The primary objective of this investigation is to optimize a microfiltration process to pretreat
agricultural drainage water prior to membrane desalination. A back-pulse optimization
approach has been developed to greatly extend fouling free microfiltration of model drainage waters, and
is 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 close
contact with MF membrane surfaces under force of permeation drag, but repulsive electrostatic
interactions may prevent irreversible adhesion for monolayer foulant coverages.
Optimization of a microfiltration process to treat agricultural drainage water consists of four steps. Step
one is to determine the critical coverage point on the membrane surface using the direct microscopic
observation system's in situ visualization, thus determining the forward filtration time. Step two is to
estimate the intensity of back-pulse required to dislodge deposited foulant particles at the membrane
surface through analysis of hydrodynamic drag and lift forces, as well as surface forces arising from van
der Waals and electrostatic interactions. Step three is to determine the back-pulse duration using direct
microscopic observation to ensure complete removal of particles. Step four is to apply the optimized
forward filtration time and back-pulse duration/frequency to a bench-scale hollow fiber microfiltration
system. The optimized scheme will be applied to model drainage waters prepared in our lab, as well as
real drainage water samples from the Alamo River. Samples of Alamo River water are analyzed to determine the nature of potential foulants. A size
fractionation procedure was employed with solids, organics, size distribution, and zeta potential
determined for each size fraction (8.0, 1.0, 0.4, and 0.1 µm). For synthetic water experiments, each size
fraction was simulated using model inorganic and organic foulants such as colloidal silica, clay, latex, and
microorganisms. The MF back-pulsing system, used to evaluate the optimized operating scheme utilizes
bench-scale, hollow fiber membrane filters with 100 dual asymmetrically skinned, polysulfone fibers per
filter. 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 observation
system consists of a flow cell constructed from polycarbonate and glass, mounted on a microscope stage
to allow direct visual observation of microbial and particle deposition optical microscopy as described
elsewhere. The direct microscopic observation utilizes a flat sheet polysulfone membrane that is
chemically and physically analogous to the polysulfone membrane used in the bench-scale hollow fiber
system.
Includes 6 references, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 410 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 4 |
| Published : | 06/17/2004 |
