Anaerobic production and degradation of volatile fatty acids in low temperature environments

Anaerobic conversion of organic matter leads to the intermediate formation of volatile fatty acids (VFA), primarily butyrate, propionate and acetate. The present investigation examined methanogenesis from the VFA by microbial populations associated with natural and man-made cold habitats. Sites that were investigated included lake sediments, tundra wetland soil, sludge lag oons, manure store and anaerobic reactors operated at 3-9 degrees C. Sharp increases in methanogenesis from VFA were observed as incubation temperatur es were increased to 30 degrees C. Low temperatures resulted in significant methane production, and butyrate was identified as an important VFA interm ediate formed and degraded during sample incubations. The addition of butyr ate and propionate to samples indicated that butyrate is degraded preferent ially over propionate. Dilution of samples and, hence, microbial population s led to the accumulation of acetate and hydrogen when butyrate and propion ate were degraded. Thus, at low temperatures, a high density of hydrogen- a nd acetate-utilizing methanogens is needed for methanogenesis from VFA to o ccur. An aggregation of proton-reducing acetogenic bacteria and methanogens accelerates this process.