Accumulation of Lactic Acid during Biodigestion of Municipal Solid Waste Leachate and Identification of Indigenous Lactic Acid Bacteria in Leachate

Abstract

Lactic acid accumulation is a common phenomenon in animal bodies during anaerobic respiration, but it is rarely found in natural systems like cattle manure digestion plants or anaerobic municipal sewage sludge bioreactors. The objective of this study was to demonstrate lactic acid production and accumulation during anaerobic digestion of municipal solid waste (MSW) leachate. Three reactors were set up containing cow dung, cow dung plus leachate, and only leachate to carry out anaerobic digestions. The amount of lactic acid accumulated in the reactor containing cow dung only was much less in comparison to the reactor containing cow dung plus leachate. This may be because of the suppression of sulphate reducing bacteria (SRB) and other groups of bacteria which utilize lactic acid, by some component in MSW leachate. The accumulated lactic acid might have come from various bacterial sources. For the identification of responsible organisms, the authors performed polymerase chain reaction (PCR), cloning, and denaturing gradient gel electrophoresis (DGGE)-based experiments. Surprisingly, lactic acid bacteria were also present in MSW leachate. A