Study On Phosphorus Removal By Enhancement And The Effects On Membrane Fouling In A/O Membrane Bioreactor

The thesis was supported by State Key Lab Foundation of Western Architecture&Technology （Cultivating Base）–Study on Sewage Treatment and Recycling Technologyin Scattered Neighborhoods （No.08KF08）. Membrane bioreactor（MBR） technology iswidely used in scattered sewage treatment for its own advantages, In MBR operationprocess, owing to longer sludge age, its TP removal efficiency cannot meet the emissionlimits. Therefore, in this thesis the MBR with the chemical phosphorus was studied, andits effects on the TP removal efficiency and membrane fouling were analyzed.The MBR technology was combined with traditional anoxic/aerobic （A/O） processto establish A/O-MBR wastewater treatment system. In the experiment, the campussewage was treated by A/O-MBR.Firstly, the removal efficiency of pollutant in this process were investigated,especially the removal efficiency of TP. The results indicated that this system had betterpollutant removal efficiencies of COD_Cr, NH₃-N, TN and turbidity, expect for TP. TheTP concentration of effluent can not meet the1B（1.0mg/L） emission limits.In order to study the effects on phosphorus removal by chemical methods inA/O-MBR, batch experiments were carried out to study the effects on the removalefficiency of TP and turbidity by adding three types of coagulants respectively,including Al₂（SO₄）₃、FeCl₃and polymeric aluminium choloride（PAC）, through the rearway and synergy way. The results showed that by the rear dosing way, FeCl₃was thebest coagulant and the dosing quantity was33mg/L; while by the synergy way, the bestcoagulant was Al₂（SO₄）₃, with the dosing quantity of67mg/L.Secondly, the best coagulant by the batch experiments was applied to the long-termoperation experiments of A/O-MBR to prove the effect of adding coagulants on the TPremoval efficiency. Meanwhile, the effects of collaborative dosing coagulant on theother pollutant removal efficiency were investigated. The results indicated that theremoval rate of TP was82%when dosing FeCl₃by the rear way and88%when doingAl₂（SO₄）₃by the synergy way. The effluent TP concentration of the two way both metthe1A（0.5mg/L） emission limits. Compared with A/O-MBR, collaborative dosing Al₂（SO₄）₃method improved the removal rate of TP and turbidity, and had no significanteffect on the efficiencies of COD_Cr, NH₃-N and TN.In addition, the impacts of collaborative dosing Al₂（SO₄）₃on operation stabilityand the properties of activated sludge mixed liquor were studied, and have a furtherexplanation from the aspects of the fouling formation mechanism and the relationshipbetween each property and the mombrane fouling. The time of TMP reaching limitvalue in the system of A/O-MBR and Al₂（SO₄）₃-A/O-MBR were investigated, it wasknown that the stable operation cycle was longer after dosing Al₂（SO₄）₃, and foulingfouling layers on membrane had bigger porosity and lower filtering resistance, based onthe SEM. At the same time, the impactes of dosing Al₂（SO₄）₃on four properties ofmixed liquor were analyzed, The results showed that the sludge particle size increased,while EPS, SMP, and mixture viscosity decreased, which can relieve membrane fouling.Then the correlation between each property and the mombrane fouling were analyed.The results indicated that the SMP was the most significant factor of membrane fouling,and membrane fouling coefficient were lower after dosing Al₂（SO₄）₃. Based on thefitting of standard plugging model, the rate of increase TMP of dosing Al₂（SO₄）₃waslower than A/O-MBR.