Control Strategy Of （Partial） Nitritation Based On Alkalinity And Characteristics Of N₂O Emissions During Denitrification Using Nitrite As Electron Acceptor

Short-cut biological nitrogen removal processes based on partial nitrification, such as partial nitrification-anaerobic ammonia oxidation and SHARON, have the advantages of saving oxygen and carbon source, and reducing the amount of excess sludge, etc. They are especially suitable for high ammonia and low COD/N wastewater treatment and have been hailed as "sustainable biological nitrogen removal processes". Partial nitritation means to controll partial nitrification process, so that approximately 50% of the influent ammonia is oxidized to nitrite; the effluent can be directly used as water of anaerobic ammonia oxidation reactor. Recent studies have found that short-cut biological nitrogen removal process can release a potent greenhouse gas, nitrous oxide（N2O）, so that pollutants pass from water on to the atmosphere, which greatly reduces its sustainability of nitrogen removal.In this study, a lab-scale SBR inoculated with normal activated sludge and fed with synthetic wastewater was examined for the partial nitritation startup and denitrification using nitrite as electron acceptor system startup. As the rate-limiting step of combined process, the stable operation of nitrification is the key to achieving good denitrification. The first part of the study based on the stable operation of the partial nitrification reactor, the influence of HCO₃^-/NH4+-N ratio on the effluent of partial nitrification were studied, control strategy of（partial） nitritation based on alkalinity was achieved. The second part was based on the influence of pH value, C/N ratio and other important operating parameters on N2 O emission. N2 O generation ways and the optimal operating conditions of the reactor were obtained, aiming to provide a basis for enrichment of N2 O emission during nitrification-denitrifition of wastewater. The results obtained were as follows:（1）The influent HCO₃^-:NH4+-N molar ratio also plays a critical role in the process under aerobic conditions. The influent HCO₃^-concentrationis governed by the influent TIC concentration and its pH. The NH4+-N conversions were 34%, 58% when HCO₃^-:NH4+-N molar ratio were 0.5 and 1, respectively, ammonia oxidation was not completed. The NH4+-N conversions were 100% when HCO₃^-:NH4+-N molar ratio were 1.5 and 2, respectively.（2）Keep the HCO₃^-:NH4+-N molar ratio remain the same while change the influent pH and replace HCO₃^- by HPO42-, the influence of carban source and alkalinity on ammonia oxidation were studied. Results show the AOB just using the CO2 from aeration can remain activity. The influent CO2-HCO₃^--CO32-was used as alkalinity.（3）The BOD/NH4+-N ratio increase from 0.5 to 1, 2, 3, 4, the conversion of the NH4+-N was decreased from 38% to 23%, results show a reduction of the conversion from NH4+-N to NO2--N with increasing BOD due to the buffer capacity loss.（4）A lab-scale SBR was used, the nitrite denitrifition was induced by using micro aeration followed by anaerobic phease methods, conventional activated sludge as seed sludge, by increasing the influent nitrite concentration of the SBR（from 20 mg·L-1 to 500 mg·L-1）, the effluent nitrite concentration was near 0 mg·L-1, Thus nitrite denitrifition of high- nitrite wastewater was successfully induced. In the next days, denitrification rate of 98 % was obtained; the reactor was in stable operation.（5）After denitrification using nitrite as electron acceptor system startup and stable operating, the change of sludge form: the inoculated sludge appear wadding, complex structures and plenty of microorganisms. After the startup, sludge was comprised of dominant bacteria. The DGGE band show the Rhodobacter and Thauera sp. were dominant microorganism.（6）The effect of different influent pH values（7.1, 8.2 and 9.3） on N2 O emission during nitrite denitrifition of high-nitrite wastewater was identified. The total amount of N2 O emitted decreased with pH value increment. At pH 7.1, 8.2 and 9.3, N2 O emission amount of 0.564, 0.200 and 0.070 mg was observed, accounting for 0.5、0.2、0.006 % of the influent nitrite nitrogen, respectively.（7）The effect of different influent C/N ratio（0, 0.375 and 2） on N2 O emission during nitrite denitrifition of high-nitrite wastewater was identified. At influent C/N ratio 0, 0.375 and 2, N2 O emission amount of 3.45, 4.64, 0.22 mg was observed, accounting for 6.00, 5.13, 0.21 % of the influent nitrite nitrogen, respectively.