Sludge was taken from laboratory-scale simulators of a landfill bioreactor (LFBR) treating the organic fraction of municipal solid wastes (OFMSW) over a period of 1 year. Population densities of acetogens, hydrogen- and acetate-utilizing methanogens and the specific methanogenic activity (SMA) on degrading butyrate, propionate, acetate and formate were measured. The results indicate that the Gompertz equation is a suitable model for describing the growth data of acetogens, hydrogen- and acetate-utilizing methanogens. The development of SMAs can be systematically described by a simple mathematical equation derived from the Gompertz equation. The measurements of bacterial population growth and methanogenic activity reveal that the SMA of acetate is an ultimate indicator for monitoring the OFMSW decomposition. Leachate recycling can stimulate the carbon flow from hydrolysis/fermentation through the hydrogen/acetate toward methane. A moisture content of 75% is suggested to be an initial rapid decomposition threshold for the anaerobic organic refuse mineralization in a landfill bioreactor.
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