Study on the effect of microbially treated municipal solid waste incineration fly ash and impurities on cement mortar performance

Microbial treatment can improve the pozzolanic activity of municipal solid waste incineration fly ash (MSWIFA) and reduce its heavy metal content. However, the effect of introduced bio-impurities and adsorbed heavy metals (BIHM) on MSWIFA treated by microorganism remains unclear. This study systematically investigates the influence of BIHM on the fluidity, compressive strength and heavy metal leaching toxicity of MSWIFA-cement mortar. The results showed that BIHM significantly improved the 28-day compressive strength from 24.62 MPa to 42.92 MPa, while enhancing fluidity by 4.08%. Heavy metals adsorbed by BIHM had no significant influence on mortar fluidity or compressive strength. Furthermore, BIHM reduced the leaching concentrations of heavy metals in the microbially treated MSWIFA-cement system. Mechanistic analysis reveals that BIHM can form a stable water film on the surface of MSWIFA particles, thereby reducing interparticle friction and enhancing particle dispersion, thus significantly improving the fluidity of the mortar. Concurrently, BIHM promotes the precipitation of CaCO₃ as crystalline phases, filling pores and facilitating matrix densification, thus enhancing the compressive strength of the mortar. Additionally, BIHM, together with the carbonate shell, forms an organic–inorganic barrier on particle surfaces, inhibiting heavy metal leaching, thereby improving the environmental safety of the material. In summary, BIHM regulates mortar performance through a multi-level mechanism of “physical dispersion–mineral filling–chemical/physical barrier”, providing a theoretical basis and technical guidance for the safe resource utilization of MSWIFA. • BIHM increases the fluidity and 28-day compressive strength of mortar by 4.08% and 16.35%. • BIHM improves the fluidity of mortar by enhancing particle dispersion and reducing friction. • The pore-filling effect of BIHM-induced CaCO₃ improves mortar compressive strength. • BIHM and its induced CaCO₃ shell reduce mortar leaching toxicity through buffering and encapsulation.