Effect of Mn2+ on the phosphorus removal and bioflocculation under anoxic condition.

Manganese ion (Mn2+) generated from metallurgical, steel making and chemical industries enters sewage treatment plants and affects the sludge activity and flocculation. The effect of Mn2+ on the removal of chemical oxygen demand (COD) and total phosphorus (TP) and sludge activity were investigated in anoxic zone of an anaerobic/anoxic/oxic (A2O) process. The compositions and structures of extracellular polymeric substances (EPS) were characterized using three-dimensional excitation emission matrix fluorescence spectroscopy (3D-EEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) to reveal the relationship among Mn2+, EPS and sludge flocculation. The results showed that low concentration of Mn2+ (<5 mg/L) improved removal efficiencies of COD and TP and increased the activity of alkaline phosphatase, acid phosphatase and dehydrogenase. Meanwhile, the addition of Mn2+ increased total EPS, sludge contact angle, Zeta potential and sludge particle size, and thus enhanced sludge flocculation. However, high concentration of Mn2+ (>10 mg/L) hindered microbial flocculation and reduced removal efficiencies of the pollutants. When Mn2+was 5 mg/L, removal efficiencies of COD and TP reached 65% and 90%, respectively. Sludge flocculation was the best and SVI was 70.56 mL/g. The changes of Mn2+ concentration caused deviation of groups' compositions in LB-EPS and TB-EPS, where the main components were always protein (PN) and polysaccharide (PS). The addition of Mn2+ resulted in the degradation of humic acids. However, it did not give rise to significant morphology changes of EPS. The changes of EPS and microbial phosphorus removal of anoxic sludge under different concentration of Mn2+ in anaerobic/anoxic/oxic (A2O) process. [Display omitted] [ABSTRACT FROM AUTHOR]