Microbial response to environmental changes in an Anaerobic Baffled Reactor (ABR).

Two 10 litre Anaerobic Baffled Reactors (ABR), with 8 separate compartments, were used to examine the effect of Hydraulic Retention Time (HRT), effluent recycle and temperature changes on the trophic groups in anaerobic digestion. A synthetic carbohydrate (sucrose)-protein substrate was used, and the reactors run at 20 h HRT, and 35 degrees C. Changing the HRT from 40 to 20 hours doubled the organic loading which caused accumulation of reduced intermediates. The pattern of Volatile Fatty Acids (VFA) at steady state due to an increase in recycle ratios led to the breakage of microbial flocs, and a reduced overall microbial activity. However, the quantity of reduced intermediates was substantially reduced. Decreasing the temperature to 25 degrees C had differing degrees of influence on reactors I & II, but the same pattern of microbial response occurred; that is the slower growing microorganisms were more affected by the temperature drop. It was found that the unique structure of the ABR brings about the partial separation of acidogenesis and methanogenesis.