Screening And Performance Study Of Denitrifying Bacteria For Low-Temperature Sewage Treatment

In northern China,the winter climate is cold,and the sewage biological treatment system is often unstable due to low temperature impact,which greatly reduces the nitrogen removal efficiency and makes it difficult for the effluent to reach the standard.Adding high-activity cold-adapted microorganisms into the sewage biological treatment system to improve the activity and biomass of functional bacteria at low temperature is an effective means to improve the biological nitrogen removal effect of low temperature sewage.In recent years,heterotrophic nitrification-aerobic denitrification bacteria,which have the advantages of strong environmental adaptability,rapid growth and metabolism,simultaneous removal of COD and NH₄⁺-N,and nitrification and denitrification in the same space,have attracted wide attention.Based on this,this paper screened and studied cold-adapted microorganisms with heterotrophic nitrification-aerobic denitrification function,in order to provide strain resources and research basis for strengthening biological treatment of low temperature sewage in winter.The main results are as follows:At 10℃,eight strains of cold-adapted denitrification microorganisms were obtained from the activated sludge of sewage treatment plant in winter through enrichment,separation,purification and primary screening.Through 16S r DNA sequence determination and analysis,the strains Z1,Z2,Z3,H2 and H3 belonged to Acinetobacter,and Z4,H1 and G5 belonged to Pseudomonas.Through secondary screening,strains Z1 and Z4 with high NH₄⁺-N removal rate were selected among Acinetobacter and Pseudomonas,respectively,and named as Acinetobacter sp.Z1 and Pseudomonas sp.Z4.Nitrogen balance experiments showed that the nitrogen transformation pathway of strains Z1 and Z4 at low temperature was mainly assimilation,and they could also remove nitrogen through heterotrophic nitrification-aerobic denitrification.Through exploring the influencing factors（COD/N,carbon source,p H,P/N,rotating speed of shaking table）,it was found that strain Z1 had good growth and nitrogen and phosphorus removal effects under the conditions that the COD/N≥20,the carbon source was sodium acetate,the p H was neutral or weakly alkaline,the P/N was 0.2,and the shaking speed≥100 r·min^-1.In addition,strain Z1 had good performance of removing nitrogen and phosphorus when NH₄⁺-N or NO₃^--N was the sole nitrogen source,and NH₄⁺-N and NO₃^--N were the mixed nitrogen sources.When NH₄⁺-N was the sole nitrogen source,the removal rates of NH₄⁺-N and PO₄^3--P for 24 h were 96%and 97.9%,respectively.The phosphorus transformation pathway of strain Z1 was preliminarily studied under different oxygen changing conditions.It was found that strain Z1 could remove phosphorus under aerobic conditions,but did not release phosphorus under anaerobic conditions.After 7 cycles of continuous subculture,strain Z1 had little influence on its growth and removal of carbon,nitrogen and phosphorus,and had good subculture stability.Through exploring the influencing factors（COD/N,carbon source,p H）,it was found that strain Z4 grew well and had good nitrogen and phosphorus removal effects under the conditions that the COD/N was 25,the carbon source was sodium citrate or sodium lactate,and the p H was neutral or weakly alkaline.In addition,strain Z4 had good performance of removing nitrogen and phosphorus when NH₄⁺-N or NO₃^--N was the sole nitrogen source,and NH₄⁺-N and NO₃^--N were the mixed nitrogen sources.When NH₄⁺-N was the sole nitrogen source,the removal rates of NH₄⁺-N and PO₄^3--P for 36 h were 100%and 98.2%respectively.The compound bacteria of strains Z1 and Z4 were constructed,and the growth,nitrogen and phosphorus removal of the compound bacteria at different compound ratios were investigated.It was found that the growth and metabolism rates of the compound bacteria Z1and Z4 at 1:1,2:1 and 3:1 were faster than those of the single bacteria,and the optimal compound ratio was Z1:Z4=2:1.The compound bacteria constructed in the optimal compound ratio were added to the actual wastewater,and it was found that the compound bacteria could remove NH₄⁺-N,PO₄^3--P and COD in the actual wastewater,and it had a good application prospect in the biological treatment of sewage in winter.