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

This is the authors' abstract. We don't add key points for this paper.

Heavy metals such as Mn2+ are common contaminants in ammonium‐rich wastewater. The information of Mn2+ effect on anammox process needs further investigation. The short‐ and long‐term effects of Mn2+ on anammox were explored by anammox granular sludge. Batch tests showed that the half inhibition value (IC50) of Mn2+ was 4.83 mg/L. The anammox activity was severely inhibited in 0.5 hr under 15 mg/L Mn2+. However, after long‐term domestication by increasing the concentration of Mn2+, both the low‐load reactor (R1) and the high‐load reactor (R2) performed well, achieving volumetric nitrogen removal rate of 6.36 kg/(m3·d) and 13.99 kg/(m3·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 Mn2+ load, and the mechanism needs to be investigated further. Practitioner Points The half inhibition value of Mn2+ on anammox sludge was 4.83 mg/L in batch experiment. 200 mg/L Mn2+ did not cause any inhibition on anammox process during long‐term operation. Granular sludge is finer under high nitrogen loads with 200 mg/L Mn stress.