High concentration of Mn2+ has multiple influences on aerobic granular sludge for aniline wastewater treatment.

In this study, the effect of high concentration of Mn2+ on the aerobic granular sludge (AGS) systems for aniline wastewater treatment was systematically investigated in terms of AGS formation and pollutant removal efficiency. Two parallel sequencing batch reactors were operated to treat the aniline-rich wastewater with and without 20 mg L-1 of Mn2+. In the presence of Mn2+, the time to granulation was prolonged from 23 d to 30 d due to the toxicity of the high concentration of Mn2+. However, the mature granules with Mn2+ produced more protein and polysaccharides, and had a larger size (870 μm) than that without Mn2+ (740 μm). The extracellular polymeric substances of the granules in the two reactors had similar protein compositions, but some functional groups increased with Mn2+. The reactors showed high overall removal efficiency of chemical oxygen demand, NH4+-N, and total nitrogen with average concentrations below 40, 1.0, and 19 mg L-1, respectively, in the effluents. In one typical operating cycle, however, Mn2+ retarded nitrification and the degradation of aniline, while promoted denitrification. The microbial community analysis revealed that the growth of Terrisporobacter, Pseudomonas, and many other bacteria responsible for aniline degradation was inhibited by Mn2+, and so were the strains involved in nitrification. In contrast, Mn2+ facilitated the growth of denitrifying bacteria.