Combusted-diesel additives containing CeO 2 nanomaterials shape methanogenic pathways during sludge digestion and enhance biogas production

International audience; This study addressed the impact of nanomaterials on anaerobic digestion and biogas production (methanogenesis pathways) whencontaminanting aerobic sludge generated during wastewater treatment. Our experimental system was based on bioreactor operationalparameters aligned with the operating conditions used in wastewater treatment plants (WWTP), a contamination scenario considering thetreatment of nano-enabled products at the last stages of their life cycle, and nanomaterial concentrations close to those predicted in WWTP.The physico-chemical, microbiological and chemical engineering proxies studied all concluded that combusted nanoCeO2-enabled fuel additivestransiently increased EPS production and specific hydrolytic enzymatic activities without altering the aerobic sludge microbial communitystructure nor the C, P, N removal capacity (spiked concentrations of 130 µg.L-1 during aerobic sludge production). However, the presence in theaerobic sludge biosolids of 99.9 % of the total CeO2 injected (without any change in speciation) altered the production, structure, and activity ofthe anaerobic sludge during digestion (impacting the EPS, ATP, lipase and α–glucosidase activities). Interestingly, these modifications of theanaerobic sludge activity shaped the methanogenesis pathways from acetoclastic to hydrogenotrophic and enhanced the biogas productionwith a significant increase in generated H2. In the context of developing a sustainable energy supply, we observed a continuous improvementof the biogas production in the contaminated bioreactor, which could increase the energy recovery potential of WWTPs.