Abstract
Six anaerobic chemostats
containing mixed microbial cultures were used to investigate the
interactions between sulfate reduction and methanogenesis for three
substrates: acetic acid, methanol and formic acid. Sulfate reducers
outcompeted methanogens in acetate-fed chemostats while methanol was not
utilized by sulfate reducers. In the formic acid-fed chemostats,
competition was observed between methanogens and sulfate reducers with
62 and 24% of the substrate utilized through sulfate reduction and
methanogenesis, respectively. Iron was added to the sulfate-reducing
chemostats to precipitate the hydrogen sulfide produced, thus eliminating
sulfide inhibition and ensuring stable chemostat operation. This study
involved the measurement of the oxidation-reduction potential (ORP) of
the chemostats using a novel technique. Batch spike tests were also
conducted to evaluate kinetic parameters for the degradation of different
substrates. Although both methanol-fed chemostats were exclusively
methanogenic, scanning electron microscopy (SEM) analysis revealed the
presence of two different strains of methanogens. This difference
was also manifested by the ORP values and the kinetic parameters.
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