New Membrane Fouling Mechanism
Published on by Water Network Research, Official research team of The Water Network in Academic
Study Finds that Organic Films that Form on RO Membranes in a Bioreactor from Organic Material in UF Permeate Irreversibly Reduce Flux in the RO Membrane, but Flux Reduction by Large Molecules Secreted by Microorganisms - Extracellular Polymeric Substances - Can Be Reversed
Scientistsproposed that the permanent damage inflicted by UF permeate arose from its arrest of the swelling in the membrane polyamide which the researchers had measured. The swelling effect is crucial to water transport through the membrane, the researchers said.
The scientists ran parallel, fouling experiments with UF permeate and EPS in an RO plate-and-frame unit. They saw reversible changes in the RO permeate flux as pH values were altered from 6 to 8 and back to 6 using pristine and fouled membranes with EPS.
On putting UF permeate-fouled membranes throughout he same pH variation the scientists found "irreversible flux decline" in the RO. The pH change, they said, promoted interaction between the UF permeate organic matter and the membrane to reduce further membrane permeability.
They concluded that substances originating in soil were binding irreversibly with the membrane surface: "More studies need to be carried out to analyse the effects of humic substances, abundant in the UF permeate fouling layer, that irreversibly interact with the polyamide surface.
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2 Comments
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We will try and find out. Here is the link to the original Report http://www.sciencedirect.com/science/article/pii/S037673881400324X
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I would be interested to learn whether any algal was present in the water that was treated via the UF plant in order to prepare permeate and also at what trans membrane pressure (TMP) the UF membranes ran when the permeate was prepared for the RO plant. In addition, it would be interested to learn whether the water with the extracellular polymeric substances (EPS) was simply clean water that was seeded with EPS or whether it was the same permeate that was seeded with EPS. It is well-known that algal cell breakage occurs at TMP pressures between 0.4 to 0.6 bar. Upon breaking, the algal cells release large amounts of biodegradable organics (AOC/TOC) which significantly accelerate RO biofouling. This could most probably have been the reason why they saw "irresistible" RO membrane fouling as the RO membranes experienced biofouling. The RO membranes could therefore have experienced a different fouling mechanism with the UF permeate than with the water that was prepared by seeding it with EPS. If, however, the same raw water was used for both tests and it was seeded with EPS before treating it via the UF plant, then both water types could possibly have seen high TMP pressures and then the research would be very interesting. Could you please confirm this?