Assessing The Impacts of Wet Treatment On Leaching Toxicity of Municipal Solid Waste Incineration Bottom Ash

Wet-treatment is usually employed to recover metals from bottom ash (BA). However, its effectiveness on regulating the leaching behavior of BA and minimizing environmental impact is still unquantified when BA is used as engineering materials. This study investigated the leaching behavior of targeted pollutants including Cu, Zn, Ni, SO42- and Cl- in fresh bottom ash (FBA) and treated bottom ash (TBA) using batch, standard column up-flow leaching and simulated rainfall down-flow leaching tests. It was firstly noted by the batch leaching that the potential ecological risk of MSWI bottom ash could not be ignore during its reutilization, and wet treatment enabled reduce the leaching concentration of Cu, Zn, Cl- and SO42- by 7.1%, 33.8%, 46.3% and 18.9%, respectively. The leaching concentrations of the targeted ions in FBA are generally higher than those of TBA. Furthermore, when BA was applied in water dynamic system such as rainfall environment, its toxicity leaching should be paid more attention onto the early leaching stage with a very high water dissolved salts release, such as Cl- and SO42-. The leaching concentration of Cu particularly exceeded the limit value before L/S=1. Meanwhile, it was also found that the leaching of SO42-, Ni, Cu and Zn in water dynamic system were directly proportionate to the liquid-to-solid (L/S) ratio. The leaching concentration of the pollutants obtained from the simulate rainfall down-flow tests was usually 4-6 times higher than those from the standard up-flow column when at the same ratio of liquid and solid.