Construction Of Membrane Aerated-algal Bacterial Consortium System And Study On Pollutant Removal Efficiency

High energy consumption is still one of the reasons for the high costs of wastewater treatment plants,by using traditional aerobic biological process.Studies have shown that microalge can produce oxygen during photosynthesis.The application of bacteria-algae symbiosis（ABS）in sewage treatment has the advantage of low energy-consumption and high COD and nutrients removal efficiency.Therefore,it has led to widespread study on ABS system utilized in polluted water treatment.However,the extensive aeration with bubbles during wastewater treatment,not only causes energy waste due to poor gas transfer efficiency,but also causes the stripping of CO₂,which inhibits the growth of algae and destorys the structure of ABS.The MABR process based on membrane aeration has the characteristics of"bubbless aeration",which not only has high gas mass transfer efficiency,but also provides a stable environment for the growth of biofilms.Therefore,the construction of the membrane aeration-bacterial algal symbiosis coupling system,and the long-term operation efficiency of the coupling system to treat simulated domestic wastewater were investigated.The main results are as follows:（1）A membrane aerated-activated sludge biofilm reactor（MA-BR）and a membrane aerated-bacterial algal biofilm reactor（MA-ABR）were set up.The biomass accumulation,pollutants removal efficiency and microbial community structure under same operating conditions were studied.The results show that the biomass and biofilm thickness of MA-ABR are 1.2～1.6 times that of MA-BR.The removal rates of COD,TN and PO₄^3--P were 93.2%,80.5%,and 98%,respectively,which were 5%,60%,and 40%higher than that of MA-BR,respectively.SEM and microbial community analysis showed that the bacteria-algae biofilms were rich in bacterial species and formed in a stable structure.MA-ABR showed higher biological activity and pollutant removal efficiency,indicating that the coupling system was successfully constructed.（2）Then the long-term operation efficiency of MA-ABR exposed to natural or artificial light under different aeration rate was investigated.The average COD removal rate of the two MA-ABRs reached more than 85%during the stable operation period.The removal rate of ammonia by natural-light MA-ABR is higher than that of artificial-light MA-ABR,when the aeration rate is 2.5 min/L with 24h,0 min/L in the day but 2.5 min/L in the night,and 2.0 min/L with 24h,the average removal rates of ammonia are 88%,70%and90%,respectively,which is about 10%,7%,and 15%higher than the artificial lighting system,respectively.The TN removal rate of the natural-light MA-ABR in the three stages is about 46%,58%,and 75%,respectively.The removal efficiency of TN in the first two stages is lower than that of the artificial-light MA-ABR,and the third stage is 8%higher than that of the artificial-light MA-ABR.（3）Microbial community analysis indicated that the abundance of bacteria involved in the denitrification process in the natural light MA-ABR was much lower than that in the artificial light system,resulting in lower TN removal rates in the first and second stages than the artificial light system.In the third stage,the increased light intensity promoted the growth of microalgae in the natural-light MA-ABR,thus the N removal in the natural light system mainly depended on the microalgal assimilation.The photosynthetic and N assimilatied ability in artificial-light MA-ABR were relatively stable when exposed to stable and low-level radiation.Denitratisoma is enriched in the artificial-light MA-ABR,as a result,the removal of TN mainly relies on the denitrification process.In conclusion,the coupled membrane aerated-bacterial algal symbiotic system is well constructed and has a certain ability of simultaneous COD and nitrogen removal,which provides a certain technical referencefor applying this process to wastewater treatment in areas with long-time and sufficient sunlight radiation.