Full Description

One of the primary drivers for the use of low pressure-driven membranes such as microfiltration (MF) and ultrafiltration (UF) for treatment of drinking water supplies has been the increased emphasis on the removal of microorganisms. There is currently no agreement on specifications that distinguish MF from UF. The traditional method for distinguishing UF from MF is pore size distribution or molecular weight cutoff. MF membranes are often considered to have pore sizes ranging from 0.05 um to 5 um and UF membranes from 0.005 um to 0.05 um. There is considerable overlap between where one may consider MF to begin and UF to end. Moreover, pore size distribution does not provide an accurate or empirically- based method to predict microbial removal. Of particular note, microbial removal does not currently play a role in determining whether a membrane is classified as MF or UF. This point leads to confusion in the water community as to the classification of low-pressure membranes. If membranes are to be employed on a more widespread basis for microbial removal, then their classification should be based on their capability to remove microorganisms, not on their pore size distribution. Microbial removal is usually evaluated through pilot testing. However, rigorous microbial challenge studies at pilot scale are often prohibitively costly. Since pilot studies are typically conducted at water facilities, opportunities for microbial challenge studies may be limited because of the potential hazard of working with microorganisms in proximity to drinking water supplies. Further, membranes are most vulnerable to microbial passage when they are first put online. The complexities of sampling for microbial agents immediately after pilot plant startup may provide inconsistent results due to cake layer accumulation or pore constriction from adsorption of natural organic matter onto the membrane. Because of these issues, a study was undertaken to evaluate microbial removal by membranes at bench scale. The specific objective of the study was to evaluate the impact of selected operational and water quality conditions on the removal of various microorganisms at bench scale. A custom fabricated Low-Pressure Membrane Testing Unit was used that was comprised of a membrane module, associated tubing and connections, pressure gauges, tanks and pumps (or nitrogen tanks). It was disinfected before performing the microbial challenge experiments. The paper lists the organisms that were used for bench-scale challenge experiments, and describes the microbial challenge experiments themselves along with the determination of specific flux and the module integrity testing. Includes 6 references, table, figures.

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Edition: Vol. - No. Published: 11/01/2002 Number of Pages: 16File Size: 1 file , 370 KB