Divalent manganese stimulates the removal of nitrate by anaerobic sludge.

This study investigated the effect of different concentrations of Mn on the removal of nitrate by anaerobic sludge and changes in the microbial communities through batch experiments. The results showed that the addition of Mn promoted nitrate removal by anaerobic sludge; the nitrate was completely removed within 6 d in the treatment group with >5 mM Mn. With the increase in Mn, the concentration of nitrite and nitrous oxide increased in the first 4 d and then decreased to 0 μM after 8 d of incubation. The increasing tendency of ammonium increased firstly and then decreased with the addition of Mn compared to A. Moreover, the Mn removal efficiency gradually decreased with the increase of Mn concentration. The changes of microflora structure in sludge before and after adding Mn were analyzed, and the results revealed that the microbial communities in the sludge may have evolved towards an energy-efficient association of short-cut nitrification, denitrification, and anaerobic ammonia oxidation after adding Mn. Mn stimulated the removal of nitrate by anaerobic sludge mainly by promoting the growth of .