RELATIONSHIP BETWEEN HYDROGEN SUPPLY RATE AND ORGANIC ACID ACCUMULATION IN BIO-METHANATION

Abstract

 Power to Gas (PtG) technology, which converts surplus electricity into hydrogen gas by water electrolysis, has been attracting attention. One of the methods to utilize this hydrogen gas by converting it into methane gas is bio-methanation in anaerobic digesters at wastewater treatment plants. Laboratory experiments are conducted to evaluate the effect of hydrogen supply on organic acid accumulation during anaerobic digestion by varying the hydrogen supply rates. In mesophilic anaerobic digestion of organic substrate at a loading rate of 0.75 g-volatile solids/(L•d), acetic acid, propionic acid, and isovaleric acid accumulated when the hydrogen supply rate was 26 NL/(L•d). Under the hydrogen supply rate of less than 18 NL/(L•d), no significant accumulation of organic acids was observed, indicating that the conversion of the supplied hydrogen to methane is possible under continuous operation conditions. Microbial structure analysis showed that detected ratios of hydrogen-utilizing methanogens increased under stable operation with hydrogen supply, while detected ratios of acetic acid-utilizing methanogens decreased under acid accumulation conditions. The results show that hydrogen supply for converting carbon dioxide produced from anaerobic digestion of sewage sludge is applicable.