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This work assesses the capacity of a microalgae-based system to remove three highly to medium polar pesticides typically found in freshwater: acetamiprid, bentazone, and propanil. Degradation of the pesticides was firstly studied individually at batch lab-scale reactors and abiotic and heated-killed controls were employed to clarify their removal pathways. At lab-scale, propanil and acetamiprid were completely removed after 7 days whereas bentazone was not removed. Four and two transformation products (TPs) were generated in the biodegradation process for acetamiprid and propanil, respectively. Then, the simultaneous removal of the pesticides was assessed in an outdoor pilot photobioreactor, operated with a hydraulic residence time of 8 days. During the steady-state, high removal efficiencies were observed for propanil (99%) and acetamiprid (71%). The results from batch experiments suggest that removal is mainly caused by algal-mediated biodegradation. Acetamiprid TPs raised throughout the operational time in the photobioreactor, while no propanil TP was detected at the pilot-scale. This suggests complete mineralization of propanil or residual formation of its TPs at concentrations below the analytical method detection limit. Aiming at biomass valorization, diverse microalgae harvesting methods were investigated for biomass concentration, and the effect of residual pesticides on the biogas yield was determined by biochemical methane potential tests. Anaerobic digestion was not inhibited by the pesticides as verified by the digestion performance. The results highlight the potential of microalgae-based systems to couple nutrient removal, biomass production, micropollutant biodegradation, and biofuel production. ; This work has been supported by the Spanish Ministry of Economy and Competitiveness State Research Agency (CTM2016-75587-C2-1-R and CTM2016-75587-C2-2-R) and co-financed by the European Union through the European Regional Development Fund (ERDF) and the Horizon 2020 research and innovation WATERPROTECT project (727450). This work was also partly supported by the Generalitat de Catalunya (Consolidate Research Groups 2017-SGR-01404 and 2017-SGR-014) and the Ministry of Science and Innovation (Project CEX2018-000794-S). ; Peer reviewed

It is possible to consult this version in open access at the following web address: arXiv:2011.11638 ; The occurrence of the extensively used herbicide diuron in the environment poses a severe threat to the ecosystem and human health. Four different ligninolytic fungi were studied as biodegradation candidates for the removal of diuron. Among them, T. versicolor was the most effective species, degrading rapidly not only diuron (83%) but also the major metabolite 3,4-dichloroaniline (100%), after 7-day incubation. During diuron degradation, five transformation products (TPs) were found to be formed and the structures for three of them are tentatively proposed. According to the identified TPs, a hydroxylated intermediate 3-(3,4-dichlorophenyl)-1-hydroxymethyl-1-methylurea (DCPHMU) was further metabolized into the N-dealkylated compounds 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and 3,4-dichlorophenylurea (DCPU). The discovery of DCPHMU suggests a relevant role of hydroxylation for subsequent N-demethylation, helping to better understand the main reaction mechanisms of diuron detoxification. Experiments also evidenced that degradation reactions may occur intracellularly and be catalyzed by the cytochrome P450 system. A response surface method, established by central composite design, assisted in evaluating the effect of operational variables in a trickle-bed bioreactor immobilized with T. versicolor on diuron removal. The best performance was obtained at low recycling ratios and influent flow rates. Furthermore, results indicate that the contact time between the contaminant and immobilized fungi plays a crucial role in diuron removal. This study represents a pioneering step forward amid techniques for bioremediation of pesticides-contaminated waters using fungal reactors at a real scale. ; This work has been supported by the Spanish Ministry of Economy and Competitiveness State Research Agency (CTM2016-75587-C2-1-R and CTM2016-75587-C2-2-R) and co-financed by the European Union through the European Regional Development Fund (ERDF) and the Horizon 2020 research and innovation WATERPROTECT project (727450). This work was partly supported by the Generalitat de Catalunya (Consolidate Research Group 2017-SGR-14) and the Ministry of Science and Innovation (Project CEX2018-000794-S). The Department of Chemical, Biological and Environmental Engineering of the Universitat Autònoma de Barcelona is a member of the Xarxa de Referència en Biotecnologia de la Generalitat de Catalunya. K. Hu acknowledges the financial support from the Chinese Scholarship Council. ; Peer reviewed