The effect of calcium addition on the nitrogen removal performance of an activated sludge system from a microbiological perspective

This study investigated the improvement effect of the addition of exogenous calcium ions on the nitrogen removal efficiency of activated sludge in laboratory scale bioreactors fed various Ca concentrations. The long-term nitrogen removal performance was significantly greater in bioreactors supplemented with 150 mg/L extra Ca than in the no-addition control. The characteristics of the bacterial communities and the abundances of ammonium-oxidizing bacteria and genes related to nitrogen cycling were different between bioreactors with 150 mg/L Ca and those with other Ca concentrations (0, 30, 50 and 200 mg/L). Ca addition caused variations in the microbial abundance and distribution of nitrifiers and denitrifiers and in the synergistic effects of nitrogen functional genes in the activated sludge system, which ultimately affected the removal of nitrogen in the bioreactors. Obviously, adding an appropriate amount of Ca to activated sludge systems modifies the microbial community, which creates a beneficial environment for enhancing the removal of nitrogen from wastewater.