The Study Of Nitritation-Denitrification SBR Real Time Control Based On DO And ORP

Nitritation-denitrification is a new biological nitrogen removal process.Compared with traditional nitrogen removal process,it has the advantages of saving energy,saving carbon source and reducing hydraulic retention time,especially suitable for treating low C/N or high ammonia wastewater.However,the operation conditions of the process are more harsh,especially difficult to operate steadily under the condition of wastewater with low ammonia.In this study,SBR reactor was used to treat simulated ammonia wastewater.Start-up,real-time control methods for nitritation-denitrification were systematically studied,the microbial community was also discussed.After 29 days of anaerobic sludge acclimation,the ammonia oxidation rate increased from 4.69 mg/?L·h?to 27.24 mg/?L·h?.By controlling pH was 8,dissolved oxygen?DO?was 0.1-0.4 mg/L,temperature was 29.5±0.5?,sludge retention time?SRT?was 14 days,on the 5^th day,nitrite accumulation rate?NAR?was more than 50%and stable nitritation-denitrification was obtained on the 35^th day,the removal rate of N-NH₄⁺and NAR were both stable and maintained above 97%.By analyzing ammonia degradation process,it was concluded that the ammonia oxidation can be divided into two stages,in which the zero-order reaction kinetics equation is fitted in the initial stage and the first-order reaction kinetics equation is fitted in the final stage.By comprehensive analyzing the whole ammonia oxidation,the degradation process of N-NH₄⁺conformed to the Michaelis-Menten equation.In a complete reaction cycle,the first derivatives of DO and ORP were significantly correlated with the reaction process.At the end of nitritation,the first derivative of DO had a peak;at the end of denitrification,the first derivative of ORP had a peak.In order to make the real-time control more stable,the traditional first derivative algorithm was optimized:the slope of the fitting curve between the data points at a certain time and nine data points before that time was taken as the first derivative at that time,which can reduce the interference signal.Under the real-time control conditions,the influent concentration,residual COD,volume exchange rate and aeration volume had no significant impact on the operation of SBR,and the real-time control performed stable.Only in the volumetric exchange ratio test,excessive matrix concentration had a slight impact on the subsequent operation of SBR.The removal efficiency of N-NH₄⁺was restored to 97%after reducing influent concentration,pH to7.5,washing SBR using tap water.The results of microbial sequencing showed that seed sludge had the largest species diversity,followed by nitrification sludge and nitritation-denitrification sludge was least.It showed that the sludge microorganisms were greatly affected by the influent water quality and reactor operation control.Long-term reactor operation would reduce the diversity and abundance of microorganisms and made the population develop towards to a single function.Chloroflexi,Bacteroidetes,Proteobacteria and Actinobacteria were the dominant bacteria.The abundance of Nitrosomonas increased gradually in nitrification sludge and nitritation-denitrification sludge,but Nitrospira could not be detected in nitritation-denitrification sludge.The community structure of denitrifying bacteria also changed greatly,and Thauera became the dominant genus.All the results indicated that SRT plays an important role in the screening and enrichment of bacteria.Nitritation-denitrification sludge showed significant species differences from seed sludge and nitrification sludge.In terms of major functional microorganisms,there were significant differences between nitrification sludge and nitritation-denitrification sludge samples at a significant level of 0.05 and a confidence interval of 95%.