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Study On Enhancing Nitrogen Removal Efficiency Of Municipal Wastewater By Partial Denitrification-Anammox

Posted on:2024-02-12Degree:MasterType:Thesis
Country:ChinaCandidate:Y L LiFull Text:PDF
GTID:2531307160953309Subject:Civil Engineering and Water Conservancy (Professional Degree)
Abstract/Summary:PDF Full Text Request
With the development of wastewater treatment technology,biological nitrification-denitrification process has been widely used in wastewater treatment plants,but the high energy consumption by aeration,the need of external carbon source to achieve efficient denitrification,and the large sludge production,still exists which is not conducive to the sustainable development of wastewater treatment.In recent years,the anammox technology has drew widely attention,because it has shown significant advantages in energy saving and environmental protection in wastewater treatment.However,anammox process has not been popularly applied in mainstream municipal wastewater treatment,and the main bottlenecks are the difficulty of stable acquisition of NO2--N substrate and the difficulty of effective enrichment of anammox bacteria.To address the above problems,this project firstly explored the feasibility of in situ enrichment of anammox bacteria in a multi-stage A/O-MBBR system.Secondly,since the partial denitrification as a new way to obtain NO2--N stably,the start-up conditions of municipal wastewater PD system were optimized,and the rapid start-up and stable operation of the system were achieved.Finally,based on the preliminary experiments,we proposed a method to enhance urban wastewater denitrification by establishing PD/A system,investigated the start-up and long-term operation performance of PD/A system,explored the changes of microbial community structure in the system,and further analyzed the advantages of PD/A to enhance urban wastewater denitrification efficiency.The main research results are as follows:(1)The feasibility of in situ enrichment of anammox bacteria in a multi-stage A/O-MBBR system was investigated.In phaseⅠ(day 1-175)of the multi-stage A/O-MBBR pilot system,the influent COD and TN concentrations were 207.3±45.4 mg/L and38.6±5.7 mg N/L,respectively,with an average C/N ratio of 5.4±1.2.At this time,the system effluent COD and TN concentrations were 37.5±10.0 mg/L and 12.5±3.3 mg N/L,respectively,and the average TN removal rate was 67.2±8.4%.In phaseⅡ(day 176-259),the average influent C/N ratio decreased to 3.5±0.8,while the average effluent TN concentration of the system was only 7.8±2.4 mg N/L,with a high TN removal rate of81.8±4.8%.According to the analysis of COD and nitrogen concentrations along the system,anammox reaction was observed in the system,enhancing the nitrogen removal performance.Microbial abundance and activity analysis further indicated that anammox bacteria were enriched in the system during the long-term operation,and anammox bacteria abundance was increased to 3.84%with activity of 2.10 mg N/L/h.The enrichment of anammox bacteria could be attributed to the low organic loading rate under step-feeding condition,effective biomass retention and unique microenvironment of biofilm.(2)The optimized start-up conditions of the municipal wastewater PD system were investigated to achieve a rapid start-up of the system.The optimized COD/NO3--N and HRT were 2.5 and 45 min,respectively,and a stable and efficient municipal wastewater PD system was successfully started up after 39 days of operation under the above conditions.The average effluent NO2--N concentration and NTR were 6.2±0.6 mg N/L and 85.2±2.6%,respectively,at an average influent NO3--N concentration of 12.7±1.5mg/L.The high-throughput sequencing results showed that the dominant genus in the system was Proteiniclasticum(26.1%),and Citrobacter,a functional genus associated with short-course denitrification,was enriched in the system,and its relative abundance increased from 0.2%at the beginning of the run to 1.8%,which may be closely related to the initiation and stable maintenance of short-course denitrification in the system.(3)The method of enhancing nitrogen removal from municipal wastewater by establishing a PD/A system was investigated.First,the recovery performance of the PD reactor at low temperature was investigated.The results showed that the reactor recovered good PD action with an average NTR of 81%after 27 days of operation,and the PD/A system for municipal wastewater was successfully constructed on the basis of the PD reactor,and its denitrification performance was investigated.The system influent NH4+-N and NO3--N concentrations were 10.0±0.5 mg N/L and 11.7±0.7 mg N/L,respectively.During the stable operation,the average effluent NO3--N of the system was almost 0,while the NTR was as high as 95.5±2.2%,and the average effluent TN concentration was8.2±0.4 mg N/L,which achieved efficient nitrogen removal.The nitrogen removal path analysis showed that anammox played a major role in nitrogen removal,and its average TN removal contribution was as high as 85.8%during the stable operation.High-throughput sequencing results revealed that the relative abundance of Candidatus_Brocadia in the PD reactor increased from 0.02%(day 10)to 5.71%(day150).The abundance of Candidatus_Brocadia in the anammox reactor without sludge inoculation also increased to 1.5%,achieving in situ enrichment.In addition,microbial activity analysis showed that both short-range denitrification activity and anammox activity increased significantly during system operation.The NO2--N accumulation rate in the PD reactor increased from 1.9 mg N/L/h at the beginning of operation to 21.5 mg N/L/h,and NH4+-N degradation rate increased gradually from 0.5 mg N/L/h at the beginning of start-up to 5.7 mg N/L/h.The NH4+-N degradation rate of the Anammox reactor increased from 0 to 1.6 mg N/L/h.PD/A system combined with traditional nitrification-denitrification process can enhance the efficiency of nitrogen removal of municipal wastewater denitrification and provide new ideas for energy saving and consumption reduction in wastewater treatment.
Keywords/Search Tags:Enhancing nitrogen removal, Microbial community structure, Partial denitrification, Anammox, Municipal wastewater
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