Abstract:

Nitrification is a crucial step in the biological removal of nitrogen from wastewaterTo investigate the mechanism of the effect of anoxic stress on nitrification, nitrification activity, catalase activity, peroxidase activity and the H₂O₂ resistance of nitrifying activated sludge were determined after 0h, 12h, and 24h exposure to anoxic environmentAfter 12h and 24h anoxic treatment, the average specific ammonia oxidation rate decreased from 0894 mg N·(g MLSS)^-1·h^-1 to 0.453, 0.387 mg N·(g MLSS)^-1·h^-1, respectively, at a decrease of 46.8% and 49.8%， meanwhile, average specific nitrite oxidation rate decreased from 0761 mg N·(g MLSS)^-1·h^-1 to 0.485, 0.459 mg N·(g MLSS)^-1·h^-1， respectively, at a decrease of 36.3% and 39.7%he results showed that anoxic stress could decrease nitrification activity of nitrifying activated sludgeThe longer the duration of anoxic stress, the lower the nitrification activityAmmonia oxidation activity was inhibited more seriously than nitrite oxidation activityAnoxic stress could influence antioxidative enzyme activityPOD and CAT activities decreased by 10%, 17% for 12hanoxic treatment, 24％, 21％ for 24hanoxic treatmentThe longer the nitrifying activated sludge exposed to anoxic environment, the lower the antioxidative enzyme activityAnoxic stress could weaken the toxicity resistance of reactive oxygen, leading to the decrease of nitrification rate.