Ozonation Of Drinking Water Research Articles

Investigating the suitability of online flow cytometry for monitoring full-scale drinking water ozone system disinfection effectiveness

While online monitoring of physicochemical parameters has widely been incorporated into drinking water treatment systems, online microbial monitoring has lagged behind, resulting in the use of surrogate parameters (disinfectant residual, applied dose, concentration × time, CT) to assess disinfection system performance. Online flow cytometry (online FCM) allows for automated quantification of total and intact microbial cells. This study sought to investigate the feasibility of online FCM for full-scale drinking water ozone disinfection system performance monitoring. A water treatment plant with high lime solids turbidity in the ozone contactor influent was selected to evaluate the online FCM in challenging conditions. Total and intact cell counts were monitored for 40 days and compared to surrogate parameters (ozone residual, ozone dose, and CT) and grab sample assay results for cellular adenosine triphosphate (cATP), heterotrophic plate counts (HPC), impedance flow cytometry, and 16S rRNA gene sequencing. Online FCM provided insight into the dynamics of the full-scale ozone system, including offering early warning of increased contactor effluent cell concentrations, which was not observed using surrogate measures. Positive correlations were observed between online FCM intact cell counts and cATP levels (Kendall's tau=0.40), HPC (Kendall's tau=0.20), and impedance flow cytometry results (Kendall's tau=0.30). Though a strong correlation between log intact cell removal and CT was not observed, 16S rRNA gene sequencing results showed that passage through the ozone contactor significantly changed the microbial community (p < 0.05). Potential causes of the low overall cell inactivation in the contactor and the significant changes in the microbial community after ozonation include regrowth in the later chambers of the contactor and varied ozone resistance of drinking water microorganisms. This study demonstrates the suitability of direct, online microbial analysis for monitoring full-scale disinfection systems.

Oxidation of 51 micropollutants during drinking water ozonation: Formation of transformation products and their fate during biological post-filtration

Micropollutants (MP) with varying ozone-reactive moieties were spiked to lake water in the influent of a drinking water pilot plant consisting of an ozonation followed by a biological sand filtration. During ozonation, 227 transformation products (OTPs) from 39 of the spiked 51 MPs were detected after solid phase extraction by liquid chromatography high-resolution mass spectrometry (LC-HRMS/MS). Based on the MS/MS data, tentative molecular structures are proposed. Reaction mechanisms for the formation of a large number of OTPs are suggested by combination of the kinetics of formation and abatement and state-of-the-art knowledge on ozone and hydroxyl radical chemistry. OTPs forming as primary or higher generation products from the oxidation of MPs could be differentiated. However, some expected products from the reactions of ozone with activated aromatic compounds and olefins were not detected with the applied analytical procedure. 187 OTPs were present in the sand filtration in sufficiently high concentrations to elucidate their fate in this treatment step. 35 of these OTPs (19%) were abated in the sand filtration step, most likely due to biodegradation. Only 24 (13%) of the OTPs were abated more efficiently than the parent compounds, with a dependency on the functional group of the parent MPs and OTPs. Overall, this study provides evidence, that the common assumption that OTPs are easily abated in biological post-treatment is not generally valid. Nevertheless, it is unknown how the OTPs, which escaped detection, would have behaved in the biological post-treatment.

Decentralized solar-powered drinking water ozonation in Western Kenya: an evaluation of disinfection efficacy

Background: Decentralized drinking water treatment methods generally apply membrane-based treatment approaches. Ozonation of drinking water, which previously has only been possible at large centralized facilities, can now be accomplished on a small-scale using microplasma technology. The efficacy of decentralized solar-powered drinking water treatment systems has not previously been described. Methods: We established a 1,000L decentralized solar-powered water treatment system located in Kisumu County, Kenya. Highly contaminated surface water is pumped to the treatment system, which includes flocculation and filtration steps prior to ozonation. Turbidity, total coliform bacteria, and E. coli were measured at various stages of water treatment, and bacterial log reduction values (LRVs) were calculated. Results: Forty-seven trials were conducted in which1000L of water were flocculated, filtered, and ozonated for 180 minutes. Baseline turbidity and E. coli concentrations were reduced from a median of 238 nephelometric turbidity units (NTU) and 2,419.7 most probable number/100mL, respectively, in surface water to 1.0 NTU and undetectable E. coli after ozonation for 180 minutes. The median E. coli LRV was 3.99. Conclusions: The solar-powered, decentralized water treatment system that utilizes ozonation for disinfection was founded to reduce E. coli by more than 3 log-orders of magnitude despite the high turbidity of the raw water. Further research is needed to characterize limitations, scalability, economic viability, and community perspectives that could help determine the role for similar systems in other settings.

Decentralized solar-powered drinking water ozonation in Western Kenya: an evaluation of disinfection efficacy

Background: Decentralized drinking water treatment methods generally apply membrane-based treatment approaches. Ozonation of drinking water, which previously has only been possible at large centralized facilities, can now be accomplished on a small-scale using microplasma technology. The efficacy of decentralized solar-powered drinking water treatment systems has not previously been described. Methods: We established a 1,000L decentralized solar-powered water treatment system located in Kisumu County, Kenya. Highly contaminated surface water is pumped to the treatment system, which includes flocculation and filtration steps prior to ozonation. Turbidity, total coliform bacteria, and E. coli were measured at various stages of water treatment, and bacterial log reduction values (LRVs) were calculated. Results: Forty-seven trials were conducted in which1000L of water were flocculated, filtered, and ozonated for 180 minutes. Baseline turbidity and E. coli concentrations were reduced from a median of 238 nephelometric turbidity units (NTU) and 2,419.7 most probable number/100mL, respectively, in surface water to 1.0 NTU and undetectable E. coli after ozonation for 180 minutes. The median E. coli LRV was 3.99. Conclusions: The solar-powered, decentralized water treatment system that utilizes ozonation for disinfection was founded to reduce E. coli by more than 3 log-orders of magnitude despite the high turbidity of the raw water. Further research is needed to characterize limitations, scalability, economic viability, and community perspectives that could help determine the role for similar systems in other settings.

Decentralized solar-powered drinking water ozonation in Western Kenya: an evaluation of disinfection efficacy.

Background: Decentralized drinking water treatment methods generally apply membrane-based treatment approaches. Ozonation of drinking water, which previously has only been possible at large centralized facilities, can now be accomplished on a small-scale using microplasma technology. The efficacy of decentralized solar-powered ozonation for drinking water treatment is not known. Methods: We established a 1,000L decentralized solar-powered water treatment system located in Kisumu County, Kenya. Highly contaminated surface water is pumped to the treatment system, which includes flocculation and filtration steps prior to ozonation. Turbidity, total coliform bacteria, and E. coli were measured at various stages of water treatment, and bacterial log reduction values (LRVs) were calculated. Results: Nine trials were conducted treating 1000L of water in three hours. Baseline turbidity and E. coli concentrations were reduced from a median of 238 nephelometric turbidity units (NTU) and 2,752 most probable number/100mL, respectively, in surface water to 1.0 NTU and undetectable E. coli per100mL in finished drinking water. The nine trials yielded a mean E. coli LRV of 3.36 (2.71-4.00, 95% CI). Conclusions: Based on the observed reduction of E. coli, the solar-powered system shows promise as a means for producing safe drinking water. Further research is needed to characterize limitations, scalability, economic viability, and community perspectives that could help determine the role for similar systems in other settings.

Solar Powered Microplasma-Generated Ozone: Assessment of a Novel Point-of-Use Drinking Water Treatment Method.

Ozonation is widely used in high-income countries for water disinfection in centralized treatment facilities. New microplasma technology has reduced the energy requirements for ozone generation dramatically, such that a 15-watt solar panel is sufficient to produce small quantities of ozone. This technology has not been used previously for point-of-use drinking water treatment. We conducted a series of assessments of this technology, both in the laboratory and in homes of residents of a village in western Kenya, to estimate system efficacy and to determine if the solar-powered point-of-use water ozonation system appears safe and acceptable to end-users. In the laboratory, two hours of point-of-use ozonation reduced E. coli in 120 L of wastewater by a mean (standard deviation) of 2.3 (0.84) log-orders of magnitude and F+ coliphage by 1.54 (0.72). Based on laboratory efficacy, 10 families in Western Kenya used the system to treat 20 L of household stored water for two hours on a daily basis for eight weeks. Household stored water E. coli concentrations of >1000 most probable number (MPN)/100 mL were reduced by 1.56 (0.96) log removal value (LRV). No participants experienced symptoms of respiratory or mucous membrane irritation. Focus group research indicated that families who used the system for eight weeks had very favorable perceptions of the system, in part because it allowed them to charge mobile phones. Drinking water ozonation using microplasma technology may be a sustainable point-of-use treatment method, although system optimization and evaluations in other settings would be needed.

Chlorination of N,N-dimethylhydrazine compounds: reaction kinetics, mechanisms, and implications for controlling N-nitrosodimethylamine formation during ozonation

Pre-chlorination can eliminate N,N-dimethylhydrazine-type ozone–NDMA precursors, which is useful for controlling NDMA in drinking water ozonation.

Improvement of the raw drinking water quality from shallow well by ozone treatment

The interests of ozonation has increased significantly in recent years and today the ozonation is used in other steps in the drinking water treatment process. Ozonation has been used in the refill drinking water depot in the region of Indonesia for several years as disinfection at the end of the drinking water treatment process. Except for the disinfection, ozone has other benefits such as oxidation of iron and manganese, micro flocculation, reduction of taste and odour and it is also effective to reduce the water colour. The micro flocculation leads to the fact that less or no coagulants need to be used in the process. This study started with a lab scale experiments on ozonation and filtration of raw drinking water taken from shallow well followed by examination in the pilot plant. Research result showed the removal efficiency for organics, iron, manganese, and turbidity is up to 75 %; 98 %; 85 %; and 98 % respectively. All the parameter is comply with the drinking water standard regulated by Indonesia Ministry of Health No. 492/Menkes/PER/IV/2010. Disinfection capability of ozone against microorganisms will be reported in the full paper.

Biofilms in Full-Scale Drinking Water Ozone Contactors Contribute Viable Bacteria to Ozonated Water.

Concentrations of viable microbial cells were monitored using culture-based and culture-independent methods across multichamber ozone contactors in a full-scale drinking water treatment plant. Membrane-intact and culturable cell concentrations in ozone contactor effluents ranged from 1200 to 3750 cells/mL and from 200 to 3850 colony forming units/mL, respectively. Viable cell concentrations decreased significantly in the first ozone contact chamber, but rose, even as ozone exposure increased, in subsequent chambers. Our results implicate microbial detachment from biofilms on contactor surfaces, and from biomass present within lime softening sediments in a hydraulic dead zone, as a possible reason for increasing cell concentrations in water samples from sequential ozone chambers. Biofilm community structures on baffle walls upstream and downstream from the dead zone were significantly different from each other ( p = 0.017). The biofilms downstream of the dead zone contained a significantly ( p = 0.036) higher relative abundance of bacteria of the genera Mycobacterium and Legionella than the upstream biofilms. These results have important implications as the effluent from ozone contactors is often treated further in biologically active filters and bacteria in ozonated water continuously seed filter microbial communities.

Biodegradability of DBP precursors after drinking water ozonation

Ozonation is known to generate biodegradable organic matter, which is typically reduced by biological filtration to avoid bacterial regrowth in distribution systems. Post-chlorination generates halogenated disinfection byproducts (DBPs) but little is known about the biodegradability of their precursors. This study determined the effect of ozonation and biofiltration conditions, specifically ozone exposure and empty bed contact time (EBCT), on the control of DBP formation potentials in drinking water. Ozone exposure was varied through addition of H2O2 during ozonation at 1 mgO3/mgDOC followed by biological filtration using either activated carbon (BAC) or anthracite. Ozonation led to a 10% decrease in dissolved organic carbon (DOC), without further improvement from H2O2 addition. Raising H2O2 concentrations from 0 to 2 mmol/mmolO3 resulted in increased DBP formation potentials during post-chlorination of the ozonated water (target Cl2 residual after 24 h = 1–2 mg/L) as follows: 4 trihalomethanes (THM4, 37%), 8 haloacetic acids (HAA8, 44%), chloral hydrate (CH, 107%), 2 haloketones (HK2, 97%), 4 haloacetonitriles (HAN4, 33%), trichloroacetamide (TCAM, 43%), and adsorbable organic halogen (AOX, 27%), but a decrease in the concentrations of 2 trihalonitromethanes (THNM2, 43%). Coupling ozonation with biofiltration prior to chlorination effectively lowered the formation potentials of all DBPs including CH, HK2, and THNM2, all of which increased after ozonation. The dynamics of DBP formation potentials during BAC filtration at different EBCTs followed first-order reaction kinetics. Minimum steady-state concentrations were attained at an EBCT of about 10–20 min, depending on the DBP species. The rate of reduction in DBP formation potentials varied among individual species before reaching their minimum concentrations. CH, HK2, and THNM2 had the highest rate constants of between 0.5 and 0.6 min−1 followed by HAN4 (0.4 min−1), THM4 (0.3 min−1), HAA8 (0.2 min−1), and AOX (0.1 min−1). At an EBCT of 15 min, the reduction in formation potential for most DBPs was less than 50% but was higher than 70% for CH, HK2, and THNM2. The formation of bromine-containing DBPs increased with increasing EBCT, most likely due to an increase in Br−/DOC ratio. Overall, this study demonstrated that the combination of ozonation and biofiltration is an effective approach to mitigate DBP formation during drinking water treatment.

Transformation products of pharmaceutically active compounds during drinking water ozonation

Ozonation and ozone-based advanced oxidation processes have been shown to be effective in the oxidation of several pharmaceutically active compounds (PhACs) routinely detected in surface waters. Under typical operating conditions of these processes, most of the parent compound oxidized is expected to lead to the formation of transformation products (TPs). For a target ozone exposure, the resulting hydroxyl radical exposure depends on the water matrix or process chosen (e.g. peroxone) which in turn may influence the degradation pathway and the TPs formed. This study was undertaken to examine the expected impact that varying ozone and hydroxyl radical exposures may have on TP formation from the oxidation of PhACs during typical drinking water ozonation. Two representative PhACs were selected for the study. Carbamazepine was chosen to represent PhACs with a fast reaction rate with ozone (kO3 &amp;gt; 104 M−1 s−1) and bezafibrate was chosen to represent PhACs with a slow to moderate reaction rate with ozone (kO3 &amp;lt; 104 M−1 s−1). The results show that under varying ozone and hydroxyl exposure scenarios examined, the major oxidation pathway for the parent compound was dominated by reaction with ozone for carbamazepine while for bezafibrate it varied.

Inhibition mechanism of [formula omitted] formation over MnOx/Al2O3 during the catalytic ozonation of 2,4-dichlorophenoxyacetic acid in water

BrO3- formation from Br− containing drinking water ozonation treatment remains an important challenge. The inhibition mechanism of BrO3- formation was investigated during the catalytic ozonation of 2,4-dichlorophenoxyacetic acid (2,4-D) in mesoporous alumina supported MnOx (MnOx/Al2O3) suspension. The catalyst exhibited both significant inhibition of BrO3- formation and highly efficient catalytic ozonation of 2,4-D. Based on the characterization of UV–Vis spectrum, H2O2 determination and CV analysis, a redox process of bromine species occurred during the oxidation of 2,4-D in catalytic ozonation system. BrO3- reduction to Br− and the reduction of HBrO were responsible for the inhibition of BrO3- formation over MnOx/Al2O3 with ozone. An inhibition mechanism of BrO3- formation was proposed for catalytic ozonation in MnOx/Al2O3 suspension based on all experimental results. These observations will facilitate the development of catalytic ozonation for drinking-water treatment, especially for purification of Br− containing water.

Approach for detecting mutagenicity of biodegraded and ozonated pharmaceuticals, metabolites and transformation products from a drinking water perspective

Many pharmaceuticals and related metabolites are not efficiently removed in sewage treatment plants and enter into surface water. There, they might be subject of drinking water abstraction and treatment by ozonation. In this study, a systematic approach for producing and effect-based testing of transformation products (TPs) during the drinking water ozonation process is proposed. For this, two pharmaceutical parent substances, three metabolites and one environmental degradation product were investigated with respect to their biodegradability and fate during drinking water ozonation. The Ames test (TA98, TA100) was used for the identification of mutagenic activity present in the solutions after testing inherent biodegradability and/or after ozonation of the samples. Suspicious results were complemented with the umu test. Due to the low substrate concentration required for ozonation, all ozonated samples were concentrated via solid phase extraction (SPE) before performing the Ames test. With the exception of piracetam, all substances were only incompletely biodegradable, suggesting the formation of stable TPs. Metformin, piracetam and guanylurea could not be removed completely by the ozonation process. We received some evidence that technical TPs are formed by ozonation of metformin and piracetam, whereas all tested metabolites were not detectable by analytical means after ozonation. In the case of guanylurea, one ozonation TP was identified by LC/MS. None of the experiments showed an increase of mutagenic effects in the Ames test. However, the SPE concentration procedure might lead to false-positive results due to the generation of mutagenic artefacts or might lead to false-negative results by missing adequate recovery efficiency. Thus, these investigations should always be accompanied by process blank controls that are carried out along the whole ozonation and SPE procedure. The study presented here is a first attempt to investigate the significance of transformation products by a systematic approach. However, the adequacy and sensitivity of the methodology need to be further investigated. The approach of combining biodegradation and ozonation with effect-based assays is a promising tool for the early detection of potential hazards from TPs as drinking water contaminants. It can support the strategy for the evaluation of substances and metabolites in drinking water. A multitude of possible factors which influence the results have to be carefully considered, among them the selectivity and sensibility of the mutagenicity test applied, the extraction method for concentrating the relevant compounds and the biocompatibility of the solvent. Therefore, the results have to be carefully interpreted, and possible false-negative and false-positive results should be considered.

Use KMnO&lt;sub&gt;4&lt;/sub&gt; to Control Bromate Formation during Drinking Water Ozonation: Influencing Factors

This formation of bromate during ozonation of polluted source water has long caused great concerns. This paper used KMnO4 to control the bromate formation during water ozonation. KMnO4 was added 10 min prior ozone to oxidize the organic pollutants. The initial Br- concentration was 1000 μg/L. The results showed that the bromate formation efficiency was low (&lt;5%) during KMnO4-ozone oxidation. Among KMnO4 dose, ozone dose, and source water TOC, the single most important factor for bromate formation was the ozone dose. When the ozone dose was 3 mg/L or higher, the bromate concentration exceeded the national standard no matter what level of KMnO4 was used. The organic pollution level had little influence on the bromate formation.

A comparison of the Eulerian and particle tracking approaches for prediction of ozone contactor performance

Research Article| June 01 2011 A comparison of the Eulerian and particle tracking approaches for prediction of ozone contactor performance Jianping Zhang; Jianping Zhang 1Hatch Ltd., Mississauga, ON, Canada L5K 2R7 E-mail: jzhang@hatch.ca Search for other works by this author on: This Site PubMed Google Scholar Peter M. Huck; Peter M. Huck 2NSERC Chair in Water Treatment, Department of Civil and Environmental Engineering, University of Waterloo, ON, Canada N2L 3G1 Search for other works by this author on: This Site PubMed Google Scholar Gordon D. Stubley; Gordon D. Stubley 3Department of Mechanical and Mechatronics Engineering, University of Waterloo, ON, Canada N2L 3G1 Search for other works by this author on: This Site PubMed Google Scholar William B. Anderson William B. Anderson 2NSERC Chair in Water Treatment, Department of Civil and Environmental Engineering, University of Waterloo, ON, Canada N2L 3G1 Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2011) 60 (4): 197–209. https://doi.org/10.2166/aqua.2011.061 Article history Received: October 09 2010 Accepted: March 19 2011 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Jianping Zhang, Peter M. Huck, Gordon D. Stubley, William B. Anderson; A comparison of the Eulerian and particle tracking approaches for prediction of ozone contactor performance. Journal of Water Supply: Research and Technology-Aqua 1 June 2011; 60 (4): 197–209. doi: https://doi.org/10.2166/aqua.2011.061 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex The Eulerian and particle tracking approaches, two commonly utilized numerical methods, were evaluated for modelling drinking water ozone disinfection systems. The Eulerian approach predicts disinfection performance by solving an advection-diffusion equation. Alternatively, the particle tracking (Lagrangian) approach calculates disinfection efficiency by numerically introducing particles into the flow and predicting their trajectories through a spatially varying field of ozone residuals. The two approaches were used for modelling two hypothetical ozone reactors and a full-scale operating ozone contactor. For ozone reactors with plug flow characteristics, the two approaches match well in evaluating disinfection efficiency (represented by the CT value). For reactors with non-ideal hydraulic performance, the particle tracking model predicted slightly lower CT values than did the Eulerian approach. This may be due to the trapping of particles in the dead zones of non-ideal reactors, and the limitation on the particle numbers that could be used for data processing. The results of a full-scale contactor study further confirmed these observations. The study also found that the effect of particle size (1–100 μm) used in this study on the particle tracking method was negligible. The Schmidt number has minor impacts on the Eulerian approach modelling results. computational fluid dynamics, disinfection, Eulerian approach, ozone contactor, particle tracking approach This content is only available as a PDF. © IWA Publishing 2011 You do not currently have access to this content.

Operator-Friendly Technique and Quality Control Considerations for Indigo Colorimetric Measurement of Ozone Residual

Drinking water ozone disinfection systems measure ozone residual concentration, C, for regulatory compliance reporting of concentration-times-time (CT), and the resultant log-inactivation of virus, Giardia and Cryptosporidium. The indigotrisulfonate (ITS) colorimetric procedure is the Standard Method for measuring ozone residual. Although the currently written Standard Method is relatively easy to implement, its accuracy depends on specific ITS quality control considerations. The Standard Method is based upon specific quantities of materials and sample volumes, which make it somewhat inflexible. Tests are often performed in plant surroundings by operating staff, as opposed to in certified laboratories by analytical chemists. In this paper, a more flexible, quality-assured and “operator-friendly” technique is presented for the ITS method. This manuscript investigates several aspects of the ITS method (e.g. effects of aging, storage temperature, ITS supplier, accuracy of ITS weight measurement, and manganese interference), which are intended to improve the quality assurance and quality control (QA/QC) of the dissolved ozone measurement. Results are presented that document the negative consequences for ignoring certain conditions. For example, ITS solution stored on a shelf for several days can cause an appreciable under-estimation of ozone residual, while storage for several weeks can cause a major under-estimation of ozone residual. Other special study results suggest that greater flexibility is possible for reagent strength, without negative consequence, as compared to the recommended strength that is currently outlined in Standard Methods.

Evaluation of pilot-scale oxidation of several PPCPs/EDCs (pharmaceuticals and personal care products/endocrine disrupting compounds) during drinking water ozonation treatment

Several PPCPs/EDCs are being detected in surface drinking water sources, which is a great concern. The efficacy of ozonation in oxidizing 13 PPCPs/EDCs frequently detected in the Detroit River watershed was examined at pilot scale in the current study. Pilot-scale experiments were conducted at ozone dosages varying between 0.3 and 1.5 mg/L with the 13 PPCPs/ EDCs spiked in raw water obtained from the Detroit River. For 10 of the 13 PPCPs/EDCs with a high reaction rate with ozone (Group A), average oxidation efficiencies exceeded 95% for all ozone dosages at a contact time of 8.6 min. For chemicals with low to moderate reaction rate with molecular ozone (Group B), the observed oxidations were variable and ranged between 3 and 62% for ibuprofen and clorfibric acid and between 28 and &amp;gt;99% for bezafibrate under the same conditions. For the Group B chemicals, the oxidation increased with increasing ozone exposure and was significantly influenced by the quality of raw water.

Early alterations in protein and gene expression in rat kidney following bromate exposure

Bromate, a common disinfectant byproduct of drinking water ozonation, has been linked to human and animal renal toxicity, including renal cell carcinomas in multiple animal species. Here, we evaluate changes in protein and gene expression through two-dimensional difference gel electrophoresis (2D-DIGE) and Affymetrix arrays to identify potential modes of action involved in potassium bromate carcinogenicity. Male rats were exposed to potassium bromate in drinking water at concentrations of 0, 1, 20 and 400ppm for two weeks. Differential expression of glycolytic proteins including enolase 1 (Eno1), triosephosphate isomerase 1 (Tpi1) and glyceraldehyde-3-phosphate dehydrogenase (Gapdh) suggests that bromate toxicity is associated with changes in energy consumption and utilization in renal cells involving up-regulation of glycolytic processes that may be the result of altered mitochondrial function. Several alterations in glycolysis and mitochondrial gene transcripts were also observed to be consistent with this mode of action. These studies provide insight into early events in renal cell physiology altered by bromate exposure.

Global sensitivity analysis for model-based prediction of oxidative micropollutant transformation during drinking water treatment

This study quantifies the uncertainty involved in predicting micropollutant oxidation during drinking water ozonation in a pilot plant reactor. The analysis is conducted for geosmin, methyl tert-butyl ether (MTBE), isopropylmethoxypyrazine (IPMP), bezafibrate, β-cyclocitral and ciprofloxazin. These compounds are representative for a wide range of substances with second order rate constants between 0.1 and 1.9 × 10 4 M −1 s −1 for the reaction with ozone and between 2 × 10 9 and 8 × 10 9 M −1 s −1 for the reaction with OH-radicals. Uncertainty ranges are derived for second order rate constants, hydraulic parameters, flow- and ozone concentration data, and water characteristic parameters. The uncertain model factors are propagated via Monte Carlo simulation and the resulting probability distributions of the relative residual micropollutant concentrations are assessed. The importance of factors in determining model output variance is quantified using Extended Fourier Amplitude Sensitivity Testing (Extended-FAST). For substances that react slowly with ozone (MTBE, IPMP, geosmin) the water characteristic R ct-value (ratio of ozone- to OH-radical concentration) is the most influential factor explaining 80% of the output variance. In the case of bezafibrate the R ct-value and the second order rate constant for the reaction with ozone each contribute about 30% to the output variance. For β-cyclocitral and ciprofloxazin (fast reacting with ozone) the second order rate constant for the reaction with ozone and the hydraulic model structure become the dominating sources of uncertainty.

Application of a multiphase CFD modelling approach to improve ozone residual monitoring and tracer testing strategies for full-scale drinking water ozone disinfection processes

A multiphase computational fluid dynamics (CFD) model has been developed to address the major components of ozone disinfection processes: contactor hydraulics, ozone decay and mass transfer. The model was applied to simulate ozone profiles and tracer residence time distributions of ozone contactors at the DesBaillets Water Treatment Plant (WTP) in Montreal, Canada. The modelling results showed that ozone residuals at the cross-section of the outlet of each chamber in the ozone contactors were very sensitive to monitoring point selection. The optimum locations were significantly affected by multiple operational parameters including water/gas flow rates, ozone dosage and baffling conditions. The modelling results suggested that multiple monitoring points should be used to obtain more representative ozone residuals. The CFD model was also used to study the factors affecting tracer residence time distribution (RTD). It was observed that the method of tracer injection could slightly affect tracer RTD results while sampling location had a significant influence on tracer RTD prediction or measurement. Therefore, it is suggested that multiple sampling points should be employed during tracer tests if possible.