OCR Text |
Show the landfill is improperly designed. The leachability characteristics of metals in the residuals are known to depend on the residual matrix (size, morphology, porosity, and permeability) and composition related properties (e.g., speciation). If the residuals have leachable toxic metals, as determined by EP or TCLP tests, then the waste is classified as hazardous and must be manifested and disposed in landfills that minimize leachate migration. This disposal requirement increases costs considerably. Currently, the EPA has no regulation which exempts municipal solid waste combustion residuals, but common practice is to dispose of the residuals as non-hazardous waste. Recent studies have indicated that these residuals will fail a TCLP test and must be classified as hazardous waste. The EPA Office of Solid Waste is currently reviewing the status of this high volume solid waste, but it is unlikely that an exemption will be granted. For hazardous waste incinerators, the residuals are classified as hazardous unless proven otherwise and a formal delisting petition is accepted. Natural gas firing potentially could be used to modify the solid · residual characteristics in such a manner to change the matrix and/or speciation and thus prevent leaching. High temperature oxidation, for example, can convert chlorinated metals to more stable oxidative states and vitrify the solid, thus reducing the leaching potential of the .residue. This process is expensive, but could be combined with heat recovery to become competitive with alternatives such as disposing as hazardous waste, solidification, or electric furnace vitrification at off-peak times. Other techniques such as lower temperature oxidation with additives will allow formation of lower temperature eutectics, and catalysts could also be attractive. These approaches need to be developed beyond the concept phase in order to define the feasibility of natural gas use. Although high temperature incineration is a proven technology which provides a permanent disposal strategy for many hazardous waste streams, incineration is costly for waste streams of low Btu content due to the initial capital costs and auxiliary fuel requirements. The auxiliary fuel costs can be exorbitant for waste streams with low fuel value such as contaminated soils and aqueous wastes. The use of natural gas in high 4 |