A full-scale (110 ML/d) potable water treatment plant (WTP) based on the MIEX process, an innovative new process based on a strong base anion-exchange resin with magnetic properties, has been operating in Perth Western Australia since 2001. This plant has been configured so that a combined MIEX-coagulation (MIEX-C) process can be operated in parallel with a conventional enhanced coagulation (EC) process, allowing comparison of the performance of the two processes. Here, we report the use of size exclusion chromatography (SEC) to compare the removal of different apparent molecular weight (AMW) fractions of DOC by the two processes. Water was sampled from five key locations within the WTP, and SEC was carried out using three different on-line detector systems, DOC-specific detection, UV absorbance detection at lambda = 254 nm, and fluorescence detection (lambda(ex) = 282 nm; lambda(em) = 353 nm). This approach provided information on the chemical nature of the DOC comprising the various AMW fractions. The study showed that the MIEX-C process outperformed the EC process with greater removal of DOC in each of the eight separate AMW fractions identified. While EC preferentially removed the fractions of highest AMW, and those exhibiting the greatest aromatic (humic) character, MIEX-C removed DOC across all AMW fractions and did not appear to discriminate as strongly on the basis of differences in aromatic character or AMW. The results demonstrate the benefits of combining these complementary treatment processes. The study also demonstrates the utility of SEC coupled with multiple detection systems in determining the characteristics of various AMW components of DOC.

14To help understand and predict the role of natural organic matter (NOM) in the fouling of low-15 pressure membranes, experiments were carried out with an apparatus that incorporates automatic 16 backwashing and long filtration runs. Three hollow fibre membranes of varying character were 17 included in the study, and the filtration of two different surface waters was compared. The 18 hydrophilic membrane had greater flux recovery after backwashing than the hydrophobic 19 membranes, but the efficiency of backwashing decreased at extended filtration times. NOM 20 concentration of these waters (7.9 and 9.1 mg/L) had little effect on the flux of the membranes at 21 extended filtration times, as backwashing of the membrane restored the flux to similar values 22 regardless of the NOM concentration. The solution pH also had little effect at extended filtration 23 times. The backwashing efficiency of the hydrophilic membrane was dramatically different for the 24 two waters, and the presence of colloid NOM alone could not explain these differences. It is 25proposed that colloidal NOM forms a filter cake on the surface of the membranes and that small 26 molecular weight organics that have an adsorption peak at 220 nm but not 254 nm were responsible 27 for "gluing" the colloids to the membrane surface. Alum coagulation improved membrane 28 performance in all instances, and this was suggested to be because coagulation reduced the 29 concentration of "glue" that holds the organic colloids to the membrane surface. 30 31

Water utilities have experienced increasing pressure to minimise the formation of disinfection by-products (DBPs), as reflected in the increasingly stringent regulations and guidelines for the concentrations of DBPs in drinking water. Understanding the disinfection characteristics and molecular weight (MW) distribution of natural organic matter (NOM) will assist in the optimisation of drinking water treatment processes to minimise the formation of DBPs. This study investigated the disinfection behaviour of MW fractions of NOM isolated from a Western Australian source water. The NOM was fractionated and separated using preparative size exclusion chromatography (SEC) and the fractions were chlorinated in the presence of bromide ion. The larger MW fractions of NOM were found to produce the highest concentrations of DBPs (trihalomethanes, haloacetic acids, haloacetonitriles, haloketones, and haloaldehydes), with the low MW fractions still producing significant amounts of these DBPs. The results also showed a trend of an increasing proportion of brominated DBPs with decreasing MW and aromatic character. Considering that the smaller MW fractions of NOM produce significant amounts of DBPs, with a higher relative contribution from brominated DBPs, water treatment processes need to be optimised for either bromide removal or the removal of aliphatic, small MW fractions of NOM, in order to meet DBP guidelines and regulations.

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