This paper presents an experimental study on the applicability of microbial induced carbonate precipitation (MICP) to treat municipal solid waste incineration (MSWI) fly ash with high alkalinity and heavy metal toxicity. The experiments were carried out on fly ashes A and B produced from incineration processes of mechanical grate furnace and circulating fluidized bed, respectively. The results showed that both types of fly ashes contained high CaO content, which could supply sufficient endogenous Ca for MICP treatment. Moreover, S. pasteurii can survive from high alkalinity and heavy metal toxicity of fly ash solution. Further, the unconfined compressive strength (UCS) of MICP treated fly ashes A and B reached 0.385MPa and 0.709 MPa, respectively. The MICP treatment also resulted in a reduction in the leaching toxicity of heavy metals, especially for Cu, Pb and Hg. MICP had a higher solidification and stabilization effect on fly ash B, which has finer particle size and higher Ca content. These findings shone a light on the possibility of using MICP technique as a suitable and efficient tool to treat the MSWI fly ash.

This paper presents a method to solidify/stabilize the municipal solid waste incineration (MSWI) fly ash by originally employing the microbial induced carbonate precipitation (MICP) technique. In this method, the rich endogenous calcium in the MSWI fly ash was utilized to induce calcite precipitation, which is different from the operation of adding extra calcium source in previous researches. The fly ash sample had a CaO content of 44.5%, and its leaching concentrations of Zn, Cr and Pb exceed the limits of the identification standard for hazardous wastes in China. The optical density at 600 nm (OD600) of the bacterial solution was about 1.0 after the processes of bacterial activation and reproduction. The prepared fly ash sample was well mixed with bacterial solution at an ash-liquid ratio of 1 kg: 0.3 L and cured at a temperature of 20 °C and a humidity of ≥95% for 7 days. After treatment, the heavy metal leachability significantly reduced to meet the standard for pollution control of landfill site, and the unconfined compressive strength increased approximately 40%. The precipitated carbonates were verified by SEM-EDS analysis and quantified by measurement of carbonate content via acid-dissolving method. The results shone a light on the possibility of using MICP technique as a useful and efficient tool to stabilize the MSWI fly ash before being reused or properly stored in landfills. •The MICP method is efficient to reduce the heavy metal leachability and increase the compressive strength of MSWI fly ash.•The endogenous calcium in MSWI fly ash was utilized to induce calcite precipitation.•The heavy metals in MSWI fly ash were well immobilized by the formation of carbonates.