Simultaneous removal of manganese and nitrate by manganese redox driven moving bed biofilm reactor: Characteristic, biological community and mechanism.

This study investigated the effects of different manganese forms (MnCl2 and MnO2) on the nitrogen and phosphorus removal performance of moving bed biofilm reactor (MBBR). Compared to the control without manganese, the addition of MnCl2 and MnO2 increased NO3--N removal efficiency by 11.47 % and 9.54 %, and total nitrogen (TN) removal efficiency by 17.91 % and 15.45 %, respectively. The average accumulation of NO2--N decreased from 3.02 to 0.04 mg/L and 0.18 mg/L, respectively. The manganese redox system induced by MnCl2 enhanced total phosephorus (TP) removal efficiency by approximately 3.5 times, while MnO2 reduced TP removal efficiency by 2.94 %. After discontinuing MnCl2 and MnO2 supplementation, denitrification efficiency significantly declined, and Mn(II) reduced by BioMnOx could not sustain the manganese cycling process long-term. Extracellular polymeric substances (EPS) analysis revealed that MnCl2 and MnO2 stimulated the production of uronic acids, amide III, and secondary amides in proteins. High-throughput sequencing indicated that Proteobacteria, Bacteroidetes, Chloroflexi, and Acidobacteria were the dominant phyla involved in denitrification, but different manganese sources altered the microbial community composition. The relative abundance of Proteobacteria generally decreased, while Bacteroidetes increased by 16.29 % and 4.14 % with MnCl2 and MnO2. MnCl2 was more conducive to the Bacteroidetes growth. This study provides a practical framework for applying manganese-enhanced MBBR system in wastewater treatment plants to improve nitrogen removal efficiency and operational stability.