Understanding biotoxicity for reusability of municipal solid waste incinerator (MSWI) ash

This feasibility study using Escherichia coli DH5alpha as a reporter microorganism tended to disclose toxicity ranking of various ashes of municipal solid waste incinerator (MSWI) in comparison with typical toxic chemicals for reusability in further applications. Previous study indicated that growth inhibition to bacterial cells occurred at concentrations above 0.156, 0.625 and 0.0195g/L for bottom ash (BA), cyclone ash (CA), scrubber ash (SA), respectively, suggesting the toxicity ranking of SA>BA>CA. This follow-up study clearly stated that compared to cadmium(II) and chromium(II) SA seemed to be the most toxic species to DH5alpha. Large amounts of supplemented lime (CaO) were used for neutralization of acid gas in incinerator, SA was thus contained high-levels of sulfate, chloride and nitrate salts. Therefore, compared to other ashes a marked increase in toxicity was observed in SA. Regarding soluble cations and anions in ashes, nitrite ion seemed to stimulate instead of repress cell growth. In contrast, nitrate ion showed so-called "sufficient challenge" characteristics for growth enhancement and inhibition at low and high concentration, respectively. Low solubility of metallic ions (e.g., Pb(II) and Cu(II)) in ashes likely resulted in low mobility in the environment and low risk to humans. The findings showed that toxicity attenuation of SA will be inevitably required as SA is even more toxic than Cr(II) and Cd(II).