Screening,identification And Influencing Factors Of Phosphate Accumulating Organisms In EBPR Process

Phosphorus is one of the causes of eutrophication of water bodies.Controlling the low-concentration discharge of phosphorus in the effluent of sewage biological treatment processes has always attracted attention.Compared with the traditional biological phosphorus removal process,the enhanced biological phosphorus removal process（EBPR）is more convenient and effective in operation.Due to its advantages of stability and low cost,it has been widely used in sewage treatment plant upgrading and renovation projects in recent years.EBPR mainly relies on the excessive absorption of phosphorus by microbial phosphorus accumulating bacteria to achieve the purpose of phosphorus removal.Therefore,it is of great significance to study the growth characteristics and metabolic mechanism of phosphorus accumulating bacteria to strengthen and improve the EBPR process.In this project,the activated sludge taken from a sewage plant in Changchun City is acclimated in the SBR reactor,and then the reactor is operated by the EBPR process to enrich the bacteria.At the same time,the water quality indicators COD,NH₄⁺-N,TN and TP,as well as parameters p H,ORP,DO were measured to explore the removal rule of pollutants and the relationship with each parameter.The activated sludge in the reactor was taken,the appearance of the sludge was observed by scanning electron microscope（SEM）,and the microbial flora structure was identified and analyzed by metagenomic high-throughput sequencing,so as to find the dominant flora in the system.Furthermore,PAM medium was used to isolate and screen the phosphorus accumulating bacteria in the reactor.In this experiment,the four-zone streak method was used to isolate and purify phosphorus accumulating bacteria,the blue-white spot screening method was used for primary screening,PHB staining and metachromatic particle staining were used for secondary screening,and morphological observation,physiological and biochemical tests and 16S r DNA were used for bacterial species identification,the growth characteristics and phosphorus uptake performance of the strains were studied.The specific research results are as follows:In the acclimation stage and the enrichment stage,various water quality indicators have a good removal effect during the operation of the reactor,and the effluent pollutant concentration has reached the"urban sewage treatment plant pollutant discharge standard（GB18918-2002）"Class A discharge According to the standard,the COD removal rate is above 90%,NH₄⁺-N removal rate is stable at more than 99%,and the TP removal rate is maintained at more than 92%.From the high-throughput sequencing results,it can be seen that the dominant flora of both are Proteobacteria and Candidatus saccharibacteria at the phylum level.Since both Proteobacteria and Candidatus saccharibacteria contain a large number of denitrifying bacteria,A good denitrification reaction can be carried out in the reactor.Compared with the domestication stage,the richness of the microbial community in the enrichment stage was basically unchanged,but the diversity of the flora was reduced.At this time,most of the obligate bacteria such as phosphorus accumulating bacteria were in the reactor.After screening and identification of phosphorus accumulating bacteria,three strains with different morphology were isolated in the SBR reactor,XC-1,XC-2,XC-3.Strong phosphorus uptake ability.Through 16S r DNA identification,the three strains were all Agrobacterium,identified as Agrobacterium tumefaciens.The growth characteristics of each strain showed that the growth of each strain tended to be stable at the 24th hour of culture,and the phosphorus uptake process ended at 18h.Among them,the growth rate of XC-1 was relatively fast,and the phosphorus removal ability was relatively high.The comprehensive ability of each strain The order is XC-1>XC-3>XC-2.The study on the influencing factors of phosphorus removal by phosphorus accumulating bacteria showed that the three phosphorus accumulating bacteria had strong phosphorus uptake when the p H value was 7～8,and the phosphorus removal effect reached the best when the temperature was 30°C,and the control inoculum amount was 6%.Conducive to phosphorus removal,the most suitable liquid volume is controlled between 50～75ml.