Abstract: Microbial defluorination has the advantages of green and low-cost relative to other technologies, but  F^- may inhibit the activities of key enzymes of microbial metabolism, thus reducing the removal effect. In this study, a carrier was prepared using oyster shell powder and the activity of carbonic anhydrase (CA) was enhanced through Fe-Al modification, to strengthen the microbially induced calcium precipitation (MICP) process for F^- removal. The orthogonal experiment results showed that the removal effect of F^- was the best (up to 92.0%) when the calcination temperature was 700 ℃, Fe∶Al=2∶1, and the mass ratio of oyster shell powder to sodium alginate (NaAlg) and ammonium bicarbonate (NH₄HCO₃) was 4∶0.1∶0.2. Moreover, after five cycles of regeneration, the removal efficiency could reach 81.5%, showing good regeneration performance. The screened Fe-Al modified substrate was used to enhance MICP for F^- removal, and the removal efficiencies of F^-, NO₃^--N and TP could reach 84.9%, 100% and 53.5%, respectively. By combining enzyme activity analysis and biological precipitation characterization, the mechanism by which the Fe-Al modified substrate enhanced MICP for F^- removal could be attributed to the complexation reaction between Fe and Al and F^-. Such interaction reduced the toxicity of F^- in the solution, improved the tolerance of microorganisms to F^-, and significantly enhanced the activity of microbial CA, thus achieving the simultaneous removal of F^-, NO₃^--N and TP through promoting the MICP process. This study provided theoretical basis and efficient and feasible technical support for treating water containing F^- through the combination of substrate preparation and microbial treatment.

Key words: defluorination, nitrogen and phosphorus removal, Fe-Al modified substrate, microbially induced calcium precipitation