Metal Leaching from Road Base Incorporating Incineration Bottom Ash

Bottom ash (BA) of municipal solid waste incinerators represents one fifth of the original weight and a pressing environmental burden for which relief in the form of BA reuse is highly desired. We examined leaching of metals and others from BA when it was incorporated as a road base ingredient. A road segment was constructed with BA and infiltration rainwater was obtained through a leachate collection system and monitored for 7 y. In addition, road base samples containing BA were collected after 7 y and studied for leaching in column experiments. The measured results of leachate pH, conductivity, chloride, total organic carbon (TOC), and metals suggested the initial occurrence of leaching of organics and metals from stabilized BA, followed by its rapid subsidence soon after (stabilized BA: TOC from 900 to ＜50 mg/L after 3 d and Cu from 10 to very low after 10 d). The results also suggested that using water-washed BA and nature aggregate-amended BA as a road base material reduced leaching of organics and metals (water-washed BA: Cu from 35 to ＜2.1 mg/L; nature aggregate-amended BA (type C and D): Cu from 10 to ＜0.8/2.5 mg/L). Both the long-term monitoring results from road segment with BA and the accelerated column results simulating 3 y of natural precipitation corroborated a low risk of using BA in road construction and thus the potential as a green engineering practice. The immediate benefits of recycling and reuse incineration bottom ash would be the conservation of natural aggregate resources thus reducing the environmental burdens.