Mary Drikas

Influence of characterised natural organic material on activated carbon adsorption: II. Effect on pore volume distribution and adsorption of 2-methylisoborneol

The adsorption of four ultrafiltration fractions of natural organic material (NOM) had a significant effect on the surface area and pore volume distributions of a coal-based activated carbon. This effect was dependent on the size of the compounds; the smaller fraction had the greatest effect on the micropore volume, and the larger fractions had a greater effect on the mesopore volume. Only the mesopore volume of a wood-based activated carbon was reduced by adsorption of the NOM fractions. The competitive adsorption between five NOM ultrafiltration fractions and 2-methylisoborneol (MIB) was greatest for the smallest fraction (ultrafiltration molecular weight <500), as this fraction was the most similar in size to MIB and therefore provided direct competition for the same adsorption sites. The NOM in a natural water sample displayed the greatest competition with MIB, due to the presence of small compounds that were lost during the concentration and desalting procedures used to obtain the NOM fractions. The competition between MIB and the largest ultrafiltration fraction was very small and could probably be attributed to smaller compounds present in this fraction.

The impact of conventional water treatment processes on cells of the cyanobacterium microcystis aeruginosa

Cyanobacteria can produce toxins, tastes and odors which significantly impair water quality. Removal of intact cyanobacterial cells with their intracellular compounds during water treatment would potentially reduce the concentration of taste, odor and toxic cell metabolites present in the treated water. In this study, the effect of conventional water treatment processes using aluminum sulphate (alum) on the integrity of cells of toxic Microcystis aeruginosa was evaluated using both jar tests and pilot plant studies. Removal of M. aeruginosa cells by alum flocculation using a jar test apparatus indicated all cells were removed without damage to membrane integrity. Thus the chemical treatment and mechanical action did not damage the cultured M. aeruginosa cells and, more importantly, did not result in additional release of cell metabolites above background concentrations. For pilot plant experiments, which consisted of coagulation/flocculation–sedimentation–filtration, most of the cells were removed intact and no additional microcystin was found in the finished water.

Comparison of NOM character in selected Australian and Norwegian drinking waters.

Observations from many countries around the world during the past 10-20 years indicate increasing natural organic matter (NOM) concentration levels in water sources, due to issues such as global warming, changes in soil acidification, increased drought severity and more intensive rain events. In addition to the trend towards increasing NOM concentration, the character of NOM can vary with source and time (season). The great seasonal variability and the trend towards elevated NOM concentration levels impose challenges to the water industry and the water treatment facilities in terms of operational optimisation and proper process control. The aim of this investigation was to compare selected raw and conventionally treated drinking water sources from different hemispheres with regard to NOM character which may lead to better understanding of the impact of source water on water treatment. Results from the analyses of selected Norwegian and Australian water samples showed that Norwegian NOM exhibited greater humic nature, indicating a stronger bias of allochthonous versus autochthonous organic origin. Similarly, Norwegian source waters had higher average molecular weights than Australian waters. Following coagulation treatment, the organic character of the recalcitrant NOM in both countries was similar. Differences in organic character of these source waters after treatment were found to be related to treatment practice rather than origin of the source water. The characterisation techniques employed also enabled identification of the coagulation processes which were not necessarily optimised for dissolved organic carbon (DOC) removal. The reactivity with chlorine as well as trihalomethane formation potential (THMFP) of the treated waters showed differences in behaviour between Norwegian and Australian sources that appeared to be related to residual higher molecular weight organic material. By evaluation of changes in specific molecular weight regions and disinfection parameters before and after treatment, correlations were found that relate treatment strategy to chlorine demand and DBP formation.

Granular activated carbon: Importance of surface properties in the adsorption of naturally occurring organics☆

Abstract The presence of dissolved organic matter (humic material in particular) in source water decreases the effectiveness of granular activated carbon filters in the treatment of drinking water. Results from potentiometric titrations, electrophoretic mobility measurements and BET surface area analyses suggest that this may be due to an increase in the negative charge on the carbon surface and a decrease in available surface area after adsorption. An increase in pH and the application of heat causes organics to desorb. After a subsequent acid treatment the carbon exhibits an increased ability to adsorb dissolved organic material. X-ray photoelectron spectroscopy was used to examine the carbon surface before adsorption, after adsorption and after regeneration treatment.

Microcystin-LR adsorption by powdered activated carbon

Abstract The adsorption of microcystin-LR by eight different powdered activated carbons (PACs) was investigated and found to vary markedly between carbons. Wood-based carbons were clearly the most effective microcystin-LR adsorbents followed by coal-based PACs. Coconut and peat moss-based carbons were the poorest microcystin-LR adsorbents. The extent of adsorption for each PAC was related to the volume of mesopores (diameters between 2.0 and 50 nm) which was dependent on the starting material. Surface characteristics, however, were not related to the starting material. Competitive adsorption with natural organics in River Murray water significantly reduced the initial rate of microcystin-LR adsorption. There was also a considerable reduction in the maximum level of microcystin-LR adsorption, the extent of which was dependent on the type of carbon.

Removal of humic acid using TiO2 photocatalytic process--fractionation and molecular weight characterisation studies.

The photocatalytic removal of humic acid (HA) using TiO2 under UVA irradiation was examined by monitoring changes in the UV(254) absorbance, dissolved organic carbon (DOC) concentration, apparent molecular weight distribution, and trihalomethane formation potentials (THMFPs) over treatment time. A resin fractionation technique in which the samples were fractionated into four components: very hydrophobic acids (VHA), slightly hydrophobic acids, hydrophilic charged (CHA) and hydrophilic neutral (NEU) was also employed to elucidate the changes in the chemical nature of the HA components during treatment. The UVA/TiO2 process was found to be effective in removing more than 80% DOC and 90% UV(254) absorbance. The THMFPs of samples were decreased to below 20 microg l(-1) after treatments, which demonstrate the potential to meet increasingly stringent regulatory level of trihalomethanes in water. Resin fractionation analysis showed that the VHA fraction was decreased considerably as a result of photocatalytic treatments, forming CHA intermediates which were further degraded with increased irradiation time. The NEU fraction, which comprised of non-UV-absorbing low molecular weight compounds, was found to be the most persistent component.

Long term case study of MIEX pre-treatment in drinking water; understanding NOM removal

Removal of natural organic matter (NOM) is a key requirement to improve drinking water quality. This study compared the removal of NOM with, and without, the patented magnetic ion exchange process for removal of dissolved organic carbon (MIEX DOC) as a pre-treatment to microfiltration or conventional coagulation treatment over a 2 year period. A range of techniques were used to characterise the NOM of the raw and treated waters. MIEX pre-treatment produced water with lower concentration of dissolved organic carbon (DOC) and lower specific UV absorbance (SUVA). The processes incorporating MIEX also produced more consistent water quality and were less affected by changes in the concentration and character of the raw water DOC. The very hydrophobic acid fraction (VHA) was the dominant NOM component in the raw water and was best removed by MIEX pre-treatment, regardless of the raw water VHA concentration. MIEX pre-treatment also produced water with lower weight average apparent molecular weight (AMW) and with the greatest reduction in complexity and range of NOM. A strong correlation was found between the VHA content and weight average AMW confirming that the VHA fraction was a major component of the NOM for both the raw water and treated waters.

Absorbance spectroscopy-based examination of effects of coagulation on the reactivity of fractions of natural organic matter with varying apparent molecular weights.

Absorbance spectra of fractions of natural organic matter (NOM) with varying apparent molecular weights (AMWs) were examined in this study. Size exclusion chromatography (SEC) was employed to obtain AMW distributions for three Australian water sources which represented low- and high-dissolved organic carbon (DOC) surface waters and a source with highly degraded NOM. These waters were coagulated with alum and other coagulants. Effects of coagulation on AMW distributions were quantified based on an absorbance slope index (ASI) calculated using NOM absorbance measured at 220, 230, 254 and 272 nm. This index can be calculated for any AMW fraction of NOM. Similarly to SUVA(254), ASI values decrease consistently in coagulated waters and are correlated with trihalomethane yields. Comparison of ASI indexes in different water sources indicates the presence of both common trends and differences indicative of NOM site-specificity.

Influence of characterised natural organic material on activated carbon adsorption: I. Characterisation of concentrated reservoir water

Natural organic material (NOM) from Myponga Reservoir in South Australia was concentrated and fractionated using ultrafiltration into nominal molecular weight fractions 30,000. The fractions were characterised using flow field-flow fractionation, 13C NMR, colour determination and potentiometric titration. The ultrafiltration fractions displayed a gradual transformation from highly coloured, highly branched, high carbohydrate structures to compounds with a prevalence of long chain aliphatic carbon with much lower carbohydrate content and colour. There were no clear trends in the carboxyl content of the fractions, as determined by both NMR and titration. Analysis of the titration data showed evidence of three distinct types of carboxyl groups and the same types of groups were present in each fraction.

Multi-wavelength spectroscopic and chromatography study on the photocatalytic oxidation of natural organic matter.

The effect of TiO2 photocatalytic oxidation on the natural organic matter (NOM) properties of two Australian surface waters were quantified using UV-vis spectroscopy, high performance size exclusion chromatography (HPSEC) with a multi-wavelength UV detector, liquid chromatography with organic carbon detector (LC-OCD), and trihalomethane formation potential (THMFP) analyses. Both the UV absorbance at wavelengths greater than 250 nm and dissolved organic carbon (DOC) content decreased significantly with treatment, although complete mineralization of NOM could not be achieved. Multi-wavelength UV detection of HPSEC analysis was shown to be useful to display further changes to NOM composition and molecular weight profiles because the organic molecules was transformed into compounds that absorb weakly at the typical detection wavelength of 250-260 nm. The multi-wavelength HPSEC results also revealed that photocatalytic oxidation yields by-products with a low aromaticity and low molecular weight. The LC-OCD chromatograms indicated that low molecular acids and neutral compounds remained after photocatalytic oxidation. Those groups of compounds did not seem to contribute significantly to the formation of trihalomethanes.