Performance And Mechenism Of SBR-PBR-Modified Membrane For Nitrogen And Phosphorus Removal Of Sewage

The traditional domestic sewage treatment process is not thorough enough for the removal of nitrogen and phosphorus due to its own limitations,and its effluent often fails to meet the first-class A discharge standard.In recent years,as the concept of using microalgae to produce biofuel has been proposed,many researchers believe that using microalgae to treat domestic sewage and recycling microalgae for resource utilization are very promising.However,to separate microalgae efficiently and economically is the bottleneck that restricts the promotion of this technology.According to the above problem,this study put forward sequencing batch type activated sludge reactor(SBR)and photobioreactor(PBR)series operation to treat domestic sewage.Based on the layer-by-layer self-assembly technology,a high electronegative catalytic polycarbonate(PC)membrane was developed,used for separating microalgae in the effluent of SBR-PBR series system.Therefore,it can be realized that the nutrient can be deeply removed from the domestic sewage,and microalgae can be efficiently separated from the water.The research results are as follows:First,the SBR-PBR series system was constructed under laboratory conditions.The operation parameters of SBR and PBR were optimized respectively to find the most suitable process parameters for the tandem operation of SBR-PBR system,and the stability of the continuous operation of the SBR-PBR series system was investigated.The experiment results showed that the Chlorella.v was the best algae speciel for treating domestic sewage in PBR.When the temperature was set as 30?,and the illumination was set as 4000 lux,the PBR could reach the best effect on the treatment of domestic sewage.When SBR was run in mode B(anaerobic program for 120 min,aerobic program for 170 min,anoxic program for 120 min,aerobic program for 10 min),the linkage effect with PBR was the optimal.When the hydraulic retention time of PBR was set as 2 d,the stability of microalgae biomass can be maintained,and the effluent water quality is the best.Under the above optimal conditions,the absolute values and removal rates of COD,TP,NH₃-N and TN in the effluent of the SBR-PBR tandem system are 6-8.5 mg/L(removal rate:95.6%),0.10-0.15 mg/L(removal rate:94.3%),1.4-3.0 mg/L(removal rate:92.0%)and 6.0-8.5 mg/L(removal rate:84.4%),respectively,all of which can meet the discharge standard of Grade A,and the effluent water quality can be ensured to be stable for a long time.The microalgae in SBR-PBR effluent must be separated to achieve the real nutrient removal.In this study,the membrane filtration technology,which has high separation efficiency and low energy consumption,was choosed to separate microalgae,but the membrane fouling problem in this process was very serious.In order to solve this problem,the dopamine-induced layer-by-layer self-assembly technology was used to modify the PC membanre.The modified PC film has high electronegativeness and hydrophilicity at the same time,its surface Zeta potential is-66.1m V,pure water contact angle is 26°.The modified membrane(PSS-PDA/PEI@PC₅)showed good anti-fouling performance in the separation of microalgae through electrostatic repulsion effect and hydration membrane effect.The flux of modified PC membrane decreased more slowly,and the average flux was up to 133.1 L/(m²?h).The flux recovery rate was 95%,and the rejection rate of microalgal cells was close to 100%.In addition,the modified PC membrane has good salt resistance and acid resistance,and can maintain the stability of its surface chemical properties in a long time operation.In order to further improve the operational flux of membrane,on the basis of high electronegative PC membanre,zero-valent iron nanoparticles were immobilized on the membrane surface.The resultant membanre(2-PAA-PDA/PEI@PC₃)not only had high electronegativeness(Zeta potential of-54.8 m V)and hydrophilic(water contact angle of22°),but also had surface catalytic effect due to the zero-valent iron nanoparticles on the surface which can activated persulfate.The generated sulfate radicals can oxidize foulants on the membrane surface,and the formation of Fe³⁺can also have the effect of micro flocculation.Under the synergism of the above dual effects,the filter cake layer on the membrane surface becomes looser.The average flux can reach 427.1 L/(m²?h),the flux recovery rate is about 92%,and the rejection rate of microalgal cells was close to 100%.Moreover,the zero-valent iron nanoparticles on the membanre surface are renewable,which can still show robust anti-pollution performance after 5 filtration/catalyst regeneration cycles.Compared with in situ activation of persulfate preoxidation by Fe²⁺,the breakage rate of algal cells caused by interfacial catalytic membanre is smaller,which is only 7.1%,the process operation is thus safer.Finally,combined with the above research results,the SBR-PBR-membrane unit combined process was constructed,the anti-fouling performance of the membrane,its influence on the overall effluent water quality and its operation stability were investigated after the membrane unit was added into the SBR-PBR series system,and the operation mechanism and feasibility of the process were analyzed.At last,the main parameters of domestic sewage treatment process with SBR-PBR-membrane unit as the core are given.The results showed that the highly electronegative catalytic PC membrane exhibited good pollution resistance(stable flux 281.6 L/(m²?h),flux recovery rate 87.3%)in the separation of PBR effluent microalgae,and did not significantly affect the effluent water quality.Treating actual domestic sewage,the SBR-PBR-membrane system had a good and stable effluent quality.With continuous operation under the best condition,the concentration of COD,TP,TN and NH₃-N in the effluent are 5.1?8.1 mg/L,0.12?0.18mg/L,6.6?10.0 mg/L and 1.3?3.5 mg/L,respectively,all of which meet the discharge requirements of Grade A.The above research shows that the SBR-PBR-membrane system proposed in this project is reasonable,and it has excellent nutrient removal effect in the treatment of domestic sewage,and solves the problem of unable to efficiently and economically separate microalgae.It provides a new insight into acheving deeply nutrient removal of domestic sewage and alleviating the eutrophication of aquatic environment,which has important social,economic and environmental benefits.