Study On Intensive Culture Of Microalgae And Sewage Treatment Efficiency In Membrane Photo Bioreactor

Given the situation of large-scale water pollution and water shortage caused by the accelerating urbanization and industrialization process and the increasing discharge of industrial,municipal,and agricultural wastewater,the ability to recycle biomass energy while purifying sewage by using microalgae,combined with the advantages of efficient interception of membrane bioreactor,In this study,Membrane photo bioreactor(MPBR)was used for gradient treatment and resource recovery of municipal wastewater.Continuous experiments were carried out on domestic sewage and secondary effluent using MPBR,and the microalgae growth,pollutant removal,and membrane pollution were systematically studied under different environmental parameters,and the feasibility of MPBR industrial application and large-scale production was evaluated.The results of the study on the effect of iron addition on the wastewater treatment of two parallel MPBR under different Hydraulic retention time(HRT)conditions show that:The addition of iron improved the ability of high-density intensive culture of MPBR microalgae,strengthened the absorption of pollutants in sewage by microalgae,and alleviated the pressure of membrane pollution.In the continuous experiment,when HRT was 12 h,the optimal average microalgae biomass production rate in MPBR was 266.04±36.89 mgL-1d-1,which was 248%higher than that in the control group without iron addition.Iron has slightly different effects on the removal of different nutrients by MPBR under different HRT conditions,which is embodied as follows:For COD,the removal efficiency of COD reaches more than 90%in all stages of operation,and the removal rate of COD can be improved by removing algae and shortening HRT.When HRT was 12 h,the maximum removal rates of ammonia nitrogen and total nitrogen were 21.27 mgL-1d-1 and 39.92 mgL-1d-1,respectively,which was increased by 36.0%and 45.4%compared with the control group without iron.The experimental group and the control group were measured by transmembrane differential pressure and soluble algal product(SAP)content in the suspension.It was found that iron supplementation could reduce SAP content in the suspension,and thus reduce membrane pollution pressure and pollution degree.The effects of different HRT on the denitrification effect,membrane fouling,and system stability of the secondary effluent treated by MPBR showed that the optimal HRT of the secondary effluent treated by MPBR was 8 h.Shortening HRT can increase membrane flux,make SAP in suspension migrate to membrane faster,and aggravate membrane fouling.However,reducing HRT can improve the stability of the system,reduce SAP content and competitive bacteria in suspension,improve the growth rate of Chlorella,and thus improve the removal rate of pollutants.When THE HRT of the MPBR reactor was 24 h,the biomass yield of algae was 5.74～6.03 mgL-1d-1,and the MPBR reactor was shortened to 12 h and 8 h.The yield of microalgae in the reactor increased to 12.66-13.25 mgL-1d-1 and 19.69-20.57 mgL-ld-1,respectively.During the whole running time,MPBR has a better removal effect on nutrients,and the effluent ammonia nitrogen and COD concentrations are lower.In addition,the longer the HRT time,the better the nutrient removal effect,longer retention time is conducive to nutrient removal.The results showed that when HRT was 8 h,the removal rates of total nitrogen,ammonia nitrogen,and COD were 19.7 mgL-1d-1,23.8 mgL-1d-1,and 105.4 mgL-1d-1,respectively.By studying the dynamic changes of microbial community and bacterial structure in the system,it can be seen that Gammaproteobacteria is the dominant species in all treatments,followed by Bacteroidia.In terms of functional prediction,lower HRT reduced the nitrogen limit of chlorella proteinosa growth by phasing out nitrogen-related functional bacteria.In conclusion,MPBR treatment of domestic sewage and secondary effluent has a good effect.By adjusting HRT and adding iron to optimize MPBR operation,the sewage treatment effect and system stability can be improved,and the membrane pollution situation can be improved,thus further improving the feasibility of MPBR industrial application and large-scale production.