To realize the purpose of enhanced nitrogen removal (TN<5 mg·L-1) in step feed process treating urban wastewater

by using SBR reactor

the nitrite accumulation

variation of pH and ORP as well as dynamic properties during denitrification with methanol and glucose as the sole carbon sources are investigated in details. The results show that for both carbon sources

serious nitrite accumulations are observed during denitrification under different ratios of nitrogen and carbon (C/N). With identical C/N

when glucose is used as carbon source there is more maximum NO2--N accumulation concentration. However

NO3--N reduction rate is faster than NO2--N reduction rate for both carbon sources. Furthermore

with the increase of C/N

the maximum NO2--N concentration increases and the time in which the NO2--N achieves the highest concentration is accordingly shortened. For glucose

however

under high C/N ratio (C/N=29.3) both the denitrification rate and NO2--N accumulation concentration decrease. Besides

the changes of pH and ORP reflect the variation of NO2--N accumulation concentration well because pH and ORP have the significant relationship with NO2--N concentration. The second inflexion on curves indicates the real end of denitrification process.