Long‐term domestication to Mn stresses alleviates the inhibition on anammox process

Heavy metals such as Mn(2+) are common contaminants in ammonium-rich wastewater. The information of Mn(2+) effect on anammox process needs further investigation. The short- and long-term effects of Mn(2+) on anammox were explored by anammox granular sludge. Batch tests showed that the half inhibition value (IC50 ) of Mn(2+) was 4.83 mg/L. The anammox activity was severely inhibited in 0.5 h under 15 mg/L Mn(2+) . However, after long-term domestication by increasing the concentration of Mn(2+) , both the low load reactor (R1) and the high load reactor (R2) performed well, achieving volumetric nitrogen removal rate of 6.36 kg/(m(3) . d) and 13.99 kg/(m(3) . d), respectively. The average ammonium and nitrite removal efficiency of both reactors under 200 mg/L Mn still maintained above 90%. The results from long-term reactors' operation showed that the serious inhibition effect indicated by the batch test was significantly exaggerated. The granules became dispersed after long-term operation in the high load reactor (R2) which might be correlated to the high osmotic pressure caused by high Mn(2+) load, and the mechanism needs to be investigated further.