BIOREACTOR LANDFILLS: THE LINER SYSTEM ISSUES

摘要

The rapid degradation of municipal solid waste (MSW) when maintained at field capacity moisture content (and neutral pH conditions) has been proven by innumerable bench and small scale laboratory studies. What is presently needed is a wealth of full scale performance data in order to make the concept of leachate recycling leading to bioreactor landfills the method-of-choice for the disposal of MSW. This paper recognizes that the concept of field capacity moisture conditions are necessary for optimal degradation of the waste. In general, co-mingling of recycled leachate with additional liquids (site precipitation water, gray-water, and/or sewage sludge) is necessary to achieve field capacity throughout the waste mass. This leads to several operations and design issues which are described in the paper. Operations must homogenize the waste to the maximum extent possible so as to provide for field capacity at all locations within the landfill. Unimpeded and uniform movement of liquids must be maintained at all elevations within the landfill. In this regard, it is usually necessary to use alternative daily cover materials on each lift of waste so as not to have perched leachate and side slope seeps. Design must focus on high quality liner systems (GM/GCL's are fully acceptable); extremely open leachate collection soils (k ≥ 1.0 cm/sec); structurally sound leachate removal piping systems (limit height of landfill); caution over filter/operations layers (omit both); placement of final cover (postpone until waste is decomposed); and proper waste stability (avoid failures arising from excess hydraulic heads). All of these issues are discussed in the paper, along with the rationale for making the respective recommendations. The paper concludes with a call for more fully operational sites and for greater instrumentation of MSW landfills practicing leachate recycling and liquids augmentation. Such information is necessary to determine if true bioreactor landfills can be realized on a universal and routine basis. Funding for such activity should come from federal and/or state agencies. Commingled public and private funding is also a possibility. Sole reliance on private funding is not likely, nor ultimately the best resolution of the unanswered issues and concerns.