Study On Phosphate Enrichment Under Low Influent Phosphorus Concentration By Biofilm Method

With the depletion of phosphate resources,phosphate enrichment and recovery from urban sewage has become a means of phosphorus resource recovery.In the previous study,the biofilm sequential batch reactor(BSBR)was used to remove/enrich phosphate simultaneously.Compared with other biofilm methods,the high enrichment can be achieved in our research group under the condition that the influent phosphorus concentration is 10mg/L and the anaerobic COD is only 200 mg/L.In order to promote the promotion and application of biofilm simultaneous phosphate removal and enrichment process in existing urban wastewater treatment plants,this study reduced the influent phosphorus concentration to 2.5mg/L,explored the enrichment performance of BSBR process on wastewater with low phosphorus concentration,optimized the process operation parameters,and analyzed the effect of low influent phosphorus concentration on microbial population and mechanism.A bioenrichment method for low concentration phosphate in municipal wastewater was proposed in this paper.In this study,biofilm sequencing batch reactor(BSBR)was used to remove and enrich phosphate in wastewater.Under the conditions of 2.5 mg/L phosphate concentration in influent and 100 mg/L COD concentration in anaerobic stage,the Phosphorus removal rate of BSBR reactor reached more than 80%and the effluent phosphorus concentration was less than 0.5mg/L.The maximum concentration of phosphorus in the recovery solution was 84.5 mg/L(enrichment ratio was 33.8 times),and the average phosphorus recovery calculated by total phosphorus(TP)was 72.80%.The carbon source consumption(COD consumption per gram of phosphorus recovered)is 37.3±2.6 mg-P/Mg-COD,which proves that BSBR process can achieve phosphorus recovery under the condition of low influent PHOSPHORUS concentration.Scanning electron microscopy(SEM-EDS)results showed that the maximum phosphorus storage capacity of the biofilm was 55 mg-P/g-MLSS,and the phosphorus storage capacity of the biofilm was positively correlated with the concentration of phosphorus recovery solution.In addition,31~P NMR results showed that phosphorus mainly existed in the form of orthophosphate in Extracellular Polymeric Substances(EPS)and intracellular,accounting for 85.28%and 68.90%at aerobic end,93.18%and86.56%at anaerobic end,respectively.Phosphate storage is one of the driving forces of high enrichment of phosphate in BSBR process under low carbon source consumption.The results of high-throughput sequencing showed that when the influent phosphorus concentration decreased from 10 mg/L to 2.5 mg/L,the dominant bacteria in the system did not change significantly,mainly Proteobacteria,Bacteroidota and Chloroflexi.At the genus level,Ca.competibacter abundance decreased from 54.4%to5.9%after domestication.However,the proportion of Flavobacterium increased from8.37%to 32.98%.After the stable operation of the reactor,the dominant bacteria in the biofilm were mainly phosphorous accumulating bacteria Flavobacterium,which has not been widely reported.Temperature has a great influence on BSBR reactor.By optimizing DO,HRT,aerobic and anaerobic influent volume ratio and other parameters,high concentration of phosphorus recovery liquid can be obtained.When the dissolved oxygen is 8mg/L,the hydraulic retention time is 6h,and V aerobic:V anaerobicis 1:0.6,the phosphate removal and enrichment effect of BSBR reactor is the best.Among them,reducing the volume of anaerobic influent can quickly obtain high concentration of phosphorus recovery liquid,but has no significant effect on phosphorus recovery efficiency and carbon source consumption.