Factors affecting rate of methane formation from acetic acid by enriched methanogenic cultures.

A stable enrichment culture converting acetic acid to methane was successfully obtained from a pear waste digester, using a synthetic substrate solution with acetic acid as the main carbon source. This enrichment culture converted up to 10 mmol of acetic acid per litre per day at 35 degrees C and did not use hydrogen or formic acid in appreciable amounts as substrate for methane production instead of, or in addition to, acetic acid. The rate of conversion of acetic acid to methane was maximum at temperature of 40-45 degrees C, at a pH of 6.5 to 7.1, and was adversely affected by exposure to air, reducing agents, and high salt concentrations. The rate of conversion was independent of acetic acid concentration between 0.2 and 100 mM, but dropped markedly at concentrations below 0.2 mM.