Migration and morphological transformation of Mn and its effect on microbial community in the AO process.

Manganese ion (Mn) was generated from metallurgical, steel making and chemical industries. It could affect microbial activity and community structure after entering sewage treatment plant. The effect of Mn on the pollutant removal, metal distribution patterns and composition of microbial communities were investigated in a an anaerobic/anoxic/oxic (AO) process. The results showed that when Mn concentration was 5 mg/L, the efficiencies for the removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) attained remarkable levels of 96 %, 93 %, and 99 %, respectively. In the sludge, the distribution pattern of Mn concentration was tightly bound extracellular polymeric substances (TB-EPS) > supernatant > loosely bound EPS (LB-EPS) > soluble microbial products (SMP). Mn was found to enrich and accumulate in the microorganism cells. In addition, Mn was mainly found in residual fractions and reducible fractions of pellet that manganese was present. The pellet was discovered to contain a substantial quantity of manganese, which was present in various oxidation states, including Mn, Mn and Mn. The escalating levels of Mn led to a reduction in the richness and diversity of microbial communities inhabiting various regions of the AO reactor. Nonetheless, the uniformity experienced only subtle alterations. Proteobacteria and Bacteroidetes emerged as the leading phyla within the microbial ecosystem, experiencing a steady rise in their respective proportions. The dominant bacterial groups, Azospira and Dechromonas, experienced an incremental increase in their relative prevalence, which played a constructive role in the process of pollutant removal.