Start-up Of The Pilot Test Of Partial Nitritation-Anaerobic Ammonia Oxidation Process For The Treatment Of Digestate Swine Wastewater

Digestate swine wastewater after anaerobic fermentation still contains a high concentration of ammonia nitrogen,but the carbon to nitrogen ratio is low.The traditional nitrogen removal process can not meet the treatment requirements of a large number of digestate swine wastewater.Therefore,it is necessary to develop a new type of denitrification process with a small area and strong economy.Anammox technology has advantages of no additional carbon source and no CO₂emission,and it has obvious application prospects in the treatment of high ammonia nitrogen wastewater.However,the current anaerobic ammonia oxidation technology still has problems such as relatively low activity of functional bacteria and long process start-up time,and less start-up test research in different reactors under pilot-scale conditions,which affect the promotion of the process in practical applications.Therefore,under the conditions of the pilot test,the start-up study of part of the nitrosation-anammox process was carried out to explore the changes of nitrogen,microbial diversity and key functions during the start-up and stable operation of the part of the nitrosation process.On this basis,the nitrogen removal performance,start-up regularity and succession of functional flora of the integrated partial nitrosation anammox process for the treatment of digestate swine wastewater were investigated.Concluded as follow:（1）A continuous-flow membrane bioreactor was used to carry out the pilot study of partial nitrosation in digestate swine wastewater in the membrane bioreactor.The results showed that the p H is controlled to be 8.0±2.0 at room temperature（22°C～33°C）.The DO value is 0.2～0.5 mg/L.When the influent NH₄⁺-N concentration is about 400 mg/L,the ammonia oxidation rate in the reactor is about 50%,and the effluent NO₂^--N and NH₄⁺-N concentrations are（197.68±27.51）mg/L and（215.61±33.91）mg/L respectively,and the ratio is stable at 1.1:1,NO₂^--N accumulates stably,and the highest accumulation rate reaches 87.95%,which realize the start-up and stable operation of partial nitrosation processes.The activities of ammonia oxidizing bacteria（Ammonia Oxidizing Bacteria,AOB）and nitrite oxidizing bacteria（Nitrite Oxidizing Bacteria,NOB）in sludge were stabilized at 0.4 g N/（g MLSS·d）and 0.1 g N/（g MLSS·d）respectively.Within a certain range,the increases of Free Ammonia（Free Ammonia,FA）concentration will promote the release of more SCOD in the reactor,at same time,it will also cause the change of EPS and SMP concentration,and then the transmembrane pressure will gradually increase.（2）The start-up of part of the nitrosation process has an impact on the microbial structure and key functional genes in the reactor.In order to better reveal the start-up mechanism of partial nitrosation,the microbial diversity and functional genes in the process were explored,and the results showed:The microbial diversity gradually increased throughout the process.After successful startup,Proteobacteria is the dominant bacteria in the reactor;The main type of NOB at the genus level,has not increased significantly,while the relative abundance of Nitrolancea gradually decreased during the whole operation,the relative abundance of Nitrosomonas in the AOB showed a significant upward trend during the start-up phase.The ratio of AOB/NOB increased,which promoted the accumulation of NO₂^--N.The concentration of functional genes（amo A,hao）in the ammonia oxidation process increases,and the concentration of the functional gene nxr A in the nitrification process remains basically unchanged,which explained the reason that nitrite nitrogen accumulated a lot and nitrate nitrogen changed little.NAR,T,FA and NO₂^--N_eff/NH₄⁺-N_eff are the main factors affecting the distribution of microbial communities.Higher FA concentration and temperature promote the accumulation of nitrite.T and NO₂^--N_eff/NH₄⁺-N_effare positively correlated with the amo A gene,which promotes the increase of amo A concentration.（3）On the basis of the partial nitrosation process,carry out the integrated partial nitrosation anaerobic ammonia oxidation process start-up research.The results showed that during the start-up process,the total nitrogen removal rate gradually increased,up to 47.17%,and the anammox reaction gradually occurred,but the temperature has a significant impact on the anammox reaction.The activity of Anammox bacteria and AOB gradually increased,and the NOB activity does not increase significantly.After the water temperature decreases,the NOB activity rises due to the influence of the water temperature,which enhanced the competitive advantage of Anammox.The relative abundance of Planctomycetota which Anammox belongs to has increased.The main genus of Anammox in the reactor are Candidatus＿Brocadia and Candidatus＿Kuenenia.Nitrosomonas was the main bacteria of AOB,which showed an upward trend in the whole start-up stage.While Nitrospira showed a downward trend as the reaction progressed,Nitrolancea remained basically unchanged,and NOB was inhibited in the reactor.