Characteristics of Nitrite Accumulation During Wastewater Denitrification

Characteristics of nitrite accumulation during denitrification process were studied by using methanol as the sole organic carbon in a batch-scale sequencing batch reactor with synthetic wastewater.Under the condition of temperature was 14℃,initial pH value was 7.33 and sludge concentration was 1 000 mg·L-1,nitrite accumulated significantly during denitrification process.Nitrite concentration increased gradually with nitrate reduction and reached its maximum value of 22.35 mg·L-1 in 2.5 h when nitrate reduction was almost completed,the amount of accumulated nitrite was equivalent to 43.2% of the amount of initial nitrate.During this period,pH value gradually increased to 7.79 in 2.67 h.Then accumulated nitrite kept decreasing until to zero.When the concentration of nitrate reduced to zero,the increasing rate of pH rise dramatically,formed a breakpoint of pH curve.Therefore,the breakpoint of pH curve can be used as an indicator to show the end of nitrate reductive reaction.The pH value reached its maximum value of 8.35 in 3.5 h and decreased a little afterward.The reason for the accumulation of nitrite is the inhibition of nitrate on nitrite reductive reaction,caused the reductive rate of nitrate was more than that of nitrite.