Optimization And Performance Evaluation Of The Oxygen-based Membrane Biofilm Reactor For Source-diverted Greywater Treatment

The shortage of water resources has become one of the biggest challenges.Water pollution caused by industrial production and human activities has posed a threat to the ecological environment and social sustainable development.The separation,treatment and reuse of greywater are an effective way to deal with the shortage of water resources and comprehensive water management.Lots of physical,chemical and biological methods were applied for greywater treatment.The in-situ treatment of grey water with high efficiency and low cost has become one of the problems to be solved during wastewater treatment.In this study,polyvinylidene fluoride（PVDF）hollow fiber membrane was used to construct an oxygen-based membrane biofilm reactor（O₂-MBfR）.The effects of different operating conditions（system pH,COD/TN ratio and lumen air pressure）on greywater treatment performance were studied;The characteristics of biofilm formation and microbial composition analyzed by infrared spectroscopy,three-dimensional fluorescence,laser confocal and high-throughput sequencing;Response surface methodology（RSM）was used to simulate and optimize the operation conditions of O₂-MBfR;Under the optimized conditions,batch-operated O₂-MBfR was used to treat greywater,and the removal kinetics of linear alkylbenzene sulfonates（LAS）and nitrogen were explored to reveal its removal mechanism.The main research contents and results are shown as following:（1）In the influent pH affecting experiment,results showed that neutral condition achieved the highest removal of both organics and,while both acidic and alkaline conditions inhibit the removal of pollutants.Compared with the inoculated sludge,silicon-contained organics and polysaccharides were produced in the system with influent pH of 5,but which almost remained stable with influent pH values of 7 and 9.The system pH significantly affects the biofilm microbial community structure in the reactor.In the system with influent pH of 5,the relative abundances ofα-Proteobacteria andβ-Proteobacteria were lower than that of corresponding microorganisms in pH 7 and 9,which may also affect the removal of carbon and nitrogen in O₂-MBfR.（2）In the COD/TN ratio influential experiment,results showed that COD/TN ratio significantly affects the performance of O₂-MBfR treating greywater.High ammonia at low COD/TN ratio（15 g COD/g TN）condition led to the competitive utilization of oxygen between aerobic ammonia oxidation process and aerobic organics biodegradation process.However,the insufficient nitrogen source at high COD/TN ratio（30 g COD/g TN）also affects the normal growth and metabolism of microorganisms,the above conditions will reduce the removal of organics and nitrogen in the system.COD/TN ratio at 25 g COD/g TN achieved the highest removal of both organics and nitrogen.Biofilm structure and compositions containing proteins,polysaccharides and lipids almost remained stable when changing COD/TN ratio.When decreasing COD/TN ratio,the relative abundances ofα-Proteobacteria andγ-Proteobacteria were the highest,the relative abundances of nitrifiers,nitrosomonas and nitrifying spirillum gradually increased,and the removal flux of ammonia and total nitrogen also increased.（3）In the lumen air pressure（LAP）affecting experiment,results showed that lack of oxygen supply at LAP of 0 and 0.5 psi inhibited organics biodegradation and nitrification.When LAP was higher than 1.0 psi,the removal rates of both organics and nitrogen were significantly improved and basically remained stable.At the same time,increasing of LAP is conducive to the accumulation of LAS-degrading bacteria and ammonia oxidizing bacteria,which improved the simultaneous removal of organics and nitrogen in the system.（4）Response surface methodology was applied to optimize the operation of O₂-MBfR with the factors of pH,COD/TN ratio and LAP.Statistically,the regression model of COD removal rate and TN removal flux were significant（P<0.05）.Factors that affecting COD and TN removal followed the order of COD/TN ratio>system pH>LAP.The interactions between COD/TN ratio and pH,COD/TN ratio and LAP have significant impact on both COD and TN removal.The optimized operation conditions of O₂-MBfR in greywater treatment are COD/TN ratio of 22 g COD/g TN,influent pH of 7.0 and LAP 0.82 psi,which achieved the removal rates of COD,LAS and TN at 95.1%,99.6%and 83.5%respectively.（5）In the batch-operated O₂-MBfR under optimized conditions,results showed that ammoniation,nitrification,denitrification and organic mineralization can be realized simultaneously in the three-dimensional dynamic biofilm.Nitrogen and organics can be effectively removed in the O₂-MBfR.In the 24-hour batch test,more than 94%of LAS can be biodegraded,4%of LAS was adsorbed by EPS,and the residual soluble LAS was less than 1%,while membrane adsorption contributed to less than 2%removal of LAS.EPS adsorption led to the gradually decreased LAS in aqueous phase,biodegradation enabled the continuous removal of LAS in the O₂-MBfR.The dynamics LAS in the system include rapid adsorption of LAS by EPS,desorption of LAS_EPS,release of LAS_EPS,and the biodegradation of LAS_EPS under aerobic conditions.