ENHANCEMENT OF MEMBRANE FOULING RESISTANCE THROUGH SURFACE MODIFICATION

aachen2010 · 发表于 2010-11-8 22:22:50

马上注册并关注水世界微信号，获得更多资料

您需要登录才可以下载或查看，没有帐号？注册扫一扫，用微信登录

x

Commercial samples of cellulose acetate and polyamide reverse osmosis (RO) and nanofiltration (NF) membranes were treated with an homologous series of polyethylene-oxide based surfactants to improve fouling resistance. Various characterization methods were used to quantify membrane surface changes with treatment and fouling with a vegetable broth solution. Streaming potential was used to characterize changes in zeta potential. Atomic force microscopy was used to evaluate changes in surface topography. Water flux and salt rejection were evaluated using a bench scale “swatch-testing” apparatus. Fouling layer thickness was evaluated using acoustic time domain reflectometry. Results from these methods were compared with performance changes. The fouling solution degraded the untreated cellulose acetate (CA) blend membrane. Therefore any surface protection provided by the surfactant was dramatically illustrated. Triton Xl00 and Pluronic P84 provided significant protection. Polyamide (PA) membranes treated with surfactant experienced a severe flux decline. A similar decline was caused by fouling of the untreated PA membrane. The treated PA membrane did not have further flux decline with fouling. These results suggest a need for further studies on whether or not a surfactant pretreatment will result in improved membrane flux and rejection over many operating and cleaning cycles when exposed to fouling waters. 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Assessing the problem - membrane plant cleaning survey . . . . . . . . . . . . . . 1.3 Plan of attack-how to prevent or minimize fouling and scaling? . . . . . . . . 1.4 How to increase a membrane’s natural fouling resistance? . . . . . . . . . . . . . . 1.5 Membrane characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Classification and mechanisms of membrane fouling and cleaning . . . . . . . . . . . . . 2.1 Categorization of membrane obstructions . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Soluble inorganic material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Effect of temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Effect of pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Effect of ionic strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.4 Effect of surface microenvironment development . . . . . . . . . . . . . . . 2.2.5 Strategy for scale removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Biological fouling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Transport to the membrane surface . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Adsorption processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Detachment of biofilms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 .. 1 Mechanical removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3.2 Bacterial surface alteration . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3.3 Changes in substratum surface properties . . . . . . . . . . . . . . 2.3.3.4 Disruption of attachment polymers . . . . . . . . . . . . . . . . . . . 2.3.3.5 Change in metabolic state . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3.6 Release of daughter cells . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Interactions between obstruction components . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Membrane treatment and performance testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1 Methods for evaluating success . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Experimentalmethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Surfactant selection and application . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Standard fouling solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Swatch testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4 Transport evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.5 Element testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Swatch testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1.1 Cellulose acetate blend . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1.2 Polyamide thin film composite . . . . . . . . . . . . . . . . . . . . . . . 3.3.1.3 Nanofiltration CA and PA membrane . . . . . . . . . . . . . . . . . . 3.3.2 Element testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 Effect of performance changes on operating costs . . . . . . . . . . . . . . . 3.3.3.1 Operating cost based on swatch test performance . . . . . . . 3.3.3.2 Operating cost based on element test performance : . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Zeta potential analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Methods and materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Reproducibility and the effect of solution conductivity and pH . . . . 4.2.2 Effect of membrane type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3 Effect of surfactant adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.4 Effect of surfactant concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.25 Effect of protein fouling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Atomic force microscopy analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Acoustic time-domain reflectometry characterization of fouling . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Materials and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 7.1 The state of membrane maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 7.2 Efficacy of surfactant adsorption in improving fouling resistance . . . . . . . . 7.1 7.3 Evaluation of membrane characterization techniques . . . . . . . . . . . . . . . . . . 7.2 7.3.1 Swatch testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 7.3.2 Element testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 7.3.3 Zeta potential analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 7.3.4 Atomic force microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 7.3.5 Acoustic time-domain reflectometry . . . . . . . . . . . . . . . . . . . .