AWWA WQTC57013

Low-pressure membrane treatment processes are an emerging alternative to conventional water clarification processes. Based on results obtained from pilot scale studies, several full-scale treatment facilities have been recently built, and many other plants are currently under construction or in their design phase. These facilities have been designed to operate under conditions that result in minimal membrane fouling. Operating conditions, such as permeate flux and cross flow velocity, have been studied by many researchers to minimize particle deposition on membrane surface. However, there is limited evidence demonstrating that these optimal conditions also correspond to maximum or at least adequate rejection of microbial pathogens throughout the operating life of the membrane system. Therefore, the effects of operating conditions on the microorganism rejection need to be studied and determination of optimal condition for maximum microorganism removal would be useful for designing or operating a full membrane system. The purpose of this study was to perform bench scale experiments with small units containing selected hollow fiber membranes to elucidate the role that operating conditions (transmembrane pressure, permeate flux, cross flow velocity) play on the rejection of microbial contaminants. Selected microorganisms are Bacillus subtilis spores and MS2 phage. A review of the literature reveals that removals observed for the common viral surrogate MS2 phage in different studies could vary widely even when the membrane has the same nominal pore size. For example, an MF membrane with a pore size of 0.2 um showed 0.2 log removal of MS2 with an outside/in operation mode but 1.2 log removal with an inside/out mode. Additional studies using MF membranes with the same pore size of 0.2 um gave 1.9 log, <1 log, and 0.8 log removals of MS2. Consequently, characterization of the membrane by its nominal pore size appears to be inadequate to explain the mechanisms responsible for the transport of microbial contaminants through microfiltration (MF) and ultrafiltration (UF) membranes. Therefore, one of the objectives of this study was to investigate the mechanisms responsible for the transport of microbial contaminants through MF and UF membranes. Membrane pore size distribution (PSD) is considered an important factor to understand the mechanism of microorganism removal by low-pressure membranes. Includes 10 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2002

Number of Pages:

9

File Size:

1 file , 1.9 MB