Elimination organischer Spurenstoffe aus kommunalem Abwasser

• Elimination of organic trace pollutants from municipal wastewater

Ivashechkin, Pavel V.; Dohmann, Max (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2006)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2006

Abstract

Municipal wastewater contains, along with suspended solids, oxygen consuming compounds and nutrients, a great number of organic trace pollutants. These are industrial chemicals, pesticides, pharmaceuticals, natural and synthetic hormones, as well as ingredients of personal care products. Even in very low concentrations (ng/L to µg/L) some of these compounds can already have a negative impact on the environment. The impact can manifest itself for example in toxic, carcinogenic and/or endocrine effects of wastewater treatment plant effluents in aquatic organisms. Nevertheless, the elimination of organic trace pollutants has not been taken into consideration yet, neither in design nor during the operation of municipal wastewater treatment plants. On the basis of the European Water Framework Directive requirements on the quality of surface waters, some changes in this attitude are to expect in the future. This study examines around 500 organic trace pollutants which are continuously monitored by the federal environmental agencies. It shows that 52 compounds are relevant for the environment, because their concentrations in wastewater treatment plant effluents and surface waters in Germany have exceeded the target values. Due to the impossibility of studying the behaviour of all 52 relevant trace pollutants during the wastewater treatment, the industrial chemicals nonylphenol and bisphenol A, natural hormone 17b-estradiol and synthetic steroid 17a-ethinylestradiol were appointed as model compounds. The criteria of choice were different biological degradation and volatilisation rates, as well as different affinity to sewage sludge. The behaviour of the model trace pollutants during the mechanic-biological treatment of wastewater and sewage sludge was studied in pilot wastewater treatment plants and in laboratory sorption and degradation experiments with radiolabelled compounds. In these experiments biodegradation was identified as the main elimination pathway. By the biodegradation of the model compounds carbon dioxide and some unidentified metabolites were generated. Further research is required to perform a risk assessment of the biodegradation products. The evaluation of elimination efficiency of various wastewater treatment plant configurations was performed using the experiment results and the mathematical model developed in this study. A conventional activated sludge plant with simultaneous aerobic sludge digestion showed the best elimination efficiency for the model compounds. It was followed by membrane activated sludge plants with simultaneous aerobic and separate anaerobic sludge digestion. The lowest elimination efficiency was observed in a conventional activated sludge plant with separate anaerobic sludge digestion. Sand filtration of the effluents of conventional treatment plants did not contribute significantly to the elimination of the model trace pollutants. Since, according to the mathematical model the studied wastewater treatment plant configurations do not retain some organic trace pollutants like 17a-ethinylestradiol and the pharmaceutical carbamazepine sufficiently, 16 various measures of enhancing the elimination of trace pollutants were assessed with respect to their technical and economical efficiency. For the smaller wastewater treatment plants (up to 5,000PE) the addition of pulverised activated carbon into the aeration tank was especially suitable. Ozonation as a downstream treatment stage was the choice for the larger plants. In dependence of the plant capacity this measures would increase the treatment costs by 20-35% (0.07-0.18€/m³).