The primary objective of this investigation is to optimize a microfiltration process to pretreatagricultural drainage water prior to membrane desalination. A back-pulse optimizationapproach has been developed to greatly extend fouling free microfiltration of model drainage waters, andis expected to reduce chemical cleaning frequency, operating costs, and membrane replacement.The back-pulse optimization scheme is based on the hypothesis that foulants are brought into closecontact with MF membrane surfaces under force of permeation drag, but repulsive electrostaticinteractions may prevent irreversible adhesion for monolayer foulant coverages.Optimization of a microfiltration process to treat agricultural drainage water consists of four steps. Stepone is to determine the critical coverage point on the membrane surface using the direct microscopicobservation system's in situ visualization, thus determining the forward filtration time. Step two is toestimate the intensity of back-pulse required to dislodge deposited foulant particles at the membranesurface through analysis of hydrodynamic drag and lift forces, as well as surface forces arising from vander Waals and electrostatic interactions. Step three is to determine the back-pulse duration using directmicroscopic observation to ensure complete removal of particles. Step four is to apply the optimizedforward filtration time and back-pulse duration/frequency to a bench-scale hollow fiber microfiltrationsystem. The optimized scheme will be applied to model drainage waters prepared in our lab, as well asreal drainage water samples from the Alamo River. Samples of Alamo River water are analyzed to determine the nature of potential foulants. A sizefractionation procedure was employed with solids, organics, size distribution, and zeta potentialdetermined for each size fraction (8.0, 1.0, 0.4, and 0.1 µm). For synthetic water experiments, each sizefraction was simulated using model inorganic and organic foulants such as colloidal silica, clay, latex, andmicroorganisms. The MF back-pulsing system, used to evaluate the optimized operating scheme utilizesbench-scale, hollow fiber membrane filters with 100 dual asymmetrically skinned, polysulfone fibers perfilter. The MF back-pulsing system is capable of any combination of inside-out, outside-in, dead-end,cross-flow, constant pressure, and constant flux modes of operation. The direct microscopic observationsystem consists of a flow cell constructed from polycarbonate and glass, mounted on a microscope stageto allow direct visual observation of microbial and particle deposition optical microscopy as describedelsewhere. The direct microscopic observation utilizes a flat sheet polysulfone membrane that ischemically and physically analogous to the polysulfone membrane used in the bench-scale hollow fibersystem. Includes 6 references, figures.
