title: Impact of external carbon dose on the removal of micropollutants using methanol and ethanol in post-denitrifying Moving Bed Biofilm Reactors.
abstract: Addition of external carbon sources to post-denitrification systems is frequently used in wastewater treatment plants to enhance nitrate removal. However, little is known about the fate of micropollutants in post-denitrification systems and the influence of external carbon dosing on their removal. In this study, we assessed the effects of two different types and availability of commonly used carbon sources -methanol and ethanol- on the removal of micropollutants in biofilm systems. Two laboratory-scale moving bed biofilm reactors (MBBRs), containing AnoxKaldnes K1 carriers with acclimated biofilm from full-scale systems, were operated in continuous-flow using wastewater dosed with methanol and ethanol, respectively. Batch experiments with 22 spiked pharmaceuticals were performed to assess removal kinetics. Acetyl-sulfadiazine, atenolol, citalopram, propranolol and trimethoprim were easily biotransformed in both MBBRs (biotransformations rate constants kbiobetween 1.2 and 12.9 L gbiomass-1d-1), 13 compounds were moderately biotransformed (rate constants between 0.2 and 2 L gbiomass-1d-1) and 4 compounds were recalcitrant. The methanol-dosed MBBR showed higher kbio(e.g., 1.5-2.5-fold) than in the ethanol-dosed MBBR for 9 out of the 22 studied compounds, equal kbiofor 10 compounds, while 3 compounds (i.e., targeted sulfonamides) were biotransformed faster in the ethanol-dosed MBBR. While biotransformation of most of the targeted compounds followed first-order kinetics, removal of venlafaxine, carbamazepine, sulfamethoxazole and sulfamethizole could be described with a cometabolic model. Analyses of the microbial composition in the biofilms using 16S rRNA amplicon sequencing revealed that the methanol-dosed MBBR contained higher microbial richness than the one dosed with ethanol, suggesting that improved biotransformation of targeted compounds could be associated with higher microbial richness. During continuous-flow operation, at conditions representative of full-scale denitrification systems (hydraulic residence time = 2 h), the removal efficiencies of micropollutants were below 35% in both MBBRs, with the exception of atenolol and trimethoprim (>80%). Overall, this study demonstrated that MBBRs used for post-denitrification could be optimized to enhance the biotransformation of a number of micropollutants by accounting for optimal carbon sources and extended residence time.
authors.affiliation: Veolia Water Technologies AnoxKaldnes, Klosterängsvägen 11A, SE-226 47, Lund, Sweden; Department of Environmental Engineering, Technical University of Denmark, Bygningstorvet B115, 2800, Kgs. Lyngby, Denmark.
authors.forename: Elena
authors.initials: E
authors.lastname: Torresi
authors.affiliation: Department of Environmental Science, Århus University, Frederiksborgvej 399, 4000, Roskilde, Denmark.
authors.forename: Mònica
authors.initials: M
authors.lastname: Escolà Casas
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Bygningstorvet B115, 2800, Kgs. Lyngby, Denmark.
authors.forename: Fabio
authors.initials: F
authors.lastname: Polesel
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Bygningstorvet B115, 2800, Kgs. Lyngby, Denmark. Electronic address: beep@env.dtu.dk.
authors.forename: Benedek G
authors.initials: BG
authors.lastname: Plósz
authors.affiliation: Veolia Water Technologies AnoxKaldnes, Klosterängsvägen 11A, SE-226 47, Lund, Sweden. Electronic address: magnus.christensson@anoxkaldnes.com.
authors.forename: Magnus
authors.initials: M
authors.lastname: Christensson
authors.affiliation: Department of Environmental Science, Århus University, Frederiksborgvej 399, 4000, Roskilde, Denmark. Electronic address: kb@dmu.dk.
authors.forename: Kai
authors.initials: K
authors.lastname: Bester
mesh_terms: D018441:Biofilms; D019149:Bioreactors; D002244:Carbon / Q000378:metabolism*; D000431:Ethanol; D000432:Methanol; D012336:RNA, Ribosomal, 16S; D014865:Waste Disposal, Fluid
chemical_list: D012336:RNA, Ribosomal, 16S; D000431:Ethanol; D002244:Carbon; D000432:Methanol
keywords: Biofilms; Carbon source; Denitrification; MBBR; Pharmaceuticals; Wastewater