Study On The Functional Mechanism Of Phosphorus Uptake And Release By Biofilm In Simultaneous Phosphate Removal/Enrichment Process

With the increasing exhaustion of phosphate resources,the removal and enrichment of phosphorus（P）from municipal sewage have become effective means of resource utilization.Currently,while the EBPR process is acknowledged as the main side-flow P recovery process,such problems like low P recovery efficiency,excessive sludge yield,additional requirement of side-flow separation process and large land occupation limited the application of EBPR.of,The mainstream biofilm P recovery process with higher P recovery efficiency has gradually attracted the attention of related studies in recent years.However,the current studies on biofilm P recovery process still have the problem of high external carbon source.Based on this problem,in the previous researches of our research group,the biofilm sequencing batch reactor（BSBR）was adopted to simultaneously remove and enrich P from artificial sewage.Compared with other researches of biofilm P removal/enrichment process,a higher P concentration of enrichment solution was achieved by adding approximately 200mg/L of chemical oxygen demand（COD）in the anaerobic phase with less carbon source consumed.Besides,it is found that the P storage capacity of biofilm is positively correlated with the concentration of P enrichment solution,verifying that extracellular polymeric substance（EPS）plays an important role in P removal by biofilm.However,the metabolic pathway of P removal by biofilm was not studied and discussed in previous researches.In addition,the performance of phosphorus removal/enrichment by BSBR was found to vary significantly with different temperatures seasonally in previous studies.Based on these phenomena,this study aims to explore the functional mechanism of P uptake-release by biofilm and to further explore the influence of temperature on the functional mechanism by biofilm under the optimal operating conditions found in the previous researches.In this study,the biofilm of BSBR was taken as the research object.Under the condition of relatively stable phosphorus removal/enrichment performance of BSBR,the transformation rule of polymers in biofilm and the results of biofilm metabolic stoichiometry parameters were obtained by detecting the change of the content of polymers in biofilm under aerobic/anaerobic phase.Meanwhile,the content and form of P in EPS/cells in the aerobic and anaerobic stage were detected to investigate the distribution and transformation rule of different forms of P in the biofilm.Combined with these rules and parameters,the functional mechanism of P uptake and release by biofilm and the influence of temperature on this functional mechanism were revealed.Besides,the microbial population structure in the biofilm was detected to identify the dominant bacteria and the dominant phosphorus accumulating organisms（PAOs）in the biofilm.The results are shown as follows:（1）The maximum concentration of P in the enrichment solution obtained by BSBR was 233.73 mg/L under the condition of 200±25 COD mg/L in the anaerobic phase.The average P concentration of the aerobic effluent was less than 0.5 mg/L.The P recovery efficiency was 62.33%,and the carbon consumption was low in the recovery stage.（2）Under the circumstance of lower external carbon source,EPS played an important role in the P uptake and release of biofilm.P in the biofilm was mainly contained in EPS.The results of ³¹P nuclear magnetic resonance showed that the form of P in EPS was mainly ortho-P,and the form of intracellular P was mainly ortho-P and short-chain poly-P.Biofilm uptakes and releases P through the adsorption/desorption of ortho-P by EPS and the cellular synthesis/decomposition of short-chain poly-Pto,evetually realizing the removal and enrichment of P in BSBR.（3）The results of biofilm metabolic stoichiometry parameters showed that the value of P_upt/PHA_degrad was as high as 1.89 P-mmol/C-mmol,and the amount of PHA synthesis was low due to the small amount of anaerobic external carbon sources.There was no sufficient PHA degradation to provide energy for the accumulation of long-chain poly-P in the aerobic stage,and the amount of short-chain poly-P accumulated in the cell increased.EPS could absorb and store a large amount of ortho-P without the energy provided by the PHA degradation.In the anaerobic phase,the value of P_rel/HAc_upt was as high as 1.47 P-mmol/C-mmol and the value of Gly_degrad/HAc_upt was as low as 0.01 C-mmol/C-mmol.The short-chain poly-P was decomposed and ortho-P was released in the cell.Due to the lower addition of carbon source,less PHA was synthesized.The reduction equivalent required for the PHA synthesis was not mainly provided by glycogen through the EMP or ED metabolic pathway.Meanwhile,ortho-P was released from the cell to EPS,and the concentration of ortho-P in EPS increased and a large amount of ortho-P was released directly under the action of concentration gradient.The value of P_rel/HAc_upt was as high as 1.47 P- mmol/C-mmol.（4）Temperature showed significant influence on the performance of BSBR and the functional mechanism of P uptake and release by biofilm.With the temperature decreasing from 28.9℃to 14.7℃,the P removal and the enrichment of BSBR were improved,and the value of P_upt/PHA_degrad,P_rel/HAc_upt increased gradually with the decrease in temperature.The ultilization efficiency of PHA and external carbon source used to uptake and release P increased.Meanwhile, the function of EPS and cell in the P uptake and release of biofilm was significantly enhanced along withthe short-chain poly-P increased gradually in the cell and the functional mechanism of P uptake and release by biofilm enhanced gradually.（5）The results of high-throughput sequencing showed that Candidatus＿Competibacter was the most dominant bacterium in the biofilm,and it was conducive to the formation of EPS with stronger adhesivity attached to the biofilm,likely enhancing the role of EPS in P uptake and release of biofilm.With the decrease in temperature,the microbial population structure in the biofilm changed significantly.The relative abundance of PAOs increased to 2.04%,improving the phosphorus absorption and release ability of the biofilm.