Study On The Municipal Wastewater Treatment With PF-MBR And Membrane Fouling Controlling

Membrane bioreactor(MBR) is a new efficient technology of sewage treatment, which combines biological treatment with membrane separation process. It is the hot spot of reuse process of reclaimed water. MBR has many advantages, such as good effluent quality, strong resistant capability to impact loading, little excessive sluge, small area occupied. Wastewater discharge standard is more and more strict. At the same time water resources shortage is becoming increasingly conspicuous. Under the circumstances, MBR will be one of the important technologies for sewage treatment and recycling. But MBR faces some problems such as membrane fouling, high energy consumption and high running expense. In existing research the removal rates of pollutants increase usually by optimizing running parameters, adding PAC filling, using combined process, etc. Some of the measures can also lighten membrane fouling. But systematic researches on raising the removal rates of pollutants and controlling membrane fouling are rare by adding cheap powdered ferrite and modifying membrane using low temperature plasma technology.Under the background, PF-MBR (MBR with powdered ferrite added) is designed and made. And experimental system is established. The effect laws of main running parameters on the removal efficiency of pollutants and membrane fouling are studied when treating urban domestic wastewater with the self-made PF-MBR. The effect of adding powdered ferrite on the removal efficiency of pollutants and membrane fouling is researched. The kinetics of treating municipal wastewater with PF-MBR is discussed. On this basis, polyvinylidene fluoride (PVDF) membrane is modified with low temperature plasma. And the effect of the modification on the removal rates of pollutants and anti-fouling property of membrane is researched.The results show that DO, HRT, MLSS, influent pH and temperature influence the removal of COD, NH₄⁺-N, TN and TP in sewage when treating domestic wastewater with the self-made PF-MBR. When magnetic powdered ferrite is added in MBR, the removal rates of COD and NH₄⁺-N increase obviously. But the removal of TN and TP is not obviously affected by the addition of magnetic powdered ferrite. Adding magnetic powdered ferrite can lessen membrane fouling to a certain extent. On the thirtieth day of stable operation, the transmembrane pressure of MBRB without powdered ferrite added is 22.9kPa. The transmembrane pressure of MBRA with powdered ferrite added is 17.2kPa. The membrane filtration resistance of MBRA is less than that of MBRB by 1.65×10¹²m^-1, in which the resistance from membrane pore plugging and adsorption of MBRA is markedly less than that of MBRB. Although critical fluxes of both MBRA and MBRB are 17～20IV(m²Â·h) under the given conditions, the growth rate of transmembrane pressure in MBRB is obviously more than in MBRA when running flux is 20L/(m²Â·J). It is 0.06kPa/min. The importance sequence of the dosage of powdered ferrite (A), the specific saturation magnetization of powdered ferrite (B), membrane flux(C) and aeration intensity(D) is arrived at through orthogonal experiments, which influence the removal rates of COD and NH₄⁺-N, the increasing rate of membrane filtration resistance. The optimum operation parameters are A₃B₃C₁D₂ when PF-MBR operates steadily.Mechanism analysis shows that the increasingof the removal rates of pollutants is due to the combined action of microbial degradation, the adsorption of powdered ferrite and magnetic field energy after adding powdered ferrite to MBR. Besides, the addition of powdered ferrite changes the structure and property of activated sludge floc and make the cake layer resistance and the resistance from membrane pore plugging and adsorption decrease. So membrane fouling is alleviated.Kinetic analysis shows that the average value of kinetic constants of substrate degradation is 0.0023 L/(mg·d) when PF-MBR treating municipal wastewater. It is more than the kinetic constant of substrate degradation in MBR without powdered ferrite. When PF-MBR treats municipal wastewater, the kinetic equation of sludgegrowth is Yield coefficient and decay coefficientare 0.2502 and 0.0371 respectively.The modification of membrane with low temperature plasma has no significant effect on the removal rates of pollutants. But it can improve the anti-fouling property of PVDF hollow fiber membrane. During stable operation, the increasing rate of transmembrane pressure of modified membrane is less than that of unmodified membrane markedly. The total resistance, intrinsic resistance of membrane, cake layer resistance and resistance from membrane pore plugging and adsorption of modified membrane are less than those of unmodified membrane. Under the same given conditions, the critical flux of modified membrane is 20～23L/(m²Â·h), which is more than it of unmodified membrane. Mechanism analysis indicates that a lot of hydrophilic polar groups such as hydroxyl, carbonyl, etc can be introduced onto the surface of membrane by modification with low temperature plasma. Meanwhile the modification can erode the surface of membrane and increase surface roughness. So the hydrophilicity and anti-fouling property of membrane are improved.PVDF membrane is modified by low temperature plasma in research, which can improve the anti-fouling property of membrane. The modification method has the advantages of high efficiency, low cost and less pollution, etc. The magnetic powdered ferrite used in the experiment may be gained from the wastewater containing heavy metals under certain conditions. The addition of powdered ferrite in MBR can increase the removal efficiency of pollutants and lighten membrane fouling. Furthermore, it materializes comprehensive utilization of wastes and incarnate the technology policy of recycling. So the research is important and has the value of application and extension.