Factors Affecting Nitrite Accumulation And Operation Stability During Biological Denitrification

As a new method of biological denitrification,part denitrification coupled with anammox has less sludge production,low energy consumption and low investment,causing widespread concern.However,nitrate has to be converted to nitrite during denitrification in order to achieve nitrite accumulation.Only in this way,the method of part denitrification coupled with anammox can be possible.So it was necessary to study nitrite accumulation during denitrification process.In this paper,we studied the factors affacting nitrite accumulation through batch testing and continuous test of SBR reactor.Batch experiment studied the effect of initial pH,temperature,sludge concentration,initial nitrate concentration,step-feeding carbon and copper concentration on the accumulation of nitrite nitrogen.By varying the reaction time,the initial pH and temperature conditions,we studied the operation stability of nitrite accumulation during biological denitrification process in SBR reactor.Finally we preliminary get the best condition of nitrate accumulation and operation stability,and explain the reasons for accumulation of nitrite during denitrification by determining the denitrification enzyme activity.The initial pH batch test results showed that when pH was 7 to 9,the nitrite accumulation rate was up to 50%.Temperature test results showed that when temperature were low at 12℃ and high at 35℃,the degree of nitrite accumulation during denitrification was higher,reaching 49.12% and 55.85%.Sludge concentration results indicated that both low sludge concentration and high concentration of sludge were not conducive to nitritre accumulation during denitrification.When concentration of reacting sludge was 3500mg/L,the maximum nitrite accumulation achieved 20.63mg/L.Initial nitrate concentration of the test results showed that along with nitrate concentration,nitrite accumulation and nitrite accumulation rate increased.Step-feeding carbon results showed that nitrite accumulated at different condition.But in case of multiple step-feeding carbon,nitrite accumulation need more time to stabilize.Copper test results showed that when copper concentration was 0.2mg/L to 1.2mg/L,it had a positive impact on nitrite accumulation.When copper concentration was 1.5mg/L to 2.0mg/L,it had a negative impact on nitrite accumulation.Part denitrification test of SBR reactor results showed that nitrite accumulation achieved stable under different stirring time during anoxic condition.When stirring time were 60 minites,the average amount of nitrite accumulation was 19.73mg/L,and nitrite accumulation rate reached 50.33%.So it was the best working conditions for nitrite accumulation in SBR reactor.The test of pH results showed that nitrite accumulation achieved stable when influent pH was 7.4,and both NAR and NTR were higher.Temperature test results showed that nitrite accumulated stable at diffferent temperatures.At cold temperature,nitrite accumulation rate was higher of 50%.By measuring denitrification sludge enzyme activity,we found that under experimental conditions,nitrate reductase activity was higher than nitrite reductase activity,which should be the main reason for nitrite accumulation.