Evaluation of methanogenic activities during anaerobic digestion of municipal solid waste

Abstract

Numerous researchers have demonstrated that the rate and extent of the degradation of municipal solid waste (MSW) can be enhanced beyond that observed in a conventional landfill by adding moisture, buffering agents and sources of microorganisms such as anaerobically digested sludge. One method of achieving the addition of these agents is by directing leachate that has trickled through a bed of anaerobically stabilised waste to beds of fresh MSW. Proper operational strategies need to be developed for successful implementation of this process on a large scale or in a landfill. Operational parameters of primary importance are the point of time at which a stabilised waste bed can be used for sequencing, the period of sequencing and the minimal amount of leachate that has to be recirculated to rapidly attain balanced microbial activity in a fresh waste bed. Assays that measure a substrate-specific methanogenic activity of an anaerobic microbial consortia have been previously developed by researchers. These assays were employed in this study to evaluate the microbial activity of the leachate for utilisation of substrates like cellulose, acetate and formate. Activity in leachate samples, taken from a batch of MSW at various times during the degradation process, was measured in terms of the amount of methane produced in 4 h after spiking the sample with one of the selected substrates. Activity resulting from the utilisation of formate and cellulose showed considerable promise as indicators for optimising operational strategies. It was observed that the formate degradation activity followed the methane production rate with both reaching a maximum at the same time and that this could be used as an indicator for determining the period of sequencing. Cellulase activity in fresh waste beds responded to flushes of mature leachate and peaked a few days after sequencing was terminated.