Environmental Impact of Municipal Solid Waste Incinerator Bottom Ash Asphalt Concrete Leachate on Surface and Groundwater

摘要

The inclusion of waste materials in mixes and fills from many industries has greatly added to the perception of highways as "linear landfills." In response to precipitation events or groundwater flow, there is a potential for leaching of the chemical constituents from highway construction and repair C&R materials and transport to adjacent surface and subsurface water bodies. Municipal solid waste incinerator bottom ash (MSWIBA) fettle residue from the incineration of urban solid wastes. In this study, MSWIBA-asphalt concrete (MSWIBA-AC) was evaluated for its potential environmental impact on surface and groundwater using a validated chemical and toxicity testing methodology. MSWIBA-AC was formulated as a standard pavement material from ash, aggregate, and asphalt binder. MSWIBA-AC leachate contained a mixture of organic compounds (Total Organic Carbon [TOC] ≈ 10 mg/L) but only one potentially toxic metallic contaminant (Al). MSWIBA-AC leachates exhibited very high aquatic toxicity. The toxicity in MSWIBA-AC leachate was completely removed by soil sorption and was not reduced by photolysis. Reduction of toxicity in the volatilization test was promoted by the aeration of the leachate, which decreased pH to near neutrality and resulted in precipitation of Al as Al(OH)_3. In the biodegradation experiment, after adjusting the leachate pH to 7 with a buffer solution, Al was precipitated and no toxicity was observed. It was concluded that Al is the primary toxicant in MSWIBA-AC leachate due to its high initial solubility in the leachate. The results, confirmed by gas chromatography/mass spectrometry analysis, showed that the organic compounds in the MSWIBA-AC leachate were nontoxic or not known to be toxic. Toxic contaminants in MSWIBA-AC leachate thus can be removed either by soil sorption or by adjusting the environmental conditions such as pH, and should not be transported into nearby soils and groundwater.