THE USE OF MUNICIPAL WASTE COMBUSTOR ASH AS A PARTIAL REPLACEMENT OF AGGREGATE IN BITUMINOUS PAVING MATERIAL

摘要

Like many states, Minnesota does not yet allow the beneficial utilization of ash generated from the combustion of municipal solid waste in a municipal waste combustor (MWC). In an attempt to "turn the tide", officials from Polk County Minnesota proposed to demonstrate the economic, structural, and environmental performance of using MWC ash as a partial replacement of aggregate in bituminous for road construction. The Polk County Solid Waste Department, located in northwest Minnesota, operates a 65-ton per day MWC that generates 12 tons per day of combined ash in the generation of energy. Due to the starved air-type combustion process employed by the Polk County facility, the combined ash consists of 98 to 99 percent bottom ash and 1 to 2 percent fly ash. The 1996 installation of an up-front materials recovery facility (MRF) resulted in the distinction of "old" ash that was generated before 1996, and "new" ash that was generated after 1996. Old ash and new ash have sufficiently distinct physical and chemical characteristics to warrant independent evaluation. Approval was obtained from the Minnesota Pollution Control Agency (MPCA) to construct a demonstration project to evaluate the viability of replacing bituminous aggregate with MWC ash. In order to obtain MPCA approval, the potential for the demonstration project to impact the environment was evaluated. The MWC ash and bench-scale samples of ash amended bituminous were evaluated for total composition and leachability of inorganic constituents of concern as well as dioxins and furans. Concentrations were compared to EPA soil screening levels, MPCA Soil Reference Values (SRVs) and Soil Leaching Values (SLVs), as well as EPA and Minnesota Department of Health drinking water standards. Environmental assessment showed that impacts were acceptable by federal and state standards. Construction of a 2.25-mile section of road surface is scheduled for the spring of 2000. The road section is to be subdivided into: 1. 0.75 miles with no ash, as a control, 2. 0.75 miles with 20 percent replacement of the bituminous aggregate using new ash, and 3. 0.75 miles with 40 percent replacement of the bituminous aggregate using old ash. The above ash percentages were used by the Minnesota Department of Transportation (MnDOT) materials research laboratory in identifying successful bituminous mix designs. The non-uniform percentages of new and old ash (20 percent versus 40 percent) were due to density and physical performance characteristics only. The road section is to be constructed with a MnDOT Standard 2340 bituminous mix design. As part of construction, environmental monitoring devices will be installed to evaluate the potential impacts to surface water and groundwater. Results of this monitoring will be used to pursue MPCA and MnDOT approval for full-scale use of MWC ash for bituminous paving. In addition to potential environmental impacts, pavement structural performance and economic assessments will be made. This project has strong support from a variety of state and county agencies and associations.