Removal of micropollutants in municipal wastewater treatment plants by powder-activated carbon.
ABSTRACT Micropollutants (MP) are only partly removed from municipal wastewater by nutrient removal plants and are seen increasingly as a threat to aquatic ecosystems and to the safety of drinking water resources. The addition of powder activated carbon (PAC) is a promising technology to complement municipal nutrient removal plants in order to achieve a significant reduction of MPs and ecotoxicity in receiving waters. This paper presents the salient outcomes of pilot- and full-scale applications of PAC addition in different flow schemes for micropollutant removal in municipal wastewater treatment plants (WWTPs). The sorption efficiency of PAC is reduced with increasing dissolved organic carbon (DOC). Adequate treatment of secondary effluent with 5-10 g DOC m(-3) requires 10-20 g PAC m(-3) of effluent. Counter-current use of PAC by recycling waste PAC from post-treatment in a contact tank with an additional clarifier to the biology tank improved the overall MP removal by 10 to 50% compared with effluent PAC application alone. A dosage of 15 g PAC m(-3) to a full-scale flocculation sand filtration system and recycling the backwash water to the biology tank showed similar MP elimination. Due to an adequate mixing regime and the addition of adapted flocculants, a good retention of the fine fraction of the PAC in the deep-bed filter were observed (1-3 g TSS m(-3); TSS: total suspended solids). With double use of PAC, only half of the PAC was required to reach MP removal efficiencies similar to the direct single dosage of PAC to the biology tank. Overall, the application of PAC in WWTPs seems to be an adequate and feasible technology for efficient MP elimination (>80%) from wastewater comparable with post ozonation.
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ABSTRACT: The competitive impacts of different fractions of wastewater treatment plant effluent organic matter (EfOM) on organic micro-pollutant (OMP) adsorption were investigated. The fractionation was accomplished using separation by nanofiltration (NF). The waters resulting from NF were additionally treated to obtain the same dissolved organic carbon (DOC) concentrations as the initial water. Using size exclusion chromatography (LC-OCD) it could be shown that the NF treatment resulted in an EfOM separation by size. Adsorption tests showed different competitive effects of the EfOM fractions with the OMP. While large EfOM compounds that were retained in NF demonstrated a reduced competition as compared to the raw water, the NF-permeating EfOM compounds showed an increased competition with the majority of the measured OMP. The effects of small size EfOM are particularly negative for OMP which are weak/moderate adsorbates. Adsorption analysis was carried out for the differently fractionized waters. The small sized EfOM contain better adsorbable compounds than the raw water while the large EfOM are less adsorbable. This explains the observed differences in the EfOM competitiveness. The equivalent background compound (EBC) model was applied to model competitive adsorption between OMP and EfOM and showed that the negative impacts of EfOM on OMP adsorption increase with decreasing size of the EfOM fractions. The results suggest that direct competition for adsorption sites on the internal surface of the activated carbon is more substantial than indirect competition due to pore access restriction by blockage. Another explication for reduced competition by large EfOM compounds could be the inability to enter and block the pores due to size exclusion.Water Research 08/2014; 65:297-306. · 5.32 Impact Factor
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ABSTRACT: Powdered activated carbon (PAC) is a promising agent for the adsorptive removal of organic micropollutants (OMP) from wastewater treatment plant (WWTP) effluents. Reliable and predictive test methods are required for the selection and for the quality control of PAC. In the present investigation, a pragmatic test method using indicative target OMP and photometric analyses was developed. Eight different PAC were compared according to the test method and according to removals of individual OMP in WWTP effluent. The test method allowed identification of the PAC with the highest and the lowest removals of benzotriazole and elucidated differences of the PAC with regard to removals of individual OMP. In WWTP effluent both positive and negative correlations between OMP removals with different PAC were observed: Some PAC removed diclofenac, carbamazepine and metoprolol to a comparatively greater extent while other PAC are comparably more efficient for benzotriazole, methylbenzotriazole and acesulfame adsorption.Chemical Engineering Journal 07/2014; 257:184-190. · 4.06 Impact Factor
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ABSTRACT: SOLUTIONS (2013 to 2018) is a European Union Seventh Framework Programme Project (EU-FP7). The project aims to deliver a conceptual framework to support the evidence-based development of environmental policies with regard to water quality. SOLUTIONS will develop the tools for the identification, prioritisation and assessment of those water contaminants that may pose a risk to ecosystems and human health. To this end, a new generation of chemical and effect-based monitoring tools is developed and integrated with a full set of exposure, effect and risk assessment models. SOLUTIONS attempts to address legacy, present and future contamination by integrating monitoring and modelling based approaches with scenarios on future developments in society, economy and technology and thus in contamination. The project follows a solutions-oriented approach by addressing major problems of water and chemicals management and by assessing abatement options. SOLUTIONS takes advantage of the access to the infrastructure necessary to investigate the large basins of the Danube and Rhine as well as relevant Mediterranean basins as case studies, and puts major efforts on stakeholder dialogue and support. Particularly, the EU Water Framework Directive (WFD) Common Implementation Strategy (CIS) working groups, International River Commissions, and water works associations are directly supported with consistent guidance for the early detection, identification, prioritisation, and abatement of chemicals in the water cycle. SOLUTIONS will give a specific emphasis on concepts and tools for the impact and risk assessment of complex mixtures of emerging pollutants, their metabolites and transformation products. Analytical and effect-based screening tools will be applied together with ecological assessment tools for the identification of toxicants and their impacts. The SOLUTIONS approach is expected to provide transparent and evidence-based candidates or River Basin Specific Pollutants in the case study basins and to assist future review of priority pollutants under the WFD as well as potential abatement options.Science of The Total Environment 06/2014; · 3.16 Impact Factor