Biomethanation in a thermophilic biotrickling filter — pH control and lessons from long-term operation

Optimum pH for methanogenesis in an anaerobic digester is well known, however, the effect of pH and its control strategy for the ex-situ biomethanation is understudied. In this study, two pH control strategies, namely the addition of buffer media and the control of CO ₂/H ₂ feed ratio, were investigated using a thermophilic biotrickling filter. Among the two, manipulating CO ₂/H ₂ feed ratio was the more effective method to maintain pH below 8.5. The biomethanation was continued for 215 days with the gas retention time sequentially lowered down to 34 min, when an average methane production capacity of 8.54 ± 0.47 Nm ³m _r ⁻³d ⁻¹ was achieved. Microbial community analysis showed that >94% total archaea were Methanobacterium and Methanoculleus validating the prevalence of hydrogenotrophic methanogens in the system.