Formation and characteristics of a ternary pH buffer system for in-situ biogas upgrading in two-phase anaerobic membrane bioreactor treating starch wastewater.

Biochemical biogas upgrading retaining more CO from biogas to form biomethane opens new avenues for sustainable biofuel production. For developing this technology, maintaining sustain pH for CO·HO is fundamental. This study proposes an innovative control strategy for in-situ biogas upgrading retaining and converting the CO in the biogas into CH, via hydrogenotrophic methanogenesis without external agent. The Biogas-pH strategy limited pH drop over 7.4 by stop feeding and maintained the methanogenesis activity by biogas flow rate over 98 ml·h. Low pH (7.37-7.80) decrease CO·HO as a substrate in stage-I, higher pH (7.40-8.41) enhances CO to CO·HO transfer by 6.29 ± 2.20% in stage-II. Because of that 95% CO·HO converts to HCO and CO when pH > 7.9, higher pH > 7.9 did not further upgrading the biogas. The carbonate buffer system shown open and close system characteristics in gas and liquid phase. The biogas CH was upgraded from 67.27 ± 5.21% to 73.56 ± 5.01%.