Ferrous ion as a reducing agent in the generation of antibiofilm nitric oxide from a copper-based catalytic system.

The work found that the electron-donating properties of ferrous ions (Fe2+) can be used for the conversion of nitrite (NO2-) into the biofilm-dispersing signal nitric oxide (NO) by a copper(II) complex (CuDTTCT) catalyst, a potentially applicable biofilm control technology for the water industries. The availability of Fe2+ varied depending on the characteristics of the aqueous systems (phosphate- and carbonate-containing nitrifying bacteria growth medium, NBGM and phosphate buffered saline, PBS at pH 6 to 8, to simulate conditions typically present in the water industries) and was found to affect the production of NO from nitrite by CuDTTCT (casted into PVC). Greater amounts of NO were generated from the CuDTTCT-nitrite-Fe2+ systems in PBS compared to those in NBGM, which was associated with the reduced extent of Fe2+-to-Fe3+ autoxidation by the iron-precipitating moieties phosphates and carbonate in the former system. Further, acidic conditions at pH 6.0 were found to favor NO production from the catalytic system in both PBS and NBGM compared to neutral or basic pH (pH 7.0 or 8.0). Lower pH was shown to stabilize Fe2+ and reduce its autoxidation to Fe3+. These findings will be beneficial for the potential implementation of the NO-generating catalytic technology and indeed, a 'non-killing' biofilm dispersal activity of CuDTTCT-nitrite-Fe2+ was observed on nitrifying bacteria biofilms in PBS at pH 6.

Chloramine demand estimation using surrogate chemical and microbiological parameters.

A model is developed to enable estimation of chloramine demand in full scale drinking water supplies based on chemical and microbiological factors that affect chloramine decay rate via nonlinear regression analysis method. The model is based on organic character (specific ultraviolet absorbance (SUVA)) of the water samples and a laboratory measure of the microbiological (Fm) decay of chloramine. The applicability of the model for estimation of chloramine residual (and hence chloramine demand) was tested on several waters from different water treatment plants in Australia through statistical test analysis between the experimental and predicted data. Results showed that the model was able to simulate and estimate chloramine demand at various times in real drinking water systems. To elucidate the loss of chloramine over the wide variation of water quality used in this study, the model incorporates both the fast and slow chloramine decay pathways. The significance of estimated fast and slow decay rate constants as the kinetic parameters of the model for three water sources in Australia was discussed. It was found that with the same water source, the kinetic parameters remain the same. This modelling approach has the potential to be used by water treatment operators as a decision support tool in order to manage chloramine disinfection.

Developing a chloramine decay index to understand nitrification: A case study of two chloraminated drinking water distribution systems.

The management of chloramine decay and the prevention of nitrification are some of the critical issues faced by water utilities that use chloramine as a disinfectant. In this study, potential association between high performance size exclusion chromatography (HPSEC) data obtained with multiple wavelength Ultraviolet (UV) detection from two drinking water distribution systems in Australia and nitrification occurrence was investigated. An increase in the absorbance signal of HPSEC profiles with UV detection at λ=230nm between apparent molecular weights of 200 to 1000Da was observed at sampling sites that experienced rapid chloramine decay and nitrification while its absorbance signal at λ=254nm decreased. A chloramine decay index (C.D.I) defined as the ratio of area beneath the HPSEC spectra at two different wavelengths of 230 and 254nm, was used in assessing chloramine decay occurrences. The C.D.Is of waters at locations that experienced nitrification were consistently higher than locations not experiencing nitrification. A simulated laboratory study showed that the formation of nitrite/nitrate and/or soluble microbial products and/or the release of extracellular polymeric substances (EPS) during nitrification may contribute to the C.D.I. increase. These findings suggest that C.D.I derived from HPSEC with multiple wavelength UV detection could be an informative index to track the occurrence of rapid chloramine decay and nitrification.

Iron Complex Facilitated Copper Redox Cycling for Nitric Oxide Generation as Nontoxic Nitrifying Biofilm Inhibitor.

In this study, we developed poly(vinyl chloride) (PVC)-solvent casted mixed metal copper and iron complexes capable of catalytic generation of the antibiofilm nitric oxide (NO) from endogenous nitrite. In the absence of additional reducing agent, we demonstrated that the presence of iron complex facilitates a redox cycling, converting the copper(II) complex to active copper(I) species, which catalyzes the generation of NO from nitrite. Assessed by protein assay and surface coverage analyses, the presence of the mixed metal complexes in systems containing water industry-relevant nitrite-producing nitrifying biofilms was shown to result in a "nontoxic mode" of biofilm suppression, while confining the bacterial growth to the free-floating planktonic phase. Addition of an NO scavenger into the mixed metal system eliminated the antibiofilm effects, therefore validating first, the capability of the mixed metal complexes to catalytically generate NO from the endogenously produced nitrite and second, the antibiofilm effects of the generated NO. The work highlights the development of self-sustained antibiofilm materials that features potential for industrial applications. The novel NO-generating antibiofilm technology diverts from the unfavorable requirement of adding a reducing agent and importantly, the less tendency for development of bacterial resistance.

Understanding, Monitoring, and Controlling Biofilm Growth in Drinking Water Distribution Systems.

In drinking water distribution systems (DWDS), biofilms are the predominant mode of microbial growth, with the presence of extracellular polymeric substance (EPS) protecting the biomass from environmental and shear stresses. Biofilm formation poses a significant problem to the drinking water industry as a potential source of bacterial contamination, including pathogens, and, in many cases, also affecting the taste and odor of drinking water and promoting the corrosion of pipes. This article critically reviews important research findings on biofilm growth in DWDS, examining the factors affecting their formation and characteristics as well as the various technologies to characterize and monitor and, ultimately, to control their growth. Research indicates that temperature fluctuations potentially affect not only the initial bacteria-to-surface attachment but also the growth rates of biofilms. For the latter, the effect is unique for each type of biofilm-forming bacteria; ammonia-oxidizing bacteria, for example, grow more-developed biofilms at a typical summer temperature of 22 °C compared to 12 °C in fall, and the opposite occurs for the pathogenic Vibrio cholerae. Recent investigations have found the formation of thinner yet denser biofilms under high and turbulent flow regimes of drinking water, in comparison to the more porous and loosely attached biofilms at low flow rates. Furthermore, in addition to the rather well-known tendency of significant biofilm growth on corrosion-prone metal pipes, research efforts also found leaching of growth-promoting organic compounds from the increasingly popular use of polymer-based pipes. Knowledge of the unique microbial members of drinking water biofilms and, importantly, the influence of water characteristics and operational conditions on their growth can be applied to optimize various operational parameters to minimize biofilm accumulation. More-detailed characterizations of the biofilm population size and structure are now feasible with fluorescence microscopy (epifluorescence and CLSM imaging with DNA, RNA, EPS, and protein and lipid stains) and electron microscopy imaging (ESEM). Importantly, thorough identification of microbial fingerprints in drinking water biofilms is achievable with DNA sequencing techniques (the 16S rRNA gene-based identification), which have revealed a prevalence of previously undetected bacterial members. Technologies are now moving toward in situ monitoring of biomass growth in distribution networks, including the development of optical fibers capable of differentiating biomass from chemical deposits. Taken together, management of biofilm growth in water distribution systems requires an integrated approach, starting from the treatment of water prior to entering the networks to the potential implementation of "biofilm-limiting" operational conditions and, finally, ending with the careful selection of available technologies for biofilm monitoring and control. For the latter, conventional practices, including chlorine-chloramine disinfection, flushing of DWDS, nutrient removal, and emerging technologies are discussed with their associated challenges.

Copper Complex in Poly(vinyl chloride) as a Nitric Oxide-Generating Catalyst for the Control of Nitrifying Bacterial Biofilms.

In this study, catalytic generation of nitric oxide by a copper(II) complex embedded within a poly(vinyl chloride) matrix in the presence of nitrite (source of nitric oxide) and ascorbic acid (reducing agent) was shown to effectively control the formation and dispersion of nitrifying bacteria biofilms. Amperometric measurements indicated increased and prolonged generation of nitric oxide with the addition of the copper complex when compared to that with nitrite and ascorbic acid alone. The effectiveness of the copper complex-nitrite-ascorbic acid system for biofilm control was quantified using protein analysis, which showed enhanced biofilm suppression when the copper complex was used in comparison to that with nitrite and ascorbic acid treatment alone. Confocal laser scanning microscopy (CLSM) and LIVE/DEAD staining revealed a reduction in cell surface coverage without a loss of viability with the copper complex and up to 5 mM of nitrite and ascorbic acid, suggesting that the nitric oxide generated from the system inhibits proliferation of the cells on surfaces. Induction of nitric oxide production by the copper complex system also triggered the dispersal of pre-established biofilms. However, the addition of a high concentration of nitrite and ascorbic acid to a pre-established biofilm induced bacterial membrane damage and strongly decreased the metabolic activity of planktonic and biofilm cells, as revealed by CLSM with LIVE/DEAD staining and intracellular adenosine triphosphate measurements, respectively. This study highlights the utility of the catalytic generation of nitric oxide for the long-term suppression and removal of nitrifying bacterial biofilms.

Tungsten trioxide as a visible light photocatalyst for volatile organic carbon removal.

Tungsten trioxide (WO3) has been demonstrated to possess visible light photoactivity and presents a means of overcoming the UV-light dependence of photocatalysts, such as titanium dioxide. In this study, WO3 nanostructures have been synthesised by a hydrothermal method using sodium tungstate (Na2WO4·2H2O), sulphate precursors and pH as structure-directing agents and parameters, respectively. By altering the concentration of the sulphate precursors and pH, it was shown that different morphologies and phases of WO3 can be achieved. The effect of the morphology of the final WO3 product on the visible light photoactivity of ethylene degradation in the gas phase was investigated. In addition, platinum (Pt) was photodeposited on the WO3 structures with various morphologies to enhance the photocatalytic properties. It was found that the photocatalytic properties of the WO3 samples greatly depend on their morphology, chemical composition and surface modification. WO3 with a cuboid morphology exhibited the highest visible light photoactivity compared to other morphologies, while adding Pt to the surface improved the performance of certain WO3 structures.

Understanding effects of water characteristics on natural organic matter treatability by PACl and a novel PACl-chitosan coagulants.

In this study, we investigated the relationship between water characteristics and removal of natural organic matter (NOM) using polyaluminium chloride (PACl) and a newly developed coagulant obtained by hybridising PACl with chitosan (PACl-chitosan) for two different types of water. Using UV-visible spectroscopy analysis, we showed that PACl-chitosan is more effective than PACl for treating water samples that contain higher levels of activated polyhydroxyaromatic moieties. As a result, a lower level of total trihalomethanes formation potential (THMFP) was detected for synthetic water treated with PACl-chitosan coagulant compared to water treated with PACl only. In contrast, no difference was observed for the total THMFP that were formed following coagulation with either coagulant, for water sample containing the same level of organic carbon concentration, but lower levels of polyhydroxyaromatic moieties. Our work shows how the complex characteristics and interactions of organic matter with coagulant component can affect the outcome of the treatment process, and in this case, enhance the treatment. The use of PACl-chitosan was also shown to produce larger floc for both water samples; this again, can lead to better removal.

Expanding the applications of the ilmenite mineral to the preparation of nanostructures: TiO2 nanorods and their photocatalytic properties in the degradation of oxalic acid.

The mineral ilmenite is one of the most abundant ores in the Earth's crust and it is the main source for the industrial production of bulk titanium oxide. At the same time, methods to convert ilmenite into nanostructures of TiO(2) (which are required for new advanced applications, such as solar cells, batteries, and photocatalysts) have not been explored to any significant extent. Herein, we describe a simple and effective method for the preparation of rutile TiO(2) nanorods from ball-milled ilmenite. These nanorods have small dimensions (width: 5-20 nm, length: 50-100 nm, thickness: 2-5 nm) and possess large specific surface areas (up to 97 m(2) g(-1)). Dissolution/hydrolysis/precipitation is proposed as a growth mechanism. The nanorods were found to have attractive photocatalytic properties in the degradation of oxalic acid. Their photocatalytic activity is close to that of the benchmark Degussa P25 material and better than that of a commercial high-surface-area rutile powder.

Preparation and characterisation of new-polyaluminum chloride-chitosan composite coagulant.

In this study, the formulation of a novel polyaluminum chloride-chitosan composite coagulant that improves the coagulation process for natural organic matter (NOM) removal was investigated. The performance of the composite coagulant was tested using two water sources (synthetic and natural water) to develop a better understanding on the behaviour of the composite coagulant. Fourier Transform-Infra red (FT-IR) spectroscopy, ferron analysis and zeta potential studies were performed to characterise the composite coagulant. FT-IR analysis showed that there is an intermolecular interaction between Al species and chitosan molecules, while ferron analysis indicated that the distributions of Al(a), Al(b), and Al(c) in PACl-chitosan are different from those in PACl. At a low Al dosage (2.16 mg L⁻¹), a much higher removal of NOM from synthetic water, as evidenced from UV254 and Dissolved Organic Carbon (DOC) measurements, was achieved by the composite coagulants in comparison to that removed by PACl or PACl and chitosan added separately. For natural water from the Myponga Reservoir, both polyaluminum chloride (PACl) and PACl-chitosan composite coagulants demonstrated similar dissolved organic carbon (DOC) percentage removal, whereas PACl-chitosan gave a slight improvement in removing the UV254 absorbing components of NOM.

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.

TiO2 photocatalysis of natural organic matter in surface water: impact on trihalomethane and haloacetic acid formation potential.

In this study, changes in the physical and structural properties of natural organic matter (NOM) during titanium dioxide photocatalytic oxidation process were investigated using several complementary analytical techniques. Potential of the treated water to form trihalomethanes (THMs) and haloacetic acids (HAAs) was also studied. High-performance size exclusion chromatography analysis showed that NOM with apparent molecular weights of 1-4 kDa were preferentially degraded, leading to the formation of lower molecular weight organic compounds. Resin fractionation of the treated water demonstrated that the photocatalytic oxidation changed the affinity of the bulk organic character from predominantly hydrophobic to more hydrophilic. Short chain aldehydes and ketones were identified by mass spectroscopy as one of the key degradation products. The addition of hydrogen peroxide to photocatalysis was found to increase the degradation kinetics but did not affect the reaction pathway, thus producing similar degradation end products. The amount of THMs normalized per dissolved organic carbon (specific THM) formed upon chlorination of NOM treated with photocatalytic oxidation was reduced from 56 to 10 microg/mg. In contrast, the specific HAAs formation potential of the treated water remained relatively unchanged from the initial value of 38 microg/mg, which could be due to the presence of hydrophilic precursor compounds that were formed as a result of the photocatalytic oxidation process.

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.