Kinetics of acetogenesis and methanogenesis in anaerobic reactions under toxic conditions

A method for assessing the impact of toxic organic compounds on the kinetics of acetogenic reactions is presented. The test program involved dosing ethanol‐enriched anaerobic cultures with an isomeric series of chlorophenols and chloroanilines. The effect on the acetogenic conversion of ethanol was monitored by measuring the residual ethanol and acetate in batch serum bottle tests, followed by mathematical analysis to determine coefficients of kinetic and inhibition models. A feature of the presently‐described research program was the use of the specific biomass responsible for acetogenesis and methanogenesis in kinetic models rather than using the total biomass. The distribution of biomass in the ethanol‐enriched test culture was 25.4% hydrogenotrophic methanogens, 41.1% acetoclastic methanogens, and 33.5% ethanol degrading acetogens. The effects of the chloroanilines and chlorophenols on both acetogenesis and methanogenesis appear to be best described as mixed inhibition, and the effects were not clearly related to the position of functional groups. In all cases, the test chemicals were more toxic to the acetoclastic methanogenesis reactions than to the ethanol‐degrading acetogenic reactions.