METHANOGENESIS AND SULFATE REDUCTION IN CHEMOSTATS .1. KINETIC-STUDIES AND EXPERIMENTS

Six anaerobic chemostats containing mixed microbial cultures were used to investigate the interactions between sulfate reduction and methano genesis for three substrates: acetic acid, methanol and formic acid. S ulfate reducers outcompeted methanogens in acetate-fed chemostats whil e methanol was not utilized by sulfate reducers. In the formic acid-fe d chemostats, competition was observed between methanogens and sulfate reducers with 62 and 24% of the substrate utilized through sulfate re duction and methanogenesis, respectively. Iron was added to the sulfat e-reducing chemostats to precipitate the hydrogen sulfide produced, th us eliminating sulfide inhibition and ensuring stable chemostat operat ion. This study involved the measurement of the oxidation-reduction po tential (ORP) of the chemostats using a novel technique. Batch spike t ests were also conducted to evaluate kinetic parameters for the degrad ation of different substrates. Although both methanol-fed chemostats w ere exclusively methanogenic, scanning electron microscopy (SEM) analy sis revealed the presence of two different strains of methanogens. Thi s difference was also manifested by the ORP values and the kinetic par ameters.