Methanogenesis of carbohydrates and their fermentation products by syntrophic methane producing bacteria isolated from freshwater sediments

Anaerobic conversion of substrates namely cellulose, cellobiose, glucose, volatile fatty acids, and methanol with a co-culture of fermentative, acidogenic, acetogenic, and methanogenic organisms isolated from freshwater sediments was performed. Maximum reduction of volatile solids (VS) was from cellulose, cellobiose and glucose followed by methanol and other compounds with a product yield coefficient (Yp/s) of 0.59 m3/kg VS consumed with a volumetric productivity (Qp) of 15.7 mmol/l/d after 12 d fermentation of cellulose. Maximum methane content in the gas mixture was 86.1% with an average of 82.5±3.6%. Batch culture methane production characteristics were analyzed and compared. The maximum values of Yp/s from cellobiose, glucose, methanol, formate, acetate, propionate, and butyrate were 4.0, 2.2, 0.71, 0.22, 0.90, 1.6 and 1.43 mmol/M substrate used and are higher than those values reported in the literature.