Enhanced nitrogen and manganese removal in a manganese redox-driven moving bed biofilm reactor: role of extracellular polymeric substances.

In this study, the continuous flow moving bed biofilm reactor (MBBR) was developed for conversion of nitrogen and manganese including MBBR1 (R1, with manganese redox cycling function) and MBBR2 (R2, control group). The result suggested that NH4+-N removal reached 95±2% and 78±1% by R1 and R2 with NO3--N effluent concentrations of 2.1±0.4 and 7.1±0.6 mg·L-1, and TN removal through R1 increased compared with R2. Fluorescence characteristics and concentration of extracellular polymeric substances (EPS) were explored, and reactive oxygen species, apoptosis and enzyme activity of biofilm including the correlation between enzyme activity and EPS were analyzed. These results showed that protein decreased in R1 at 0-10 h, and it decreased in R2, and manganese addition promoted the development of an EPS-rich biofilm matrix. β-sheet content of EPS proteins increased from 29.9% in R2 to 34.6% in R1, and EPS mediated manganese redox might stimulate EPS production and simultaneously modified the chemical properties of EPS. Morphology, electrochemistry, and electron transport system activity of EPS/biofilm were investigated, and transcriptomic characteristics of biofilm were elaborated. These representations demonstrated that manganese redox cycling intensified the redox stress signal within biofilm. EPS mediated manganese redox might trigger oxidative stress, but the manganese-amended biofilm in R1 maintained the stronger antioxidant capacity and cell viability. Furthermore, manganese-amended biofilm from R1 had a strong response for protein synthesis and cellular machinery. This study deepens the application of EPS mediated manganese redox for nutrient removal.