Novel test procedure to evaluate the treatability of wastewater with ozone
Organic micropollutants such as pharmaceuticals, estrogens or pesticides enter the environment continuously through the effluent of municipal wastewater treatment plants (WWTPs). Enhanced treatment of wastewater (WW) by ozone (O-3) is probably one of the simplest measures for abatement of organic micropollutants to avoid their discharge to the aquatic environment. During zonation most organic micropollutants present in treated WW are oxidized either by a direct reaction with O-3 or by secondarily formed hydroxyl radicals ((OH)-O-center dot). However, undesired oxidation by-products from the oxidative transformation of matrix components can also be formed. A modular laboratory decision tool based on the findings of previous investigations is presented to test the feasibility of zonation as an option to upgrade specific WWTPs. These modules consist of investigations to assess (i) the matrix effects on ozone stability, (ii) the efficiency of micropollutant removal, (iii) the oxidation by-product formation, as well as (iv) bioassays to measure specific and unspecific toxicity of the treated WWs. Matrix effects on ozone stability (quantified as O-3 and (OH)-O-center dot exposures) can give first indications on the suitability of an ozonation step. Ozonation of WWs yielding O-3 and (OH)-O-center dot exposures and micropollutant abatement similar to reference values evoked a significant improvement of the water quality as indicated by a broad range of bioassays. Irregular behavior of the ozonation points towards unknown compounds, possibly leading to the formation of undesired degradation products. It has been observed that in such WWs ozonation partly enhanced toxicity. In summary, the presented tiered laboratory test procedure represents a relatively cheap and straight-forward methodology to evaluate the feasibility of ozonation to upgrade specific WWTPs for micropollutant removal based on chemical and biological measurements. (C) 2015 Elsevier Ltd. All rights reserved.