Anaerobic Methods of Waste Treatment

Technical Information W2e

Technical Field: Anaerobic Methods Of Waste c Energy / Environment (E) g Water / Sanitation (W) c Agriculture (A) Treatment c Foodprocessing (F) c Manufacturing (M) This Technical Information is available in: Naturgerechte Technologien, Bau und g English (e) g French (f) Wirtschaftsberatung (TBW) GmbH g German (g) c Spanish (s) (March 2000) c Other:......

1. Introduction structural and technical – often quite cost- intensive - means of addressing them. The Terms of reference most obvious first step is to limit the Population growth in combination with expansion of waste quantities and to hold altered production and consumption habits the originators responsible for their own has caused a dramatic global increase in wastes ("polluter-pays principle"). The next waste-related health burdens and most logical step is to recycle as much environmental pollution. This applies more waste as possible. However, the material to urban areas than to rural areas. Water, and energetic potentials of recyclable soil, air and climate are all suffering waste are still seldom utilized and then detriment, and the health of human only in isolated cases. populations, as well as that of the world's flora and fauna, is suffering the Disposal consequences. Due to the sheer bulk, In countries rich and poor, different types altered properties and compositions of the of dunps or landfills are the most accumulating residues from production widespread method of waste disposal. and consumption, nature alone is no This presupposes, of course, that the longer able to accommodate and reduce – waste is collected and transported at much less make use of – all this waste regular intervals. Waste dumps, or material without further treatment. landfills, can reflect a wide diversity of standards, from putrid piles of uncovered Especially in the poorer countries of the garbage around urban peripheries, with world, scattered trash and unauthorized corresponding jeopardization of garbage dumps are promoting the groundwater and the local population, up frighteningly rapid spread of infectious to modern, controlled sanitary landfills with diseases and odor nuisances and causing high-quality base seals for collecting diverse damage to the environment. Often, leachate and with daily and final covers garbage and sundry trash are simply serving to prevent or to collect climate- tossed into rivers or onto cultivated soil – damaging gaseous emissions. The main with accordingly serious consequential problems with this type of waste disposal impairment of waters, food resources and and landfills in general are their decades- nature per se. long, potentially damaging impacts on the environment, their substantial site-area Potential solutions requirements, and the immediate danger Thanks to increased problem awareness of health hazards, explosions and fires. among the population in general, and in Consequently, Germany is attempting to view of the follow-on costs of such avoid approving even new sanitary problems, industrialized countries in landfills by imposing restrictions on the particular are increasingly adopting legal, nature and quantity of acceptable waste – 1

JDWH Information Service / , PO Box 5180, 65726 Eschborn, Germany Phone: +49 (0)6196 / 79-3093, Fax: +49 (0)6196 / 79-7352, Email: [email protected], Internet: http://www.gtz.de/gate/gateid.afp Technical Information W2e the long-term goal being to dispense with Composting sanitary landfills altogether by the year For some 20 years now, Germany in 2020. particular, and a number of other central European countries as well, have been Refuse incineration developing and utilizing various methods Part of the energy content of solid waste of sorting and separate composting for can be recouped via incineration, or application to dry organic waste (hedge thermal waste processing, though this trimmings, yard and garden waste, etc.) involves technology that is much more and have even adopted laws demanding complicated than that required for the separate treatment of bio-waste. The landfilling. State-of-the-art equipment is compost yield is used in agriculture garden able to extensively preclude harmful and landscape for purposes of soil emissions, but the cost is high (processing conditioning and fertilization. The costs of DM 200 – 350/Mg waste). Both composting of biological waste cons- approaches – incineration and dumping – tituents generates thermal energy that is involve mixed refuse, and neither not actually used but does contribute to approach if solely applied includes any the waste's hygienization. The space recycling or material use component. requirements and process duration are relatively high. If the exhaust from a Waste recycling composting plant is to be cleaned in order Hence, various countries have introduced to prevent the emission of odors and systems in which waste is separated, germs, the necessary closed-cycle sorted and/or returned (possibly on a operating mode will make the plant deposit basis) with the intention of accordingly expensive to build and reducing ultimate waste quantities while operate. recycling such raw materials as metals, glass, paper, plastics and biomass. In Anaerobic waste treatment some countries and locations, waste Consequently, over the past 15 years or separation takes place at the household so, substantial effort has been invested in level, while in others it is accomplished at developing methods of anaerobic special sorting stations, treatment facilities fermentation for the treatment of primarily or directly at the landfill. biological waste. Such facilities were developped about 10 years ago and are In all countries, the main single waste now operated in most of Germany's larger constituent in terms of volume and weight cities. A number of corresponding is biodegradable (organic) waste consis- decentralized units are in service in ting of biogenic ingredients. Accounting for smaller towns and rural areas as well. anywhere between 35 % and 90 % of the overall waste incidence, organic waste Anaerobic waste treatment offers the offers the greatest potential for recycling following advantages: and quantity reduction. Of course, the • In addition to dry bio-waste, moist biologically active components of organic constituents like table scraps and waste are responsible as well for most waste from food processing and landfill emissions in the form of leachate, farming also can be handled. gas and odours. Consequently, in • The biogas yield, i.e., its energy accordance with Germany's new Waste potential, can be used for generating Avoidance and Waste Management Act, electricity, heat and refrigeration. waste containing more than 5 % organic • The fermented substrate can be constituents should no longer be landfilled. recycled in liquid or dry condition. • The requisite equipment takes up relatively little space. 2

• The closed-cycle mode of operation The following chapters are intended to enables extensive reduction of odors, help decision makers in the field of waste so such facilities can be located closer treatment and disposal in financially weak to built-up areas, thus decreasing the countries by outlining the various methods cost of transportation. of organic waste fermentation used in • Anaerobic waste treatment reduces Germany, their various forms of the quantities to be handled by – and application and environmental impacts, the emissions to be expected from – and the potential of both the technology sanitary landfills and refuse and the corresponding waste management incineration plants. concepts for application in countries outside of Europe. It does, however, have certain drawbacks: • The technology is in most cases still relatively complicated. 2. Survey of important waste • Consequently, the cost of construction treatment techniques and operation differs widely and can be quite high, depending on the Anaerobic bacteria can look back on a employed mode of construction. long history. Methane bacteria • Despite revenues from the produced (methanobacters) are widely regarded as energy and fertilizer, it is in most cases the oldest form of life on earth (dating back still necessary to levy waste disposal some 3.5 billion years). In the year 1682, fees, because treating the waste costs BOYLE became the first to describe the between 50 and 200 DM/t. process of biogas formation, or • The technology is relatively young and methanogenesis. The first documented therefore still widely unknown in operation of a biogas digester took place emerging countries. in Bombay in 1859. Then, in 1967, • The efficient use and handling of BRYANT described his anaerobic energy and compost and other hydrocarbon degradation model, which to byproducts and their quality control this very day remains practically demands appropriate know-how. unchanged. The activity of anaerobic microbes can be technologically exploited Thanks to low levels of odor nuisance, a under different sets of conditions and in broad spectrum of substrates and a different kinds of processes, all of which, positive energy balance, anaerobic however, rely on the exclusion of oxygen. fermentation has become an established component of the waste market, at least in The following table summarizes the Germany; the technology gap in favor of important characteristics and requisite composting, resulting from its earlier specifications for classifying the various development and application, has closed, fermentation processes and essential and the number of anaerobic waste steps in the treatment of organic waste. treatment facilities is growing steadily.

Systematic overview of fermentation processes (acc. to TBW GmbH, Frankfurt)

1 Requirements concerning the composition of the input material(s) i.e.: limits, e.g., TS content, fiber content and length, particle size, viscosity, foreign-substance content 2 Pretreatment for reducing the pollutant and inert-material contents e.g.: manual sorting, mechanical/magnetic separation, wet processing 3 Pretreatment required for the process e.g.: size reduction and substance exclusion: mechanical, chemical, enzymatic, thermal, bacteriological [methods, employed process additives] TS-content range: admixture of process water [dry/wet fermentation processes], monocharges requiring admixture of other fermentable starting materials 4 a) Processes Single-phase ferment. Two-phase fermentation Single- Multiple- Stationary Mobile Upgrading Downgradi stage stage solid solid (concentra ng process process phase / phase / tion) (deconcen mobile stationary tration) liquid liquid phase phase b) Fermentation temperature range(s) (mesophilic / thermophilic) c) Stirring / mixing – stirring / mixing system d) Interstage conveyance [e.g., pump, gravimetric] e) In-process separation of sediments / floating matter f) Retention time(s) g) Equipment for controlling the process milieu h) Phase separation at the end of fermentation 5 Posttreatment processes Secondary fermentation [e.g., time span for degree of fermentation V, time history of temperature during secondary fermentation], drying, disinfection, reduction of (nutrient) salinity, wastewater treatment 6 End product(s) i.e.: specification according to recognized criteria e.g., degree of fermentation, degree of hygienization, nitrate/salt content

3. Application of anaerobic While some companies have since the methods to waste treatment mid-1980s been promoting the establishment of anaerobic organic waste As a result of the oil crisis in the 1970s, treatment techniques, it was not until 1992 anaerobic methods of treating high-carbon that Germany's first large-scale substrate came into intensified use, fermentation facility for biodegradable because they constituted a means of waste was commissioned in Kaufbeuren energy recovery. Then, in the 1980s, fuel (NIEDERMEIER et al., 1994). Since then, prices dropped again, and such methods however, the number of waste lost significance – except for sludge- fermentation facilities and methods has digestion processes, which are still used in increased tremendously. practically all large sewage treatment facilities. 4

The history of large scale anaerobic agricultural and/or industrial solid and treatment of organic waste from human liquid waste settlements (municipal solid waste) 3. co-fermentation of separately collected therefore extends back hardly 20 years. biodegradable waste in the digesting The most commonplace applications for towers of municipal waste treatment anaerobic solid-waste treatment include: facilities 4. fermentation of the residual mixed 1. the anaerobic treatment of biogenic waste fraction.within the scope of a waste from human settlements mechanical-biological waste-treatment 2. the co-fermentation of separately concept collected biodegradable waste with

Suitability of organic wastes for fermentation or composting

FERMENTATION COMPOSTING Liquid manure / sewage sludge Offal Table scraps Kitchen scraps Organic industrial waste Biodegradable waste (rural/urban) Lawn mowings / leaves Hedge trimmings, yard rubbish Decreasing moisture

Substrates of preference for waste • distiller's residues (slops) marc / draff / fermentation facilities: pomace • • biogenic household waste tea and coffee grounds • • kitchen scraps, including meat residue from starch processing • • table scraps from communal feeding organically contaminated / materially facilities unsuitable paper / cardboard • • vegetable scraps specific biomass plantations for energetic purposes (i.e. grass, maize) • field crop scraps • residues from sugar production • organic waste from food processing • organic residue from the chemical • fish-processing scraps industry • dairy products • residue from the cosmetics industry • slaughterhouse wastes (a.o offals) • lawn mowings and grass from, e.g., fallow fields • mixed green residue, e.g., from public parks and cemeteries, wild plants • organic waste from agriculture, e.g., plant residue, straw litter, spoiled silage • residue from fodder production • liquid and solid manure

3.1. Anaerobic Treatment of Biogenic DR. Like in a composting process, the Waste from Human Settlements interfering substances are separated out before and/or after biological treatment, Preparation either by screening, magnetic separation, Waste fermentation processes can be manual sorting, or some combination classified according to how the thereof. As a rule, manual sorting of the biodegradable waste is prepared for incoming material will always be required. fermentation. Thus, differentiation is made between dry and wet fermentation For wet fermentation processes the processes. The type of preparation incoming biodegradable material is mixed essentially determines the throughput with fresh and/or circulating water to capacity of the downstream biological obtain a suspension with a solids content treatment, the quality of the fermented of roughly 10 % DR. This pumpable, sludge, and the nature and quantity of any stirrable suspension can be put through a wastewater that will be requiring screen upstream of the biological treatment. treatment stage in order to remove interfering substances. After biological In a dry fermentation process the bio- treatment, the mashing water has to be degradable waste enters the biological removed with the aid of appropriate treatment process with no alteration of its dewatering equipment, e.g., a decanter or as-delivered water content. The waste's a chamber filter press. biodegradable solids content (dry residue) normally ranges between 35 % and 45 %

Combined anaerobic/aerobic composting Bio-active air filter

Biowaste Building ventilation

Bunker Rotary screen Sorting table Shredder Bunker Fresh compost

Inert substances Sludge Sorting table

Feed tank

Separator Surplus water Mash

Pond Digester I Digester II Feed tank Feed tank

Hygienization

Grid input

Heating power plant

Gas flare Gas dryer

Fig. 1: Exemplified wet fermentation process

Biological treatment subjects the microorganisms to minimal The fermentation processes for shear forces despite intensive agitation. biodegradable waste are very similar to However, it also increases the danger of those used in the treatment of sewage scum formation. sludge, agricultural waste and highly The effects of a high solids concentration emburdened wastewater. Accordingly, in a dry fermentation process demand many digester models and combination close attention: Since it is very difficult to processes are nothing really new, but keep the contents of the digester in a state have only been modified to accommodate of agitation, plug-flow digesters are often the peculiarities of biowaste. There are given preference over completely mixed three basic choices for a combination agitating chamber digesters, because the process: feedstock passes through the digester in • single-stage processes the form of a "plug". Active biomass is • multiple-stage processes added to the biowaste by inoculating the • two-phase processes feedstock with digested material. Since every supplier of biowaste The advantage of a plug-flow digester is fermentation plants on the market relies on that the material remains in the digester one of these three basic variants, all three for a defined length of time, because are explained below. The digesters can be short-circuit flow can be practically ruled operated continuously, quasi-continuously out. Particularly with regard to the need for (charged 3 to 6 times a day) or hygienization in thermophilic operations, intermittently (single batch per full targeted this can be very important. retention time). Percolator digesters dispense with agitation altogether. The biodegradable Single-stage processes waste, usually mixed with digested Single-stage digesters can be operated in material, is fed into the digester in the mesophilic (35°C) or the thermophilic batches. During the fermentation process, (55°C) range. However, only thermophilic sprayed-in water percolates down through operation enables complete hygienization the substrate. The limited exchange of of the process residue. Mesophilic material keeps the production of methane treatment often includes upstream or to a minimum, hence also minimizing the downstream pasteurization to homogenize stability of the fermentation residue. the biowaste or process residue. Percolator reactors are therefore often Due to the high concentration of solids in used as an initial stage of hydrolysis the waste itself or in the suspension, high- upstream of a methane digester (cf. performance digesters such as anaerobic multiple-stage and two-phase processes). filters and UASB digesters cannot be used for single-stage processes. For single- Multiple-stage processes stage biowaste treatment processes, then, The term multiple-stage process means the choice is reduced to agitating chamber that several digesters, each with a digesters, percolator digesters or plug-flow different process environment, are digesters, with the biowaste retention time connected in series. corresponding to that of the active One frequently employed combination is biomass. Agitating chamber digesters of an initial hydrolysis stage followed by a the kind used in sludge digestion are often thermophilic or mesophilic digestion stage. chosen for use in treating wet-processed Such an embodiment has the advantage biowaste. The contents of the digester – of a low first-stage pH and correspondingly also referred to as a reactor - are kept in a faster hydrolysis than could be achieved in state of agitation by external pumps, screw the digester itself, which requires a pH of pumps, or injected methane. The latter is 6.5 – 7.5. Consequently, the hydrolyzer particularly advantageous, because it can have a relatively small volume, and 7

JDWH Information Service / , PO Box 5180, 65726 Eschborn, Germany Phone: +49 (0)6196 / 79-3093, Fax: +49 (0)6196 / 79-7352, Email: [email protected], Internet: http://www.gtz.de/gate/gateid.afp Technical Information W2e the resultant feedstock for the digester is mesophilic reduction of complex extensively solute and, hence, rapidly compounds to methane. Such "teamwork" decomposable, meaning that the digester enhances both the stability of the can also be made smaller than normal. fermentation process and the achievable Because biowaste makes a very throughput rates. The reverse sequence heterogeneous substrate, its various (mesophilic → thermophilic) would appear components hydrolyze at different rates. to be less practical, because mesophilic Biowaste components that hydrolyze less anaerobic bacteria are more sensitive to quickly (in the hydrolyzer) than they would pollution than are thermophilic bacteria. methanize (in the digester) draw no Also, it is much more difficult to extract the advantage from a two-stage arrangement. water from thermophilically stabilized And since the pre-acidified biowaste from biowaste (CHRIST et al., 1997). Thus, the the hydrolysis stage naturally contains a mesophilic digester should always be very large share of dissolved substrate, arranged as the last stage. the methanization process requires enough biomass to prevent acidification of Two-phase processes the digester content. Most notably, the In a manner similar to the two-stage bacteria which are active in the mesophilic approach, i.e., to separate hydrolysis and temperature range react sensitively to a methanogenesis, a two-phase process high percentage of dissolved substrate, involves the use of a high-performance while those which are active in the methane reactor to enable methanization thermophilic range are hardly problematic of the necessarily high biomass in that sense. concentration (e.g., an anaerobic filter, a Whether or not intentional pre-acidification contact-sludge process or a UASB of biowaste can save more digester process [KUNST, 1982]). volume than that required for the Two-phase processes are very well suited hydrolyzer ultimately depends on the type for application to, say, market-hall waste of substrate to be handled. Since the and other easily hydrolyzable substrates. various processes of anaerobic However, since biowaste tends to contain decomposition are closely interlinked, it a substantial share of substances that are can be quite difficult to separately control difficult to hydrolyze, hydrolysis constitutes the hydrolysis / acidification and the the rate-limiting step of decomposition for acetogenesis / methanogenesis. It is not the major part of the substrate. As such, easy to separately conduct the hydrolysis no appreciable reduction in retention time and methanogenesis of such complex can be expected. Again, the question of substrates as biodegradable waste. It how much expenditures on equipment and could therefore be practical to include a energy inputs would be justifiable has to generously sized bunker to hold fresh be decided on a case-by-case basis. deliveries of biowaste, so the easily decomposable substrates contained in the biowaste can hydrolyze in advance of the 3.2. Co-fermentation of Biowaste with actual degrading process. Farm Waste in an Agricultural Another promising approach – as opposed Biogas Plant to the separate stages of decomposition described above – is to separate the Integration of agriculture and horticulture different temperature ranges. For in the biogenetic cycle is often indicated, example, the first stage can consist of since farms, truck gardens and nurseries thermophilic conversion of extensively count among the main users of the solute substrates, plus general digested product (effluent sludge or hygienization, while the downstream compost). second stage would attend to the

Many farmers, though, take a skeptical fermentation of farm waste together with view of using compost derived from presorted biowaste: "anonymous" sources of municipal • Decentralized preparation and biowaste. This is mainly because the fermentation of biowaste by farmers, farmer has no way of knowing where the and decentralized use of the digested waste came from or what kind of treatment sludge at the same locations. it may have had in the past. In a worst- Wherever waste treatment is combined case scenario, a widespread lack of with animal husbandry, utmost acceptance can jeopardize entire cleanliness must be maintained in biological waste treatment programs. order to prevent the transmission of Thus, the co-fermentation of organic pathogens which may be present in residue in on-farm biogas plants can the waste. improve both the utilization of end • Centralized treatment of biowaste by products and the overall performance of farmers, possibly including centralized existing on-farm plants. fermentation and decentralized use of Disposal fees provide an additional source the digested sludge by the individual of income for farmers. In Germany, there farmers. The main argument in favor of are already more than 100 such co- this approach is that the centralized fermentation plants. treatment of biowaste is less expensive than the decentralized The following forms of organization are option on a quantity specific basis. becoming widely accepted for the co-

Biowaste treatment in Rhadereistedt Biofilter Interfering b

Biowaste Dry Inoculator preparation Mashing Size Hygienization Digester Sludge dti

Steam

Slurry tank

Biogas purifier

Pump waste- tank Power grid CHP input

Slurry, table scraps, etc.

Power grid CHP input

on-farm for biogas plant on-farm use

Municipal Industrial Agricultural

Fig. 2: Co-fermentation of presorted biowaste with agricultural and industrial wastes 9

Conversely, centralized facilities • The co-fermentation of additional involve higher transportation costs, substrates increases the digester's because the farm waste first has to be utilization rate. It also raises the hauled to the plant. The extent to digester's solids content and which such additional costs can be accelerates gas production. This, in offset by the lower cost of investment turn, improves the facility's energy for a centralized facility has to be balance and overall efficiency. determined on a case-by-case basis. In addition to the problematic treatment of Figure 2 is a schematic diagram of a co-substrates, including potential centralized biowaste treatment facility. The supplementary investments, the operator resultant biowaste slurry is co-fermented of the sewage treatment plant must also in decentralized on-farm biogas plants. watch for changes in the consistency of Centralized treatment of the biowaste, the digested sludge and of the expressed which would be very difficult to implement water, because both can show varying on a farm-by-farm basis, can guarantee behavior, depending on their momentary that the digested sludge will be of high structural fractions and compositions. quality and contain little interfering Additionally, co-fermentation often substances. The sludge can be applied produces somewhat higher environmental directly to the cropland of the biogas- burdens in terms of Chemical Oxygen generating farms and their neighbors. Demand (COD), Biological Oxygen ) Demand (BOD5 and Total Kjeldahl Nitrogen (TKN). 3.3. Co-fermentation of Biowaste with Sludge in Sewage Treatment Plants 3.4. Mechanical-biological Mixed-waste The co-fermentation of biosubstrates in and Residue Treatment with the anaerobic digesting towers of sewage Anaerobic Biological Stage treatment plants is an option that has rarely been put into practice. While there The amount of household waste that are some legal uncertainties involved, the actually remains behind for the garbage co-fermentation of biowaste appears can after all recoverables have been attractive in many cases, both for removed is referred to as the residual economic and logistical reasons: waste, or residue. In Germany, at least, • If, for example, the design degree of the residual waste will contain little or no effectivity is not achieved – as is the glass, paper, packing material, case in most German sewage biodegradable substances or hazardous treatment plants, where the digesters material. However, despite all sorting are often sized with broad safety efforts, the residual waste, though margins (with fluctuating sewage significantly reduced in volume, is still sludge quantities or expected growing likely to contain substantial amounts of quantities due to a growth in organic material including paper and popuulation often cited as the main cardboard (25 – 50 %) that still require reason in conjunction with biological degradation. Thus, the various uncertainties regarding concentrations steps of waste treatment (size reduction, or the requisite retention times), screening, etc.) are being increasingly though this may well prove supplemented with biological processes unnecessary in practice. such as anaerobic fermentation designed to stabilize and extract energy from the

JDWH Information Service / , PO Box 5180, 65726 Eschborn, Germany Phone: +49 (0)6196 / 79-3093, Fax: +49 (0)6196 / 79-7352, Email: [email protected], Internet: http://www.gtz.de/gate/gateid.afp Technical Information W2e residual waste. What then remains is fuel) that also have negative climatic usually pressed and either taken to a effects, though on a lower scale. If landfill or incinerated. proper ventilation is ensured by merely turning the material, the energy requirement will be accordingly lower. 4. Environmental impacts of Of course, this also increases the anaerobic (bio)waste treatment likelihood that anaerobic zones will form and that the material could 4.1. Climate Protection become mouldy. • The methane emissions generated by • From the climatic point of view, landfills anaerobic processes can be with no provisions for collecting, harnessed as a source of process cleaning and utilizing the gas yield of energy, perhaps even to the point of waste containing a high percentage of generating surplus energy that can be organic material – i.e., especially in used in place of fossil energy sources. emerging countries, are the most This amounts to the best contribution problematic form of waste disposal. toward climate protection in the waste • The main cause of damage to the treatment sector. climate is the high overall incidence of • Any degree to which transport costs gaseous emissions, particularly in the can be reduced will also translate into form of methane (which, depending on lower climate-relevant emissions (from the time horizon, can be 21 to 56 times the combustion of fossil fuels), as damaging to the climate than CO2). because fewer vehicles will have to In Germany, for example, the Waste travel shorter distances. Avoidance and Waste Management Comparing the alternatives fermentation, Act aims to protect the climate (while composting and landfilling (excluding gas reducing odor emissions and the capture, with gas flaring, and with gas danger of fires/explosions) by utilization), one arrives at something like prohibiting the deposition of any waste the following climate-impact table. with an organic content in excess of 5 % - even after composting. 4.2. Water Protection • Due to their inadequate emission control capabilities, most waste Leachate emissions from landfills are incinerators in emerging countries are causing pollution of groundwater a source of major problems. In resources in many places: addition, such facilities are hardly • The long-term effects of inadequately affordable, both in operation and in sealed landfills on water is particularly terms of initial investment. problematic. Consequently, composting and • The composition and toxicity of fermentation are usually the only leachate is rarely known and can practical alternatives for waste change over time as new and different disposal and recycling from the materials are washed out. standpoint of climate protection. • Many rivers and streams from which • Depending on the quality and potable water is taken are being uniformity of compost-heap ventilation, misused as open dumps. some parts of the heap are likely to Anaerobic waste treatment processes can remain anaerobic, so that methane also generate substantial amounts of can evolve and escape to the press water (liqueur) that require atmosphere. Forced ventilation purification to keep it from causing water requires substantial energy expen- pollution. ditures (usually in the form of fossil 11

Table 1: The climatic effects of waste treatment processes (trends)

Fermentation Landfilling* Composting with gas without gas with gas with gas utilization capture capture + utilization flaring Avoidance of yes no yes/no** yes/no** yes methane emissions Reduced yes no no yes no emissions via energy substitution for external users Low fossil-fuel yes yes yes yes no requirement *To the extent that no air can enter a given landfill, the resultant degradation process is, in principle a controlled or uncontrolled "anaerobic process". **Avoidance, in this sense, is a function of the quality of gas capture, i.e., the extent to which landfill gases can be prevented from escaping.

4.3. Conservation of Resources causalities, soil fertility, the water cycle, air quality and climate. Returning the waste nutrients and organic • If the thusly produced material were to material to the soil is a means of contribute toward an increase in the preserving resources. The same applies to percentage share of public park areas, the utilization of energy extracted from the the number of plant-covered walls and waste as a renewable source of energy. roofs and the overall area of lawns, • Presuming adequate awareness of vegetable gardens, fruit groves and and tradition for the recycling and use agricultural activities, considerable of organic waste materials and their additional advantages could be gained nutrients and of/for the resultant to the benefit of air quality, hygiene, opportunities for improving the soil, water management and even nutrition waste residue can be employed as and employment. high-quality fertilizer and soil conditioner. • The increased use of organic fertilizers 5. Applicability of recycling options can contribute toward the sustainable and processes to threshold / improvement of soil fertility (ventilation, emerging countries water retention, soil organisms, disease prevention). It will also help Direct application of the waste build up humus and counter the global management concepts and technologies trends toward soil degradation and employed by central European countries erosion. to financially weaker countries of the • Cases located in or near a town or city South is only conditionally possible due to can also serve environmental- differences in waste composition, an educational purposes by sharpening extensive lack of waste separation, and people's awareness of ecological warmer, humid climates. On the other hand, the waste generated in emerging

JDWH Information Service / , PO Box 5180, 65726 Eschborn, Germany Phone: +49 (0)6196 / 79-3093, Fax: +49 (0)6196 / 79-7352, Email: [email protected], Internet: http://www.gtz.de/gate/gateid.afp Technical Information W2e countries tends to contain a particularly cities than it would be to haul the large percentage of organic material; the waste to remote landfills. Of course, ambient temperatures are amenable to fermentation also helps reduce the anaerobic fermentation; and there is waste volume to about one-third that of usually demand for energy, fertilizer and the original substance. soil conditioners. Until now, the only anaerobic methods of The cost situation is site-dependent and waste treatment that have been brought to can hardly be generalized. Any cost- "technical maturity" in emerging countries benefit comparison of such investments have been limited to those involving the will be heavily dependent on the level of sludge and wastewater. There has been technology, human-resource qualifica- practically no industrial-scale application of tions, the form of organization, urban- fermentation processes for waste from planning and geographic aspects, as well human settlements in emerging countries. as on such individual cost components as area, energy, compost, wastewater, In Germany and other European countries, transport, qualified and unqualified labor, automatic preparation and selection of the etc. waste material constitutes a particularly The introduction of anaerobic waste cost-intensive aspect of waste treatment methods calls for attendant fermentation plants. In emerging countries, infrastructural and training measures. these aspects can be organized Consequently, funding will be needed for differently. Anaerobic processes can local adaptation of the most suitable reliably generate – often a crucial limiting fermentation technology. factor – more than enough energy to cover the plant's own auxiliary power/heat requirements. 6. Summary

Major financial aspects of anaerobic Anaerobic waste treatment processes for processes include: municipal solid waste are still relatively • The overall operating costs of such young technologies that have not yet plants can be covered, at least in part, become established in emerging by revenues from the sale of countries. However, thanks to their generated energy, digested sludge simultaneous exploitation of waste and/or compost. Indeed, a favorable materials and energy contents, they offer price situation can even yield a profit. promising economic and ecological • The use/substitution of fuel, power and potentials for the waste treatment sector. fertilizer that otherwise would have to Particularly in emerging countries with be purchased, can yield savings on scarce resources but favorable foreign currency. temperatures and low labor costs, • Depending on the distances involved, anaerobic waste treatment processes can it can, in the long term, be less play a relevant role in future waste expensive to build and operate treatment activities. centralized or decentralized waste fermentation facilities near towns and

7. Rules of thumb for anaerobic waste treatment

Waste quantities Waste from human settlements 360–400 kg/P*a Organic content 120-150 kg/P*a 30-40 kg TOS/P*a

Optimal inputs TS content 10-15 % including anaerobically degradable fraction 95 % low levels of toxic substances

Process data for organic waste Mesophilic range 35°C Thermophilic range 55°C Retention time 20 d Compost output 0.2 t/t input Hygienization / pasteurization at least 1 h at 65 – 70°C

Energy balance 1 Auxiliary power requirement 150-200 kWhel/t TVS input Power produced 600-800 kWhel/t TVSinput Surplus power 400-650 kWhel/t TVSinput Auxiliary heat requirement 200-300 kWhtherm/t TVSinput Heat produced 1000-1200 kWhtherm/t TVSinput Surplus heat 700-1000 kWhtherm/t TVSinput

1 TVS = Total Volatile Solids

8. Literature ANS – Arbeitskreis zur Nutzbarmachung von • CHRIST, O., FAULSTICH, M., (1997): Siedlungsabfällen The TherMes-Process – Two-stage Fachausschuß Vergärung thermophilic/mesophilic anaerobic Ernst-Moritz-Arndt-Straße 2 treatment of suspended or-ganic 40822 Mettmann waste; in: 1st International Conference, Germany Narbonne, 28.-29. April 1997; Tel: ++49-2104-958874 Treatment of Solid Waste and Fax: ++49-2104-958875 Wastewater; Hrsg. Wilderer, Delgenes, Tartler, Graja; Pg. 265 - 271. TBW GmbH – Naturgerechte Technologien, Bau und • KUNST, S. (1982): Untersuchungen Wirtschaftsberatung zum anaeroben Abbau polymerer Baumweg 10 Kohlenhydrate zur Optimierung der 60316 Frankfurt Versäuerungsstufe bei anaeroben Germany Abwasserreinigungsanlagen. In: Tel: ++49-69-943507-0 Institut für Siedlungswas-serwirtschaft Fax: ++49-69-943507-11 und Abfalltechnik der Universität Email: [email protected] Hannover; Heft 54, Hannover. Knoten Weimar • NIEDERMEIER, K., CHRIST, O., Bauhaus-Universität Weimar WILDERER, P. (1994): Biostabilisation Lehrstuhl Abfallwirtschaft Process of the model Kaufbeuren; 17th Coudraystr. 7 International Symposium on anaerobic 99423 Weimar Digestion; 23-27 January 1994, Cape Germany Town, South Africa, S. 128 - 131. Tel: ++49-3643-584644 Fax: ++49-3643-584643 • Statusbericht des GTZ- e-mail: [email protected] Sektorvorhabens „Förderung der Anaerobtechnologie zur Behandlung Proceedings Kasseler Abfallforum kommunaler und industrieller K. Wiemer, M. Kern (Hrsg.), M.I.C. Baeza- Abwässer und Abfälle“, Band 3: Verlag Witzenhausen Abfallbehandlung. Kirchstraße 8 37213 Witzenhausen Germany 9. Further addresses Tel.: ++49-5542-72720 Fax: ++49-5542-4509 Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH JDWH Information Service Internet addresses: Postfach 5180 • http://www.gtz.de/anaerob 65726 Eschborn • http://www.tbw-frankfurt.com Germany Tel: ++49-6196-79-3093 Fax: ++49-6196-79-7352 Email: [email protected] Internet: http://www.gtz.de/gate/gateid.afp

JDWH Information Service / , PO Box 5180, 65726 Eschborn, Germany Phone: +49 (0)6196 / 79-3093, Fax: +49 (0)6196 / 79-7352, Email: [email protected], Internet: http://www.gtz.de/gate/gateid.afp