Kinetics of the methanogenic fermentation of acetate

Abstract The kinetics of methanogenesis from a stirred batch‐fed calcium acetate enrichment culture have been studied. A detailed kinetic analysis of the culture allowed four distinct phases to be distinguished. Phase 1 was a period of very rapid increase (from low initial values) in the rate of methanogenesis upon addition of acetate, and was not thought to be associated with cell growth. In Phase 2 the rate of methanogenesis increased exponentially with time reflecting exponential growth. Phase 3 was characterised by an approximately constant rate of methane production, and is discussed in relation to the uncoupling of growth and methanogenesis. Phase 4 is a period of rapid decline associated with depletion of acetate. The apparent size of the population of the acetate‐utilising methanogenic bacteria subsequently declined, with a specific decay constant of 0.4 ± 0.1 d−1. The significance of these phases, in particular 2 and 3, for industrial anaerobic digestion is discussed.