Isolation Of Partial Denitrifying Bacteria And The Study On Nitrite Accumulation Technology

As a new biological nitrogen removal process,anammox has the advantages of no carbon source input and low aeration energy consumption,which has great application potential in wastewater nitrogen removal.Nitrite and ammonia are common substrates of anammox reaction.How to provide nitrite has always been a difficulty in the research and application of the process.In this study,a variety of samples with nitrite were screened,and finally a strain with high efficiency accumulation of nitrite was obtained,and the technological conditions of nitrite accumulation were studied.The main results are as follows:（1）552 strains were obtained from the anoxic pool bottom sludge of sewage treatment plant,the underground soil of the experimental field of Huazhong Agricultural University and the silt at the bottom of the pool near South Lake.Denitrification separation medium was designed,and 19 strains to be selected were screened from the medium through the concentration changes of NO₃^--N and NO₂^--N.Finally,a bacillus strain was selected as the target strain and named as PDB19.Through whole genome sequencing,it was found that PDB19 was a Bacillus thuringiensis and it lacked nir K or nir S gene encoding nitrite reductase.（2）PDB19 is a compositive anaerobic bacterium.Under the condition of sufficient oxygen,oxygen is used as electron acceptor for growth and metabolism;under the condition of insufficient oxygen,NO₃^-is used as electron acceptor and reduced to NO₂^-.The growth and metabolism of PDB19 is inseparable from organic nitrogen,and the usual nitrogen sources such as soybean meal,peptone,gelatin and yeast extract can be used.The optimal carbon source for nitrate denitrification accumulation in strain PDB19 was glucose,and the denitrification accumulation of NO₂^-could also be carried out when there was only organic nitrogen.In the medium with gelatin as the only organic substance,the accumulation rate could reach 2.19 mg/（L*h）,and the denitrification rate is the highest when yeast leaching powder is used as the nutrient,which can reach 9.72 mg/（L*h）.When the concentration ratio of COD to NO₃^--N in the medium based on yeast immersion powder reaches 3,NO₃^-can be completely converted into NO₂^-.（3）PDB19 can effectively accumulate NO₂^--N at p H 5.0 to 10.0,and the rate is 2.91 to4.8 mg/（L*h）.Temperature has a great influence on PDB19.At 37℃,the accumulation rate of NO₂^--N can reach 8.69 mg/（L*h）.When the temperature is lower than 25℃,the NO₂^--N accumulation rate of PDB19 decreases to 1.01 mg/（L*h）.（4）The PDB19 was immobilized with sodium alginate,the partial denitrification reactor was started in SBR.The initial nitrite translation rate（NTR）reached 77.65%by using simulated sewage containing yeast leaching powder and KNO₃ components.After 48 days of operation,The final NTR can be stabilized at about 50%,and NO₃^--N in effluent is almost0.（5）Finally,taking the actual aquaculture sewage as the object of treatment,a new process idea was adopted.The aquaculture sewage was mixed with raw water after nitrification,and intermittent batch water inlet and exit were used.After denitrification by PDB19,the final effluent NH₄⁺-N is 60.06 mg/L,NO₂^--N is 58.32 mg/L,COD is 105.81 mg/L.The concentration ratio of NH₄⁺-N to NO₂^--N was 1.03,which reached the ideal influent index of anammox,and verified the application potential of PDB19.In this study,A strain of Bacillus thuringiensis PDB19 capable of efficient denitrification accumulation of NO₂^-was screened,which could utilize most common carbon sources and had strong tolerance to temperature and p H,which had great application value in anammox process.