Saponification with calcium has different impacts on anaerobic digestion of saturated/unsaturated long chain fatty acids

Little is known about the influence of the saturation degree of long chain fatty acids (LCFAs) on the bio-methane potential of calcium-LCFAs salts. In this study, palmitic acid and oleic acid were chosen as the model compounds to investigate the impact of saponification between calcium and saturated/unsaturated LCFAs on the methane recovery from LCFAs in anaerobic digestion. A 2.2-fold enhancement of methane yield was obtained due to the formation of calcium palmitate, which was primarily attributed to the enhanced bio-aggregation and significant change of microbial community. However, saponification between calcium and oleic acid decreased the methane recovery from oleic acid digestion. Only partial saponification with excess oleic acid led to 4% increment of methane production. The low bio-accessibility of calcium oleate and the little change of microbial community may be responsible for the small difference of methane recovery due to the formation of calcium oleate