Study On The Membrane Foulingin Mechanism Of Mixture Solution Of Model Extracellular Polymer Substance (EPS)

In recent years, ultrafiltration and microfiltration technology with its advantagesis widely used in waste water treatment and reuse. However, the membrane fouling is considered to be the major drawback towider application of microfiltration and ultrafiltration.The membrane fouling causing by Extracellar Polymers Substance (EPS) is one of the hot research areasin membrane separation fields. It is, however, lack of research on the membrane fouling mechanism causing by synergistic effectbetweenEPS and synthetic polymers or salts. Inthis study, the certain proportion of mixture solution of alginate (SA), bovine serum albumin(BSA) and humic acid (HA) are used to stimulate EPS and investigate the membrane fouling characteristics andmechanismby adding polyvinyl alcohol (PVA)and different salts (NaCl, CaCl2, AlC13).This paper analyzes the particle size distribution and Zata potential changes of model EPS solution and mixed solution.The decline of flux, membrane resistance distributionand contact angle of membrane was also analysed. The experimental data for the flux decline is examined by Hemia’s laws in order to analyze the membrane fouling mechanisms.Italso studies the different factorscausing membrane fouling under differentmolecular weight cut andoperating pressure. Attenuated total reflectanceFourier transform infrared spectroscopy (ATR-FTIR)and scanning electronic microscope are used to measure and analysis the fouling material of membrane surface.The following conclusions are obtained:(1) With a decrease of the MWCO of UF membranes, theretention rate increased gradually. Microfiltration shows lowerrate of EPS rejection about60%. The conductivity and turbidity of ultrafiltration effluent are lower than that of microfiltration.(2) With the increasing of TMP of ultrafiltration and microfiltration, the initial flux increased for both SA solution and SA+PVA solution. It reaches steady-state for two kinds of model solutions regardless of the difference in TMP. When SA solution contains PVA, it causes quicker permeate flux decline and more severe membrane fouling.When added calcium and alum, the permeate flux became larger, especially at the presence of alum. However, the addition ofNa+had little influence in flux decline and resistances.(3) In the study of membrane resistance distribution, it found that the gel layer resistance was largest when filter the SA and SA+PVA solution byultrafiltration and microfiltration. In the ultrafiltration process, the gel layer resistance is the largest when Na+and Ca2+added into the EPS solutions.But whenEPS solutions containing Al3+, the gel layer resistance became smaller. In the microfiltration process, when Al3+added into the solution, the gel layer resistance and the pore blocking resistance are similar taking the largestproportion of total resistance the solution containing.When added Ca2+,the gel layer resistance is larger than that of other two mixtured solutions with Na+and Al3+(4)Through the fitting equation of Hermia’s laws, the dominant fouling mechanism was found to be cake blockage model when filer the SA and SA+PVA solution in ultrafiltration process. When Al3+added in the EPS solutions, the four kinds of models do not fit very well. In the microfiltration process, when model EPS solution contains Na+, the cake blockage model is the best one. While addition of Al3+and Ca2+, thedominantmodel is intermediate blocking model and cake blockage model.The results in this paper can provide the specific support on process optimization of membrane in water treatment technology and the research of membrane surface modification. It also extends the research field of the membrane fouling in membrane bioreactor.