Research and development to overcome fouling of membranes Page: 3 of 47
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SUMMARY
During this first year of the program, we have successfully accomplished the main
objective of demonstrating the feasibility of using piezoelectrically assisted ultrafiltration to reduce
membrane fouling and enhance the flux through ultrafiltration membranes. A preliminary
economic evaluation, accounting for the power consumption of the piezoelectric driver and the
extent of permeate flow rate enhancement, has also shown that piezoelectrically assisted
ultrafiltration is cost effective and economically competitive in comparison with traditional
separation processes.
Piezoelectric transducers, such as a piezoelectric lead zirconate titanate (PZT) disc or a
piezoelectric horn, driven by moderate power, significantly enhance the permeate flux on fouled
membranes, presumably because they promote local turbulence. Several experiments were
conducted on polysulfone and regenerated cellulose UF membranes fouled during filtration of
model feed solutions. Solutions of poly(ethylene glycol) and of high-molecular weight dextran
were used as models,. We found that we could significantly increase the permeate flux by
periodically driving the piezoelectric transducer, horn, or PZT disc, by application of moderate
power over short periods of time, from 20 to 90 seconds. Enhancements as high as a factor of 8
were recorded within a few seconds, and enhanced permeate fluxes were maintained over a
prolonged period (up to 3 hours). The prolonged flux enhancement makes it feasible to drive the
piezoelectric transducer intermittently, thereby reducing the power consumption of the piezoelectric
driver.
As piezoelectric drivers of sonically assisted ultrafiltration, PZT disc transducers are
preferred over the piezoelectric horn because of their small size and ease of adaptability to
ultrafiltration test cells. The horn transmits sonic energy to the UF membrane through a titanium
element driven by a separate piezoelectric transducer, but a piezoelectric ceramic disc transmits
energy directly to the UF membrane. Moreover, because piezoelectric ceramic elements can be
fabricated in several configurations, they are potentially feasible for piezoelectrically driven
ultrafiltration spiral-wound membrane modules.
Piezoelectrically assisted ultrafiltration by means of conventional UF membranes backed
with piezoelectric polyvinylidene fluoride (PVDF) films showed the poor properties of PVDF filmsi
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Narang, S. C.; Sharma, S. K.; Ventura, S. C.; Roberts, D. L. & Ahner, N. Research and development to overcome fouling of membranes, report, June 1, 1992; Menlo Park, California. (https://digital.library.unt.edu/ark:/67531/metadc1447425/m1/3/: accessed July 15, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.