The fate of heavy metals and salts during the wet treatment of municipal solid waste incineration bottom ash

Abstract

Bottom ash contains unfavorable contaminants that could leach into the circulating water used for wet treatment, and its improper disposal of bottom ash could cause ecological pollution. This study was to discuss the partition of heavy metals and salts of bottom ash into circulating water and ash stockpile runoff in wet treatment plants in southern China. The leachability of bottom ash before and after the wet treatment was also investigated. The checked heavy metals Pb, Cu, and Ni and dissolved salts Cl^- and SO₄^2- show lower available fractions in leachate from the treated bottom ash than that in raw bottom ash. Circulating water is contaminated by target heavy metals, which the contents of Cu and Pb is higher than its limit for urban wastewater discharge. The circulating water owned the highest concentration of Cl^- and SO₄^2-, above10000 mg/L, and 1100 mg/L, which is far higher than the limits. The detected heavy metals, Cl^- and SO₄^2- in runoff also exceed the limits for urban wastewater discharge. Locations for bottom ash processing and storage sites should be selected to control and prevent any leaching and runoff impacts. Any runoff and circulation water should be discharged to the lined landfill's leachate collection system or suitable industrial wastewater treatment facilities.

Keywords: Bottom ash; Heavy metals; Leaching; Municipal solid waste incineration; Salts; Wet treatment.