Effect of membrane character and solution chemistry on microfiltration performance

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

Characterization of the Molecular Weight and Reactivity of Natural Organic Matter in Surface Waters

Natural organic matter (NOM) can impact on all aspects of water treatments processes. Understanding the physical and chemical characteristics of NOM is essential to improving drinkingwater treatment processes. The size of NOM has important implications for drinking water treatment and the formation of DBPs, where the high molecular weight, hydrophobic components of NOM have been found to be effectively removed by conventional drinking water treatment processes, while the lower molecular weight and certain hydrophilic components of NOM are more difficult to remove using these processes. In our study, we collected raw (untreated) watersfrom three different drinking water reservoirs, characterised the molecular weight (MW) distribution of the NOM in these waters using analytical scale high performance size exclusion chromatography (HPSEC), and isolated apparent MW (AMW) fractions of the NOM using preparative scale HPSEC. We also investigated the reactivity of the AMW fractions of NOM interms of disinfection by-products (DBP) formation potential from chlorination and chloramination. We focused on the formation potential of halogen-specific adsorbable organic halogen (AOX) and nitrogen-containing DBPs (N-DBPs), since brominated and iodinated DBPs and N-DBPs have beenreported to be significantly more cytotoxic, genotoxic, and carcinogenic than the regulated DBPs. Our study found that the AMW fractions of NOM with higher SUVA254 values generally produced higher concentrations of halogenated DBPs, measured as halogen-specific AOX. Halogenated N-DBPs formed only a small fraction of AOX in both chlorination and chloramination, with higher relative contributions from halogenated N-DBPs in chloraminated samples. The propensity of the formation of N-DBPs, especially N-nitrosamines and haloacetamides, was higher in chloramination. Since these DBPs are more toxic than the regulated DBPs, further evaluation of the health risk trade-offs when selecting chlorine or chloramine as a disinfectant is essential. The size of NOM had little influence on the formation of halogenated N-DBPs, but the low to medium AMW fractions of NOM tended to form higher concentrations of N-nitrosamines. Chlorine tended to be incorporated into the higher AMW fractions of NOM, while bromine and iodine seemed to be preferentially incorporated into the lower AMW fractions of NOM. Since conventional water treatment processes are ineffective for the removal of the low to medium MW fractions of NOM, improved water treatment processes may be needed to minimise the formation of brominated andiodinated DBPs, as well as N-nitrosamines, especially for source waters that contain significant amounts of organic matter of low to medium MW

Physicochemical Characterization of Organic Matter in Bayer Liquor

Organic matter in Bayer liquor from an alumina production facility in Australia was characterized in terms of its molecular weight distribution and molecular structure using a suite of complementary chromatographic, spectroscopic, and thermal and chemical degradation methods. The organic matter was characterized using high-performance size-exclusion chromatography with UV-vis detection (HPSEC-UV), Fourier transform infrared (FTIR) spectroscopy, and solid-state 13C nuclear magnetic resonance (13C NMR) spectroscopy. These techniques provided information on the apparent molecular weight distribution of the organic matter contained in the Bayer liquor, its alkyl/aromatic characteristics, and the presence of specific functional groups. The techniques of microscale sealed vessel (MSSV) pyrolysis-gas chromatography-mass spectrometry (GC-MS), flash pyrolysis-GC-MS, and online tetramethylammonium hydroxide (TMAH) thermochemolysis-GC-MS provided detailed information at a molecular level. Information on individual low-molecular-weight organic acids in the sample was also obtained using liquid chromatography- tandem mass spectrometry (LC-MS-MS). The novelty of this work is the molecular identification of nitrogen compounds, pyridines, pyrenes, quinolones, benzoquinolines, indoles, carbazoles, bipyridines, and phenylpyridines that derive from organic matter in the bauxite or its transformation products. The results from the other analysis techniques largely confirm the high aromatic content of the liquor, with varying degrees of alkyl (predominantly methyl), carboxylic, ketone, nitrile, and hydroxyl substitution. Aromatic acids were found to be abundant, although they were poorly detected using pyrolysis methods, highlighting the importance of using a suite of complementary techniques for the analysis of Bayer liquor samples