Fractionation of organic substances during anaerobic digestion of farm wastes for biogas generation

Abstract

Generation rate of biogas and its methane component, as well as changes of major organic fractions during anaerobic digestion of fresh cow dung alone and in combination with each of air-dry rice straw, maize stalks, and cotton stalks at a ratio of 1∶1 (on the basis of 70°C dry weight of either source) have been monitored in laboratory fermenters for 75 days at 35°C. Mixtures of cow dung + maize stalks produced the highest cumulative volumes of both biogas and its methane component; i.e. 17.9 and 8.31/1 fermented material respectively, cow dung alone surpassed all of the tested biomass regarding the yield of methane production in relation to the volatile solids consumed which gave 636 l/kg; the other materials came in the succession: cow dung + maize stalks, cow dung + rice straw and cow dung + cotton stalks. Acetic, propionic, and butyric were the major detectable fatty acids formed during the digestion course. Cow dung excelled the other treatments in amounts of such acids produced. Combination between cow dung and crop residues resulted in reducing the formation of fatty acids and NH 4 + and loss of nitrogen, but enhanced the disappearance of volatile solids, fats, hemicellulose and cellulose. The lignin content remained unchanged.