Study On The Treatment And Reuse Of Domestic Sewage By Combined A/O-MBR-NF Process

The problem of water shortages has become increasingly prominent in recentyears, restricting the development of social economy. If we treat and reuse domesticsewage which is discharged a lot, not only reducing the pollution of the environment,but also easing the problem of water resources shortage, which has goodenvironmental benefit, economic benefit and social benefit. The membrane bioreactor(MBR) has been widely applied in wastewater treatment because of small footprintand excellent effluent quality generally conforming to wastewater reuse standards.However, the membrane fouling problem has not been effectively resolved, limitingits development. The effluent of membrane bioreactor still contains some harmfultrace contaminants, such as pesticides, detergents, trihalomethans precursors and othertoxic substances, needing to further improve the security of MBR effluent withnanofiltration process. Therefore, depth treatment of domestic wastewater by theanoxic/aerobic-membrane bioreactor (A/O-MBR) combined with nanofiltrationprocess was studied in this paper.Through single factor experiments, the paper has respectively explored theinfluence of hydraulic retention time (HRT) and aeration way to the A/O-MBReffluent quality. The experiment results show that the optimal hydraulic retention timeof simulated domestic sewage was5hours with the A/O-MBR system running at theconditions of the temperature of20℃to25℃, mixed liquor suspended solids ofabout6mg/L, dissolved oxygen of about2mg/L, membrane component extractiontime dividing stop time of8min dividing2min, gas water ratio of40:1. Though theinfluence of two kinds of aeration mode of constant flow aeration (gas-water ratio of40:1) and variable intensity aeration (gas-water ratio of20:1when the system working,gas-water ratio of40:1when the system stopping) to wastewater treatment effect canbe seen that the treatment effect in two ways was similar. However, variable aeration intensity is more energy-efficient, so the choice of variable intensity aeration way ismore appropriate. Running A/O-MBR system with the conditions of hydraulicretention time of5hours and variable intensity aeration mode, the removal rate ofCODCr, ammonia nitrogen mainly remained above90%and95%, effluent quality wasgood.The influence of operating pressure on the performance of three kinds ofnanofiltration membranes has been studied, the experimental results showed that thecomprehensive performance of NF270is the best and the best operating pressure is0.7MPa.On the basis of the above experiments, combined the A/O-MBR system withnanofiltration membrane system, in the whole test process, the average effluentconcentrations of CODCr, ammonia nitrogen, TN, TP are below5mg/L,0.4mg/L,10mg/L,1.5mg/L respectively, the average removal rates are98%,99%,81%,82.49%respectively.In addition, this paper also has studied the cleaning effect in different fouledmembrane cleaning ways, the experimental results showed that the mixed solution of0.3%sodium hypochlorite and0.1%sodium hydroxide has the best cleaning effect,substantially removing the membrane surface contaminants, the flux recovery rate isas high as93.07%.The effluent quality of A/O-MBR-NF combined system has reached the mostconventional test items of drinking water sanitary standard, which can be used forlaundry, bathing and other non-potable domestic water, improving the safety of thewater, broadening the scope of domestic sewage reuse.