AWWA WQTC62468

The objective of this study was to characterize and identify the nature of the organic foulants responsible for flux declines of low and high pressure membranes. Experiments with lab-scale or pilot scale units were conducted on both clarified surface waters during periods of more intense microbial activity and on solutions of natural organic matter (NOM) (especially cell wall residues and also humic-like substances). HPSEC and Pyrolysis GC/MS analyses were the two major analytical tools used in this study. Several TOF SIMS and amino acids and aminosugars analyses were also performed. This work confirmed that during intense microbial activity in the source water (spring, summer time), conventionally treated water exert stronger membrane fouling. This study showed that the organic foulant that remains after backwash and chemical cleaning was a mixture of several biopolymers (proteins, polysaccharides, aminosugars and polyhydroxyaromatics). Aminosugars and polysaccharides which originate from microbial activity (microbial cell wall residues and/or exopolymers from DOM constituents and/or biofilm) appeared to be the major constituents of the fouling material. However, results from experiments with NOM fractions have shown that aromaticity appears to be a secondary parameter which influences PES membrane fouling. The second part of this article is focused on the membrane foulant autopsy conducted on nanofiltration membranes isolated before and after cleaning from the M¿¿ry sur Oise filtration train. Elemental analysis, Pyrolysis GC/MS, FT-IR, 13C- NMR analyses were performed on both insoluble and soluble phases of the deposit extracted from nanofiltration (NF) modules. Again, results confirmed the microbial origin of the fouling material. Polysaccharides and aminosugars were found to be the major organic constituents of the fouling material. In addition, the inorganic content (calcium, phosphorous and aluminum as major constituents) was found to increase significantly from stage 1 to stage 3 of the filtration train. After chemical cleaning a significant reduction of the inorganic content was noticed, however the organic composition of the foulant remained unchanged. Includes 8 references, table, figures.