Treated municipal wastewater may contain pathogenous micro-organisms and persistent trace organics leading to problems when being discharged into the surface waters. The investigations of the research project PILOTOX aimed at their elimination from treated municipal wastewater through subsequent oxidation by ozone. For this purpose, the TU Berlin (department of Water Quality Control) in cooperation with the Berliner Wasserbetriebe at the WWTP Berlin-Ruhleben, carried out several tests with a pilot plant by the company WEDECO aiming at the ozonation of the effluent. The results show that ozonation is a suitable procedure to remove and transform respectively, substantial quantities of the pharmaceutical residues detected in the effluent of the Ruhleben WWTP and, at the same time, to achieve a germ reduction complying with the threshold values stipulated in the European directive on bathing water. It was found that many trace organics such as the anti-epilepticum carbamazepin or the hormone estron can be removed at a very low ozone dosage to below their analytic detection limit. The X-ray contrast media however, turned out to be more resistant: even at a high ozone dosage, their concentrations could be reduced only partially. In this context, the tests detected that through the combination of H2O2 and ozone, an elevated elimination rate for the substances iopamidol and iohexol can be achieved. The elimination of the analysed trace organics correlated with the decrease of the water’s UV activity. Thus, it is advisable to use the rapidly and simply traceable parameter SAK254 as process control parameter to determine the necessary ozone dosage. In addition, it could be proven that ozonation increases the biological degradability of water components. Laboratory test looking at recontamination levels however, indicate that the threshold values stipulated in the EU directive on bathing water will not be exceeded if the ozone-treated effluent is mixed with water originating from the River Spree. A study regarding the water’s acute and chronic toxicity, to its gene toxicity and endocrine impacts, revealed that – compared to the untreated effluent - no eco-toxicological risk potential can be detected in the ozone-treated water samples.The specific treatment cost covering the large-scale application of ozone treatment at the WWTP Ruhleben range between 1,0 cent/m3 and 2,2 cent/m3, of which the investment costs account for a percentage of 20-30 %.

Recent research projects have shown a good suitability of the ozonation process to transform trace concentrations of most pharmaceuticals in wastewater treatment plant (WWTP) effluents. The concentrations of carbamazepine and 17a-ethinylestradiol, for instance, were reduced below their detection limits by use of ozone dosages resulting in a specific ozone consumption of 0.5 mg O3/ mg DOC0. At the same time a good disinfection performance was achieved. The given hygienic requirements of the EU bathing water directive (e.g. 2000 N / 100 ml faecal coliforms) are fulfilled without the formation of bromate (< 10 µg/L). As technical control parameter of the ozonation process usually the residual ozone in the liquid phase or in the off-gas are used. However, at very low specific ozone consumptions, ozone reacts instantaneously with dissolved compounds and can not be detected. Hence alternative parameters should be used for effective operation control. The present paper evaluates the relation between UVA decrease and the removal of different compounds (endocrine disrupting compounds, pharmaceuticals, iodinated Xray contrast media), microbial parameters and bromate formation. The results can be used as a guideline for the control of the oxidation performance at large scale ozonation units.

The secondary effluent of Berlin's sewage treatment plant Ruhleben was oxidized by dosages of 2.5-22 mg/L ozone and varying operation conditions to remove pharmaceutical compounds and disinfect water in parallel. The majority of analysed neutral and acidic drugs were efficiently removed to the detection limit at ozone consumptions equal to a dosage of < 10 mg/L O3. However, certain compounds like clofibric acid, ketaprofen and traced metabolites required higher dosages of > 10-15 mg/LO3 for complete removal. A series of four iodinated organic contrast media (ICM) persisted the ozone treatment even at high consumption rates. Related to disinfection, the legal requirements (EU bathing water directive) could be fulfilled by a consumption of < 10 mg/L O3. For a combined oxidation by ozone and H2O2 (perozone) higher conversion rates for clofibric acid, naproxen and ketaprofen could be obtained at lower dosage (6 mg/L O3). For two ICM, namely iopamidol and iohexol, this was the case at higher ozone consumption. The removal of adsorbable organic iodine (AOI) > 10% could not be achieved by any treatment. The initial genotoxicity of the secondary effluent was stated by four independent tests. Due to the application of ozone, this genotoxicity was completely removed. The presented results confirm that ozonation can be a suitable advanced wastewater treatment at varying operation conditions to lower effluent concentrations of pharmaceuticals and active micro-organsisms.