2. Potentially Toxic Elements

2. POTENTIALLY TOXIC ELEMENTS: SOURCES, PATHWAYS, AND FATE THROUGH URBAN WASTEWATER TREATMENT SYSTEMS

The aim is to reduce inputs of pollutants entering the wastewater system to background levels because this represents the minimum potential extent of contamination that can be achieved. Potentially toxic elements are of concern because of their potential for long-term accumulation in soils and sediments.

The majority of metals transfer to sewage sludge (see Fig 2.1). However, 20% may be lost in the treated effluent, depending on the solubility and this may be as high as 40% - 60% for the most soluble metal, Ni. Although the use of sludge on agricultural land is largely dictated by nutrient content (nitrogen and phosphorus), the accumulation of potentially toxic elements in sewage sludge is an important aspect of sludge quality, which should be considered in terms of the long-term sustainable use sludge on land. Application of sludge to agricultural land is the largest outlet for its beneficial use and this is consistent with EC policy of waste recycling, recovery and use. This is a critical issue due to the increasing amount of sludge produced, the increasingly stringent controls on landfilling, the public opposition to incineration (a potential source of further atmospheric pollution), and the ban on disposal at sea. Consequently sludge quality must be protected and improved in order to secure the agricultural outlet as the most cost effective and sustainable option.

Figure 2.1: Origin and fate of metals during treatment of wastewater [from ADEME, 1995]

Pollutants in Urban Waste Water and Sewage Sludge 12 2. Potentially Toxic Elements

2.1. Sources and pathways of potentially toxic elements in UWW

The average concentrations of potentially toxic elements in domestic and commercial wastewater are given in Table 2.1. The maximum concentrations of potentially toxic elements found in commercial wastewater are generally greater than those in domestic wastewater. This is supported by Scandinavian studies [SFT-1997a, 1997b, 1999] considering all urban sectors together, which judged that commercial and light industrial sectors contributed larger loads of potentially toxic elements to urban wastewater than household sources.

Table 2.1 Concentrations of metals in domestic and commercial wastewater [Wilderer and Kolb, 1997 in Munich, Germany]

Element Domestic Commercial Wastewater [mg.l-1] Wastewater [mg.l-1]

Pb 0.1 £ 13 Cu 0.2 0.04-26 Zn 0.1-1.0 0.03-133 Cd <0.03 0.003-1.3 Cr 0.03 £20 Ni 0.04 £7.3

Table 2.2 Potentially toxic elements in UWW from various sources (% of the total measured in the UWW)

Pollutant Country Domestic Commercial Urban Not Reference Wastewater Wastewater Runoff Identified Cd France 20 61 3 16 ADEME, 1995 Norway 40 SFT report 97/28 UK 30 29 41 WRc, 1994 Cu France 62 3 6 29 ADEME, 1995 Norway 30 SFT report 97/28 UK 75 21 4 WRc, 1994 Cr France 2 35 2 61 ADEME, 1995 Norway 20 SFT report 97/28 UK 18 60 22 WRc, 1994 Hg France 4 58 1 37 ADEME, 1995 Pb France 26 2 29 43 ADEME, 1995 Norway 80 SFT report 97/28 UK 43 24 33 WRc, 1994 Ni France 17 27 9 47 ADEME, 1995 Norway 10 SFT report 97/28 UK 50 34 16 WRc, 1994 Zn France 28 5 10 57 ADEME, 1995 Norway 50 SFT report 97/28 UK 49 35 16 WRc, 1994

Pollutants in Urban Waste Water and Sewage Sludge 13 2. Potentially Toxic Elements

Cd distribution Cu distribution

Domestic Domestic Storm events Storm events Commercial Commercial Non Identified Non Identified

Cr distribution Hg distribution

Domestic Domestic Storm events Storm events Commercial Commercial Non Identified Non Identified

Pb distribution Ni distribution

Domestic Domestic Storm events Storm events Commercial Commercial Non Identified Non Identified

Zn distribution

Domestic Storm events Commercial Non Identified

Figure 2.2 Pie charts showing the breakdown of potentially toxic elements entering UWW from different sources in France (ADEME 1995) This uses the French data in Table 2.2 but is included to give a clearer visual representation of the source breakdown for the different metals.

Pollutants in Urban Waste Water and Sewage Sludge 14 2. Potentially Toxic Elements

The data in Table 2.2 and Figure 2.2 show that for some elements over 50% of the potentially toxic elements in wastewater are unaccounted for. This is in line with findings by Critchley & Agy [1994] Better source inventory data is essential in order to effectively target reductions in emissions from all the different sources. It may be that identification of some of the industrial sources will require increased trade effluent discharge controls if concentrations of pollutants are to be reduced. Domestic and urban run-off sources may require different types of action, such as changes in products used.

Emissions of potentially toxic elements from industrial point sources were the major sources of pollution to urban wastewater. However, stringent and more widespread limits applied to industrial users has reduced the levels of potentially toxic elements emitted by industry into urban wastewater considerably. This continues a general decline of potentially toxic elements from industrial sources since the 1960s, due to factors such as cleaner industrial processes, trade effluent controls and heavy industry recession. For example, the liquids used in metal finishing typically contain 3-5 mg.l-1 of copper, 5-10 mg.l-1 of chromium, 3-5 mg.l-1 of zinc, 5-10 mg.l-1 of zinc, 1-5 mg.l-1 of cyanide, and 10-50 mg.l-1 of suspended solids [Barnes, 1987]. However, metal finishing industries are now required to pre-treat these liquids before disposal, reducing toxic discharges by 80-90%.

In the Netherlands, a survey of potentially toxic element load in UWW influent [SPEED, 1993], also made estimations for 1995 and forecasts up to 2010. The overall prevalence of potentially toxic elements in the UWW system is expected to decrease, mainly due to a decrease in runoff and industrial sources, while the potentially toxic elements share in WWTS loads from households was expected to increase. As industrial sources of potentially toxic elements in UWW decline, the relevant importance of diffuse sources will increase.

Wiart and Reveillere [1995] carried out studies at the Achères WWTS in France. Their studies showed a significant decrease (50-90%) in the potentially toxic element content of sewage sludge since 1978, following the application of the "at-source discharge reduction" policy [Bebin, 1997]. However, the main concern is now with organic pollutants, and current regulations require monitoring of the influent, in order to set up a baseline database from which limits may then be devised.

Pollutants in Urban Waste Water and Sewage Sludge 15 2. Potentially Toxic Elements

2.1.1 Domestic sources

Domestic sources of potentially toxic elements in wastewater are rarely quantified due to the difficulty in isolating them. Domestic sources include the potentially toxic elements discharged from the household to UWW collecting systems and, in addition, corrosion from materials used in distribution and plumbing networks, tap water and detergents.

A study by RIVM (Dutch Institute of Public Health and the Environment) in the Netherlands [SPEED, 1993], quantified the waterborne emissions of potentially toxic elements from household sources, dentistry and utility buildings in the urban environment. Table 2.3 shows the data of waterborne potentially toxic elements emissions in tonnes per annum.

Table 2.3 Emissions by Dutch households of potentially toxic elements [adapted from SPEED, 1993].

Potentially Gross waterborne emissions* tonnes.y-1 to surface toxic element water (1993) Household Dentistry Utility buildings sources Copper 94 0.6 27 Zinc 118 - 26 Lead 13 - 3.1 Cadmium 0.7 - 0.2 Nickel 7.3 - 0.9 Chromium 2.9 - 0.3 Mercury 0.3 2.3 0.01 * 96 % of the waterborne emissions are expected to go to the UWW collecting systems, with 4% going directly to surface waters.

Domestic products containing potentially toxic elements used on a regular basis at home and/or at work, are also reviewed by Lewis [1999]. The following lists the principal PTEs and products containing them that may enter urban wastewater;

Cadmium: is predominantly found in rechargeable batteries for domestic use (Ni-Cd batteries), in paints and photography. The main sources in urban wastewater are from diffuse sources such as food products, detergents and bodycare products, storm water [Ulmgren, 2000a and Ulmgren, 2000b].

Copper: comes mainly from corrosion and leaching of plumbing, fungicides (cuprous chloride), pigments, wood preservatives, larvicides (copper acetoarsenite) and antifouling paints.

Mercury: most mercury compounds and uses are now banned or about to be banned, however, mercury is still used in thermometers (in some EU countries) and dental amalgams. Also, mercury can still be found as an additive in old paints for water proofing and marine antifouling (mercuric arsenate), in old pesticides (mercuric chloride in fungicides, insecticides), in wood preservatives (mercuric chloride), in embalming fluids (mercuric chloride), in germicidal soaps and antibacterial products (mercuric chloride and mercuric cyanide), as mercury-silver-tin alloys and for "silver mirrors".

Nickel: can be found in alloys used in food processing and sanitary installations; in rechargeable batteries (Ni-Cd), and protective coatings.

Lead: The main source of lead is from old lead piping in the water distribution system. It can be found in old paint pigments (as oxides, carbonates), solder, pool cue chalk (as carbonate), in certain cosmetics, glazes on ceramic dishes and porcelain (it is banned now

Pollutants in Urban Waste Water and Sewage Sludge 16 2. Potentially Toxic Elements for uses in glazes), also in "crystal glass". Lead has also been found in wines, possibly from the lead-tin capsules used on bottles and from old wine processing installations.

Zinc: comes from corrosion and leaching of plumbing, water-proofing products (zinc formate, zinc oxide), anti-pest products (zinc arsenate - in insecticides, zinc dithioamine as fungicide, rat poison, rabbit and deer repellents, zinc fluorosilicate as anti-moth agent), wood preservatives (as zinc arsenate), deodorants and cosmetics (as zinc chloride and zinc oxide), medicines and ointments (zinc chloride and oxide as astringent and antiseptic, zinc formate as antiseptic), paints and pigments (zinc oxide, zinc carbonate, zinc sulphide), printing inks and artists paints (zinc oxide and carbonate), colouring agent in various formulations (zinc oxide), a UV absorbent agent in various formulations (zinc oxide), "health supplements" (as zinc ascorbate or zinc oxide).

Silver: originates mainly from small scale photography, household products such as polishes, domestic water treatment devices, etc. [Shafer, et.al, 1998, Adams and Kramer, 1999]

Arsenic and Selenium: are among the potentially toxic metalloids found in urban wastewaters. These are of importance due to their potential effects on human/animal health. Only a limited number of studies have taken these into account. Arsenic inputs come from natural background sources and from household products such as washing products, medicines, garden products, wood preservatives, old paints and pigments. Selenium comes from food products and food supplements, shampoos and other cosmetics, old paints and pigments. Arsenic is present mainly as DMAA (dimethylarsinic acid) and as As (III) (arsenite) in urban effluents and sewage sludge [Carbonell-Barrachina et.al., 2000].

Pollutants in Urban Waste Water and Sewage Sludge 17 2. Potentially Toxic Elements

Household products

Household products were investigated as potential sources of PTE pollution entering the WWTS. Table 2.4 shows metal concentrations in various household products in UK Table 2.4 Metal concentrations in household products [Comber and Gunn, 1996, WRc report, 1994].

Product Zinc Copper Cadmium Nickel (µg g-1) (µg g-1) (µg g-1) (µg g-1) Washing Powders a 37.9 1.4 74.3 <0.5 ‘Big Box’ b 35.9 <0.5 136.0 <0.5 c 3.3 <0.5 6.6 <0.5 Washing Powders ‘Ultra’ a <0.1 <0.5 24.0 <0.5 b 2.3 1.40 10.6 <0.5 c 1.0 1.38 11.8 <0.5 Fabric Conditioners a 0.1 <0.5 9.4 0.6 b <0.1 <0.5 9.0 <0.5 c 0.1 <0.5 10.7 <0.5 Hair Conditioners a <0.1 <0.5 16.8 <0.5 b 1.0 1.4 17.2 <0.5 c 1.7 <0.5 8.6 <0.5 d 0.5 1.4 68.0 1.0 Cleaners a 0.3 2.8 26.0 <0.5 b <0.1 <0.5 17.8 <0.5 Shampoo (medicated) a 4900 1.4 17.4 <0.5 Washing Up Liquid a 0.2 1.1 11.0 0.8 Bubble bath a 0.2 <0.5 13.6 <0.5 b <0.1 1.4 10.4

As can be seen from Table 2.4 there is a great deal of variability between products and also between types of the same products in terms of potentially toxic element content.

The high variability of cadmium concentrations found in the big box washing powders can be explained by the differences in the composition of phosphate ores used in their production. Cadmium impurities in these phosphate ores have been shown to vary greatly depending on mining source [Hutton et al reported in WRc report 1994]. Reducing the amount of phosphate in washing powders, or choosing phosphate ores with low Cd concentration could lead to a reduction in Cd in wastewater from diffuse sources. In Sweden the amount of cadmium in sewage sludge was reduced from 2 mg kg-1 ds to 0.75 mg kg-1 ds [Ulmgren, 1999], and cadmium discharges from households in the Netherlands have been substantially reduced due to the switch to phosphate-free detergents [SPEED, 1993]. The 'Ultra' washing powders, usually phosphate-free, have smaller potentially toxic element contents than the traditional powders, and are designed to be used in smaller quantities. A shift to these newer products will reduce the overall metal load from this source.

The products with the highest metal contents are shown in bold in Table 2.4. The medicated (anti-dandruff) shampoos contain zinc pyrithione and the high zinc concentrations will thus raise the zinc inputs to the UWW collecting system. In 1991 these shampoos were estimated to represent 26% of the market [*BLA Group 1991- reported in Comber and Gunn 1996 and WRc 1994]. Cosmetics are not included here but they may also contain high levels of zinc and several of these products are likely, at least in part, to enter in the waste water system. One study in France [ADEME, 1995a] identified that the main sources of potentially toxic elements in domestic wastewater came from cosmetic products, medicines, cleaning products and liquid wastes (including paint), which were directly discharged from the household sink.

Pollutants in Urban Waste Water and Sewage Sludge 18 2. Potentially Toxic Elements

Table 2.5 provides a general picture of some of the potentially toxic elements in various domestic products including food products [after Lester, 1987 and WRc report 1994]. Sources for each metal are marked with a tick. In addition to the main metals considered in this study, cadmium, chromium (III and VI), copper, mercury, nickel, lead and zinc, silver, arsenic, selenium and cobalt are also included. Other metals and metalloids for which more information is necessary include manganese, molybdenum, vanadium, antimony and tin.

TABLE 2.5 Domestic sources of potentially toxic elements in urban wastewater [modified from Lester, 1987, and WRc, 1994] Product type Ag As Cd Co Cr Cu Hg Ni Pb Se Zn Amalgam fillings Ö and thermometers Cleaning products Ö Ö Cosmetics, Ö Ö Ö Ö Ö Ö Ö shampoos Disinfectants Ö Fire extinguishers Ö Fuels Ö Ö Ö Ö Inks Ö Ö Lubricants Ö Ö Ö Medicines and Ö Ö Ö Ö Ö Ointments Health supplements Ö Ö Ö Ö Ö Food products Ö Ö Ö Ö Ö Oils and lubricants Ö Ö Ö Ö Paints and Ö Ö Ö Ö Ö Ö Ö Ö Ö Ö pigments Photographic Ö Ö Ö (hobby) Polish Ö Ö Ö Pesticides and Ö Ö Ö Ö Ö gardening products

Washing powders Ö Ö Ö Wood- Ö Ö Ö preservatives Other sources Faeces and Urine Ö Ö Ö Ö Ö Ö Ö Ö Ö Tap Water Ö Ö Ö Ö Ö Water treatment Ö Ö Ö Ö Ö and heating systems

Domestic activities

The main domestic sources of potentially toxic elements in wastewater were estimated by WRc [1994] to be (in order of importance): cadmium: faeces > bath water > laundry > tap water > kitchen chromium: laundry > kitchen > faeces > bath water > tap water copper: faeces > plumbing >tap water > laundry > kitchen lead: plumbing > bath water > tap water > laundry > faeces > kitchen nickel: faeces > bath water > laundry > tap water > kitchen zinc: faeces > plumbing > tap water > laundry > kitchen.

Pollutants in Urban Waste Water and Sewage Sludge 19 2. Potentially Toxic Elements

Estimates of the mean potentially toxic element inputs to UWW collecting systems from domestic activities are presented in Table 2.6. The results show that for the particular UK (hard water) catchment studied in 1994, the domestic inputs of copper and zinc are major contributors to the overall level of potentially toxic elements reaching the WWTS. Most of the zinc is derived from faeces and household activities such as washing and cleaning. Chromium, lead and cadmium were also found to be mainly from domestic activities rather than from plumbing.

Table 2.6 Potentially toxic element loads to the UWW collecting systems from domestic activities [adapted from Comber and Gunn, 1996]

Activity (study in a hard Load (µg.person-1.day-1) water catchment area) Zn Cu Pb Cd Ni Cr Washing Machine Input Water 662 6859 36.0 0.6 27 4 Washing 4452 977 515 11 52 238 Dishwashing Input Water 39 69 2.9 0.03 2 0.3 (machine) Washing 42 8 6 1.3 2 10 Dishwashing Input Water 591 6125 32 0.5 24 3.7 (hand) Washing 1010 <20 46 7.8 138 136.7 Bathing Input Water 1140 10651 46 1.0 40 5.9 Bathing 1095 67 45 13.1 9 7.4 Toilet Input Water 2531 8082 63 2.0 77 8.5 Faeces 11400 2104 121 48.0 284 51.5 Miscellaneous Input Water 1453 6951 62.7 1.2 54 7.0

Predicted Total 24416 41894 978 86 710 464.2 Measured mean from Catchment 15314 46772 1237 71 925 686 housing estates Population 50 000 Predicted load to UWW 1.2 2.1 0.05 0.01 0.04 0.02 collecting systems from domestic sources (kg/day) Measured mean total load to 2.6 3.3 0.3 N/A 0.1 0.15 the WWTS kg per day % of potentially toxic 46.0 64.2 16.9 N/A 25.7 15.3 elements from domestic sources in the UK

Based on the above results, changes in population behaviour, such as a shift to dishwasher use rather than washing up by hand, would reduce potentially toxic element input into the WWTS.

It is noted that, while the quantities of potentially toxic elements dissolved in water from plumbing will vary across the Europe they will make up a significant proportion of the potentially toxic element loading going to any WWTS.

Table 2.7 summarises the percentages of the domestic inputs at the Shrewsbury WWTS, in the UK. As can be seen over a fifth of the copper, zinc, cadmium and nickel entering the wastewater treatment plant from domestic sources are from faeces. This emphasises the fact that faeces are an important source of potentially toxic elements pollution. This source is also very difficult to reduce. The percentage inputs of chromium and lead from this source are much lower.

Pollutants in Urban Waste Water and Sewage Sludge 20 2. Potentially Toxic Elements

Table 2.7 Potentially toxic elements entering wastewater, breakdown by source [WRc, 1994] Cu Zn Cd Ni Pb Cr Percentages of total load Break down of domestic sources as percentage of total metal entering WWTS Plumbing Input Bathing 12.4 1.2 0.3 1.6 4.4 0.1 (% of total entering WWTS) Toilet 8.9 2.1 0.5 4.3 8.1 0.2 Washing 8.0 0.7 0.2 0.9 3.2 0.1 Machine Miscellaneous 8.0 1.2 0.3 2.4 6.1 0.2 Dishwashing 7.1 0.6 0.2 0.8 2.7 0.1 Activities Faeces 20.6 28.0 20.0 23.6 3.1 2.1 (% of total metal entering Washing 9.53 10.8 4.6 4.4 18.6 9.3 WWTS) Machine Bathing 0.2 2.6 0.9 0.8 1.1 0.3 Dishwashing 2.6 4.6 11.2 1.1 5.1

Human faeces contain high concentrations of potentially toxic elements from normal dietary sources and this represents a principal input of metals to domestic wastewater and sludge of domestic origin. The normal dietary contribution of metals represents the background metal concentration represents the background metal concentration and is the minimum achievable in waste water and sludge.

Concentrations are expected to vary with the intake of metals in the diet, drinking water and medication and may also be influenced by the increasing prevalence of mineral supplementation of food, for example with zinc, iron, selenium, and manganese. One study in France (ADEME 1997) found the following concentrations of potentially toxic elements in faeces (as dry matter): Zn: 250mg kg-1, Cu: 68mg kg-1, Pb: 11mg kg-1, Ni: 4.7mg kg-1, and Cd: 2mg kg-1. Differences can also occur due to geographical variations in the dietary habits. For some elements, such as Cd, the weighted average concentration in sludge (e.g. 3.3 mg kg-1 in the UK) is typical of the amount originating naturally in faeces from the normal trace amounts of this element ingested in food (typically 18.8 mg d-1). Other differences in reported concentrations of Cd in different EU member states is discussed in section 2.3.

Domestic water and heating systems

Studies in the USA [Isaac et.al, 1997], and Europe [WRc 1994] show that corrosion of the distribution-plumbing-heating networks contribute major inputs of Pb, Cu and Zn. Lead concentration for instance can vary between 14 µg.l-1 at the household input and 150 µg.l-1 at the output.

It has been found that concentrations of copper in sewage sludge are directly proportional to water hardness [Comber et al 1996]. Hard water (high pH) is potentially more aggressive to copper and zinc plumbing, increasing leaching. However, the opposite is true for lead in that it dissolves more readily in than soft, acidic water. The high lead levels in drinking water in Scotland due to its soft waters are a major concern.

Reductions in the amounts of copper and lead in wastewater have been reported by pH adjustment of tap water and addition of sodium silicate. The addition of alkali agents to water at the treatment stage and the replacement of much lead piping has led to reductions in lead concentration [Comber et al., 1996]. Adjusting the pH of tap water may be limited by practical and economic factors.

Zinc in domestic plumbing comes from galvanised iron used in hot water tanks but is less problematic than lead and copper because the amount decreases with the ageing of the installations. Copper corrosion and dissolution is also greater in hot water than in cold water

Pollutants in Urban Waste Water and Sewage Sludge 21 2. Potentially Toxic Elements supplies [Comber et al 1996]. The 'first draw' (initial flow of water in the morning) has higher amounts of copper and lead compared to subsequent draws [Isaac et.al., 1997]. The Cu content was found to be between 73.7 and 1430 µg l-1, and Pb content between 8.3 and 22.3 µg l-1, much greater than in the average effluent from households. Water treatment would be recommended for certain water domestic uses, such as boilers and heating systems, in order to reduce the metal corrosion.

The type of housing was also found to be important by the WRc report [1994]. Table 2.8 gives an average concentration of effluent from two types of estates, "1960s residential" and "1990s residential" from daily bulk- and flow-weighted samples. The larger copper levels from the "modern estate" can be explained by the newer plumbing system. In many countries copper is the major element used in plumbing. In the UK it has been estimated that leaching from copper plumbing accounts for over 80% of the copper entering domestic wastewater [Comber et al 1996]. The higher lead level found in the newer housing did not correlate with similar studies comparing old and new housing and could not be explained satisfactorily; as in general older houses in the UK contain more lead plumbing. Lead from solders in the piping system may also be an important source. In other regions of the EU steel and zinc galvanised iron are used widely. This may explain why zinc in sludge is proportionally greater than Cu in other member states compared with the UK.

Table 2.8 Mean concentration of potentially toxic elements in the effluent from households in two types of residential areas [WRc Report, 1994]

Potentially toxic Zn Cu Ni Cd Pb Cr Hg element concentration µg.l-1 " 1960s residential" 74.3 219.4 5.2 0.71 9.02 5.65 0.114 " 1990s residential" 147.0 458.3 7.56 0.34 90.61 3.3 0.088

In summary, potentially toxic elements entering UWW collecting systems from domestic sources are related to:

· household water consumption · the plumbing and heating system in the household · the concentrations of potentially toxic elements in the products used in the household and quantities of the products used · any grey water recycling schemes · how much of the products are discharged into wastewater.

Pollutants in Urban Waste Water and Sewage Sludge 22 2. Potentially Toxic Elements

2.1.2 COMMERCIAL SOURCES

Limited data is available for the potentially toxic element contribution from commercial sources and health care inputs (such as hospital and clinical wastes). Inputs from artisanal sources are looked at in more detail in a separate Case Study in Section 6.

Cadmium could originate from laundrettes, small electroplating and coating shops, plastic manufacture, and also used in alloys, solders, pigments, enamels, paints, photography, batteries, glazes, artisanal shops, engraving, and car repair shops. Data from ADEME [1995], estimated that worldwide, 16000 tonnes of cadmium were consumed each year; 50- 60% of this in the manufacture of batteries and 20-25% in the production of coloured pigments.

Chromium is present in alloys and is discharged from diffuse sources and products such as preservatives, dying, and tanning activities. Chromium III is widely used as a tanning agent in leather processing. Chromium VI uses are now restricted and there are few commercial sources.

Copper is used in electronics, plating, paper, textile, rubber, fungicides, printing, plastic, and brass and other alloy industries and it can also be emitted from various small commercial activities and warehouses, as well as buildings with commercial heating systems.

Lead, as well as being used as a fuel additive (now greatly reduced or banned in the EU) it is also used in batteries, pigments, solder, roofing, cable covering, lead jointed waste pipes and PVC pipes (as an impurity), ammunition, chimney cases, fishing weights (in some countries), yacht keels and other sources.

Mercury is used in the production of electrical equipment and is also used as a catalyst in chlor-alkali processes for chlorine and caustic soda production. The main sources in effluent are from dental practices, clinical thermometers, glass mirrors, electrical equipment and traces in disinfectant products (bleach) and caustic soda solutions.

Nickel is used in the production of alloys, electroplating, catalysts and nickel-cadmium batteries. The main emission of nickels are from corrosion of equipment from launderettes, small electroplating shops and jewellery shops, from old pigments and paints. It also occurs in used waters from hydrogenation of vegetable oils (catalysts).

Zinc is used in galvanisation processes, brass and bronze alloy production, tyres, batteries, paints, plastics, rubber, fungicides, paper, textiles, taxidermy (zinc chloride), embalming fluid (zinc chloride), building materials and special cements (zinc oxide, zinc fluorosilicate), dentistry (zinc oxide), and also in cosmetics and pharmaceuticals. The current trend towards electrolytic production of zinc which, in contrast to thermally produced zinc, has virtually no cadmium contamination. This means that cadmium pollution to UWW due to the corrosion of galvanised steel will in time become negligible. [SPEED 1993].

Platinum and platinum group metals (PGMs) such as palladium and osmium can enter UWW from medical and clinical uses, mainly as anti-neoplastic drugs. The amount in hospital/clinical effluent has been estimated to be between 115 and 125 ng l-1 [Kümmerer and Helmers, 1997, Kümmerer et.al., 1999] giving a total emission of 84-99 kg per annum from hospitals in Germany. Other sources of platinum metals in the environment related to commercial activities come from catalysts used in petroleum/ammonia processing and wastewaters, from the small electronic shops, jewellery shops, laboratories and glass manufacturing. Section 6 contains a detailed Case Study (a) on PGMs in urban waste water and sewage sludge.

Pollutants in Urban Waste Water and Sewage Sludge 23 2. Potentially Toxic Elements

Silver could potentially be emitted from photographic and printing shops, from jewellery manufacturers and repairers, plating and craft shops, glass mirror producers and small- scale water filters.

Studies in Spain showed the presence of elevated concentrations of Cd, Cu, Hg, Pb and Zn in urban wastewater and in the coastal environment [Castro, et.al., 1996], with large concentrations of copper and zinc possibly due to the use of fungicides in glass-houses.

A summary of concentrations of metals found in effluent from commercial sources in different regions in Europe is given in Table 2.9.

Table 2.9 Summary of potentially toxic elements in UWW from commercial sources ( g l-1) Element Country Industry Industrial Effluent Reference (mg l-1) Cd Germany All sectors 3-1,250 Wilderer et al 1997 Greece Petroleum industries 300-400 NTUA, 1985 Cu Germany All sectors 37-26,000 Wilderer et al 1997 Greece Metal and electrical industries 5,000-10,000 NTUA, 1985 Italy Artisanal galvanic shops 20,500 EBAV, 1996 Goldsmiths and jewellery 700-1,900 shops (max.13,300) Cr Germany All sectors <10-20,100 Wilderer et al 1997 Greece Metal and electrical industries 500-13,000 NTUA, 1985 Tanneries 100-7,000,000 Italy Artisanal galvanic shops 16,000 EBAV, 1996 Pb Germany All sectors <50-13,400 Wilderer et al 1997 Greece Metal and electrical industries 500 NTUA, 1985 Italy Ceramics and photoceramics 6,000 EBAV, 1996 shops Ni Germany All sectors <10-7,300 Wilderer et al 1997 Greece Metal and electrical industries 500-14,500 NTUA, 1985 Italy Artisanal galvanic shops 19,700 EBAV, 1996 Zn Germany All sectors 30-133,000 Wilderer et al 1997 Greece Metal and electrical industries 60-2,830 NTUA, 1985 Italy Goldsmiths and jewellery 1,000 (max. 7,000) EBAV, 1996 shops As Spain Paper mills 3.4 Navarro, et.al 1993

In 1999, a project carried out by Anjou Recherche [LIFE, 1999], attempted to classify all commercial sources of wastewater pollution based on a matrix of 73 main pollutants including many potentially toxic elements and certain organic pollutants. The UWW collecting system of Louviers, for example, had listed 1054 establishments of which 39% were capable of emitting at least one of these pollutants. Ten classes of activities were recorded, of which health and social action (33.5%), manufacturing industry (20%), hotels and restaurants (17.8%), and collection services (10%) appeared most often as potential polluters. It was found on average, that between a third and a half of the activities emitted pollutants. In the Louviers area, it was found that 53 urban businesses and institutions could potentially emit cadmium, 168 chromium, 147 copper, 35 nickel, 167 mercury, 50 lead, and 63 zinc. This suggests that more can be done to reduce trade effluent discharges.

Between 1990 and 1992, Stockholm Water Company investigated measures to reduce discharges of potentially toxic elements into the UWW collecting system. This programme involved the following groups: the city council, neighbouring municipalities, small businesses and industry, professional associations and NGOs as well as local households. Efforts to reduce pollution entering the wastewater system were divided among all the major sources i.e., small businesses and industry, wastewater from urban runoff, household wastewater and storm water.

Pollutants in Urban Waste Water and Sewage Sludge 24 2. Potentially Toxic Elements

Collaborative projects were developed both for research, product development and educational programmes. Local commercial organisations (particularly the Swedish Dental Federation) co-operated in the project; new technologies were developed and an evaluation of alternative products was carried out. Pollution limits were imposed that were determined to be appropriate to encourage the purchase of the endorsed environmental products. This programme of research, and earlier work during the 1980s led to a reduction of between 50 and 80% of potentially toxic elements in sewage sludge [Ulmgren 2000a].

The results of some more specific investigations into sources of potentially toxic elements in UWW are outlined below.

Motor industry - vehicle washing

Scandinavian studies [SFT-1997a, 1997b, 1999] showed that the motor industry, followed by vehicle workshops contribute most to the potentially toxic element load in UWW. Vehicle washing, particularly heavy goods vehicles (HGVs), was found to be an important source of potentially toxic element contamination.

In Sweden, oil separators are commonly used in vehicle washing and motor industries before discharging effluent to UWW collecting systems. Most facilities in Sweden are reported to be equipped with combined oil separators and sludge traps where the dispersed oil and sludge should be retained. However, tests at one of the light vehicle (LV) washing facilities showed that this equipment was ineffective with practically no difference between the influent (before the separator) and the effluent (after the separator). This was due to the formation of stable emulsions in the wastewater caused by the detergents in the microemulsion formulations used for vehicle washing [Paxéus, 1996b].

A study by the Norwegian Pollution Control Authority [SFT, 1999] examining potentially toxic element pollutants in Norway found that out of six petrol stations investigated, only one had an oil separator/sand trap that worked effectively. Although designed to reduce the contamination of urban wastewater, oil separating devices are generally ineffective at reducing pollutant emissions from vehicle washing and motor industry facilities.

Dental practices and healthcare (mercury)

In the late 1980s, the high concentration of mercury in sewage sludge (SS) at Henrikdal WWTS, Stockholm, prompted an investigation to identify potential sources (Table 2.10). It was concluded that the high mercury content of sludge was attributable to dental practices and the use of mercury in dental amalgams. Amalgam separators were ineffective at retaining mercury and new legislation was introduced to combat this [Ulmgren, 2000a]. Recent reduction or bans on the use of mercury in various products, such as batteries and thermometers, has led to a reduction of mercury input into UWW [Ulmgren, 2000a and Ulmgren, 2000b]. Mercury recycling schemes have also proved to be successful, and could be extended to other countries and activities.

Other discharges from dental technicians shops are covered in detail in Section 6, Case Studies.

Pollutants in Urban Waste Water and Sewage Sludge 25 2. Potentially Toxic Elements

Table 2.10 Sources of mercury in urban wastewater in Sweden [Table adapted from text, Ulmgren 2000a]

Source Comments Heavy Industry no Ruled out as a source of mercury to UWW and SS as these were not connected to the UWW collecting system Small and no Ruled out as they were operated in such a way that no Medium contamination of the wastewater was likely Enterprises (18 Companies) Storm Drains yes 20% of the total mercury load came from storm drains. This was largely traced to the deposition of particulates emitted from crematoria which are estimated to be about 50 kg of mercury a year Household yes About 15% of the mercury entered the waste water system through Wastewater the use of mercury thermometers in the home, and also from small amounts of mercury in food and amalgam fillings in teeth Dentists and yes High mercury content of sludge was largely attributable to dental Dental practices and the use of mercury in dental amalgams Technicians Hospitals yes Samples indicated that hospitals emit 10% of the mercury loading Old Sewage yes Investigations in the last few years have found many sources of Pipes mercury in old pipes

Similar findings have been reported in other countries. A WRc report [1994] established that in the UK mercury emissions are much higher from commercial, rather than domestic sources, mainly due to dental practices. In France, it is estimated [Agence de l'Eau, 1992] that between 73 and 80 % of the mercury in UWW is from dental practices and amalgam fillings corrosion. In the Louviers area of France, the analysis of wastewater and sewage sludge showed that out of the total load of mercury, 50% was lost from medical practices, 13% from dentistry practices, 28% from medical auxiliaries (nurses etc.), 4% from hospital activities, 4% from veterinary activities, and 1% from ambulance activities. Thus, in this instance, targeting medical/dental practices may help reduce pollution from mercury [LIFE, 1999].

Other sources of mercury In 1993, the amount of mercury entering France was 209 tonnes, the amount leaving France was 87 tonnes, and hence 122 tonnes were entering the environment in the form of waste [AGHTM, 1999-2000] (see Table 2.11).

Table 2.11: Mercury contained in waste [from Dossier sur les dechets mercuriels en France: AGHTM, 1999]. Activity Amount (tonnes) % Treated and recycled Zinc and lead metallurgy 18 4.8 Thermometers 9 5.6 Dentistry amalgams 9 11.4 Batteries 6.8 7.4 Laboratories 0.9 0.0 Fluorescent tubes 0.8 12.5 Barometers 0.4 10.0 High intensity lamps 0.2 10.0 Chlorine production 77 ?

Table 2.11 highlights the amount of mercury waste produced by zinc/lead metallurgy and chlorine production. In Galicia, north-western Spain, high mercury levels in UWW and sewage sludge are attributed to chlor-alkali production in the Pontevedra area [Cela et.al. 1992]. In Portugal too, the presence of mercury in treated wastewater, sewage sludge and the lagoons of Aveira is linked with chlor-alkali production [Lucas et.al, 1986 and Pereira

Pollutants in Urban Waste Water and Sewage Sludge 26 2. Potentially Toxic Elements et.al, 1998]. There appears to be potential for improved control and recycling of mercury waste associated with these activities.

Sources of chromium

Mine production of chromium in Finland has increased from 348 thousand tonnes to just over a million tonnes in 1990 [Mukherjee 1998], representing just under 10% of world production. The main sources of chromium in wastewater are from the metal, chemical and leather industries (Table 2.12). As can be seen, the chemical industry contributes over half of the total emissions to UWW and surface waters in this region.

Table 2.12 Chromium emissions to water in Finland [adapted from Mukherjee, 1998] Source Category Emissions to water (not exclusively UWW) tonnes per annum % of total contribution Chemical Industry 14.3 58.1 Paint Manufacture 0.01 <0.1 Electroplating 0.1 0.4 Ferro-chrome and Stainless Steel 4.6 18.7 Plants Leather Processing 5.5 22.5 Total 24.6 100.0

Mukherjee [1998] reports that in Scandinavia, chromium compounds are also used in wood preservatives, along with arsenic compounds (As2O5) and an oily mixture of organic chemicals (phenol and creosol).

All wet-textile processing in Finland discharges its wastewater, containing chromium and other metals, to the WWTS. The textile companies studied [Kalliala, 2000] produced between 50 and 500 litres of wastewater per kg of textile produced. Wastewater analyses were carried out at six major Finnish textile companies (two of these include analysis for potentially toxic elements (Table 2.13)):

Table 2.13 Potentially toxic elements in wastewater from textile processing in Finland [Kalliala, 2000] Wastewater analysis (µg l-1) Company 2 Company 4 Lead 0.11 - Chromium 0.03 60 Copper 0.4 80 Zinc - 20

There is a very high variation in the process emissions between these two plants. Company 2 was noted to use cellulose blends while company 4 was noted to have mainly polyester and polyester blends.

Pollutants in Urban Waste Water and Sewage Sludge 27 2. Potentially Toxic Elements

Sources of lead

Data from ADEME [1995] showed that worldwide consumption of lead is around 5.4 million tonnes per year. In a Swedish study [Palm, Östlund, 1996] in the Stockholm area the total amount of lead used in products such as those listed previously, was estimated at between 44,000 and 47,000 tonnes per annum. Clearly the potential for lead entering UWW from these sources will vary greatly. The largest amount of lead that finds its way to the WWTS is likely to be contributed by piping. Estimates for the amount of lead used are 8,000 tonnes in lead jointed water pipes used inside buildings, followed by 2,000 tonnes used in lead jointed water pipes used outdoors (higher replacing rate), and 120 tonnes used in PVC piping.

In the case of Finland, the Ministry of the Environment report that the drinking water pipelines are predominantly plastic (85% PVC and PEH), with 11% cast iron; no lead is used for pipes conveying water. The wastewater pipes for the UWW collecting system are 57% concrete and 41% plastic.

Pollutants in Urban Waste Water and Sewage Sludge 28 2. Potentially Toxic Elements

2.1.3 URBAN RUNOFF

Runoff to UWW collecting systems and waterways has been intensely studied due to its potentially high loading of potentially toxic elements [WRc, 1994]. Atmospheric inputs to the urban runoff depend on the nature of surrounding industries, on the proximity of major emission sources such as smelters and coal fired power stations and the direction of the prevailing wind. Potentially toxic element loads can be five fold greater in runoff near commercial activities, than in residential areas far from industrial emitters. Roof runoff and building runoff also contribute to the total runoff loading and may be a source of considerable amounts of potentially toxic elements such as zinc, lead, copper and cadmium. Road and roof runoff sources are particularly important during storm events, which will allow flushing of potentially toxic elements and other pollutants from surfaces. Furthermore, it is important to note that the metal species released are usually in a freely dissolved, bioavailable form. Nevertheless, these sources are very variable, as every event is different and depends on traffic, material and age of roofs and other surfaces, and meteorological and environmental conditions.

Although a number of studies had focused on the effects of urban land use in the quantification of precipitation runoff, it was not until the 1950s that the first qualitative1 studies were undertaken [Palmer, 1950 and 1963; Wilkinson, 1956]. Table 2.14 provides concentrations for a number of potentially toxic elements in urban runoff, as a summary of various investigations from 1975 to 1978. It is important to note that the measured concentrations differ considerably. The main sources of pollution in urban precipitation runoff can be summarised as follows [based on Mitchell, 1985]:

· Road and vehicle related pollution · Degradation of roofing materials · Construction · Litter, vegetation and associated human activities · Erosion of soil

Table 2.14 Maximum and mean concentrations of potentially toxic elements (mg l-1) in urban precipitation runoff pollutants [after Mitchell, 1985]

Droste and Hartt, Mance and Harman, Mattraw and Pollutant 1975 1978 Sherwood, 1977 Mean Max Mean Max Mean Max Lead 0.205 3.7 0.21 Iron 0.317 4.2 5.3 Copper 0.028 0.35 Manganese 0.11 1.7 Zinc 0.271 1.63

A comparative analysis between the different sources of pollution in urban precipitation runoff is subject to variation, dependent on catchment characteristics, time of year and measurement procedures. Urban precipitation runoff pollution has received far less attention than other forms of urban pollution (i.e. atmospheric). Table 2.15, gives an indication of the geographic and temporal variability involved.

1 Focusing on pollutant loads in rainfall runoff

Pollutants in Urban Waste Water and Sewage Sludge 29 2. Potentially Toxic Elements

Table 2.15 Mean concentrations in rainwater runoff (in µg/l)

Site Cd Cu Pb Zn Reference Urban (Netherlands) 0.9 8 20 31 Van Daalen, 1991 Central Paris 2.4 60 140 Granier, 1991 Central Paris 0.11 6 13.7 38.8 Garnaud et al., 1996-1997

Garnaud et.al., [1999] attempted a comparative study between the main sources of pollution in urban precipitation in Paris. In this recent study of individual rain events, bulk samples were collected within four gutter pipes (roof runoff), three yard-drainage pipes (yard runoff), six gullies (street runoff) and one combined UWW collecting system, at the catchment outlet. The results can be seen in Figure 2.3. The values are median values.

Figure 2.3 Comparison between main elements contributing to precipitation runoff in respect to potentially toxic elements pollution load [after Garnaud et al., 1999]

A comparison of samples from consecutive phases of precipitation runoff (precipitation to roof runoff to urban runoff to catchment outlet) indicated that the potentially toxic element concentration increased by a factor of 12, 30, 30 and 60 for cadmium, copper, lead and zinc, respectively. Corrosion of roof and urban surfaces as well as human activities contributes to this contamination, including corrosion or emission from vehicles and commercial activities. Bulk metal concentrations were similar within all urban runoff samples except for zinc and lead, which were particularly concentrated in roof runoff samples, due to their contamination by corrosion of roof materials. At all sites it appeared that bulk metal concentrations could be ranked as: Cd << Cu < Pb << Zn.

Differences in potentially toxic elements concentration in precipitation water and runoff from roofs and streets have also been found in a German study (Table 2.16). In this case it can be seen that runoff from streets has the highest potentially toxic element content.

Pollutants in Urban Waste Water and Sewage Sludge 30 2. Potentially Toxic Elements

Table 2.16 Concentration changes of certain contaminants in precipitation water and runoff from different outflow paths, Germany. [Xanthopoulos and Hahn, 1993] LOD Limit of detection

Pollutant Precipitation Run-off from Run-off from [µg/l] roofs [µg l-1] streets [µg l-1] Pb 5 104 311 Cd 1 1 6.4 Zn 5 24 603 Cu 1.5 35 108 Ni 5

A study carried out by Rougemaille (1994) analysed the wastewaters of the treatment plant in Achères in the Paris region and found that lead concentrations varied between 0.05 and 0.5mg l -1 and that the average concentration was 0.1mg l-1. These wastewaters come from four different urban areas. The study showed that lead concentrations were 3 times larger during wet weather than during dry weather, hence proving the importance of the runoff sources.

A study carried out around the region of Nantes in France in 1999, analysed road runoff from a major highway for a year showing that lead and zinc are the main pollutants present in runoff waters (Table 2.17).

Table 2.17: Analysis of raw runoff waters [Legret, 1999]

PAH Pb Cu Cd Zn (ng l-1) ( g l-1) ( g l-1) ( g l-1) ( g l-1) Mean <96 58 45 1 356 Median <74 43 33 0.74 254 Range <11-474 14-188 11-146 0.2-4.2 104-1544 SD 76 44 27 0.86 288

The Swedish study mentioned in previous sections [Palm, Östlund, 1996], estimated the total amount of zinc passing into wastewater at 6,300 tonnes per annum. Most of the zinc present in the urban environment was generated by urban runoff and rain; from roofs and building surfaces (1,600 tonnes), from cars excluding tyres (1,500 tonnes), from tyres (200 tonnes), and from lampposts and street furniture (an estimated 1,142 tonnes). Zinc was also attributed to water pipe couplings (1,000 tonnes).

Pollutants in Urban Waste Water and Sewage Sludge 31 2. Potentially Toxic Elements

A Road and vehicle contribution

Roads are a major source of pollution in urban environments and contribute to wastewater pollution both directly and indirectly (airborne pollutants generation). Sartor and Boyd [USEPA, 1972] determined the major constituents of road related runoff to be inorganic matter, but the total mass of inorganic matter present seemed to increase as the antecedent dry period (ADP) increased. Sources of the organic and inorganic fraction of road-produced pollutants are summarised as follows:

· Vehicle lubrication systems losses · Vehicle exhaust emissions · Degradation of automobile tyres and brakes · Road maintenance · Road surface degradation · Load losses from vehicles (accidental spillages) · Precipitation (wet deposition) · Atmospheric deposition (dry deposition)

Potentially toxic elements in runoff occur from motor fuel combustion, brake linings, tyre wear and road surface wear. Motor fuel combustion was the largest source of lead to runoff but it is on the decrease due to the gradual phasing out of leaded fuel in the EU. Other metals emitted from exhausts are zinc, chromium and more recently tin from the replacement anti-knock compounds in petrol. The presence of Zn and Cd in road surface sediments can also be explained by the addition of Zn dithiophosphate in the manufacturing of lubricating oil, Cd being present as an impurity of the original Zn. Brake lining wear contributes copper, nickel, chromium and lead to runoff. Tyre abrasion contributes to the load of zinc, lead, chromium and nickel due to the soot and metal oxides constituents. Cadmium in car tyres is attributed to zinc-diethylcarbonate, which is used during the vulcanisation process. Road surface wear contributes to emissions of nickel, chromium, lead, zinc and copper.

Legret and Pagotto (1999) produced estimates of potentially toxic element content from vehicle related pollution sources (Table 2.18), and contributions to road runoff (Table 2.19).

Table 2.18 Potentially toxic element contents in vehicle and road materials (mg kg-1) [after Legret and Pagotto, 1999]

Sources Pb Cu Cd Zn Leaded petrol 200 - - - Unleaded petrol 17 - - - Brake linings 3900 142000 2.7 21800 Tyre rubber 6.3 1.8 2.6 10250 De-icing agent 3.3 0.5 0.2 0.5

Pollutants in Urban Waste Water and Sewage Sludge 32 2. Potentially Toxic Elements

Table 2.19 Emissions fluxes in precipitation runoff (kg km-1 annum) and percentage removed in drainage waters [after Legret and Pagotto, 1999]

Sources Solids Pb Cu Cd Zn Vehicles Tyre wear 314 0.002 0.0006 0.0008 3.22 Brake 100 0.390 14.2 0.0003 2.17 linings Petrol - 13.0 - - - Road Safety - 0.002 0.0002 0.0002 0.95 fence De-icing 130 0.015 0.002 0.0007 0.002 agent Air deposition 86 0.014 0.015 0.0009 0.21 Drainage water %2 235 5 2 313 37

The percentages of these potentially toxic elements entering the drainage systems show that a large proportion of the pollutants released do not end up in the runoff waters but are probably emitted into the atmosphere. The Zn content in urban runoff remains highly variable depending on the use of safety barriers made from galvanized steel or from an alternative material. All parameters are affected by traffic and by variables connected to the meteorological and environmental conditions of the sites concerned, which make the comparison highly uncertain (Montrejaud-Vignoles et al., 1996).

The following mechanisms summarise the way the pollutants are transported (pathways) from the catchment over the roads and finally in the drainage network:

- Soluble contaminants dissolved in the runoff water - Insoluble particles acting as sorbents for potentially toxic elements and organic contaminants which are transported by the runoff water [Ellis, 1976; Sylvester and DeWalle, 1972] - Removal by air-dispersal involving transfer of the surface contaminants to the atmosphere either as dry particles or dissolved in surface water.

Note that the first two mechanisms above result in pollutants being transferred ultimately into receiving waters or sewage sludge, while the last mechanism removes pollutants prior to their ultimate disposal. The general conclusion, however, is that the majority of road surface runoff contamination is sediment associated. In particular, the prime transport mechanisms and pathways with respect to road-runoff sediment transport are [Sartor and Boyd, 1972]:

- Particle entrapment - Cross surface transport by overland sheet-like flow to the gutter as turbulent heavy fluid transport process - Linear transport of the particle material parallel to the kerb line into the road gully.

The transportation of surface particulates is sporadic in nature [Mitchell, 1985]. Metal levels tend to fall after periods of rain, whilst elevated concentrations have been recorded after prolonged dry periods. Also introduced in the movement patterns are local storage and residence effects due to the intrinsic configurations and micro-topography of the road surface [Harrop, 1983]. The fact that contaminants move through this sequence is well known, however, the relationship between the contaminants and the various mechanisms involved are poorly understood. Comparison of metal distribution during particle transport,

2 For value >100% the research identified larger concentrations in the samples than expected from the sources that were taken into account. This is particularly true for Cd concentrations. Additional sources of Cd (such as lubricating oils, as discussed earlier) may account for this underestimation.

Pollutants in Urban Waste Water and Sewage Sludge 33 2. Potentially Toxic Elements from atmosphere to receiving water body, clearly demonstrates a metal mobility evolution (Garnaud et al., 1999). Extremely labile (i.e. hydrosoluble or exchangeable), within dry atmospheric deposits Cd, Pb and Zn, become bio-available within street runoff and stable within UWW collecting system or river sediment. In conclusion particulate metal mobility may be classified as: Cu<

Potentially toxic elements are predominantly associated with inorganic particles and research indicates that potentially toxic element concentrations increase as particle size decreases (Sansalone and Buchberger, 1997; Lloyd and Wong, 1999). In particular Colandini and Legret (1997), found a bimodal distribution with the highest concentrations of Cd, Cu, Pb and Zn being associated with particles of less than 40 µm in size. Table 2.18 indicates the potentially toxic elements distribution across the particle size distribution for a number of potentially toxic elements.

Table 2.20 Approximate concentration of potentially toxic elements associated with particles [after Colandini and Legret, 1997]

Approximate concentration of potentially toxic elements Inorganic -1 particle size associated with particles (mg kg ) fraction (µm) Zinc Lead Copper Cadmium <40 900 920 240 24000 40-63 275 100 100 5000 63-80 300 100 125 5000 80-125 350 150 175 5000 125-250 400 200 200 5000 250-500 450 175 300 3000 500-1000 240 225 30 3000

Table 2.21 summarises measurements from 1975 to 1982 on concentrations of potentially toxic element pollutants in road runoff in three German towns:

Table 2.21 Summary of pollutant loads in urban runoff caused by road related sources from 1975 to 1982 [after Klein, 1982]

Pollutant mean Test catchments concentrations Pleidelsheim Obereisesheim Ulm / West (mg/l) Cd 0.0059 0.0059 0.0028 Cr 0.0096 0.02 0.0052 Cu 0.097 0.117 0.058 Fe 3.42 5.16 2.18 Pb 0.202 0.245 0.163 Zn 0.36 0.62 0.32

Pollutants in Urban Waste Water and Sewage Sludge 34 2. Potentially Toxic Elements

Vehicle emissions: Prior to the lead ban in fuel3, research had identified exhaust lead emissions to account for more than 90% of atmospheric lead pollution. Although the main source of lead in the average urban atmosphere is lead from fuel additives, it appears that only 5% of the lead can be traced in runoff water. The greatest part may, therefore, disperse in the atmosphere or settle on the soil by the roadside (Hewitt and Rashed, 1990). The actual rate and form of lead emission is crucially dependent on driving conditions. High engines speeds and rapid acceleration can increase emission levels due to reactivation of particles deposited on the exhaust system. Total lead emissions can double if the engine and/or weather is cold. The deposition from petrol to the road surface was estimated to be 0.049g Pb.vehicle-1. km-1. In the case of lead-containing fuel, approximately 75% of lead is discharged to the atmosphere (Hewitt and Rashed, 1990) and a further 20% is retained in engine sump oil (Wilson, 1982).

Concentration of lead added to petrol has rapidly declined in the EU during the 1980s due to legislation. In Austria for example, the lead emissions between 1985 and 1995 have been reduced by approximately 88 % [UBA, 1999]. Figure 2.4 is indicative of this period of policy change (between 1972 and 1992). Note the high correlation between lead in petrol and lead air pollution despite the large rise in traffic flow experienced in the same period.

Figure 2.4 Reduction in lead concentrations in air and petrol between 1972-1992 in the EU [after Montague and Luker, 1994]

Platinum group metals4 (PGMs) are increasingly used in vehicle exhaust catalysts (VECs) and can be traced in the urban environment [Farago et al., 1995]. These are covered in detail in Section 6, case studies.

3 Amid mounting concern that the lead dispersed in the environment was causing damage to humans and the environment, a series of regulations and directives have been adopted in Europe since the 1980s, in order to phase out the use of leaded petrol. Lead content of petrol has been reduced from 0.4g l-1 to 0.15gl-1, following the Lead In Petrol Directive 85/210/EEC. Further regulations on air quality have now come into force limiting the levels of lead in air, with an attainment date of 2005. Some countries, namely: Austria, Denmark, Finland, Germany, the Netherlands, Norway, Sweden, and the UK have already phased out its use. However, in some countries in Eastern Europe, higher levels of lead are permitted, up to 0.4g l-1. In most of the newly independent states and the Russian Federation, permitted lead levels are 0.15-0.37 g l-1. Various strategies for reduction of lead in petrol have been made in these countries, though it is expected that some will have difficulty in achieving these targets. 4 Platinum, palladium in vehicle exhaust catalysts and rhodium in three-way catalysts

Pollutants in Urban Waste Water and Sewage Sludge 35 2. Potentially Toxic Elements

Vehicle degradation:

Tyre wear releases lead, zinc and hydrocarbons, either in particulate form or in larger pieces as a result of tyre failure. The deposition of Zn on the road surface from tyres has been determined to be 0.03g vehicle km-1 (Mitchell, 1985). Metal particles, especially copper and nickel, are released by wear of clutch and brake linings. Additionally, the presence of Ni and Cr in storm runoff can result from the degradation of car bumpers and window sealings where both metals are used in the manufacture of chrome plating. Copper is a common constituent of piping and other components of the engine and chassis work. The contribution to road surface material of vehicle tyres and brake linings from different road types has been summarised in Table 2.22.

Table 2.22 Input from tyre wear and brake lining degradation for each road category [after Muschack, 1990] Type Total Individual elements of street Abrasion (g ha of road-1 annum-1) (kg ha of road-1) Pb Cr Cu Ni Zn Tyre Brake Tyre Brake Tyre Brake Tyre Brake Tyre Brake Tyre Brake wear lining wear lining wear lining wear lining wear lining wear lining Residential way 137 6.8 60 7.3 10 13.7 12 210 10 51 35 0.9 Residential street 62 8.5 76 9.0 13 17.0 17 260 12 63 43 1.7 Distributor 72 12.4 112 16.6 19 24.9 26 381 18 93 63 2.4 road Main distributor 109 19.1 172 20.4 29 38.3 39 586 27 143 96 2.6 road Main road 127 30.3 266 32.2 44 60.5 60 926 42 226 149 2.1 Dual 120 43.4 382 46.3 64 86.9 72 1329 61 324 214 5.8 carriageway Motorway 328 82.1 572 87.6 120 164 164 2513 115 613 405 11.0

These findings are also supported by evidence in non-EU countries. Drapper et al. (2000) in an experimental site in Australia concluded that brake pad and tyre wear, caused by rapid vehicle deceleration, contributes to the concentrations of copper and zinc in road runoff. Laser particle sizing indicated that the median size (by volume) of the sediment found was 100 µm, but have settling times of around 24 hours under laboratory conditions. The explanation offered to this unexpected behaviour is the presence of potentially toxic elements. One of the most important findings of this study (which took into account both Australian and US research), was that traffic volume cannot account for more than 20-30% of the variability of pollutant load variations and therefore a traffic volume criterion on whether or not the precipitation runoff should be treated may not be acceptable. Drapper et al. (2000) also stated that precipitation intensity and preceding dry days could be a significant factor influencing actual pollutant concentrations. It can be argued that a more suitable criterion for treatment need assessment would be the environmental significance of the receiving waters.

Road related sources: Pollution in precipitation runoff from road-related sources stems mainly from maintenance practices including de-icing, road surface degradation and re-surfacing operations.

De-icing agents include large amounts of sodium chloride, and may also contain smaller concentrations of iron, nickel, lead, zinc chromium and cyanide as contaminants. Their use can greatly increase corrosion rates in vehicles and metal structures leading to increased metal deposition. Salt in solution can also create conditions that allow the release of toxic metals such as mercury from silts and sludge [WRc, 1993]. It is likely that de-icing is a major source (at least in the winter) of bromide, nickel and chromium [Hedley and Lockley, 1975]

Pollutants in Urban Waste Water and Sewage Sludge 36 2. Potentially Toxic Elements and it is suggested it may affect the solubility and mobility of other metals, notably of lead, which may precipitate more readily in the presence of sodium [Laxen and Harrison, 1977].

The use of NaCl as a de-icing agent may change the behaviour of the accumulated contaminants in roadside soils. In soils exposed to high Na concentrations with a subsequent supply of lower salinity water, as in snowmelt periods and storm flow events, there is a risk of colloid dispersion and mobilization [Norrstrom and Jacks, 1998]. Soil column leaching experiments with NaCl and low-electrolyte water have provided evidence for the mobilisation of organic colloids and Fe-oxides, suggesting that potentially toxic elements may reach the groundwater via colloid-assisted transport [Amrhein et al., 1992, 1993]. Moreover, the use of road-salt may result in the increased mobilisation of potentially toxic elements due to complexation with chloride ions [Doner, 1978; Lumsdon et al., 1995].

Complexed cyanide ion (in the form of sodium ferrocyanide) is added as anti-caking agent to de-icing agents, and compounds containing phosphorus may also be added as rust inhibitors. Novotny et al. (1998) argue that although ferrocyanide is non-toxic in its original form, its instability under predominant natural surface waters conditions, results in decomposition to free cyanide which is toxic (free cyanide« HCN(aq)+CN-(aq)). The initial cyanide form is only stable within the pH range 8 to 14 and zero to –600mV redox potential (Eh). The rate of decomposition is estimated around 10.2µg l-1 h-1 in salt water. Meeusen et al. (1992) estimated similar rates of decomposition.

Road surface degradation is likely to release various substances: bitumen and aromatic hydrocarbons, tar and emulsifiers, carbonate and metals depending on the road construction techniques and materials used. The following table provides some indication of the concentrations of potentially toxic elements released from road surface abrasion, classified by type of road encountered in urban areas.

Pollutants in Urban Waste Water and Sewage Sludge 37 2. Potentially Toxic Elements

Table 2.23 Emissions from abrasion of urban streets surface material [after Muschack, 1990] Type Total abrasion Individual elements of street (kg ha of road-1 (g ha of road-1annum-1) annum-1) Pb Cr Cu Ni Zn Residential way 1734 177 619 88 2030 285 Residential street 2148 219 767 110 2513 352 Distributor road 3152 322 1125 161 3688 517 Main distributor 4850 495 1731 247 5674 795 road Main road 7665 782 2736 391 8965 1257 Dual carriageway 11000 1124 3927 561 12870 1804 Motorway 10000 1020 3570 510 11700 1640

Accidental discharges: Although spillages can be considered a minor add-in in terms of total pollutant loading, they can be one of the most serious sources of contaminants in urban areas. They can range from minor losses of fuel to major losses from fractured tanker vehicles. The resulting impact on wastewater treatment plants or directly to water receptors is hard to estimate due to the random nature and the unpredictability to both the extent of the spill and its position relative to the precipitation runoff system.

In the case of chemical accidents, water or foam medium are used for road cleaning purposes or for fire fighting. The compositions of a typical and unusual load of the surface run-off are compared in Table 2.24.

Table 2.24 Example of a typical and unusual load in run-off water from a German motorway [Ascherl, 1997, Krauth and Klein, 1982]

Parameter Run-off rain water- mean value Water for firefighting- [mg l-1] [mg l-1] Cd 0.0059 0.057 Cr 0.0096 0.053 Cu 0.097 0.203 Fe 3.42 4.0 Pb 0.202 0.439 Zn 0.36 4.7

Information relating to the frequency of accidental spillages is presented in Table 2.25, based on data extracted from NRA (Thames Region, UK), indicating pollution incidents registered from 1988 to 1993 (July):

Table 2.25 Accidental spillages in Thames Region (UK)

Year 1988 1989 1990 1991 1992 1993(July) Number of incidents reported 2811 3613 3444 3417 3598 1979 Road incidents reported 125 177 175 136 212 104 Road incidents where pollution 88 63 64 42 58 36 substantiated

Pollutants in Urban Waste Water and Sewage Sludge 38 2. Potentially Toxic Elements

B Roof runoff

Runoff from roof surfaces constitutes a significant fraction of the total sealed surface runoff and is often regarded as unpolluted. Assessment of roof runoff quality found in literature gives rather contradictory results. Some authors conclude that rain runoff from roof surfaces is polluted (e.g. Zillich 1991; Good 1993); others found that there is a low pollution potential associated with roof runoff (Shinoda 1990). For the specific case of potentially toxic elements pollution however, the literature seems to agree that roof runoff can be at least as polluted as road runoff (Herrmann et al., 1994; Förster, 1999). The pollution effect is much greater when the source of pollutants is the roof material itself. Förster (1999) found that zinc concentrations in runoff from zinc sheet roof were actually two or three orders of magnitude above those measured in runoff from roofs without any metal components (i.e. fibrous cement roof).

However, even in the case of normal rooftops (non-metal dominated) there is a concentration of potentially toxic elements to be expected due to various metal components (gutters, downspouts, fittings etc.). The main pollutants in this case are zinc and copper. The runoff rate of zinc was proven to be considerably lower than its corrosion rate, varying between 50±90% for zinc and 20±50% for copper during exposures up to five and two years, respectively (Wallinder et al., 2000). Similar to its corrosion rate, runoff rates of zinc are strongly related to the atmospheric SO2 concentration and are, as such, different for a rural, compared to an urban or an industrial, environment. Observed lead pollution from roof runoff (which can be considered significant in many cases compared to other sources) can be explained by the use of lead in window frames and rooftops (the case of slate roofs in Figure 2.5) and the use of lead sheeting, particularly in the UK. The lead emission factor from lead flashing and roofing in Denmark is estimated at 5.10-4 kg kg-1year-1 (Jøergensen and Willems, 1987]. The presence of cadmium can be explained by the fact that cadmium is a minor contaminant of zinc products.

A study in Calais, France, and its surrounding area found that concentrations of cadmium, mercury, and lead in roof sludge were: 34.5 mg kg-1, 4.4 mg kg-1, and 4mg kg-1 respectively in the urban areas [ADEME, 1997]. A study carried out in Nancy in 1996 analysed wet weather runoff and determined the main metal-contributing sources. For zinc, roof runoff was the largest source as it contributed 72%, and road runoff only contributed 12%. For lead, the main source was again roof runoff with 33% contribution and then road runoff with 32% [Autugelle et al., AGHTM, 1996]. However, these data may not be typical, as they represent one storm event.

Relationships between rooftop material and runoff pollutant load can be observed in Figure 2.5 and Table 2.27

Pollutants in Urban Waste Water and Sewage Sludge 39 2. Potentially Toxic Elements

Figure 2.5 and Table 2.27 Rooftop material and runoff pollutant load [after Gromaire- Mertz et al., 1999] Roof Name Covering Gutter Material Material

Tile 1 Interlocking Zinc Clay Tiles

Tile 2 Flat clay tiles Copper (70%) + zinc sheets Zinc Zinc Sheets Zinc

Slate Slate Zinc

Table 2.28 provides some indicative ranges of potentially toxic element pollution concentrations from roof runoff. For comparison purposes the ranges of concentrations of the same pollutants from other sources in the same study, are also included. The median value is used, instead of the mean, to filter out the effect of isolated extreme events.

Table 2.28 Potentially toxic element pollution concentrations from roof runoff [after Gromaire – Mertz et al., 1999]

Roof runoff Yard runoff Street runoff Min. Max. Median Min. Max. Median Min. Max. Median Cd (µg l-1) 0.1 32 1.3 0.2 1.3 0.8 0.3 1.8 0.6 Cu (µg l-1) 3 247 37 13 50 23 27 191 61 Pb (µg l-1) 16 2764 493 49 225 107 71 523 133 Zn (µg l-1) 802 38061 3422 57 1359 563 246 3839 550

Lead pollution from roof degradation is strongly particle-bound (measurements indicated median values of 87%), whereas the distribution between particle and dissolved pollution fluctuates for the rest of the potentially toxic elements. Although solids are the main vector of pollution in street and yard runoff, literature agrees that in the case of roof runoff the dissolved phase is of primary importance [Gromaire – Mertz et al., 1999; Förster, 1996; Förster, 1999; Wallinder et al., 2000]. The very high concentrations of dissolved potentially toxic elements in roof runoff make its infiltration hazardous and highly dependent on roof materials. Low settling velocities for roof runoff particles in conjunction with high percentage of dissolved pollutants make settling alone an insufficient technique for treatment. Uncontrolled local infiltration practices (infiltration trenches etc) may lead to serious local soil contamination and present a threat to groundwater quality.

In conclusion it can be said that roof runoff pollution is influenced by roof material, air pollution, the precipitation event (intensity, antecedent dry period), the meteorology (season, wind speed and direction) and the pollutants’ physico-chemical properties. It can under certain conditions by far exceed threshold toxicity values. The following suggestions (Förster, 1999) summarise a number of research areas that should be considered to minimise roof runoff pollution.

Pollutants in Urban Waste Water and Sewage Sludge 40 2. Potentially Toxic Elements

· First flush diversion valves and their automated control · Sorbents for potentially toxic elements · Durable coating for potentially toxic element surfaces · Alternative materials for gutters and downpipes (eg plastics or carbon fibre based materials, not metals or PVC) · Roof runoff quality database sufficient for predictive modelling.

C Construction and building maintenance

Contaminants from paints: While lead concentrations in consumer products (i.e. petrol) continue to decrease, there seems to be enough residual material from historic lead use to cause high lead concentrations in the environment. In a recent study by Davis and Burns (1998) in the US, lead runoff from painted structures in an urban setting was assessed. Although construction practices in the US can be considered different from those in EU, the conclusions of the Davis and Burns (1998) study should be taken into account due to the variability of the structures investigated. In many cases, high lead concentrations were found. Lead concentrations (100 ml over 1600 cm) from washes of 169 different structures followed the order (geometric mean, median, Q10±Q90): wood (40, 49, 2.6±380 mg.l-1)>brick (22, 16, 3.3±240 mg.l-1)>block (9.7, 8.0, <2±110 mg.l-1). Lead concentration depended strongly on paint age and condition. Lead levels from washes of older paints were much higher than from freshly painted surfaces, which were demonstrated quantitatively as: paint age [>10 y] (77, 88, 6.9±590 mg.l-1)>>[5±10 y] (22, 16, <2±240 mg.l-1)>[0±5 y] (8.4, 8.1, <2±64 mg.l-1). Lead from surface washes was found to be 70% or greater in particulate lead form, suggesting the release of lead pigments from weathered paints. High intensity washes were found to liberate more particulate lead than lower intensities. It can be concluded that old surface paints can contribute high masses of lead into a watershed, targeting these structures for source preventive actions to curtail future lead input into the environment.

Contaminants from concrete leaching: Concrete is one of the main materials used in building and road construction and is systematically in contact with precipitation, much of which ends up in the UWW collection systems. Recent work (PCA, 1992) identified As, Be, Cd, Cr, Hg, Ni, Pb, Sb, Se and Th in concrete in detectable concentrations. Hillier et al. (1999) discuss the importance of the concentrations of these pollutants in leachate from Portland cement. They concluded that leaching of well-cured Portland cement produces undetectable concentrations of toxic metals (such as the ones outlined in 80/778/EEC for water fit for human consumption). In poorly cured (1 day) Portland cement there were detectable concentrations of vanadium (reaching concentrations of 61.7 ppb). However, even this cannot be considered very significant, as the leaching was restricted to the surface of the samples. Furthermore, the water-to-cement ratio has no significant impact on the leaching potential of the cement. This study suggests that concrete leaching is not a major source of metals to UWW.

D Wet and dry deposition

Rainwater can add its own absorbed and dissolved pollutants to the loads generated from other sources. This was shown in Figure 2.3, which shows the initial potentially toxic element loading of precipitation and the subsequent additional loading from roof, pavement and road surfaces. Both traffic density and location of industry have a strong influence on the deposition of potentially toxic elements in precipitation.

The composition of atmospheric loaded precipitation water in urban regions in Germany, contaminated with atmospheric wash-out, is represented in Table 2.29.

Pollutants in Urban Waste Water and Sewage Sludge 41 2. Potentially Toxic Elements

Table 2.29 Composition of atmospheric loaded run-off water in German urban regions [Freitag et al. 1987, Göttle 1988, Hahn 1995].

PTE Values Munich (Pullach/ Harlaching) Mean value Extreme values 1988 [mg l-1] [mg l-1] [mg l-1] Zn 0.05-0.15 0.02-1.9 0.0945 Cu 0.007-0.2 <0.06 0.0355 Pb 0.03-0.11 <0.24 0.0121 Cd 0.001-0.003 <0.13 0.0014 Mn 0.05 <0.1 - Cr 0.002 <0.08 -

Currently, vehicle traffic, steel and glass production, and combustion processes represent the main sources of lead in the atmosphere. Data by ADEME studies have shown that atmospheric fallout contributes 87-536 g ha-1year-1 of lead, and is particularly high in urban areas. These studies determined that 70-80% of lead present in UWW comes from runoff, 15-20% from commercial sources and 5% from domestic sources. The main cadmium sources are from combustion processes (vehicle traffic, waste combustion in incineration plants). Combustion processes and chlorine and steel production represent the main sources of the atmospheric mercury emissions in the Central Region. Table 2.30 shows the reduction in Cd, Hg and Pb emissions in Austria between 1985 and 1995 as a result of legislative controls.

Table 2.30 Emissions and predicted yearly emissions of potentially toxic elements in Austria, 1985-2010 [UBA, 1999]. PTEs 1985 1990 1995 Prediction Prediction [t y-1] [t y-1] [t y-1] 2005 2010 [t y-1] [t y-1] Cadmium 4.80 3.10 1.80 1.20 1.30 Mercury 4.30 2.70 1.50 1.20 1.10 Lead 320.00 202.00 39.00 24.00 21.00

The presence of impermeable surfaces in urban areas prevents natural filtration processes in the soil zone from removing the pollution. The actual quality of the rain can vary dependent on pollution sources other than urban traffic. In coastal areas the increased concentrations of sodium and chloride in precipitation will increase the susceptibility of vehicles to corrosion. A road drainage study in Sweden noted precipitation pH of between 3.8 and 4.9 [Morrison et al. 1988].

Atmospheric sources contribute significantly to the mass of contaminant available on an impervious urban surface for transport by surface runoff. This deposition may occur during a storm event or as dust fall during dry periods. Cattell and White (1989) [as reported in Ball et al. 2000] in their study in Sydney reported that the geometric mean of the total phosphorous concentration is 29 µg l-1. If the mean annual precipitation for Sydney of approximately 1600 mm is considered, then the likely annual phosphorus load is approximately 0.5kg ha-1y-1, which is more than half the likely annual phosphorus load from an urban catchment of 0.7kg ha-1y-1 [Lawrence and Goyen, 1987] to 1.1kg ha-1y-1 [Cullen, 1995].

The second of the two atmospheric sources of contamination is dry deposition in the period between storm events. For dry deposition, removal by stormwater runoff is not the sole mechanism responsible for depletion of the contaminant store, which is developed on the catchment surface. As well as removal by storm events, removal also can occur through street sweeping, through the local turbulence arising from the motion of vehicles on roads, and through wind events where the wind has sufficient capacity to entrain the contaminant and to move it from the surface of the urban catchment [Ball et al., 2000].

Pollutants in Urban Waste Water and Sewage Sludge 42 2. Potentially Toxic Elements

Table 2.31 Dry Weather Build-up of Contaminants on Road Surfaces [after Ball et al., 1998]

Constituent Load (mg/m of gutter) Constituent Minimum Maximum Mean Pb 1.4 7.4 3.7 Zn 0.7 3.9 1.8 Cu 0.3 1.8 0.9 Cr 0.02 0.61 0.14 P 0.23 1.9 0.8

Dry atmospheric fallout can be responsible for large proportions of road dust but estimates vary according to atmospheric and weather patterns, as well as with different sampling and estimation methods. Nevertheless, atmospheric deposition can be very significant proportion of the total particulate/sediment input to a highway and since much of it is inert, inorganic and often calcareous in nature (depending upon local geology and building stone), it can prove beneficial in neutralising acid emissions, reducing potentially toxic element solubility and assisting in the binding of organic and other pollutants [Luker and Montague, 1994].

Snowfall has an increased pollutant scavenging efficiency because of the large snowflake surface area and the increased ionic strength of the melt water provides enhanced metal exchange capabilities. Trees in urban settings are also effective scavengers of metals, which are deposited on surfaces at leaf fall.

Atmospheric contaminants are deposited during the early stages of a precipitation event and therefore the resulting impermeable surface loading tends to be independent of both precipitation volume and intensity, with the pollutant load tending to increase with the length of antecedent dry period and with local traffic density.

E Sewer cleaning Sewer cleaning is carried out for a number of reasons, but principally to deal with blockages or to remove sediment in order to restore hydraulic capacity and limit pollutant accumulation. A number of cleaning techniques and methods is in use, depending particularly on location and severity, including rodding, winching, jetting, flushing and hand excavation (Lester & Gale, 1979). A combination of more than one method may well be used in any particular locality.

The frequency with which sewers are cleaned will depend on the maintenance strategy in operation. If reactive maintenance is used, problems are dealt with on a corrective basis as they arise (i.e. after failure). This approach will always be required to a certain extent, as problems and emergencies occur from time-to-time in every system. However, its frequency cannot be predicted. In planned maintenance, potential problems are dealt with prior to failure. Unlike reactive maintenance, planned maintenance is proactive and has the objective of reducing the frequency or risk of failure (Butler & Davies, 2000). Planned maintenance differs from routine maintenance (operations at standard intervals, regardless of need), and involves identifying elements that require maintenance and then determining the optimum frequency of attention. Frequency of cleaning will thus vary from place to place but is usually less than once per year even in heavily affected sewers.

Sediment removed from sewers during cleaning is normally classified as a controlled waste, and is therefore disposed of to licensed landfill sites.

Pollutants in Urban Waste Water and Sewage Sludge 43 2. Potentially Toxic Elements

2.2 Influence of various treatment processes on the fate of potentially toxic elements through WWTS and SST

PTE transfers to sewage sludge Sludges from conventional sewage treatment plants are derived from primary, secondary and tertiary treatment processes. The polluting load in the raw waste water is transferred to the sludge as settled solids at the primary stage and as settled biological sludge at the secondary stage. Potentially toxic elements are also removed with the solids during the primary and secondary sedimentation stages of conventional wastewater treatment. Metal removal during primary sedimentation is a physical process, dependent on the settlement of precipitated, insoluble metal or the association of metals with settleable particulate matter. Minimal removal of dissolved metals occurs at this stage and the proportion of dissolved metal to total metal in the effluent increases as a result. The efficiency of suspended solids removal is the main process influencing the extent of metal removal during primary wastewater treatment. However, the relative solubilities of different elements present in the wastewater are also important. Thus, nickel shows the poorest removal (24 %) during primary treatment whereas 40 % of the Cd and Cr in raw influent is transferred to the primary sludge. Primary treatment typically removes more than 50 % of the Zn, Pb and Cu present in raw sewage.

The removal of metals during secondary wastewater treatment is dependent upon the uptake of metals by the microbial biomass and the separation of the biomass during secondary sedimentation. Several mechanisms control metal removal during biological secondary treatment including:

· physical trapping of precipitated metals in the sludge floc; · binding of soluble metal to bacterial extracellular polymers;

In general; the patterns in metal removal from settled sewage by secondary treatment are similar to those recorded for primary sedimentation. However, the general survey of removal efficiencies listed in Table 2.32 suggests that secondary treatment (by the activated sludge process) is more efficient at removing Cr than the primary stage. Operational experience and metal removals measured by experimental pilot plant systems provide guidance on the overall likely removal and transfers to sludge of potentially toxic elements from raw sewage during conventional primary and secondary wastewater treatment. This shows that approximately 70 – 75 % of the Zn, Cu, Cd, Cr, Hg, Se, As and Mo in raw sewage is removed and transferred to the sludge (Blake, 1979) and concentrations of these elements in the final effluent would be expected to decrease by the same amount compared with the influent to the works. Lead may achieve a removal of 80 %, whereas the smallest overall reductions are obtained for Ni and approximately 40 % of this metal may be transferred to the sludge.

The majority of potentially toxic elements in raw sewage are partitioned during wastewater treatment into the sewage sludge or the treated effluent. However, atmospheric volatilisation of Hg as methylmercury, formed by aerobic methylation biotransformation processes, is also suggested as a possible mechanism contributing to the removal of this element during secondary wastewater treatment by the activated sludge system (Yamada et al., 1959). Whilst some of the Hg removal observed in activated sludge may be attributed to bacterially mediated volatilisation, it is unlikely that this is a major route of Hg loss because of the significant quantities of Hg recovered in surplus activated sludge (Lester, 1981).

Pollutants in Urban Waste Water and Sewage Sludge 44 2. Potentially Toxic Elements

Table 2.32 PTE removals and transfer to sewage sludge during conventional urban wastewater treatment [Lester, 1981] PTE Removal (%) Primary(1) Secondary(2) Primary + Primary + secondary secondary(3) Zn 50 56 78 70 Cu 52 57 79 75 Ni 24 26 44 40 Cd 40 40 64 75 Pb 56 60 70 80 Cr 40 64 78 75 Hg 55 55 80 70 Se 70 As 70 Mo 70 (1)Mean removal (n = 5) from raw sewage and transfer to sludge during primary sedimentation (2)Mean removal (n = 9) in activated sludge from settled sewage, (3)Blake (1979)

Predicting the fate of potentially toxic elements during WWT and sludge treatment Chemical contaminants present in UWW are associated principally with the organic and mineral fractions in sewage. The microbial biomass in secondary treatment is also effective at scavenging potentially toxic elements from the settled sewage transferring metals to the activated sludge. About 60 - 80 % of the wastewater load of potentially toxic elements such as Cu and Pb is transferred into sludge (Table 2.32) and the sludge contains approximately 1000 times (mg kg-1 ds basis) the concentration of these metals present in the wastewater (mg l-1). The relationship between metal concentrations in wastewater and in sludge can be determined empirically as follows (after Blake 1979):

S = P / ((Ws/1x106) x (100/T)) mg kg-1 ds

Where P = Concentration of contaminant in wastewater mg l-1 S = Concentration of contaminant in sludge mg kg-1 ds Ws = Dry solids content of wastewater mg l-1 T = Transfer efficiency of contaminant from wastewater to sludge during sewage treatment % Ds = Dry substance

For example, a wastewater containing 1.3 mg l-1 of Zn (P) and 450 mg l-1 of dry solids (Ws) would produce sludge with a Zn concentration of 2000 mg kg-1, assuming a transfer factor of 70 % (T):

S = 1.3 / ((450/1x106) x (100/70)) mg kg-1 = 2000 mg kg-1

This relationship can also be used to estimate the concentrations of metals in the raw sewage effluent, based on analytical data for the metal content in sludge and the dry solids in the raw wastewater:

P = S x ((Ws/1x106) x (100/T)) mg l-1

The concentration in the final effluent, F mg l-1, can therefore be estimated from:

F = (1-T/100) x (S x ((Ws/1x106) x (100/T))) mg l-1

Based on the above assumptions, the Zn content in the final effluent in this example is estimated to be:

Pollutants in Urban Waste Water and Sewage Sludge 45 2. Potentially Toxic Elements

F = (1-70/100) x (2000 x ((450/1x106) x (100/70))) mg l-1

= 0.4 mg l-1

A more mechanistic approach to predicting the fate of metals during wastewater treatment is described by Monteith et al. (1993) using a computer-based mathematical model. The mechanistic model, TOXCHEM (Bell et al., 1989), includes both steady state and dynamic models to simulate operation of a conventional activated sludge plant, incorporating grit removal, primary clarification, aeration and secondary clarification unit processes. Biodegradation, surface volatilisation, air stripping, precipitation and sorption removal mechanisms are determined for trace metallic and organic contaminants in the model’s database. A sensitivity analysis feature allows the user to investigate the impact of design and operating conditions and the contaminant’s physical/chemical properties on removal by unit process and by mechanism.

Inputs to the TOXCHEM model include influent wastewater flow rate, influent metals concentrations, dimensions of individual process units, plant operation conditions (e.g. mixed liquor suspended solids concentration), and raw wastewater, primary effluent, and secondary effluent suspended solids concentrations. The model then predicts metal concentrations in primary sludge, return activated sludge, surplus activated sludge, and secondary settler effluent, based on mass balance calculations and removals through precipitation and sorption. The steady-state model accounts for removal by sorption of soluble metals onto settleable solids and precipitation of the metals into a settleable form. The following assumptions were used to develop the model equations:

1, The system is at equilibrium with regard to sorption and desorption; 2, Sorption follows a linear isotherm; 3, Precipitation and dissolution are instantaneous; 4, Precipitated metals are integrated into the biomass and are removed at the same efficiency as the bulk solids during primary and secondary settlement.

In both the primary settlement and aeration tanks, the model calculates the metal concentrations in the soluble and solid phases:

Ct = Cs + Cx Cx = Cp + KpXCs

Where:

-1 Ct = total metal concentration, mg l -1 Cs = soluble metal concentration, mg l -1 Cx = solid-phase metal concentration, mg l -1 Cp = concentration of precipitated metal, mg l -1 Kp = linear sorption coefficient, l g X = mixed liquor volatile suspended solids (MLVSS) concentration, g l-1

The values of Kp and metal solubilities are experimentally defined. Solubility was determined from dosing studies in which metal concentrations were measured in filtered and unfiltered wastewater samples at equilibrium. The soluble, sorbed and precipitated metal fractions are calculated by the expression:

Ctest = CT,0/(1 + KP.1Xo) Where CT,0 = influent total metal concentration KP.1 = primary clarifier sorption coefficient Xo = influent volatile suspended solids (VSS) concentration.

Pollutants in Urban Waste Water and Sewage Sludge 46 2. Potentially Toxic Elements

Fractional removal of metals in the primary and secondary settlers is calculated by: FRm = (FRsolidsCx)/CT,0

Where FRm = fractional removal of metal in settler, and FRsolid = fractional removal of solids in settler.

Fractional removal of the solids is input by the user based on site-specific experience. The output for the primary and secondary settlers is calculated by:

Ct,out = (1-FRm) CT,0 Where Ct,out = total outlet metal concentration.

The TOXCHEM model was validated against operational data on effluent metal contents collected from a full-scale wastewater treatment plant (Table 2.33). The predictions were compared to observed values in the final effluent using linear regression analysis and the r2 statistic. Copper exhibited the highest correlation between predicted and observed effluent concentrations of the elements tested and the r2 value for this metal was 0.96. The model predicted that 70 % of this element would be transferred to the sewage sludge. Zinc also gave relatively good agreement between predicted and observed effluent concentrations and the results showed that 50 – 60 % of Zn in wastewater would be recovered in the sludge. The poorest correlation of modelled and actual values was obtained for Ni and the r2 was 0.41 in this case. The model underestimated the removal of Ni by the wastewater treatment plant and the predicted value was 26 % compared with the observed removal of 37 %. Lead and Cr have low solubilities and in both cases, the TOXCHEM model predicted much larger removals of approximately 70 % for these metals than was observed in practice at the sewage treatment works. However, the model predictions for Pb and Cr were comparable with operational experience at other wastewater treatment plant (Table 2.32). The slopes of the regressions lines fell within the range 0.58 – 1.96 bracketing the ideal slope of 1.0. The model provided good representations of the concentrations of Cu, Ni and Zn in the final effluent, but was less satisfactory for Pb or Cr. Cadmium was not subject to the verification exercise because concentrations in the effluent were below the analytical limit of detection. The modelling and experimental studies showed that Cd and Ni were the most soluble metals, and the most poorly removed, while Pb and Cr were the least soluble. The majority of metals, with the exception of Ni, were maintained in the mixed liquor, and the mass collected in effluent was small in comparison to the total influent mass. At low metal concentrations (0.02 – 0.1 mg l-1), the soluble fraction is controlled by sorption to solids. At larger influent metal concentrations, precipitation is the main process controlling soluble metal fractions. In consequence of this differential fate of metals in WWTS, nickel may need tighter regulation at source to reduce the amount in the effluent.

The mechanistic approach to model development incorporates the main chemical and physical processes that are recognised as being important in removing metals from wastewater. However, in some circumstances, there may be specific properties of a wastewater at a particular treatment works that influence metal behaviour and removal efficiency that are not accounted for by these basic assumptions. For example, recoveries of insoluble elements such as Cr or Pb in sewage sludge are usually relatively high and of the order >75 % (Table 2.33). This contrasts with the recoveries of these elements measured by Monteith et al. (1993), which were much lower than those normally observed in practice. Operational and mechanistic models have the capability to predict partitioning and distribution of potentially toxic elements from raw sewage during conventional wastewater treatment. They provide insights into the physico-chemical processes controlling metal removal in terms of solubility, sorption and precipitation mechanisms, and calculate the mass balance and partitioning of metals into sewage sludge and the final effluent. The metal concentration in sludge can be calculated using the estimated partitioning coefficients and the mass of primary and biological sludge produced by primary sedimentation and secondary wastewater treatment.

Pollutants in Urban Waste Water and Sewage Sludge 47 2. Potentially Toxic Elements

Table 2.33 Predicted metal concentrations in sewage effluents estimated by the TOXCHEM model relative to observed values at a full-scale sewage treatment plant (adapted from Monteith et al., 1993)

PTE Mean concentration (mg l-1) r2 for Removal (%) Influent Observed Predicted predicted Observed Predicted effluent effluent vs. observed Zn 0.120 0.051 0.057 0.61 58 53 Cu 0.120 0.041 0.034 0.96 66 72 Ni 0.027 0.017 0.020 0.41 37 26 Pb 0.069 0.051 0.022 0.66 26 68 Cr 0.026 0.016 0.007 0.63 39 73

Effect of stabilization processes on metal concentrations in sewage sludge Potentially toxic element concentrations in sewage sludge are influenced significantly by the type of stabilization process operated at a WWTS. For example, the destruction of volatile solids by microbial decomposition of putrescible organic matter in sludge by mesophilic anaerobic digestion or aerobic composting processes increase the metal content in direct relation to the extent of volatile solids removal by microbial decomposition.

Unstabilised, co-settled primary + activated sludge typically contains 75 % of volatile matter on a dry solids basis. During anaerobic digestion, 40 % of the volatile matter is destroyed reducing the volatile solids concentration in digested sludge by about 50 % compared to the undigested product. Potentially toxic elements are conserved and are retained in the sludge during the digestion process. As a consequence of the microbial decomposition of organic matter, metal concentrations increase in direct proportion to the loss of solids and are typically raised by approximately 40 % compared with undigested sludge.

Volatile matter is also lost during aerobic composting of sewage sludge (Figure 2.6). Composting dewatered sewage sludge cake requires a bulking agent, such as straw or woodchips, to increase porosity and reduce moisture content to values that will support aerobic microbial decomposition processes. Straw is often used for this purpose and may be mixed with sludge cake at 25 % ds at a rate of 5 – 10 % on a fresh weight basis (Smith and Hall, 1991). The addition of bulking agent to sludge reduces the initial metal concentration. However, metal concentrations in the composting material increase proportionally in linear relation to the extent of volatile matter destruction by microbial activity. In windrow composting trials (Smith and Hall, 1991), for example, the volatile solids concentration of composting sewage sludge and straw decreased by 21 % during a period of 100 days (Figure 2.6). During that period, the metal concentration in the composted product was increased above the value in the original sludge (Figure 2.7).

Pollutants in Urban Waste Water and Sewage Sludge 48 2. Potentially Toxic Elements

Figure 2.6 Volatile solids content of sludge-straw compost at different rates of straw addition (fresh weight) to sludge cake (25 % ds) over time (Smith and Hall, 1991)

75

70 Volatile Solids 65 5.0% Content (%) 7.0% 60 8.5%

55

50 0 20 40 60 80 100 120 Time (days)

Sludge stabilisation processes reduce the fermentability of the sludge and the potential odour nuisance and health hazards associated with its use on agricultural land. However, the loss of volatile matter during microbial decomposition also significantly increases its metal content by as much as 40 % compared with material that has not been subject to a biological stabilisation process. More than 75 % of the sludge produced in the EU is treated by anaerobic or aerobic digestion. Despite the wide adoption of biological stabilisation processes for sludge throughout the EU, which generally increase the metal content of sludge, reported potentially toxic element concentrations in sewage sludge continue to decline (e.g. Figure 2.7).

This further emphasizes the major and significant improvements in sludge quality, in terms of potentially toxic element content, that have been achieved in the past 20 years through improved industrial practices and the successful and effective implementation of trade effluent controls.

Pollutants in Urban Waste Water and Sewage Sludge 49 2. Potentially Toxic Elements

1300 1200 1100

ds) 1000 -1 900 800 700 600 Cu (mg kg 500 50 55 60 65 70 75

1600 1400

ds) 1200 -1 1000 800 600 400

Zn (mg kg 200 0 50 55 60 65 70 75 Volatile Solids Content (%) Figure 2.7 (a) Cu and (b) Zn concentrations in sewage sludge-straw compost in relation to volatile solids content (Smith and Hall, 1991)

Pollutants in Urban Waste Water and Sewage Sludge 50 2. Potentially Toxic Elements

(a) Zinc (b) Cadmium 2000 2

1800 1.8

ds) 1.6 ds) -1

-1 1600 1.4 1400 1.2 mg kg 1200 1

1000 0.8 0.6

Total Zn (mg kg 800 0.4 600 0.2 Total Cd (Log 400 0 1978 1983 1988 1993 1998 1978 1983 1988 1993 1998 Year Year

Figure 2.8 Reduction in (a) zinc and (b) cadmium concentrations (untransformed and log10 transformed data, respectively) in sewage sludge from Nottingham STW, UK during the period 1978 – 1999

Pollutants in Urban Waste Water and Sewage Sludge 51 2. Potentially Toxic Elements

2.3 Quantitative assessment of potentially toxic elements in untreated UWW, treated UWW and treated SS

There is limited information available on pollutant concentrations in influent and effluent from WWTS. Concentrations may also be less than the detection limit of the analytical techniques used. It must be noted that the variability of influent concentrations within a WWTS can be very high due to season, precipitation, and levels of industrial and domestic activities. This means that comparisons based on small numbers of samples must be made with caution.

Table 2.34 Concentrations of potentially toxic elements found in influents and effluents of WWTS

PTE Country Domestic Urban WWTS Reference Wastewater Runoff ( g l-1) ( g l-1) Influent Effluent ( g l-1) ( g l-1) Cd Austria 30 (<20-60) 70 (<20- Hohenblum et al., 170) 2000 France 6-85 ADEME, 1995 0.2-4.2 Legret,1999 Germany 0.5 80* 0.4 0.1 Raach et al., 1999 <5 Wilderer et al 1997 Greece <1 <1 Greek report, 2000 Italy: < 5 Braguglia, et.al., 2000 Central n.a Northern Sweden* 200-800 100 Adamsson et al 1998 (domestic) Cu Austria 120 (90- 120 (<70- Hohenblum et al., 130) 190) 2000 Germany 150 Wilderer et al 1997 Greece <100 <100 Greek report, 2000 Sweden* 350000- 50000 Adamsson et al 1998 800000 (domestic) Italy: 20-900 Braguglia, et.al., 2000 Central 2-25 Northern France 0.011- Legret,1999 0.146 Cr Austria 7100 3900 Hohenblum et al., (6200-7900) (<900- 2000 5600) Germany 30 Wilderer et al 1997 Italy: < 20 Braguglia, et.al., 2000 Central 0.5-32 Northern Sweden* 4000-14000 3000 Adamsson et al 1998 (domestic)

(Table 2.34 continued) Hg Austria <10 <10 Hohenblum et al., 2000 France 1-8 ADEME, 1995 Germany 0.4 1* 0.6 0.1 Raach et al., 1999 Greece <1-3 <1-9 Greek report, 2000 Italy: < 1 Braguglia, et.al., 2000 Central n.a Northern Pb Austria 30 (<20-60) 70 (<20- Hohenblum et al., 2000 160)

Pollutants in Urban Waste Water and Sewage Sludge 52 2. Potentially Toxic Elements

France 14-188 51-630 ADEME, 1995 Legret,1999 Germany 100 110* 81 31 Raach et al., 1999 100 Wilderer et al 1997 Greece <1-5000 <1-17 Greek report, 2000 Italy: < 20 Braguglia, et.al., 2000 Central 0.3-9 Northern Spain 10-64 Cabrera, et.al,1995 Sweden* 4000-23000 2000 Adamsson et al 1998 (domesti c) Ni Austria <40-170 240 Hohenblum et al., 2000 (<40- 620) Germany 40 Wilderer et al 1997 Italy: < 50 Braguglia, et.al., 2000 Central 0.5-95 Northern Sweden* 3000-10000 3000- Adamsson* et al 1998 5000 (domesti c) Zn Austria 1000 2500 Hohenblum et al., 2000 (<20-3700) (20- 5000) France 104-1544 Legret,1999 Germany 100-1000 Wilderer et al 1997 Greece 450-3200 <20-900 Greek report, 2000 Italy: 100-900 Braguglia, et.al., 2000 Central 12-185 Northern *Sweden 150000- 50000 Adamsson et al 1998 1300000 (domesti c) As Spain 2.2 Navarro, et.al. 1993 Se Spain: Diaz, et.al., 1996 Se (IV) 0.4 Se (VI) 0.3 Fe France 60-999000 ADEME, 1995 *The data from Sweden are from a very small aquaculture wastewater plant, which only serves a few houses and may not be typical of other WWTS.

Organotin compounds were the subject of monitoring in Switzerland by Fent and Müller [1991], and Fent [1996]. Monobutyltin (MBT), dibutyltin (DBT), and tributyltin (TBT) were monitored in raw wastewater (influent), effluent and sewage sludge (Table 2.35). Phenyltin compounds were also investigated.

Table 2.35 Organotin compounds in Zürich WWTS

Unit MBT DBT TBT Raw wastewater ng l-1 140 to 560 130 to 1,030 60 to 220 Digested sludge mg kg-1 ds 0.3 to 0.8 0.5 to 1.0 0.3 to 1.0

The potentially toxic element loading per inhabitant, per year has been determined in two German studies (Table 2.36). There is a good correlation between these studies for zinc, copper, lead and cadmium concentrations in the influent and effluent of WWTS.

Pollutants in Urban Waste Water and Sewage Sludge 53 2. Potentially Toxic Elements

Table 2.36 Potentially toxic element loading per member of population in two German towns [Raach et al.,1999; DAF, 1995]

Flow Element Raach et al.,1999 DAF, 1995 [g inhabitant-1 a-1)] [g inhabitant-1 a-1)] Influent Zn 69 75 Cu 19 28 Pb 14 32 Cd 0.1 0.5 Effluent Zn 26 39 Cu 6.3 6.9 Pb 5.1 5.0 Cd 0.03 0.07

In Norway and Sweden; emissions of potentially toxic elements from WWTS serving more than 20,000 persons account for almost 80 percent of the wastewater. The discharges of metals from these WWTS in Sweden and Norway are summarised in Table 2.37. This shows that, for Sweden, the amount of potentially toxic elements discharged with urban wastewater decreased over the period 1992 to 1998 for all metals, except for copper. The statistical data do not take into account the WWTS size and also the potentially toxic elements reported are for the treated sewage sludge. There is only limited data available on potentially toxic element content in the treated wastewater (effluent), due to the low concentration, often below detection limits.

Table 2.37 Emissions of potentially toxic elements from WWTS in Sweden and Norway 1998

Element Sweden Sweden Norway 1992 1998 1998 (kg.annum-1) Cadmium 325 137 150 Chromium 5420 3308 3000 Copper 14060 15377 15000 Mercury 530* 304 300 Nickel 8165 7603 8000 Lead 2960 1464 1500 Zinc 37420 32346 32000 * data for 1995 [Statistika centralbyrån Sweden, 1998; SFT-1999]

Power et al. [1999] monitored water in the Thames, UK and found statistically significant reductions in the concentrations of Cd, Cu, Hg, Ni and Zn over the period 1980 to 1997. For lead, the initial improvements were reversed by drought in the period 1990-1997 resulting in a slight, though statistically significant rise in Pb concentrations. However; Pb had fallen prior to this and was still found to have a statistically significant decrease overall in the period 1980-1996 (Table 2.38).

Pollutants in Urban Waste Water and Sewage Sludge 54 2. Potentially Toxic Elements

Table 2.38 Achieved concentration reductions of potentially toxic elements in waters in the Thames estuary, compared with other European estuaries

PTE Thames Thames % Elbe Rhine Humber Severn 1986/7 1995 reduction 1983 1984 1984 1988 µg.l-1 µg.l-1 µg.l-1 µg.l-1 µg.l-1 µg.l-1 Cd 0.43 0.32 24.1 0.10 0.30 0.31 0.25 Cu 31.30 10.70 65.8 2.00 5.50 2.17 5.00 Hg 0.24 0.09 63.0 - - - - Ni 17.30 6.30 63.4 3.25 3.20 - 4.50 Pb 16.30 9.90 39.4 1.90 - 1.24 <0.03 Zn 92.00 29.10 68.4 - 21.80 - 17.50 [from Power et al 1999, data included from *Mart 1985, *Nolting 1986, *Balls 1985, *Apte 1990]

The overall reductions in most metal concentrations in the Thames was greater than 50 percent over the years 1986-1995, with lower reductions being experienced for lead and cadmium. This complements evidence for sludge quality that overall PTE emissions have markedly improved.

In spite of the reductions achieved by 1995 in the River Thames, potentially toxic element concentrations are still high compared to the levels found in the 1980s in the other rivers in the study. It is concluded that while much progress has been made in reducing the anthropogenic sources of potentially toxic element pollution discharged into the Thames, improvements are still needed if water is to approximate to background levels. For cadmium and mercury; the year 2000 levels are forecast to be about twice estimated background levels [Power et al 1999].

A study carried out in the Rhine region in France [Commission Internationale pour la Protection du Rhin, 1999] examined all pollutant sources entering the river over a period of 10 years. The study showed that the decrease in certain pollutants was due to pre- treatment, cleaner technologies and more care in the handling of the priority substances. Nevertheless, in 1996, the study showed that diffuse and domestic (communal) sources are important contributors, particularly storm runoff for mercury, lead, and copper.

The study further divided the sources for each metal and other pollutants into greater detail for each of the riverine countries in the region (France, Switzerland, Belgium, Luxembourg, Netherlands, Germany). An estimate into the source breakdown of metal pollution into the Rhine is included in Figure 2.9.

Pollutants in Urban Waste Water and Sewage Sludge 55 2. Potentially Toxic Elements

Percentage contribution of heavy metals for the different sources in the Rhine 100%

90%

80% Diffuse

70%

60%

50% Communal

40%

30% Industrial 20%

10%

0% Hg Cd Cu Zn Pb Cr Ni

Figure 2.9 The percentage of potentially toxic elements in the Rhine from different sources (France, 1999)

The communal sources of wastewater into the river Rhine (in France), include wastewater from the UWW collecting system, hence showing the widespread presence of these pollutants (Table 2.39). For mercury, lead, and copper more than half is due to storm runoff. Erosion and drainage are also important sources, contributing 18% of the mercury and 55% of the chromium. Atmospheric deposition generally tends to contribute around 8% of the total diffuse metal contribution, particularly for cadmium and zinc.

Table 2.39: Potentially toxic element pollution contribution by different sources in kg a-1. [from Commission Internationale pour la Protection du Rhin, 1999]

Diffuse sources Hg Cd Cr Cu Zn Pb Ni kg.annum-1 Erosion 18 53 5144 3547 10642 4789 5853 Surface runoff 1 10 474 229 1013 67 62 Drainage 7 286 429 2145 28600 2145 1430 Atmospheric deposition 8 75 189 1131 9425 1508 566 Separating system 8 57 475 1900 7600 1520 855 Storm discharge 32 126 630 3780 17640 3780 1890 Untreated wastewater 16 62 310 1860 8680 1860 930 Houses not connected to 2 7 36 216 1008 216 108 UWW collecting systems Point sources Industry 74 242 5548 11190 41100 3120 14300 Communal sources 40 200 1400 12470 30000 2700 3500

Pollutants in Urban Waste Water and Sewage Sludge 56 2. Potentially Toxic Elements

A comparison of potentially toxic element concentrations in sewage sludge applied to farmland in different countries within the EU (Table 2.40) indicates there is some variation apparent in the metal contents of sludges used in agriculture. For example the reported average concentrations of Cd in German and UK sludges in 1996 were 1.5 and 3.5 mg kg-1, respectively (CEC, 2000a). This could indicate differences in the amount of Cd discharged to sewer in these countries from industrial, domestic and diffuse inputs or the adoption of different sludge treatment practices and regulatory procedures influencing metal content. However, these issues are difficult to reconcile given the policies on preventing industrial discharges of Cd followed in both countries and that both states practice extensive sludge stabilisation treatment. A possible explanation may be related to the statistical characteristics of metal concentration data and how data on metal contents in sludge are reported. For example, CEC (2000a) does not state whether arithmetic averages or weighted averages are given for metal contents. The UK figures are weighted according to works size and provide a conservative estimate of sludge metal content because sludge from large treatment works usually have larger metal concentrations compared with smaller works (EA, 1999). For example, the median Cd concentration in sludge used on to farmland from large works (2.9 mg Cd kg-1, pe>150000) in the UK was more than twice that from small works (1.3 mg Cd kg-1, pe<10000) in 1996/97. This trend could be interpreted as being the result of higher industrial inputs of metals to the large works, although it may also be explained by the greater interception of atmospheric deposition of metals by paved areas in urban centres that are served by the largest sewage treatment works. The majority of sludge recycled to land in the UK is produced by 55 large works (160,000 t ds y-1) whereas approximately 840 small works generate sludge (45,000 t ds y-1) for agricultural use. Therefore, an arithmetic mean would indicate a significantly lower concentration was apparent for sludge because all works would have equal weighting. Indeed, the median concentrations recorded for UK sludge are comparable to the values reported for Germany.

Table 2.40 Comparison of potentially toxic element concentrations (mg kg-1) in sewage sludge applied to agricultural land in Germany and the United Kingdom in 1996 (CEC, 2000)

Potentially toxic Germany United Kingdom United Kingdom element (average) (weighted average) (median) Zn 776 792 559 Cu 305 568 373 Ni 24 57 20 Cd 1.45 3.3 1.6 Pb 57 221 99 Cr 40 157 24 Hg 1.35 2.4 1.5

Pollutants in Urban Waste Water and Sewage Sludge 57 2. Potentially Toxic Elements

Table 2.41 Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Cadmium

CADMIUM Country Mean Median Min. Max. Survey Year/s Austria 1.5 1.2 0.4 3.4 1994/95 (11) Germany 1.5 1995-97 (4) Denmark 1.4 1995-97 (4) France 4.1 1995/97 (4) Finland 1.0 1995-97 (4) Greece (a) 1.6 1996 (6) (b) 1.4 1997 (1) Italy 0.8 23 1998/99 (10) Ireland 2.8 1997 (4) Luxembourg 3.8 1997 (4) Netherlands 3 1990 (16) Sweden 1.5 1995/96 (4) UK 3.5 1995/96 (4) Norway 0.97 1998 (12) Poland 9.93 13.5 0.8 15.3 1999 (3) EU 4.0 1992 (9) 2.2 1994-98 USA 38.1 8.95 1988 (13) 25 1992 (2)

Limits Agricultural Sewage Sludge Soils EU 1-3 10 1* (4) WHO 7 (5) USEPA 39 (14)

Table 2.41b Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Chromium CHROMIUM Country Mean Median Min. Max. Survey Year/s Austria 62 54 25 130 1994/95 (11) Germany 50 52 46 52 1995-97 (4) Denmark 33 34 24.8 40.3 1995-97 (4) France 69.4 58.8 80 1995/97 (4) Finland 85.7 84 82 91 1995-97 (4) Greece (a) 885.8 1996 (6) (b) 43.8 1997 (1) Italy 14.8 1400 1998/99 (10) Ireland 165 1997 (4) Luxembourg 51 1997 (4) Netherlands 64 1990 (16) Sweden 38.4 37.7 39 1995/96 (4) UK 159.5 157 162 1995/96 (4) Norway 28.5 1998 (12) Poland 144.2 136.5 6.8 289.0 1999 (3) EU 145 1992 (9) 74 1994-98 USA 589 150 1988 (13) 178 1992 (2)

Limits Agricultural Sewage Sludge Soils EU 30 –100 1000 600* (8) (proposed) USEPA 1200 (14)

Pollutants in Urban Waste Water and Sewage Sludge 58 2. Potentially Toxic Elements

Table 2.41c Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Copper COPPER Country Mean Median Min. Max. Survey Year/s Austria 264 240 170 540 1994/95 (11) Germany 275 1995-97 (4) Denmark 284 1995-97 (4) France 322 1995/97 (4) Finland 288 1995-97 (4) Greece (a) 302 1996 (6) (b) 103 1997 (1) Italy 160 373 1998/99 (10) Ireland 641 1997 (4) Luxembourg 206 1997 (4) Netherlands 190 1990 (16) Sweden 522 1995/96 (4) UK 562 1995/96 (4) Norway 287.1 1998 (12) Poland 237.5 183.4 24.1 592.0 1999 (3) EU 380 1992 (9) 365 1994-98 USA 639 444 1988 (13) 616 1992 (2)

Limits Agricultural Sewage Soils Sludge EU 50-140 1000-50* (4) USEPA 1500 (14)

Table 2.41d Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Mercury

MERCURY Country Mean Median Min. Max. Year/s of Survey Austria 5.1 2.1 1.0 48.0 1994/95 (11) Germany 1.2 1995-97 (4) Denmark 1.29 1995-97 (4) France 2.85 1995/97 (4) Finland 1.4 1995-97 (4) Greece 4.1 1996 (6) Italy 0.46 5 1998/99 (10) Ireland 0.6 1997 (4) Luxembourg 1.9 1997 (4) Netherlands 1.8 1990 (16) Sweden 1.85 1995/96 (4) UK 2.50 1995/96 (4) Norway 1.34 1998 (12)

EU 2.7 1992 (9) 2.0 1994-98 USA 3.24 2.3 1988 (13) 2.3 1992 (2)

Limits Agricultural Sewage Soils Sludge EU 1-1.5 10 0.5* (4) WHO 5 (15) USEPA 17 (14)

Pollutants in Urban Waste Water and Sewage Sludge 59 2. Potentially Toxic Elements

Table 2.41e Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Nickel

NICKEL Country Mean Median Min. Max. Year/s of Survey Austria 39 35 14 94 1994/95 (11) Germany 23.3 1995-97 (4) Denmark 22.8 1995-97 (4) France 35.5 1995/97 (4) Finland 41 1995-97 (4) Greece (a) 67 1996 (6) (b) 23.6 1997 (1) Italy 25 182.5 1998/99 (10) Ireland 54 1997 (4) Luxembourg 24 1997 (4) Netherlands 37 1990 (16) Sweden 19.3 1995/96 (4) UK 58.5 1995/96 (4) Norway 15.4 1998 (12) Poland 41.1 36.7 8.4 78.8 1999 (3) EU 44 1992 (9) 33 1994-98 USA 90.6 46.5 1988 (13) 71 1992 (2)

Limits Agricultural Sewage Sludge Soils EU 30-75 300 50* (4) WHO 850 (5) USEPA 420 (14)

Table 2.41f Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Lead

LEAD Country Mean Median Min. Max. Year/s of Survey Austria 109 100 40 290 1994/95 (11) Germany 67.7 1995-97 (4) Denmark 59.9 1995-97 (4) France 119.9 1995/97 (4) Finland 43 1995-97 (4) Greece (a) 283 1996 (6) (b) 140.6 1997 (1) Italy 41 560 1998/99 (10) Ireland 150 1997 (4) Luxembourg 128 1997 (4) Netherlands 145 1990 (16) Sweden 48.2 1995/96 (4) UK 221.5 1995/96 (4) Norway 21.7 1998 (12) Poland 211.8 190.6 27.7 456.5 1999 (3) EU 97 1994-98

USA 204 152 1988 (13) 170 1992 (2)

Limits Agricultural Sewage Sludge Soils EU 50-300 750-70* (4) WHO 150 (5) USEPA 300 (14)

Pollutants in Urban Waste Water and Sewage Sludge 60 2. Potentially Toxic Elements

Table 2.41g Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Zinc

ZINC Country Mean Median Min. Max. Year/s of Survey Austria 1188 1250 700 1700 1994/95 (11) Germany 834 1995-97 (4) Denmark 777.2 1995-97 (4) France 837.6 1995/97 (4) Finland 606 1995-97 (4) Greece (a) 2752 1996 (6) (b) 1236 1997 (1) Italy 391 4213 1998/99 (10) Ireland 562 1997 (4) Luxembourg 1628 1997 (4) Netherlands 1320 1990 (16) Sweden 620.5 1995/96 (4) UK 778 1995/96 (4) Norway 340 1998 (12) Poland 3641 2948 546 7961 1999 (3) EU 1000 1992 (9) 817 1994-98 USA 1490 970 1988 (13) 1285 1992 (2)

Limits Agricultural Sewage Sludge Soils EU 150-300 2500-150* (4) USEPA 2800 (14)

Table 2.41h Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Arsenic

ARSENIC Country Mean Median Min. Max. Year/s of Survey Italy 1.1 1.8 1998/99 (10) UK 2.5 1996/97 (7) USA 11.0 6.7 1988 (13) 4.9 1992 (2)

Limits Agricultural Sewage Sludge Soils WHO 9 (5) USEPA 41 (14)

Table 2.41i Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Selenium

SELENIUM Country Mean Median Min. Max. Year/s of Survey UK 1.6 1996/97 (7) USA 6.14 4.5 1988 (13) 6.0 1992 (2)

Limits Agricultural Sewage Soils Sludge WHO 140 (5) USEPA 36 (14)

Pollutants in Urban Waste Water and Sewage Sludge 61 2. Potentially Toxic Elements

Table 2.41j Survey of potentially toxic elements in sewage sludge: values in mg.kg-1 DS-Silver

SILVER Country Mean Median Min. Max. Year/s of Survey USA 48.2 852 1988 (15)

Limits Agricultural Sewage Sludge Soils WHO 3 (5) Notes: *For sludge applied to soil lower and higher limits are allowed for soil with pH in the range 5-6 and >7 respectively (Commission of the European Communities (2000) working document on Sludge: 3rd draft. ENV.E.3.LM, 27 April, Brussels EU 1992 is for B, DK, F, D, EL, IRL, I, L, NL, P, ESP, UK EU 1994-98 is derived from table values for AT, D, DK, F, FI, IRL, L, SE, UK and NO. UK and EU is sludge used in agriculture USA is for all sludge: detection limit set at minimum level Greece: (a) values are specific to Athens WWTS; (b) values are average of two rural WWTS.

References

Agelidis M.O. et al, 1997 Bastian, R.K. 1997 Bodzek, B. et al, 1999. CEC, 1999. Chang, A.G et al, Cristoulas, D.G et al, 1997. Environment Agency of England and Wales, 1999 European Union, 2000 Hall, J.E. et al, 1994 Braguglia et al 2000 Scharf, S et al, 1997 SFT, 2000 USEPA 1992 USEPA 1993 USEPA 1999 Wiart, J. et al, 1995.

Pollutants in Urban Waste Water and Sewage Sludge 62 2. Potentially Toxic Elements

In the particular case of Greece, Voutsa et al. [1996] have compared the potentially toxic element content of municipal and industrial sludge for Thessaloniki. The results are illustrated in Figure 2.10. Sludge A is municipal sludge from Thessaloniki’s main WWTS and sludge B is from a WWTS treating partially treated industrial wastes from the greater Thessaloniki region.

Figure 2.10. Potentially toxic element concentrations in sewage sludge from biological treatment of municipal and industrial wastewater (Municipal sludge: Dark, Industrial sludge: Light Grey)

As shown concentrations of most metals are 2-9 fold higher in municipal sludge than in industrial (except for Cd and Cu where the contents are similar). This interesting fact, due possibly to pre-treatment of the most toxic industrial wastewater on site, is not adequately explained by the authors.

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