Chapter Four - Weathering Process and Biological Dechlorination of Bottom Ash

Abstract

Copper leaching of bottom ash (BA) codisposed with refuse subject to short-term accelerated weathering, preparation of fresh simulated municipal solid waste (MSW) landfill leachate, evolution of mineralogical and chemical properties, changes of thermal analysis patterns are fully provided. Influences of weathering on Cu fractionation, Cu leaching in synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP), Cu leaching in codisposal leaching procedure are presented. The higher contents of plastics and kitchen waste lead to the higher chlorine level (0.6–0.7wt.%) of the BA. Biological dechlorination of incineration BA and geoenvironmental weathering/deterioration of landfilled BA glass are explored. The codisposal of refuse and BA has been widely used in the form of either multilayered landfill or mixed landfill, and the BA is commonly utilized as landfill cover. Weathering process transforms some Cu that is bound to organic matter and carbonates in BA into the residual fractions. The results of SPLP and TCLP leaching study shows that Cu leachability increases. Weathering could be an effective method for decreasing Cu leaching when BA is codisposed with refuse. The high content of chlorine causes the corrosion of reinforce steel in concrete, so it is necessary to remove the chlorine from BA before it can be reused as the raw material for cement production. A correlative analysis is conducted to evaluate the effect of the MSW components and collection mode on the heavy metal and chlorine characteristics in BA. The insoluble chlorine in BA exists primarily as aluminum oxide chloride, which is produced under the high temperature (1250°C) in incinerators. Biological dechlorination process of BA with aged refuse in landfill can decrease the Cl to less than the target level (0.18wt.%) within 30 weeks. It is still hard to give a definite conclusion regarding whether glass evolution in BA may decrease or increase the leaching amount of toxic elements from ash deposit, but can provide information in terms of assessment of the long time-scale behavior of pollutants in ashes and thus helps choose environmentally sound management strategy for ash deposits.