During in situ biogas up-gradation by supplying hydrogen from an external source and enrichment of hydrogenotrophic methanogens, high pressure of H2 negatively affects hydrolytic and fermentative activities. To overcome this problem, the present study aimed to enrich the hydrogenotrophic methanogens by optimization of various parameters associated with gas recirculation along-with hydrogen supply from the external source. Due to recirculation of gases and supplied hydrogen, methane generation was two-fold higher in the optimal condition than in conventional anaerobic digestion, with the highest methane content of 99%. Additionally, the hydrogenotrophic methanogens were enriched, with a decrease in acetoclastic methanogens and an increase in Bathyarchaeia population, which utilizes H2 and CO2 to produce acetate and lactate as end products. The study concludes that recirculation increases methane production by converting H2 and CO2 into methane and enhances the degradation of organic matter left over undigested in the hydrolytic reactor.
Keywords: Anaerobic digestion; Biogas up-gradation; Hydrogenotrophic methanogens; In-situ up-gradation; Methane content.
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