Removal of micropollutants in municipal wastewater treatment plants by powder-activated carbon
Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Duebendorf, Switzerland E-mail: .Water Science & Technology (Impact Factor: 1.11). 09/2012; 66(10):2115-21. DOI: 10.2166/wst.2012.353
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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- "This approach has proven to be suitable in the case of dyes or aromatic hydrocarbons with positive results  . Other studies have shown an effective removal of OMPs, even for the more recalcitrant compounds, in a process that combines adsorption by activated carbon and biological transformation     . Since these studies have focused on the removal efficiencies in the water line (without considering the OMPs present in sludge), further research providing information on the complete mass balances is needed in order to elucidate the role of the different removal mechanisms. "
ABSTRACT: SeMPAC is an innovative process based on a membrane sequential batch reactor to which powdered activated carbon (PAC) is directly added. It was developed with the aim of obtaining a high quality effluent in terms of conventional pollutants and organic micropollutants (OMPs). High COD removal and nitrification efficiencies (>95%) were obtained already during the operation without PAC, although denitrification was enhanced by PAC addition. OMPs were followed in the solid and liquid matrixes so that biotransformation, sorption onto the sludge and adsorption onto the PAC could be assessed. Recalcitrant compounds, such as carbamazepine and diazepam, were readily removed only after PAC addition (>99%). Progressive saturation of PAC was observed, with increasing concentrations of OMPs in the solid phase. Removal efficiencies for recalcitrant compounds were used as indicators for new additions of PAC. An improvement in the moderately biodegradable OMPs removal was observed after PAC addition (e.g. fluoxetine, trimethoprim) which was attributed to the biofilm that grew onto the sorbent, as well as to adsorption onto PAC.
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- "Then, the micropollutant removals at two μGAC doses (10 and 20 g μGAC / m 3 ) are presented, as well as those of conventional wastewater quality parameters. The choice of both μGAC doses have been made based on the PAC doses tested in a previous study of this pilot (Mailler et al., 2015b), and considering the knowledge about the high efficiency of such low doses of PAC to remove micropollutants in wastewater (Boehler et al., 2012, Margot et al., 2013, Snyder et al., 2007). In addition, the influence of the μGAC dose on performances and the μGAC residence time (SRT) are also discussed, as well as the use of UV absorbance at 254 nm (UV-254) as a performance indicator. "
ABSTRACT: Among the solutions to reduce micropollutant discharges into the aquatic environment, activated carbon adsorption is a promising technique and a large scale pilot has been tested at the Seine Centre (240,000 m3/d — Paris, France) wastewater treatment plant (WWTP). While most of available works studied fixed bed or contact reactors with a separated separation step, this study assesses a new type of tertiary treatment based on a fluidized bed containing a high mass of activated carbon, continuously renewed. For the first time in the literature, micro-grain activated carbon (μGAC) was studied. The aims were (1) to determine the performances of fluidized bed operating with μCAG on both emerging micropollutants and conventional wastewater quality parameters, and (2) to compare its efficiency and applicability to wastewater to former results obtained with PAC. Thus, conventional wastewater quality parameters (n = 11), pharmaceuticals and hormones (PPHs; n = 62) and other emerging pollutants (n = 57) have been monitored in μGAC configuration during 13 campaigns.
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- "Adsorption of organic micropollutants (OMP) onto powdered activated carbon (PAC) is a promising option to reduce OMP emissions from wastewater treatment plants (WWTP) into the aquatic environment and drinking water sources (Eggen et al., 2014; Jekel et al., 2013). In advanced wastewater treatment, PAC is typically dosed continuously into the WWTP effluent and separated after a certain contact time by sedimentation or filtration (Boehler et al., 2012; Margot et al., 2013; Meinel et al., 2015). Typical residence times of the PAC in the range of minutes to a few hours until separation are not sufficient to fully exploit the adsorption capacity of the PAC. "
ABSTRACT: PAC adsorption is a widespread option for the removal of organic micropollutants (OMP) from secondary effluent. For an optimal exploitation of the adsorption capacity, PAC recirculation is nowadays a common practice, although the mechanistic interrelations of the complex recirculation process are not fully resolved. In this work, extensive multi-stage batch adsorption testing with repeated PAC and coagulant dosage was performed to evaluate the continuous-flow recirculation system. Partly loaded PAC showed a distinct amount of remaining capacity, as OMP and DOC removals considerably increased with each additional adsorption stage. At a low PAC dose of 10 mg/L PAC, removals of benzotriazole and carbamazepine were shown to rise from <40% in the first stage up to >80% in the 11th stage at 30 min adsorption time per stage. At a high PAC dose of 30 mg/ L PAC, OMP and DOC removals were significantly higher and reached 98% (for benzotriazole and carbamazepine) after 11 stages. Coagulant dosage showed no influence on OMP removal, whereas a major part of DOC removal can be attributed to coagulation. Multi-stage adsorption is particularly beneficial for small PAC doses and significant PAC savings are feasible. A new model approach for predicting multi-stage OMP adsorption on the basis of a single-stage adsorption experiment was developed. It proved to predict OMP removals and PAC loadings accurately and thus contributes towards understanding the PAC recirculation process.
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