D10: Impact of Contaminants - Hydromod

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Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas EUROLAKES D10: Impact of Contaminants FP5_Contract No.: EVK1-CT1999-00004 Version: 4.0 Date: 25/07/01 File: D10-vers.4.0.doc Page 96 of 136 Anaerobic digestion In an anaerobic digester the organic material is metabolised into approx. 2 /3 CH4, 1 /3 CO2 and biomass. The process is performed in a stirred reactor at a temperature between 30-37 °C. The gas can be used for heating or energy generation. After anaerobic digestion the stabilised sludge is thickened to the extent required for the final disposal. Aerobic stabilisation Excess sludge can also be stabilised aerobically by increasing the aerobic sludge age to an extent where organic material is aerobically degraded and mineralised. This is practically done simultaneously in the aeration tank in small plants (up to 10.000 P.E), or in a separate aerated stabilisation basin. The aerobic stabilisation process is much more energy consuming than anaerobic fermentation. Also the de-watering of the aerobically stabilised sludge is more difficult and energy consuming. For this reason aerobic stabilisation is only applied in small treatment plants. (up to 10.000 – 25.000 PE). Supernatant liquids and process water The supernatant liquids from all processes for thickening (static thickeners, mechanical de-watering) are usually charged with high loads of nutrients and also COD. For that reason different strategies for adding the waters to the plant or even for separate treatment are applied. A general flow sheet showing the mass streams in a typical wastewater treatment plant designed according to the state of the art is shown in Figure 11-2 Figure 11-2 Mass streams in a typical wastewater treatment plant, according to [KREUZINGER, 1998]
Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas EUROLAKES D10: Impact of Contaminants Final disposal of excess sludge The following disposal routes for excess sludge are mainly used in the EC: 1. Use in agriculture (sludge spreading) 2. Use on other land (recultivation) 3. Disposal on landfills 4. Disposal (on landfills) after incineration FP5_Contract No.: EVK1-CT1999-00004 Version: 4.0 Date: 25/07/01 File: D10-vers.4.0.doc Page 97 of 136 Partly sludge is further treated by composting together with other organic waste prior to beneficial use in agriculture or on other land. Which pathways are used in which country and the tendency on European level for the future is depending on a variety of factors like ecology, economy, social aspects, the current knowledge about the benefits and potential harmful effects of the utilisation of sewage sludge, and the trends in European legislation [WITTE, 2000]. The existing and extrapolated future pathways for Germany and the EC according to WITTE (2000) and MARMO (1999) are given in the following Figure. Figure 11-3 Pathways of sewage sludge disposal According to MARMO (1999) for the year 2000 53 % of the sludge are used for agriculture and recultivation of soils, 23% of the sludge is disposed in landfills, 22% of the sludge is incinerated and 2% is disposed by other ways.
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D10: Impact of Contaminants - Hydromod

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