Microbial populations and moisture content in a conventionally operated municipal solid waste landfill

Landfills are not sterile environments. In fact it can be argued that they are the ultimate reactors for biodegradation as they contain nutrients, bacteria, and various redox conditions which, then, change over time. Enhancement of the landfill environment to optimize the rates of biodegradation and to ensure more rapid stabilization of the waste mass and availability of land fill volume needs to be developed. Research has progressed from laboratory to pilot to full-scale landfill studies. As part of a Cooperative Research And Development Agreement, Waste Management, Inc. and the United States Environmental Protection Agency's Office of Research and Development are studying bioremediation in full scale municipal solid waste landfills operated conventionally and as bioreactors over time and developing methods to monitor the degradation to ensure optimum operation. The microbial enumeration of harvested wastes landfilled for approximately five years conventionally in Unit 5, cell 1, coring 23 in the Outer Loop Landfill in Louisville, KY has been studied. The results of these analyses indicate that there is no statistically significant correlation between moisture content (47 to 65%) of the wastes and depth in the landfill (r(2) = 0.027), numbers of total aerobic (r(2) = 0.085), total anaerobic (r(2) = 0.179), sulfate reducing (r(2) = 0.185) and denitrifying bacteria (r(2) = 0.048). There is also no statistically significant correlation between the numbers of sulfate reducing and denitrifying bacteria (r(2) = 0.018). After addition of nitrified leachate to the landfill cell, it will be determined if this retrofit bioreactor demonstrates increased moisture content and numbers of bacteria.