet for sewage sludge, accounting for about 2.7 million t DM representing about 38 % of total sludge production. Landfilling is the second major route, representing 37 % of total sludge production. Incineration accounts for about 9% of sludge produced in the Member States. Countries present very diverse profiles: agricultural use counts for about a few percents in Netherlands, up to 70 % in Luxembourg. In addition, as these data were collected before the ban on the disposal to sea on December 31st, 1998, a part of the sludge produced in UK and Ireland has since been redirected to other routes. In the case of Ireland, the sludge that was disposed to sea is at present directed to agricultural use. When trying to obtain a more accurate view of alternative outlets such as land reclamation or use in forestry, we found that relevant data is differently integrated to national statistics. Land reclamation and silviculture are often considered as agricultural use, or integrated to other uses, without being precisely documented. Tsagarakis HWDO [1999] performed a survey on sewage sludge disposal in Europe. 80 % of the sludge is disposed of via landfill, whereas use in agriculture and use in forestry only concerns 6 % and 4 %, respectively, of sludge. The remaining 10 % is disposed of within the WWTP. However, we found that other uses in Member States cover: - for Austria: composting and revegetation - for Spain: disposal to sea when allowed - for the Netherlands: composting - for Portugal: discharge to the surface waters - for Denmark: use in cement kilns

0HPEHU6WDWHVIRUHFDVW According to the European Commission, a general increase by 18 % in the sludge quantity is foreseen by 2005. It must be stressed that this figure should be higher, as it does not take into account Italy and Sweden, from which no data were available. This average increase does not reflect the situation in each country. While in Austria, sludge production is expected to stay even, it should grow by 197 % in Ireland.

   (YROXWLRQ  Belgium 85 159 87 Denmark 151 160 6 Ge rman y 2 227 2 787 25 Greece 59 99 68 Spain 685 1 088 59 France 820 1 172 43 Italy 800 N/A Ireland 38 113 197 Luxembourg 8 14 75 Netherlands 209 401 92 Austria 200 195 -3 Portugal 245 359 47 Finland 136 160 18 UK 1 195 1 583 32 Sweden 230 N/A 7RWDO   18

17 7DEOH forecast of the production of sludge in the Member States by the year 2005 France, UK, Luxembourg, Germany and The Netherlands plan to further develop incineration. Agricultural use of sewage sludge will also increase in Ireland, Finland, UK and Portugal. It should concern about 55 % of the sludge produced in the European Union, whereas landfilling should concern about 19 % and incineration 23 %.

100%

80% Other Surface Water 60% Landfilling Incineration 40% Agricultural use

20%

0%

g rk n ia UK a r land ur pai eland bo S ust tugal lands reece Ir Fin France A or elgium G Denm Germany P B uxem L Nether

)LJXUH forecasts of the destination of sludge in the Member States by the year 2005

$FFHVVLRQ&RXQWULHV Figure 20 presents the current situation of sewage sludge disposal and recycling in Accession Countries. These data are taken from the screening realised by DG Environment or from the questionnaire sent for the purpose of this study. Some data are still partial (Poland) or not available at all (Bulgaria, Cyprus and Lithuania).

17 Source: Report from the Commission, Implementation of Council Directive 91/271/EEC of 21 May 1991 concerning urban wastewater treatment, as amended by Commission Directive 98/15/EC of February 1998; COM(98)775; 1999; Sweden and Italy have not provided any data on the destination of sludge.

 100 90 80 Other 70 Green areas 60 Sylviculture 50 40 Land reclamation 30 Disposal to sea 20 Landfilling 10 0 Incineration

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18 )LJXUH sewage sludge routes in the Accession Countries

Agricultural use and landfilling are the two major outlets for sewage sludge in Accession Countries accounting for about 250 000 and 400 000 t DM i.e. respectively 31 and 50 % of total sludge production. Disposal to sea is the only disposal route in Malta, as agricultural landscape and types of culture (horticulture and fruit production) make the use in agriculture difficult. In Slovakia, other routes are the use of sludge in silviculture, green areas and land reclamation. As incineration is a rather expensive technology for all kinds of wastes, it is not a widespread technique: it is only performed in the Czech Republic, concerning 1 % of the sludge.

18 Source : questionnaire established for the purpose of the study and European Commission