Effect of Co-combusted Sludge in Waste Incinerator on Heavy Metals Chemical Speciation and Environmental Risk of Horizontal Flue Ash

Incineration of sludge in waste incinerators is a trend of sludge disposal, and the problem of heavy metal in horizontal flue ash is a concern. Horizontal flue ash in waste incinerator was collected before and after the sludge was co-combusted. XRF, SEM-DES, and ICP were used to characterize the effect of sludge on the distribution of heavy metals on different heated surfaces. Potential ecological risk index of all horizontal flue ash was higher than 600, indicating the high ecological risk. After adding sludge for co-combustion, heavy metals content in all ash sample increased. As for chemical speciation of heavy metals, the addition of sludge increased the content of mild acid-soluble fraction, reducible fraction and oxidizable fraction of heavy metals, while decreased that of the residual fraction. Environmental pollution and potential ecological risks of heavy metals were increased when sludge was co-combusted. The fitting relation between the heavy metals content of each speciation and the gas temperature and the sludge mixing amount was given, which could be used to predict the heavy metal content in horizontal flue ash.