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This study addressed the impact of nanomaterials on anaerobic digestion and biogas production (methanogenesis pathways) when contaminating aerobic sludge is generated during wastewater treatment. Our experimental system was based on bioreactor operational parameters aligned with the operating conditions used in wastewater treatment plants (WWTP), a contamination scenario considering the treatment 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 additives transiently increased EPS production and specific hydrolytic enzymatic activities without altering the aerobic sludge microbial community structure nor the C, P, N removal capacity (spiked concentrations of 130 μg L−1during aerobic sludge production). However, the presence in the aerobic sludge biosolids of 99.9% of the total CeO2injected (without any change in speciation) altered the production, structure, and activity of the anaerobic sludge during digestion (impacting the EPS, ATP, lipase and α-glucosidase activities). Interestingly, these modifications of the anaerobic sludge activity shaped the methanogenesis pathways from acetoclastic to hydrogenotrophic and enhanced the biogas production with a significant increase in generated H2. In the context of developing a sustainable energy supply, we observed a continuous improvement of the biogas production in the contaminated bioreactor, which could increase the energy recovery potential of WWTPs.