Screening And Application Of Efficient Denitrification And Dephosphorization Strains From Dairy Farm Sewage

The wastewater from dairy farms contains high concentration of ammonia nitrogen,total phosphorus,BOD₅and COD,etc.The direct discharge will cause eutrophication of water body and cause serious damage to the ecological environment.At present,how to solve the problem of standard discharge of sewage from dairy farms is an urgent demand of actual production.The cost of traditional sewage treatment is high and it is difficult for the breeding terminal to accept.The purpose of this study was to isolate and screen microbial strains that can effectively remove nitrogen and phosphorus and put them into the sewage treatment system of dairy farms,so as to further reduce the water quality index of final water and reduce the cost of comprehensive sewage treatment.The results are as follows:1.Six strains which can remove nitrogen were screened from the laboratory preserved strains:B168,B169,B170,B174,B177 and B178,and the ammonia nitrogen removal rate was 22.4%-27.7%.The three strains SP-3,SN-4 and AGL-1 screened from the farms had higher nitrogen removal rates,which were 62.5%,41.4%and 43%,respectively.Nine strains with better phosphorus removal efficiency were determined as B9,B11,B13,B172,B177,B178,LB-5,LB-7 and LB-9.Among them,three strains with higher phosphorus removal rates were B9(83.2%),B177(67.7%)and LB-5(64.6%).B177 and B178 have both nitrogen and phosphorus removal abilities.Based on the above results,SP-3,SN-4,AGL-1,B9,B177,LB5 and B178 were selected as candidate strains of the mixed microbial agents to remove total nitrogen and total phosphorus efficiently from cattle farms sewage system.2.The seven screened high-efficiency denitrification and total phosphorus removal strains were cultured to obtain complex microbial agents,which were put into the biochemical dispose pool system of sewage in dairy farms to estimate the effect of the strains on the practical application of dairy cattle farms.The consistence of BOD₅,COD,ammonia nitrogen,total phosphorus and other ingredient in the sewage treatment system and the final effluent were sampled and detected at diverse time periods.meanwhile,high-thro?ghput sequencing was used to research the abundance changes of mixed microbial agents and the changes of microbial community structure in sewage treatment pool system.The sewage samples collected from the sewage treatment pool system of dairy cattle farms were used as the research objects.The V₃V₄sequence of 16S r DNA in the samples was determined by high throughput,and the microbial community structure was analyzed.The results showed that the microbial community in the sewage system was mainly dominated by Comamonadaceae,Ruminococcaceae,Pseudomonadaceae and Porphyromonadceae.From the classification level of phylum,the mixed bacteria did not lead to the significant change of microbial community in the wastewater treatment tank,and the main dominant strains stably existed in the wastewater treatment tank were Bacteroidetes,Firmicutes and Protebacteria,Chloroflexi and Actinobacteria,etc.3.The strains for denitrification and phosphorus removal in this study were effective in practical applications.The addition of mixed bacterial agents can significantly improve the water quality of the sewage treatment system,especially the COD and total nitrogen.After the mixed bacteria were added,the COD of the fifth biochemical tank decreased from 19,475 mg/L to 249 mg/L,the ammonia nitrogen concentration decreased from 550mg/L to 60 mg/L,the total nitrogen concentration decreased from 1,025 mg/L to 480 mg/L,and the total phosphorus concentration decreased from 183 mg/L to 65 mg/L.Before the addition of microbial agents,the COD,NH₄⁺-N,TN and TP of the final effluent were 650mg/L,27 mg/L,275 mg/Land 8.7 mg/L,respectively.After the addition of mixed microbial agents,the COD,NH₄⁺-N,TN and TP of the final effluent decreased to 90 mg/L,17mg/L,135 mg/L and 5 mg/L,respectively.The final effluent could meet the standard discharge after the determination of various water quality indexes.4.The key genes of nitrogen metabolism pathway were nar G,nap A,nir S,nir K,nor B,and nos Z.In this study,16 nir gene fragments,8 nor gene fragments and 6 nos gene fragments were cloned from several nitrogen removal strains,which laid the foundation for further study of the molecular mechanism of nitrogen removal.This research on dairy farms wastewater treatment system under different working conditions of microbial composition and structure carried on the thorough analysis,screening to a batch of high efficient nitrogen and phosphorus strains,and further analyzes the different strains of denitrification and phosphorus removal performance of the class and investigates strains in the application of dairy wastewater treatment effect,in order to cows farm wastewater biological removal of ammonia nitrogen,total phosphorus scheme to provide theoretical basis and technical support.