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The study compares the potential to produce volatile fatty acids (VFA) from sewage sludge, both raw and thermally pre-treated in two modes of operation. In batch mode, raw sludge at pH 8 obtained the highest maximum VFA yield (0.41 g COD-VFA/g CODfed) whereas pre-treated sludge achieved a lower value (0.27 g COD-VFA/g CODfed). The operation of 5-L continuous reactors showed that thermal hydrolysis pre-treatment (THP) did not have any significant influence on VFA yields, averaging 15.1 % g COD-VFA/g COD with raw sludge and 16.6 % g COD-VFA/g COD with pre-treated one. Microbial community analysis showed that phylum Firmicutes was predominant in both reactors and that the enzymatic profiles involved in VFA production were very similar regardless of the substrate fed This work is part of the ECOVAL and CIGAT CIRCULAR projects, which are funded by Interreg Sudoe (SOE4/P1/E1104) and by the Xunta de Galicia and Viaqua (IN853C2022/03), respectively. Juan M. Lema belongs to the Galician competitive research group ED431C-2021/37 co-funded by Xunta de Galicia and ERDF (EU) SI

Biotransformation of trace-level organic micropollutants (OMPs) by complex microbial communities in wastewater treatment facilities is a key process for their detoxification and environmental impact reduction. Therefore, understanding the metabolic activities and mechanisms that contribute to their biotransformation is essential when developing approaches aiming to minimize their discharge. This review addresses the relevance of cometabolic processes and discusses the main enzymatic activities currently known to take part in OMPs removal under different redox environments in the compartments of wastewater treatment plants. Furthermore, the most common methodologies to decipher such enzymes are discussed, including the use of in vitro enzyme assays, enzymatic inhibitors, the analysis of transformation products and the application of several -omic techniques. Finally, perspectives on major challenges and future research requirements to improve OMPs biotransformation are proposed This research was funded by the Spanish Government (Agencia Estatal de Investigación) through the ANTARES project (PID2019-110346RB-C21) and a PhD Xunta de Galicia Grant (ED481A-2018/113, David Kennes). Authors from Universidade de Santiago de Compostela belong to Galician Competitive Research Group (GRC ED431C 2017/29), which is co-funded by FEDER (EU) SI

Current mechanistic anaerobic digestion (AD) models cannot accurately represent the underlying processes occurring during food waste (FW) AD. This work presents an update of the Anaerobic Digestion Model no. 1 (ADM1) to provide accurate estimations of free ammonia concentrations and related inhibition thresholds, and model syntrophic acetate oxidation as acetate-consuming pathway. A modified Davies equation predicted NH3 concentrations and pH more accurately, and better estimated associated inhibitory limits. Sensitivity analysis results showed the importance of accurate disintegration kinetics and volumetric mass transfer coefficients, as well as volatile fatty acids (VFAs) and hydrogen uptake rates. In contrast to the default ADM1, the modified ADM1 could represent methane production and VFA profiles simultaneously (particularly relevant for propionate uptake). The modified ADM1 was also able to predict the predominant acetate-consuming and methane-producing microbial clades. Modelling results using data from reactors dosed with granular activated carbon showed that this additive improves hydrogen uptake Gabriel Capson-Tojo is grateful to the Xunta de Galicia for his postdoctoral fellowship (ED481B-2018/017). Sergi Astals is thankful to the Spanish Ministry of Science, Innovation and Universities for his Ramon y Cajal fellowship (RYC-2017-22372). Ángel Robles is grateful for the support from the Spanish Ministry of Science and Innovation and the Partnership for Research and Innovation in the Mediterranean Area (Grant PCI2020-112218) SI

This study investigates the influence of pH on protein conversion into volatile fatty acids by anaerobic mixed-culture fermentation, a topic that, in contrast to glucose fermentation, only had scarce and contradictory information available. Several experiments were performed with two model proteins (casein and gelatin) at three different pH values (5, 7 and 9) using chemostats and batch tests. Highest conversion was reached at neutral pH although complete acidification was never achieved. Longer chain carboxylates production was favoured at low pH, while acetic acid was the main product at pH 7 and 9. Amino acids preferential consumption also varied with pH and protein composition. In fact, protein conversion stoichiometry is mainly driven by energetic yields and amino acid molecular configuration. Overall, this study identifies pH adjustment as a way to steer volatile fatty acid production during mixed-culture fermentation of proteins This research is funded by the Spanish Government through BIOCHEM project (PCIN-2016-102, ERA-IB-2 7th call, ERA-IB-16-052) and by the Spanish Ministry of Education (FPU14/05457). Authors belong to the CRETUS Strategic Partnership (ED431E 2018/01) and to the Galician Competitive Research Group (ED431C2017/029). All these programs are co-funded by ERDF (EU) 2022-10-28 SI