Migration and morphological transformation of Mn²⁺ and its effect on microbial community in the A²O process

Manganese ion (Mn²⁺) 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 Mn²⁺ on the pollutant removal, metal distribution patterns and composition of microbial communities were investigated in a an anaerobic/anoxic/oxic (A²O) process. The results showed that when Mn²⁺ 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 Mn²⁺ concentration was tightly bound extracellular polymeric substances (TB-EPS) > supernatant > loosely bound EPS (LB-EPS) > soluble microbial products (SMP). Mn²⁺ was found to enrich and accumulate in the microorganism cells. In addition, Mn²⁺ 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 Mn⁴⁺, Mn³⁺ and Mn²⁺. The escalating levels of Mn²⁺ led to a reduction in the richness and diversity of microbial communities inhabiting various regions of the A²O 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.