Felicity A. Roddick

Influence of the characteristics of natural organic matter on the fouling of microfiltration membranes

Natural organic matter (NOM) plays a significant role in fouling microfiltration membranes in drinking water treatment processes even though the NOM is retained only to a small extent. The aim of this study was to obtain a better understanding of the interactions between the fractional components of NOM and microfiltration membranes. Filtration experiments were performed using 0.22 microm hydrophobic and hydrophilic polyvinylidene fluoride (PVDF) membranes in a stirred-cell system on the NOM isolated from three Australian surface waters. As expected, the fouling rate for the hydrophobic membrane was considerably greater than for the hydrophilic membrane. Focusing on the hydrophobic membrane, it was shown that the high molecular weight fraction of NOM ( > 30 kDa) was responsible for the major flux decline. Filtration tests on the four fractions of NOM isolated on the basis of hydrophobicity and charge using non-functionalised and anionic resins revealed that the fouling potential for the three waters was hydrophilic neutral > hydrophobic acids > transphilic acids > hydrophilic charged. The low-aromatic hydrophilic neutral compounds were the main determinant of the rate and extent of flux decline. This was linked to the colloidal size fraction ( > 30 kDa) and to the selective concentration of calcium in the fraction leading to organics-Ca2+ bridging. It was also shown that the higher the aromaticity of the NOM the greater the flux decline, and the aromatics mainly resided in the hydrophobic acids fraction. Overall, the fouling mechanism controlling the flux decline involved the combined effects of adsorptive and colloidal fouling by the hydrophilic neutral fraction in the internal pore structure of the membrane.

Biosorption of metals in brown seaweed biomass

Biosorption of Cd by biomass of the brown seaweeds Durvillaea, Laminaria, Ecklonia and Homosira presaturated with Ca, Mg or K was coupled with the release of these light ions. The feasibility of biomass pre-treatment to develop a better biosorbent was evaluated by its biosorption performance, the degree of its component leaching (measured by the weight loss and TOC) as well as by the number of ion-exchange sites remaining in the biomass after the pre-treatment. Multicomponent Langmuir and ion exchange models applied to the equilibrium sorption data for pH 4.5 confirmed the ion exchange mechanism involved in the biosorption of metals. Both models fitted well the experimental data and their parameters can be used in the derivation of dimensionless ion-exchange isotherms which are instrumental in predicting the behavior of the biosorbents in dynamic flow-through biosorption systems. The sequence of biomass affinities established for the selected heavy metals can be correlated with the chemical pretreatment of the biomass.

Biofouling of Water Treatment Membranes: A Review of the Underlying Causes, Monitoring Techniques and Control Measures

Biofouling is a critical issue in membrane water and wastewater treatment as it greatly compromises the efficiency of the treatment processes. It is difficult to control, and significant economic resources have been dedicated to the development of effective biofouling monitoring and control strategies. This paper highlights the underlying causes of membrane biofouling and provides a review on recent developments of potential monitoring and control methods in water and wastewater treatment with the aim of identifying the remaining issues and challenges in this area.

Understanding the factors controlling the removal of trace organic contaminants by white-rot fungi and their lignin modifying enzymes: A critical review

White-rot fungi (WRF) and their lignin modifying enzymes (LME) can degrade a wide range of trace organic contaminants (TrOC), which are suspected to cause adverse health effects in humans and other biota. Recent studies have successfully applied either whole-cell WRF or their extracellular culture extract to remove TrOC from the aqueous phase. TrOC removal by a WRF system is dependent on a range of factors including molecular structure of the TrOC, fungal species and their specific LME, culture medium composition, and methods to enhance fungal degradation capacity; however, the specific relationships between these factors have not been systematically delineated. The aim of this review paper is to fill this important gap in the literature by critically analysing the ability of WRF and their LME specifically to remove TrOC. Mechanisms and factors governing the degradation of TrOC by WRF and their LME are reviewed and discussed.

Application of ozone for the removal of bisphenol A from water and wastewater--a review.

The extensive use of Bisphenol A (BPA) in the plastics industry has led to increasing reports of its presence in the aquatic environment, with concentrations of ng L(-1) to μg L(-1). Various advanced oxidation processes, including ozonation, have been shown to effectively degrade BPA. This paper reviews the current advancements in using ozone to remove BPA from water and wastewater. Most of the published work on the oxidation of BPA by ozone has focused on the efficiency of BPA removal in terms of the disappearance of BPA, and the effect of various operational parameters such as ozone feed rate, contact time and pH; some information is available on the estrogenic activity of the treated water. Due to increasing operational reliability and cost effectiveness, there is great potential for industrial scale application of ozone for the treatment of BPA. However, there is a significant lack of information on the formation of oxidation by-products and their toxicities, particularly in more complex matrices such as wastewater, and further investigation is needed for a better understanding of the environmental fate of BPA.

A review of the use of sonication to control cyanobacterial blooms

The development of cyanobacterial blooms in water bodies imparts undesirable characteristics to the water such as odours, tastes and the potential presence of toxins. Several chemical and physical methods have been used to control the blooms, but have limitations in terms of pollution and application on a large scale. A more recent approach has been the use of sonication in the control of cyanobacteria (also referred to as blue-green algae). This paper reviews current advancements in research on using sonication to control cyanobacteria, particularly Microcystis aeruginosa, as it is a prevalent and a major bloom-forming toxic species. The impact of sonication on the structure and function of M. aeruginosa is discussed, including the influence of sonication parameters such as power intensity, frequency and exposure time. Alternate strategies of cyanobacterial control in combination with sonication are also reviewed.

Removal of trace organic contaminants by an MBR comprising a mixed culture of bacteria and white-rot fungi

The degradation of 30 trace organic contaminants (TrOC) by a white-rot fungus-augmented membrane bioreactor (MBR) was investigated. The results show that white-rot fungal enzyme (laccase), coupled with a redox mediator (1-hydroxy benzotriazole, HBT), could degrade TrOC that are resistant to bacterial degradation (e.g. diclofenac, triclosan, naproxen and atrazine) but achieved low removal of compounds (e.g. ibuprofen, gemfibrozil and amitriptyline) that are well removed by conventional activated sludge treatment. Overall, the fungus-augmented MBR showed better TrOC removal compared to a system containing conventional activated sludge. The major role of biodegradation in removal by the MBR was noted. Continuous mediator dosing to MBR may potentially enhance its performance, although not as effectively as for mediator-enhanced batch laccase systems. A ToxScreen3 assay revealed no significant increase in the toxicity of the effluent during MBR treatment of the synthetic wastewater comprising TrOC, confirming that no toxic by-products were produced.

Impact of sonication at 20 kHz on Microcystis aeruginosa, Anabaena circinalis and Chlorella sp.

Blooms of toxic cyanobacteria such as Microcystis aeruginosa periodically occur within wastewater treatment lagoons in the warmer months, and may consequently cause contamination of downstream water and outages of the supply of recycled wastewater. Lab-scale sonication (20 kHz) was conducted on suspensions of M. aeruginosa isolated from a wastewater treatment lagoon, and two other algal strains, Anabaena circinalis and Chlorella sp., to investigate cell reduction, growth inhibition, release of microcystin and sonication efficiency in controlling the growth of the M. aeruginosa. For M. aeruginosa, for all sonication intensities and exposure times trialled, sonication led to an immediate reduction in the population, the highest reduction rate occurring within the initial 5 min. Sonication for 5 min at 0.32 W/mL, or for a longer exposure time (>10 min) at a lower power intensity (0.043 W/mL), led to an immediate increase in microcystin level in the treated suspensions. However, prolonged exposure (>10 min) to sonication at higher power intensities reduced the microcystin concentration significantly. Under the same sonication conditions, the order of decreasing growth inhibition of the three algal species was: A. circinalis > M. aeruginosa > Chlorella sp., demonstrating sonication has the potential to selectively remove/deactivate harmful cyanobacteria from the algal communities in wastewater treatment lagoons.

Impact of salinity and pH on the UVC/H2O2 treatment of reverse osmosis concentrate produced from municipal wastewater reclamation.

While reverse osmosis (RO) technology is playing an increasingly important role in the reclamation of municipal wastewater, safe disposal of the resulting RO concentrate (ROC), which can have high levels of effluent organic pollutants, remains a challenge to the water industry. The potential of UVC/H(2)O(2) treatment for degrading the organic pollutants and increasing their biodegradability has been demonstrated in several studies, and in this work the impact of the water quality variables pH, salinity and initial organic concentration on the UVC/H(2)O(2) (3 mM) treatment of a municipal ROC was investigated. The reduction in chemical oxygen demand and dissolved organic carbon was markedly faster and greater under acidic conditions, and the treatment performance was apparently not affected by salinity as increasing the ROC salinity 4-fold had only minimal impact on organics reduction. The biodegradability of the ROC (as indicated by biodegradable dissolved organic carbon (BDOC) level) was at least doubled after 2 h UVC/H(2)O(2) treatment under various reaction conditions. However, the production of biodegradable intermediates was limited after 30 min treatment, which was associated with the depletion of the conjugated compounds. Overall, more than 80% of the DOC was removed after 2 h UVC/3 mM H(2)O(2) treatment followed by biological treatment (BDOC test) for the ROC at pH 4-8.5 and electrical conductivity up to 11.16 mS/cm. However, shorter UV irradiation time gave markedly higher energy efficiency (e.g., EE/O 50 kWh/m(3) at 30 min (63% DOC removal) cf. 112 kWh/m(3) at 2 h). No toxicity was detected for the treated ROC using Microtox(®) tests. Although the trihalomethane formation potential increased after the UVC/H(2)O(2) treatment, it was reduced to below that of the raw ROC after the biological treatment.

The impact of alum coagulation on the character, biodegradability and disinfection by-product formation potential of reservoir natural organic matter (NOM) fractions

Natural Organic Matter (NOM) from Myponga Reservoir, South Australia, was separated into four organic fractions based on their hydrophobic and hydrophilic properties using a sequence of non-ionic and ionic resins. NOM fractions were isolated for the purpose of determining the impact of alum coagulation on removal of these fractions in conventional water treatment, and their potential as precursors in the formation of disinfection by-products (DBP) and in supporting microbial growth. The NOM comprised VHA (very hydrophobic acids), SHA (slightly hydrophobic acids), CHA (charged hydrophilics) and NEU (neutral hydrophilics) fractions. These fractions were then jar tested with alum using low (50 mg/L), operational (100 mg/L) and very high (200 mg/L) doses to assess the removal capacities for these fractions in a conventional treatment plant. High-performance size exclusion chromatography-UV-DOC (HPSEC-UV-DOC) revealed that alum removed more of the hydrophobic and higher molecular weight components of NOM, but less of the NEU fraction and lower molecular weight components of NOM. Determination of biodegradable dissolved organic carbon (BDOC) indicated that the NEU fraction had the highest biodegradability, followed by the CHA, SHA and VHA fractions. The VHA fraction had the highest total-trihalomethane formation potential (t-THMFP), followed by NEU, SHA and CHA. The NOM not removed by alum coagulation had the potential to support microbial growth (NEU fraction), and disinfection by-product (DBP) formation (VHA and NEU fractions). To obtain treated water with lower overall residual NOM, other treatment methods would need to be applied in addition to alum coagulation in order to reduce the concentration of the neutral fraction.