Nitrite Accumulation Control Condition And Microorganisms Characteristics On Partial Denitrification

Partial denitrification as a new process is characterized of reducing nitrate to nitrite by controlling reaction during denitrification in a sequencing batch reactor(SBR)to attain to stable nitrite accumulation for Anammox.In our study,reducing nitrate to nitrite by controlling reaction time in SBR was successfully achieved,and investigated nitrite accumulation under different C/N(COD/NO3--N)ratios(C/N=1,2.5,4)and different temperature(15?,25?,35?)in SBR for acquiring best control condition of partial denitrification.In addition to study of the quantities and communities of microorganism in SBR to enrich denitrifiers with sole nitrate reductase.Some main conclusions are as follows:(1)SBR1,SBR2 and SBR3 were achieved partial denitrification,which is reducing nitrate to nitrite in denitrification by controlling reaction time and C/N after108 days' cultivating.When the reaction time was 20 minutes,the concentration of nitrate was 31.55mg/L and the concentration of accumulated nitrite was 17.91 mg/L in SBR1(C/N=1);the concentration of nitrate was 9.29mg/L and the concentration of accumulated nitrite was 39.05mg/L in SBR2(C/N=2.5);nitrate was totally reduced and the concentration of accumulated nitrite was 38.72 mg/L in SBR3(C/N=4).(2)C/N ratio was one of the most important influence factors on nitrite accumulation in denitrification,the nitrate reduction rate and the nitrite accumulation rate increased as the C/N ratio increased,and the low C/N ratios were favorable for nitrite accumulation.The nitrite ratio was 93% under C/N=1;The nitrite ratio was 96%under C/N=2.5;The nitrite ratio was 78% under C/N=4.(3)The nitrate reduction rate and the nitrite accumulation rate increased as thetemperature increased.The concentration of nitrate was 34.92mg/L and the concentration of nitrite was 18.22mg/L in 10 minutes under the reaction temperature was 15?;The concentration of nitrate was 15.60mg/L and the concentration of nitrite was 34.58mg/L in 10 minutes under the reaction temperature was 25?;The nitrate was totally reduced and the concentration of nitrite was 45.66mg/L in 15 minutes under the reaction temperature was 35?.(4)The electron acceptor competition for carbon source of nitrate and nitrite caused accumulation of nitrite,and the inhibition of nitrite reduction because of nitrate existence.(5)The result of high-throughput sequencing showed that the dominant microorganism was Thauera,accounting for 71.83 % of total effective bacterial sequences.Thauera genus in the partial denitrification with high NO2--N accumulation was possibly related to the NO2--N reduction inhibition in the presence of NO3--N,which was most likely caused by the asynchronism of denitrifying enzyme synthetization for different electron acceptors(NO3--N and NO2--N).