Heavy metals volatilization characteristics and risk evaluation of co-combusted municipal solid wastes and sewage sludge without and with calcium-based sorbents

Abstract

Heavy metals, especially gaseous heavy metals, have high toxicity and do harm to human. Heavy metal volatilization characteristics of co-combusted municipal solid wastes (MSW) and sewage sludge (SS) from different mass fraction of MSW and SS, different temperature and different O2 concentration atmosphere was investigated. Performance of calcium-based sorbents was also studied. Volatilization efficiency of As, Cr, Cu, Ni, Pb and Zn in MSW was 100%, 45.89%–66.58%, 75.62%–92.45%, 42.33%–65.70%, 39.25%–68.76% and 53.57%–84.62%, and that in SS was 28.37%–40.75%, 33.78%–43.42%, 46.08%–56.69%, 35.04%–51.52%, 18.54%–44.99% and 14.72%–48.88%. Volatilization efficiency of heavy metals increased as mass fraction of SS in a blend decreased and as temperature increased. Volatilization efficiency of all heavy metals examined decreased as O2 concentration increased at high temperature and that of Cu, Pb and Zn increased as O2 concentration increased at low temperature. CaO, Ca(OH)2 and CaCO3 declined the volatilization of As, Cr, Cu, Ni, and Zn, while enhanced that of Pb. With calcium-based sorbents, volatilization efficiency of As, Cr, Cu, Ni, and Zn decreased from 70.06%, 39.91%, 75.52%, 44.08% and 40.10% to 54.24%, 33.73%, 39.98%, 20.56% and 32.06%, while that of Pb increased from 47.23% to 100%. Fitting formula was set to predict the heavy metals volatilization, and risk evaluation of gaseous heavy metals was exhibited.