Preparation Of PVDF/PVC/PMMA Blend Membrane And Its Application To Wastewater Treatment

Wastewater treatment by the technology of membrane has been regarded as a hotspot by many researchers currently, but the shortcoming of its lower output, easier to be polluted, and higher price seriously obstructes its development. Based on the design concept that the membrane structure and performance could be improved by adjusting the compatibility between polymer blends, a new blend hollow fiber membrane which had big water flux, high intension and lower price was prepared. At the same time, this new kind membrane was employed to fabricate membrane module of membrane bioreactor to treat simulating wastewater. Through combining the process of activated sludge wastewater treatment and the process of filtration in membrane module, a mathematic model of membrane bioreactor system based on ASM3 was established. Moreover, the model was validated by experiment. In terms of originality and theoretical value, the following aspects are among the most telling:1. Originally, the compatibility of PVDF, PVC and PMMA was predicted and analyzed by means of calculation of?Hm, FTIR, Differential Scanning Calorimetry method, and Solution Viscosity method respectively. It was demonstrated that PVC/PMMA possesses complete compatibility, and PVDF/PVC/PMMA possesses partial compatibility which is depended on and influenced by blend ratio, concentration of polymers in solution, temperature, etc. The compatibility in PVDF-rich phase is greater than in PVC/PMMA-rich phase.2. In order to investigate the effects of different factors on the properties of hollow-fiber membrane, the orthogonal table was designed with five factors and four levels. Through analysis of the conclusions of orthogonalizing experiment systematically, it confirmed that the membrane with PVDF/PVC/PMMA mass ratio 7: 1.2: 1.8, polymer concentration 17%, with 6% content of tween-80 as addition possessed the best-integrated property. Further more, the hollow fiber membrane prepared according to above optimum casting solution was proved to be the best.3. Based on large amounts of studies of the influence of the technologcial conditions on the structures and properties of hollow fiber membrane, the results showed that it was the optimum conditions of casting solution that 40%DMAC used as coagulation bath and temperature of coagulation bath was 35?and inner solution concentration was 40% and dry length was 30mm.Under this conditions, the best performance of membrane was produced with the intention as 45.6KN/cm², tensility as 1.63, water flux as 537L/m²·h, and retention ratio as 87%.4. In chemical expansion of pores, by studying the effects of the solution of NaClO on the property of prepared membranes, it was showed that the water fluxes of all treated membranes with pH as 11 and duration as 60h was 50% greater than the initial ones. At the same time, the retention for BSA and mechanical properties were not changed greatly by this treating process. It suggested that the solution of NaClO with pH as 11 can upgrade the performance of membrane effectively.In the causticity bearing test, it was showed that the membrane had great ability in bearing acid and alkali, and can run in the solution of broad pH range.5. In this work, the mathematic model of continues aerobic MBR model was developed which was divided into bioreactor unit and membrane filtration unit. Furthermore, the biochemical process within the bioreactor was used the form of the activated sludge model ASM3. The model supposed that the activated sludge was running in a normal state. In stead of the second precipitation tank, the membrane module functioned as equipment to separate the water and sludge. The model of membrane filtration process was divided into two fractions, i.e. simple component filtration model and membrane flux filtration model. Through 13 components of ASM3 and flux, three different mechanism models were connected and then form the whole MBR model.6. Membrane pollution has great influence on the decrease of membrane flux. In order to explain the reasons of membrane pollution, a flux model was achieved, which was based on the Darcy equation. In order to enhance the forecast correctness and reduce the restrict conditions, the model associated many related parameter such as MLSS, trans-membrane pressure difference, viscidity and other operation process parameters, Moreover, many parameters related to membrane materials were taken into accounted.7. The model comprising the biological and filtration parts was implemented using a Matlab/Simulink programming package and a flow-sheet simulation interface was developed, which was mainly composed by influent distribute and effluent combination module, mix and reaction module, simple membrane filtration module and membrane flux module. This MBR model could be used to simulate varies kinds of membrane bioreactor systems since it took following into consideration: the process of mass transfer in the membrane bioreactor, the process of biological degradation, the process of filtration and also the effects of operation conditions such as volume and quality of influent wastewater, characters of activated sludge and the temperature. The kinetics parameters and function parameters are also confirmed and the model was verified by experiments. The results of the model verification showed that this model could simulate the process in a membrane bioreactor well and predict the treatment results in the bioreactor and in the effluent with a satisfying precision. Therefore, this model can help to analyze, design and run membrane bioreactors8. Through continuous operation, it was founded that with the increase of water flux and sludge concentration, shortening of HRT and extending of SRT would prick up the membrane pollution. From test of resistance distributing of membrane pollution, it was showed that the main reason of membrane flux decreasing was the biology pollution caused by biological degradation. By measuring the flux of membrane and cleaning membrane module by different methods, it was founded that wash out by water and H₂O₂ was effective in control MBR module pollution.