Michael Schärer

Treatment of micropollutants in municipal wastewater: Ozone or powdered activated carbon?

Many organic micropollutants present in wastewater, such as pharmaceuticals and pesticides, are poorly removed in conventional wastewater treatment plants (WWTPs). To reduce the release of these substances into the aquatic environment, advanced wastewater treatments are necessary. In this context, two large-scale pilot advanced treatments were tested in parallel over more than one year at the municipal WWTP of Lausanne, Switzerland. The treatments were: i) oxidation by ozone followed by sand filtration (SF) and ii) powdered activated carbon (PAC) adsorption followed by either ultrafiltration (UF) or sand filtration. More than 70 potentially problematic substances (pharmaceuticals, pesticides, endocrine disruptors, drug metabolites and other common chemicals) were regularly measured at different stages of treatment. Additionally, several ecotoxicological tests such as the Yeast Estrogen Screen, a combined algae bioassay and a fish early life stage test were performed to evaluate effluent toxicity. Both treatments significantly improved the effluent quality. Micropollutants were removed on average over 80% compared with raw wastewater, with an average ozone dose of 5.7 mg O3 l(-1) or a PAC dose between 10 and 20 mg l(-1). Depending on the chemical properties of the substances (presence of electron-rich moieties, charge and hydrophobicity), either ozone or PAC performed better. Both advanced treatments led to a clear reduction in toxicity of the effluents, with PAC-UF performing slightly better overall. As both treatments had, on average, relatively similar efficiency, further criteria relevant to their implementation were considered, including local constraints (e.g., safety, sludge disposal, disinfection), operational feasibility and cost. For sensitive receiving waters (drinking water resources or recreational waters), the PAC-UF treatment, despite its current higher cost, was considered to be the most suitable option, enabling good removal of most micropollutants and macropollutants without forming problematic by-products, the strongest decrease in toxicity and a total disinfection of the effluent.

Reducing the Discharge of Micropollutants in the Aquatic Environment: The Benefits of Upgrading Wastewater Treatment Plants

Micropollutants (MPs) as individual compounds or in complex mixtures are relevant for water quality and may trigger unwanted ecological effects. MPs originate from different point and diffuse sources and enter water bodies via different flow paths. Effluents from conventional wastewater treatment plants (WWTPs), in which various MPs are not or not completely removed, is one major source. To improve the water quality and avoid potential negative ecological effects by micropollutants, various measures to reduce the discharge should be taken. In this feature we discuss one of these measures; the benefits of upgrading WWTPs toward reduced MP loads and toxicities from wastewater effluents, using the recently decided Swiss strategy as an example. Based on (i) full-scale case studies using ozonation or powder activated carbon treatment, showing substantial reduction of MP discharges and concomitant reduced toxicities, (ii) social and political acceptance, (iii) technical feasibility and sufficient cost-effectiveness, the Swiss authorities recently decided to implement additional wastewater treatment steps as mitigation strategy to improve water quality. Since MPs are of growing global concern, the concepts and considerations behind the Swiss strategy are explained in this feature, which could be of use for other countries as well. It should be realized that upgrading WWTPs is not the only solution to reduce the discharge of MPs entering the environment, but is part of a broader, multipronged mitigation strategy.

Targeting aquatic microcontaminants for monitoring: exposure categorization and application to the Swiss situation

Background, aim, and scopeAquatic microcontaminants (MCs) comprise diverse chemical classes, such as pesticides, biocides, pharmaceuticals, consumer products, and industrial chemicals. For water pollution control and the evaluation of water protection measures, it is crucial to screen for MCs. However, the selection and prioritization of which MCs to screen for is rather difficult and complex. Existing methods usually are strongly limited because of a lack of screening regulations or unavailability of required data.Method and modelsHere, we present a simple exposure-based methodology that provides a systematic overview of a broad range of MCs according to their potential to occur in the water phase of surface waters. The method requires input of publicly available data only. Missing data are estimated with quantitative structure–property relationships. The presented substance categorization methodology is based on the chemicals’ distribution behavior between different environmental media, degradation data, and input dynamics.ResultsSeven different exposure categories are distinguished based on different compound properties and input dynamics. Ranking the defined exposure categories based on a chemical’s potential to occur in the water phase of surface waters, exposure categories I and II contain chemicals with a very high potential, categories III and IV contain chemicals with a high potential, and categories V and VI contain chemicals with a moderate to low potential. Chemicals in category VII are not evaluated because of a lack of data. We illustrate and evaluate the methodology on the example of MCs in Swiss surface waters. Furthermore, a categorized list containing potentially water-relevant chemicals is provided.DiscussionChemicals of categories I and III continuously enter surface waters and are thus likely to show relatively steady concentrations. Therefore, they are best suited for water monitoring programs requiring a relatively low sampling effort. Chemicals in categories II and IV have complex input dynamics. They are consequently more difficult to monitor. However, they should be considered if an overall picture is needed that includes contaminants from diffuse sources.ConclusionsThe presented methodology supports compound selection for (a) water quality guidance, (b) monitoring programs, and (c) further research on the chemical’s ecotoxicology. The results from the developed categorization procedure are supported by data on consumption and observed concentrations in Swiss surface waters. The presented methodology is a tool to preselect potential hazardous substances based on exposure-based criteria for policy guidance and monitoring programs and a first important step for a detailed risk assessment for potential microcontaminants.

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 (O3) is probably one of the simplest measures for abatement of organic micropollutants to avoid their discharge to the aquatic environment. During ozonation most organic micropollutants present in treated WW are oxidized either by a direct reaction with O3 or by secondarily formed hydroxyl radicals (OH). 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 ozonation 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 O3 and OH exposures) can give first indications on the suitability of an ozonation step. Ozonation of WWs yielding O3 and OH 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.

Micropollutant Removal from Wastewater: Facts and Decision-Making Despite Uncertainty

Making Despite Uncertainty Christian Stamm,*,† Rik I. L. Eggen,†,‡ Janet G. Hering,†,‡ Juliane Hollender,†,‡ Adriano Joss,† and Michael Schar̈er †Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland ‡Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, CH-8092, Zürich, Switzerland FOEN, Federal Office for the Environment, Water Division, CH-3003, Bern, Switzerland