| Short-cut biological nitrogen removal processes based on partial nitrification (suchas partial nitrification-anaerobic ammonia oxidation, CANON process, etc.) have theadvantages of saving oxygen and carbon source, shortening the biological reactionprocess and reducing the amount of excess sludge, etc. They are especially suitable forhigh ammonia and low C/N wastewater treatment, and have been hailed as "sustainablebiological nitrogen removal processes". Partial nitritation means to controll partialnitrification process, so that approximately50%of the influent ammonia is oxidized tonitrite; the effluent can be directly used as water of anaerobic ammonia oxidation reactor.Partial nitritation is the pre-process of the combined short-cut biological nitrogenremoval process. However, recent studies have found that short-cut biological nitrogenremoval process can release a potent greenhouse gas, nitrous oxide (N2O), so thatpollutants pass from water on to the atmosphere, which greatly reduces its sustainabilityof nitrogen removal.In this study, a lab-scale SBR inoculated with normal activated sludge and fed withsynthetic high-ammonium wastewater was examined for the autotrophic partialnitritation startup, stable operating characteristics and the influence of pH value, DOconcentration and other important operating parameters on N2O emission. N2Ogeneration ways and the optimal operating conditions of the reactor were obtained,aiming to provide a basis for reduction of N2O emission during partial nitritation of high-ammonia wastewater. The results obtained were as follows:（1）On the basis of partial nitrification, partial nitritation was induced. Withconventional activated sludge as seed sludge, by increasing the influent ammoniaconcentration of the SBR (from200mg·L-1to600mg·L-1) under low DO condition(after10mins’aeration, DO concentration was maintained between0.2and0.6mg·L-1),ammonia nitrogen conversion rate of96%and nitrite accumulation rate of90%wasobtained in the SBR56days later, high-ammonium wastewater partial nitrification wassuccessfully achieved. On this basis, maintained the influent ammonia concentrationconstant, while shortening the aeration time (from440min to320min) of the reactorand decreasing the aeration rate (from0.4min to0.32min), after9days’ operation, theammonia nitrogen conversion rate dropped to55.9%, and the effluent ammonia nitrogento nitrite ratio reached1:1.1. In the next33days, the reactor reactor was in stableoperation. Thus partial nitritation of high-ammonium wastewater was successfullyinduced.（2）The effect of different influent pH values (7.5,8.0and8.5) on N2O emissionduring partial nitritation of high-ammonium wastewater was identified. The totalamount of N2O emitted decreased with pH value increment. At pH7.5,8.0, and8.5,N2O emission amount of71.8,44.2and37.7mg was observed, accounting for3.81,2.35and2.00%of the influent ammonium nitrogen, respectively.（3）The effect of different DO concentrations (the average DO concentration were0.34,0.60and0.85mg·L-1) on N2O emission during partial nitritation ofhigh-ammonium wastewater was identified. The total amount of N2O emitted decreasedwith DO concentration increment. At an average DO concentration of0.34,0.60and0.85mg·L-1, N2O emission amount of44.2,21.0and6.6mg was observed, accountingfor2.35%,1.12%and0.35%of the influent ammonium nitrogen, respectively.（4）Under different operating conditions, the N2O emission rate decreased after aninitial increase in the early aeration time.With the extension of aeration time, the N2Oemission rate was almost constant at pH7.5but increased gradually at pH8.0and8.5,while showing an overall increased trend under different DO concentrations.（5）At the early time of the aeration stage, NH2OH oxidation was the main way togenerate N2O, and thereafter, AOB denitrification was. At precipitation stage, it was mainly due to the coexistence of NH4+and NO2-, and autotrophic denitrification byAOB was the way.（6）In the autotrophic partial nitritation SBR system, the initial N2O peak wasformed by the stripping of the accumulated N2O during precipitation stage and N2Oproduced by NH2OH oxidation at the early time of aeration, among which the formeraccounted for a considerable proportion, which was the main reason for N2O emission,while the latter accounted for small. But after the initial stage, AOB denitrification wasthe main way to generate N2O. |
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