Influence of phase separation on the anaerobic digestion of glucose—I maximum COD-turnover rate during continuous operation

Abstract

A mineral medium containing 1% of glucose as the main carbon source was subjected to one-phase and to two-phase anaerobic digestion processes under comparable conditions. The one-phase system consisted of an anaerobic up-flow reactor containing both acidogenic as well as methanogenic populations allowing a complete conversion of the carbon source into gaseous end products and biomass. The two-phase system consisted of an acid reactor and a methane reactor connected in series allowing sequential acidogenesis and methanogenesis of the glucose. Performance of the one-phase system and of the methane reactor of the two-phase system is presented by carbon mass balances. By gradually increasing the feed supply to both systems, maximum turnover of COD was determined. Maximum specific sludge loadings of the methanogenic phase of the two-phase system was over 3 times higher than that of the one-phase system. In a second experiment both systems were subjected to overloading, resulting in the accumulation of volatile fatty acids (VFA). In the one-phase system propionate and acetate were formed in considerable amounts. Although acetate disappeared rapidly after cessation of the feed supply, no turnover of propionate was observed within one week. On overloading the methane reactor of the two-phase system accumulation of several fatty acids within the reactor was observed. Rapid conversion of all fatty acids took place immediately after interruption of feed supply. The eco-physiological significance of phase separation is discussed briefly.