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 104 of 136 Due to the fact that the distribution function of technical products (which is following a Poisson distribution) is differing from the bimodal distribution of the NPnEOs in the influent to the plant, and since only etoxylated NPs can be found in the influent, it is assumed that initial transformation processes are taking place already in the sewer system. Figure 11-4 Distribution of NPnEO oligomeres Transformation of NPnEOs in aerobic biological wastewater treatment processes In the aerobic biological treatment stages in which the oxidation of organic wastewater substances takes place the Ethoxyl and Alkyl-Side Chains are reduced to NP2EO and NP1EO and carboxylation of Ethoxyl and Alkyl-Side Chains takes place. In the effluent of the treatment plants with biological treatment mainly NP2EO and NP1EO (also a few traces of NP3EO – NP10 EO) can be found, long chain oligomeres are missing. The publication of [GIGER (1986] compares the distribution of NPnEO groups in the effluent of two treatment plants (WWTP Opfikon and WWTP Bassersdorf) which are designed and operated at different levels (one with high sludge age and nitrification, the
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 105 of 136 other with low sludge age). The results clearly demonstrate that there is a relation between reduction of NPnEOs and the process parameters like sludge age, sludge load, nitrification and reduction of organic wastewater contents as outlined above. Transformation of NPnEOs in anaerobic sludge stabilisation The further degradation of NPnEOs (NP2EO and NP1EO) which are adsorbed to the excess biological sludge, takes place during anaerobic stabilisation in the sludge digester, by elimination of the Ethoxy groups down to NP. Tschui et al (18) could verify this reduction in a batch test. After a retention time of 20 days some 60% of the NP2EO and NP1EO were decomposed and the amount of NP was doubled. They could even notice a surplus of NP which did not result from the degradation of NP2EO and NP1EO. This could be explained by the fact that probably remaining NP3EO – NP10 EO chains and CAPEs as well as CAPECs (which were not measured) are reduced to NP under anaerobic conditions. 11.2 SUMMARY AND OUTLOOK Obviously endocrine substances can be reduced in wastewater treatment plants but not fully. With the Council Directive 91/271/EEC on urban waste water treatment, May 21 th , 1991, most European WWTPs are obliged to apply aerobic biological treatment processes with high sludge age what favours the growth of bacteria capably of metabolising substance which are contained in low concentrations in the wastewater. Further advantageous are aerobic conditions for the deposed excess sludge as provided in agricultural use or composting of the sludge. According to studies regarding future trends in the European Union it may be expected that an increase of the sludge used for agriculture will take place. However, still the information required to prepare strategies in design and operation of WWTPs is insufficient, and most probably it will not be able to completely eliminate the substances in the course of the treatment. Theoretically the effluent could be further treated by membrane processes or activated carbon processes which can completely eliminate nearly all substances targeted. In other words “technically everything is possible”, but these processes are extremely costly and it is not considered a sound approach to invest in end of pipe technology. Avoiding of these substances by production restrictions and strict regulations would be a much more economic and reasonable approach for reducing the emission of endocrine modulators into the environment. 11.3 PROCESSES TO ELIMINATE CONTAMINANTS FROM SOURCES FOR DRINKING WATER SUPPLY General considerations
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D10: Impact of Contaminants - Hydromod

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