Migration and Morphological Transformation of Mn2+ and its Effect on Microbial Community in the A2o Process

Abstract

The role of manganese ion (Mn2+) distribution and transformation was significant in gauging the efficacy of wastewater treatment processes and in ecological risk assessment. Confirming the fate and transformation behavior of manganese ions in wastewater biological treatment systems had guiding significance for promoting the development of reuse of residue sludge. In this study, high-throughput sequencing technology was used to conduct in-depth analysis of changes in the composition of microbial communities. In the meantime, the existing morphology and structural characteristics of Mn2+ were analyzed combining multiple advanced characterization techniques. The data from the research indicated that concentrations of Mn2+ below the 5 mg/L threshold improved microbial activity. The oxidation product Mn3O4 of Mn2+ as a chemical catalyst was beneficial for improving pollutant removal. In the presence of 5 mg/L Mn2+ concentration, 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 EPS (TB-EPS)>supernatant> loosely bound EPS (LB-EPS)>soluble microbial products (SMP). Mn2+ could 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+.Simultaneously, the escalating levels of Mn2+ led to a reduction in the richness and diversity of microbial communities inhabiting various regions of the anaerobic/anoxic/oxic (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. By elucidating these complex relationships, it would provide important guiding suggestions for the development of wastewater biotechnology and theoretical research.

Keywords: Mn2+, Anaerobic/anoxic/oxic (A2O) reactor, Migration and transformation, Morphology, Microbial community