Effect of various leachate recirculation strategies on batch anaerobic digestion of solid substrates

Various leachate recirculation strategies were applied to a batch-wise operated solid-phase digestion system in laboratory-scale tests. Comparative experiments with both continuous and intermittent leachate recirculation revealed no advantages of a continuous flow. Results suggest that leachate recirculation should not be carried out continuously during process initialisation when methanogenesis is the rate-limiting step. Continuous watering resulted in the accumulation of Volatile Fatty Acids (VFA) during process start-up. In addition, no need for continuous water circulation was found for the following digestion process when hydrolysis was rate-limiting. Even in the absence of liquid recirculation, degradation was only slightly retarded when the biomass moisture content was adjusted.

Keywords: biogas, dry digestion, leachate recirculation, one-stage systems, batch process, batch anaerobic digestion, solid substrates, volatile fatty acids, water circulation, hydrolysis, biomass moisture content