Biogas upgrading by in-situ biomethanation in high-rate anaerobic bioreactor treating biofuel condensate wastewater

This study aims to explore the potential integration of H-2-driven in-situ biomethanation into existing high-rate industrial anaerobic wastewater treatment. It specifically addresses key challenges such as hydrogen loading rates, pH effects (6.7-7.5), and gas diffusion devices. The study was conducted through a continuous long-term operation (>350 days) of an expanded granular sludge bed reactor treating biofuel condensate wastewater at high organic loading rates. The membrane gas exchanger exhibited the best performance compared to coarse- and fine-bubble diffusers, achieving a maximum H-2 utilization efficiency of 99 %. No inhibition of methanogens was observed within the tested pH range, and the long-term (>350 days) process stability of continuous in-situ biomethanation was demonstrated despite operational changes. The best biogas composition (92:4:4 for CH4:CO2:H-2) was obtained at pH 7.5 with a H-2 feeding rate of 4.39 NLH2.L-1.d(-1) and a high volumetric loading rate (VLR) of 13 g(COD).Lr-1.d(-1). An increase in syntrophic bacteria, such as Geobacter and Syntrophomonas, may suggest the stimulation of DIET-mediated methanogenesis, potentially enhancing biogas upgrading.