Kinetics of Nutrient Removal by Nano Zero-Valent Iron under Different Biochemical Environments

The effectiveness of nano zero-valent iron (NZVI; an average size of 55 nm at a concentration of 200 mg Fe/L) in nutrient removal was determined under anaerobic, anoxic, and aerobic conditions. Compared to the rate of reduction of nitrate nitrogen (NO3-, N) to ammoniacal nitrogen (NH4+, N) by NZVI alone, the presence of activated sludge increased the rate of complete reduction by 300%. About 31% of NO3-, N was converted to NH4+, N through NZVI-facilitated dissimilatory nitrate reduction to ammonium, while 56% of NO3-, N was removed by heterotrophic denitrification. The presence of sludge reduced the rates of phosphorus removal by NZVI, with the first-order reaction rate constants of 0.06/hour, 0.42/hour, and 0.18/hour under anaerobic, anoxic, and aerobic conditions, respectively. The highest phosphorus removal efficiency (95%) by NZVI was observed under anoxic abiotic conditions, whereas the efficiency dropped to 31% under anaerobic biotic conditions, which was attributed to significant sludge-facilitated NZVI agglomeration.