Nitritation Process Control And Anammox Process Performance And Their Microbial Characteristics

Nitritation and Anaerobic ammonium oxidation(Anammox)are core technologies of novel biological nitrogen removal processes with promising application prospects.Aiming at the subsistent problems of nitritation and Anammox,such as high complexity of manipulation,low sustainability,low proliferation rate of Anammox bacteria and relatively long start-up period,the corresponding control strategies of nitritation and Anammox processes were studied in the present research.With the aid of high-throughput sequencing,the succession of microbial community structure and predominant bacteria under different selective pressures(influent and control parameters)and different environmental conditions(reactor type and seeding sludge type)were also investigated to establish an internal connection of "impact factors-functional microbial community structure succession-reactor performance",and to provide theoretic support and practical reference to novel biological nitrogen removal processes.By seeding the municipal aerobic activated sludge taken from the secondary clarifier of Shenyang the South Sewage Treatment Plant into a lab-scale Sequencing Batch Reactor(SBR)R0,nitration process was successfully started up in 84 days as the control strategy of low Dissolved Oxygen(DO)concentration with synergistic effect of chemical inhibitors of potassium chlorate and hydrazine was adopted.The ammonia nitrogen oxidation rate and the nitrite nitrogen accumulation rate were at 86.02%and 83.13%in several.By adding 10mg/L of hydrazine and rapidly increasing the substrate concentration of ammonia nitrogen in influent to 550 ± 10 mg/L,partial nitritation was attained with a NO2--N:NH4+-N molar ratio of 1.07 in the effluent which has met the demand of the influent condition of Anammox process.The results of single-factor experimental analysis taken in a serious of identical 9 L SBRs showed that the optimal pH value and DO concentration for nitritation were at 8.0 and 0.5 mg/L.The optimal dosage of potassium chlorate and hydrazine were 5 mmol/L and 5 mg/L respectively that the average ammonia nitrogen oxidation rates could be achieved to 92.93%and 98.36%,and the corresponding nitrite nitrogen accumulation rates were at 78.89%and 86.08%separately.Hydrazine exhibited a better ability to promote nitrite nitrogen accumulation rate over potassium chlorate.In order to provide more direct and comprehensive insights into the nitritation systems,microbial communities and predominant bacteria were studied.The results of high-throughput sequencing analysis indicated that the microbial community diversity fell along with time.The dominant bacteria at phylum level were Proteobacteria,Chloroflexi and Bacteroidetes.The Ammonia Oxidizing Bacteria(AOB)-Uncultured Nitrosomonadaceae was the primary functional stakeholders of nitritation whose relative abundance was directly related to the ammonium-oxidizing ability of the nitritation system.In reactor RO,the relative abundance of Proteobacteria raised from 36.37%in seeding sludge to 62.34%(SNROK)and 72.33%(SNRON)by adding potassium chlorate and hydrazine respectively,and correspondingly the relative abundance of Nitrosomonadaceae reached at 51.55%and 59.49%at the time in several.The relative abundance of Nitrite Oxidizing Bacteria(NOB)-nitrospira deceased from 5.64%to 0.01%.Anaerolineae SBR1031 and WS6 bacteria arose in relative abundance and became dominant under the condition of low oxygen.In the parallel test,by adding the optimal dosage of potassium chlorate of 5 mmol/L,the relative abundance of Nitrosomonadaceae reached at 29.51%.In comparison,by adding 5mg/L hydrazine,the relative abundance of Nitrosomonadaceae was elevated to 60.20%.Hydrazine has been proved to be more conductive to improving the abundance of AOB in bacterial community over potassium chlorate.Based on the above results,the operation of nitritation process under low DO condition combined with the usage of appropriate inhibitors could efficiently inhibit the proliferation of NOB and promote the abundance of AOB which brought out higher ammonia oxidizing rate and nitrite accumulation rate,and ensured the stablity of the nitritation process.For purpose of research on the effects of seeding sludge types and reactor types on nitrogen removal performance of Anammox process,with artificial sewage as treatment object,three reactors AR1.AR2 and AR3 were set up according to pre-set design of scheme by inoculating with two kinds of seeding sludge.i.e.one from a Single-Stage Nitrogen removal using Anammox and Partial Nitritation(SNAP)process and the other one from an Up-flow Anaerobic Sludge Bed/Blanket(UASB)Anammox process,using two types of reactor,i.e.two 1.2 L UASB and one 6 L continuous stirred tank reactor(CSTR).All three reactors were successfully started up in 73,53 and 50 days respectively.The maximum nitrogen loading rate of the reactors AR1,AR2 and AR3 were achieved to 11.51 kg-N/(m3·d)?16.43 kg-N/(m3.d)and 27.44 kg-N/(m3·d)with the corresponding nitrogen removal rate of 9.53 kg-N/(m ·d)?14.09 kg-N/(m3 ·d)and 24.00 kg-N/(m3·d)in 290,276 and 289 days severally.The results indicated that the granular Anammox sludge and CSTR reactor with the advantage of high substrate transfer property were considered to be better suited for Anammox process.Affected by seeding sludge type and reactor type,the succession of microbial community structure?the numbers and kinds of predominant species were significantly varied in all three Anammox reactors.The 16S rRNA results showed:the dominant bacteria at phylum level were Proteobacteria and Firmicutes in ARl;Planctomycetes,Chloroflexi and Chlorobi raised in abundance and became dominant along with time;Candidatus Brocadia was the primary functional stakeholders of Anammox reaction with a relative abundance of 10.71%at stationary phase;Rhodocyclaceae Dok59,OD1 and Clostridium were also the dominant species.In reactor AR2?the dominant bacteria at phylum level were Proteobacteria,Planctomycetes,Chloroflexi and Chlorobi?Bacteroidetes and Acidobacteria became dominant at stationary phase;the relative abundance of premier Anammox bacteria Brocadiaceae fell from 31.24%to 7.00%;C omamonadaceae,Rhodocyclaceae Dok59,Thermomonas,Anaerolineae and Ignavibacteriaceae were coexisted as the dominant species in AR2.Same as in AR2,the dominant bacteria at phylum level were Proteobacteria,Planctomycetes,Chloroflexi,Chlorobi and Bacteroidetes in AR3;Anammox bacteria Brocadiaceae became the most abundant species with a relative abundance of 30.86%at stationary phase;Comamonadaceae,Rhodocyclaceae Dok59,Anaerolineae and Ignavibacteriaceae were the dominant species in AR3.It was found that all three reactors had high abundance of heterotrophs related to the function of denitrification and phosphate metabolism etc..AR3 had the greatest abundance of Anammox bacteria that may prove the conclusion in the previous section.Based on the findings above,reactors types had greater effect than of seeding sludge types on the abundance of Anammox bacteria.The source of the seeding sludge determined the numbers and kinds of the Anammmox bacteria.The denitrogenation performance of Anammox processes is the result of common function of the two factors above.Metabolic pathway analysis illustrated that,Candidatus Kuenenia stuttgartiensis encountered gene defect in synthesizing a series of metabolic cofactors for growth,such as TetraHydroFolate(THF),Coenzyme A(CoA),Coenzyme Q(CoQ)and biotin,implying that Kuenenia stuttgartiensis is auxotrophic and living in a manner of mutualism.It might be the reason why Anammox bacteria cannot be obtained their pure culture.It has very important significance to establish a more stable Anammox system and conduct further study on Anammox metagenomics.The results of this study are benefical to the improvement of the control strategies of nitritation and Anammox processes,and have guiding significance for the application of novel biological nitrogen removal technologies.