Impact Of SRT On Phosphorus Removal Performance In EBPR Systems

Enhanced Biological Phosphorus Removal（EBPR）is the most widely used phosphorus removal technology in urban sewage treatment.Although a lot of research has been done on the related microorganisms,biochemical reaction paths,kinetic parameters and process performance in EBPR,the phosphorus removal effect in actual engineering is still difficult to maintain stable,and further research is needed.Sludge retention time（SRT）is one of the key factors affecting the phosphorus removal performance and microbial community structure of the EBPR system,and it is also an important parameter for the design and operation of wastewater treatment processes.Therefore,it is of great significance to study the effect of sludge age on the phosphorus removal performance of the EBPR system.In this paper,the sludge from the A²/O treatment system in Xi’an Fourth Sewage Treatment Plant was used as inoculation sludge,and simulated wastewater was used for continuous cultivation in the SBR reactor.It mainly explored the EBPR system in different sludge ages（SRT）（5 d,10 d,15 d）,analyze the phosphorus removal of PAOs by SRT by measuring the maximum phosphorus uptake and release rate of the sludge,the absorption rate of acetic acid,and the amount of phosphate released per unit of consumption of acetic acid Performance impact.At the same time,fluorescence in situ hybridization（FISH）was used to determine the changes of functional flora in activated sludge under different SRT conditions,and to analyze the fate of phosphorus in the EBPR system under different sludge ages（SRT）（5 d,10 d,15 d）,The main conclusions are as follows:（1）Under the conditions of C/P ratio of 25,HRT of 9.6 h and SRT of 10 d,the reactor was enriched for 116 days.The maximum phosphorus release rate,phosphorus absorption rate,acetic acid absorption rate and the amount of phosphate released by acetic acid per unit were 13.61 mg P·g VSS^-1h^-1,8.46 mg P·g VSS^-1h^-1,35.52 mg HAc·g VSS^-1h^-1and 0.37 P-mol/C-mol of inoculated sludge was increased to 93.04 mg P·g VSS^-1h^-1,67.18mg P·g VSS^-1h^-1,189.94 HAc·g VSS^-1h^-1 and 0.47 P-mol/C-mol.The proportion of PAO and GAO in total bacteria in sludge was 80.62%±2%and 0.51%±2%respectively.The phosphorus content of sludge was 148.21 mg P·g VSS^-1.The reactor runs stably and the phosphorus removal rate is over 95%.（2）The longer the reactor SRT,the smaller the maximum phosphorus release,phosphorus absorption rate,the amount of phosphorus released per unit of acetic acid consumed and the phosphorus content of the sludge,and the greater the absorption rate of acetic acid.When the SRT was 5 d,10 d,and 15 d,the maximum phosphorus release rates corresponding to activated sludge were 124.86,89.84,and 59.42 mg P·g VSS^-1h^-1,respectively,and the maximum phosphorus absorption rates were 57.72,47.02 and25.24 mg P·g VSS^-1h^-1,respectively.,the absorption rate of acetic acid is 198.02,205.13and 252.45 HAc·g VSS^-1h^-1,ΔP/ΔHAc is 0.61,0.42,0.23 P-mol/C-mol;sludge contains The phosphorus content was 189.74,148.21 and 130.65 mg P·g VSS^-1,respectively.When the SRT of the reactor was 10 d and 15 d,the corresponding phosphorus removal rates were 95%and 99%,respectively.When the SRT was 5d,the phosphorus removal ability of the EBPR system decreased rapidly due to the high sludge load.In addition,with the increase of the reactor SRT,the share of PAO in the total bacteria in the activated sludge decreased,while the share of GAO in the total bacteria increased.When SRT 5 d,10 d and 15 d,PAO accounted for 92.2%,80.62%and 69.8%of the total bacteria in the activated sludge,respectively.The phosphorus removal efficiency of the reactor at different stages and the matrix competitiveness of PAO were comprehensively compared.The best phosphorus removal performance of the reactor was when SRT was 10 days.（3）When the sludge age of EBPR system was 5 d,10 d and 15 d,cell-P in the corresponding sludge accounted for 35%,29%and 27%of the removed phosphorus,and poly-P accounted for 65%,71%and 73%of the removed phosphorus.The proportion of cell-P in phosphorus removal decreased with the increase of SRT,while the proportion of poly-P in phosphorus removal increased with the increase of SRT.（4）The settling property of sludge is closely related to SRT.When SRT was 10 d and 15 d,the SV of sludge was 15.5%±3.2%,30.5%±1.6%,and the SVI value of sludge was 63±4%m L/g,105±4.7%,respectively.When SRT was 5 d,the values of SV and SVI increased rapidly,SV exceeded 40%and SVI exceeded 350 m L/g,and non-filamentous sludge bulking occurred.