Appropriate Use of MSW Leachate Recycling in Municipal Solid Waste Landfilling1

There is considerable interest today in the so-called “biocell” approach toward municipal solid waste (MSW) landfilling in which leachate is introduced back into the landfill. This approach reduces the cost of leachate management and is said to reduce/eliminate the potential for long term landfill gas production and groundwater pollution. However, a critical review of the typical approach being used today in biocell landfilling in Subtitle D landfills shows that the biocell approach will fall far short of appropriate landfilling of MSW that will prevent long-term gas production problems and groundwater pollution. Today’s minimum Subtitle D landfills can cause groundwater pollution at the time of landfill construction due to the inherent rates of leakage of leachate associated constituents through the liner system. Further, over time the flexible membrane liners’ (FMLs’) ability to collect leachate will decrease as the FML deteriorates. The groundwater monitoring systems allowed by regulatory agencies at minimum Subtitle D landfills have a low probability of detecting leachate polluted groundwaters before significant offsite groundwater pollution occurs. Leachate recirculation in a minimum Subtitle D landfill increases the hydraulic loading of the landfill which can lead to increased groundwater pollution. One of the principal problems with reintroduction of leachate into today’s MSW landfills as a means of decreasing the time for landfill “stabilization” is that a large part of today’s MSW is disposed of in plastic bags that are not shredded at the time of burial. These plastic bags “hide” the waste from the moisture which would allow increased landfill gas formation rates and leachate generation during the time that the landfill liner system can possibly be an effective barrier to groundwater pollution. While the addition of moisture to shredded municipal waste can greatly reduce the time of landfill gas production, unshredded solid waste will produce landfill gas and leachate over very long periods of time related to the rate of decomposition of the plastic bags. This paper discusses the problems with current approaches for leachate recycle (biocell landfilling) and recommends how such landfilling should be practiced to achieve increased rates of landfill stabilization while protecting nearby groundwater resources from leachate pollution. Biocell landfilling should be practiced using shredded MSW in a double composite lined landfill