Tests were made to determine the effects of agitation speeds, sand and clay addition, and sulfide and cysteine concentrations on methane production from coal, yeast extract, and cysteine in a chemically defined acetate-free medium. The consortium was enriched from a Powder River Basin well water sample using Wyodak sub-bituminous B coal as the primary carbon source. The results show that without agitation, methane production was 20% and 44.4% greater than like cultures agitated at 50 and 100 rpm, respectively. Agitation enhanced coal dissolution and provides for the mixing of other nutrients, but may hinder the formation of microbial biofilms on the coal surfaces. In separate experiments, methane production increased in proportion to the concentration of cysteine reductant in the culture medium. This suggests that cysteine is also used as a carbon substrate in methanogenesis. The optimal concentration of sulfide reductant in both coal and no-coal systems was 0.38 mM. The presence of coal in the cultures may reduce the inhibitory nature of sulfide at concentrations greater than 0.38 mM.
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