The Preliminary Study On Low C/N Wastewater Treatment And Membrane Fouling Of A/O/A-MBR Process

In recent years,the domestic urban domestic sewage generally has a low C/N situation,and the traditional sewage treatment process has an unsatisfactory effect on the denitrification and phosphorus removal of low C/N sewage.The continuous flow anaerobic with endogenous denitrification is good.The oxygen-anoxic(A/O/A)process provides a new idea for the treatment of low-C/N sewage.However,the traditional A/O/A process also has problems such as low endogenous denitrification intensity and slow rate,and low system nitrogen load.This paper chooses to combine the Membrane Bioreactor(MBR)with the A/O/A process,couple the two in situ in the form of anoxic MBR,and build an A/O/A-MBR coupling process.The ordinary A/O/A process using the secondary settling tank was used as a control to investigate the effect of the introduction of MBR on the improvement of the wastewater treatment efficiency of the A/O/A process.The two sets of reactors will be started up and some operating parameters will be optimized,the wastewater treatment efficiency will be comprehensively evaluated,the membrane fouling characteristics during the operation of the A/O/A-MBR process will be studied,feasible schemes for membrane fouling mitigation will be proposeed.The coupling process has lower operating costs and good effluent quality in similar MBR processes,and has certain research value and application potential in the field of low-C/N sewage advanced treatment processes with MBR as the upgrade direction.The start-up culture of the two reactors showed that the removal rates of COD,ammonia nitrogen,total nitrogen and total phosphorus of the target sewage by the A/O/A-MBR reactor reached 94.31%,98.82%,88.40% and 98.61%,respectively;The removal rates of COD,ammonia nitrogen,total nitrogen and total phosphorus in the control group A/O/A reactor reached 93.27%,96.48%,79.79% and 89.52%,respectively,and the total nitrogen load of the control group was significantly lower than the experimental group coupling process,indicating The introduction of MBR has greatly increased the pollutant load of the A/O/A system.The operation cycle of the two reactors was analyzed.The utilization efficiency of the internal carbon source in the endogenous denitrification stage of A/O/A was significantly lower than that of the A/O/A-MBR coupling process,and it was confirmed that the two reactors the way to make orders is nitrification-denitrification,and no nitrosation is found.From the perspectives of optimizing nitrogen and phosphorus removal performance and reducing operating costs,the two operating parameters of the aerobic zone dissolved oxygen and sludge reflux ratio of the two reactors are optimized,and the final optimization result is: A/O/A-MBR The best aerobic zone dissolved oxygen concentration of the reactor is 2-3 mg/L,and the best reflux ratio is 200%;the best aerobic zone dissolved oxygen concentration of the A/O/A reactor is 2-3 mg/L,the best The sludge return ratio is 100%.The membrane fouling characteristics during the operation period of the reactor were explored.During the operation,the membrane water flux was reduced to slow down the membrane fouling rate.On-line backwashing effectively alleviated the formation of irreversible membrane pore resistance and prolonged the service life of membrane modules.Analyzed the change trend of TMP during startup and the composition of membrane fouling resistance under two operating conditions with or without online backwashing.It was confirmed that membrane fouling resistance was mainly caused by the filter cake layer,and it was confirmed that the main membrane contaminants were dissolved during process operation.Changes and composition of sexual microbial product(SMP)and microbial extracellular polymer(EPS).200 mg/L polyaluminum chloride(PAC)has been dosed into the MBR to alleviate membrane fouling.The results shows that the dosing of PAC has a certain adsorption effect on SMP,and the average particle size of activated sludge is increased from 122.1 μm to161.1 μm.The degree of looseness of the filter cake layer is increased,the membrane fouling speed is slowed down,and the membrane fouling cycle is extended to 19-20 d.This paper shows that the introduction of MBR can greatly improve the effluent quality and pollutant load of the A/O/A process,and proves that the addition of flocculant has a good effect on the alleviation of membrane pollution.