AWWA WQTC60553

Membrane filtration has become an accepted process for potable water production, but membrane foulingremains a significant problem. Natural organic matter (NOM) and in particular residues of microbialactivities are frequently cited as one of the major membrane foulant. The objective of this work was toevaluate the fouling properties of bacterial cell wall residues isolated from surface waters andExtracellular Polymeric Substances (EPS) isolated from algae. In addition alginic acid (polymer anddimer) were also studied. Some humic materials (NOM fractions isolated from rivers and commercialhumic substances) were also studied for comparison. The experimental approach was based on both flatsheet cell membrane tests (bacterial cell wal residues, alginic acid) and hollow fiber membrane tests(EPS). Two 100 KDa flat sheet membranes (regenerated cellulose membrane - YM and polyethersulfonemembrane - PES) and 100 KDa polysulfone hollow fibers (ID : 380 µm ; ED : 720 µm, 0.02 m²) wereselected for this study. Flux decline under constant TMP was monitored as an indication of fouling.The first part of this study was dedicated to the isolation and characterization of the isolated microbialresidues. Bacterial cell wall residues (i.e. fraction of NOM retained in a 3.5 KDa dialysis bag after 1 µmfiltration) were isolated from two natural waters according to the protocol proposed by Leenheer et al(2000). A battery of analytical tools (FTIR, NMR, Fluorescence, HPSEC, Pyrolysis-GC/MS,total amino acid and amino sugars) confirmed that this fraction of NOM (20 to 30 % of the TOC) iscomprised of a mixture of polysaccharides (aminosugars) and proteins as predominant biopolymers. In the second part of the study, a large diversity of analytical tools were developed in order tocharacterize the morphology (AFM, FESEM) and physical-chemical properties (Contact angle, streamingpotential) of the selected membranes. The two flat sheet membranes showed significant differences interms of hydrophobic/hydrophilic character, zeta potential (negatively charged membranes), roughness andpore density. The hollow fibers were found to exhibit a negatively charged surface.In the third phase of this study, the foulant properties of the selected microbial residues were evaluated.Experiments with natural waters were also conducted. Organics were resolubilized (bacterial cell wallresidues and alginic acid) or diluted (EPS) in MilliQ water (DOC : 5 to 10 mg/L C) and filtered throughthe membranes (TMP : 1 bar for the flat sheet membrane, TMP : 0.45 bar out/in filtration for the hollowfibers) at neutral pH. Whatever the membrane used, solutions of bacterial cell wall residues,EPS and polymeric alginic acid showed very severe fouling properties as compared to humic materials.Analyses conducted on permeates indicated a significant reduction of the DOC content with apredominant retention of higher molecular weight structures (HPSEC analyses). Includes figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

6

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1 file , 460 KB