| The reduction of membrane productivity (i.e. membrane fouling) during operation occurs in virtually all membrane applications. Membrane fouling originates from the method by which membranes operate: contaminants are rejected by the membrane and retained on the feed side of the membrane while treated water passes through the membrane. The accumulation of these contaminants on the feed side of the membrane results in increased operating pressures, increased backwashing frequencies, increased chemical cleaning frequencies, and increased membrane replacement frequencies. The most significant practical implication of membrane fouling is increased operating and maintenance costs. As such, membrane fouling must be properly managed to ensure successful and efficient operation of membrane systems. This document presents four independent studies regarding the fouling of size exclusion and diffusion controlled membranes. A brief description of each study is presented below.; The first study systematically investigated the fouling characteristics of various thin film composite polyamide reverse osmosis (RO) and nanofiltration (NF) membranes using a high organic surficial groundwater obtained from the City of Plantation, Florida. Prior to bench-scale fouling experiments, surface properties of the selected RO and NF membranes were carefully analysed in order to correlate the rate and extent of fouling to membrane surface characteristics, such as roughness, charge and hydrophobicity. More specifically, the surface roughness was characterized by atomic force microscopy, while the surface charge and hydrophobicity of the membranes were evaluated through zeta potential and contact angle measurements, respectively. The results indicated that membrane fouling became more severe with increasing surface roughness, as measured by the surface area difference, which accounts for both magnitude and frequency of surface peaks. Surface roughness was correlated to flux decline; however, surface charge was not. The limited range of hydrophobicity of the flat sheet studies prohibited conclusions regarding the correlation of flux decline and hydrophobicity.; Mass loading and resistance models were developed in the second study to describe changes in solvent mass transfer (membrane productivity) over time of operation. Changes in the observed solvent mass transfer coefficient of four low pressure reverse osmosis membranes were correlated to feed water quality in a 2,000 hour pilot study. Independent variables utilized for model development included: temperature, initial solvent mass transfer coefficient, water loading, ultraviolet absorbance, turbidity, and monochloramine concentration. Models were generated by data collected throughout this study and were subsequently used to predict the solvent mass transfer coefficient. The sensitivity of each model with respect to monochloramine concentration was also analyzed.; In the third study, mass loading and resistance models were generated to predict changes in solvent mass transfer (membrane productivity) with operating time for three reverse osmosis and nanofiltration membranes. Variations in the observed solvent mass transfer coefficient of these membranes treating filtered secondary effluent were correlated to the initial solvent mass transfer coefficient, temperature, and water loading in a 2,000 hour pilot study. Independent variables evaluated during model development included: temperature, initial solvent mass transfer coefficient, water loading, total dissolved solids, orthophosphorous, silica, total organic carbon, and turbidity. All models were generated by data collected throughout this study. Autopsies performed on membrane elements indicated membranes that received microfiltered water accumulated significantly more dissolved organic carbon and polysaccharides on their surface than membranes that received ultrafiltered water.; Series of filtration experiments were systematically performed to investiga... |
