Michael S. Elovitz

Hydroxyl Radical/Ozone Ratios During Ozonation Processes. I. The Rct Concept

Abstract The ozonation of model systems and several natural waters was examined in bench-scale batch experiments. In addition to measuring the concentration of ozone (O3), the rate of depletion of an in situ hydroxyl radical probe compound was monitored, thus providing information on the transient steady-state concentration of hydroxyl radicals (√OH). A new parameter, Rct , representing the ratio of the √OH-exposure to the O3-exposure was calculated as a function of reaction time. For most waters tested, including pH-buffered model systems and natural waters, Rct was a constant value for the majority of the reaction. Therefore, Rct corresponds to the ratio of the √OH concentration to the O3 concentration in a given water (i.e. Rct = [√OH]/[O3]). For a given water source, the degradation of a micropollutant (e.g. atrazine) via O3 and √OH reaction pathways can be predicted by the O3 reaction kinetics and Rct .

Hydroxyl Radical/Ozone Ratios During Ozonation Processes. II. The Effect of Temperature, pH, Alkalinity, and DOM Properties

Abstract The influence of temperature, pH, alkalinity, and type and concentration of the dissolved organic matter (DOM) on the rate of ozone (O3) decomposition, O3-exposure, •OH-exposure and the ratio Rct of the concentrations of •OH and O3 has been studied. For a standardized single ozone dose of 1 mg/L in all experiments, considerable variations in O3-exposure and •OH-exposure were found. This has important implications for water treatment plants regarding the efficiency of oxidation and disinfection by O3. In oligotrophic surface waters and groundwaters, minimal calibration experiments are needed to model and control the ozonation process, whereas in eutrophic surface waters more frequent measurements of O3 kinetics and Rct values are required to evaluate seasonal variations.

Redox Interactions of Cr(VI) and Substituted Phenols: Products and Mechanism.

The mechanisms of aqueous oxidation-reduction interactions between Cr(VI) and substituted phenols (RArOH) were characterized by kinetic analysis and determinations of reaction products and intermediates. A rapid, preoxidative equilibrium between HCrO 4 - and RArOH forms chromate ester intermediates, as verified by spectroscopy. The subsequent rate-limiting ester decomposition proceeds via innersphere electron transfer. The overall rate dependence on [H + ] is well accounted for by three parallel redox pathways involving zero, one, and two protons. The two-proton pathway dominates at pH ≤ 2, the single-proton pathway for 2 < pH < 5, and the proton-independent pathway at pH ≥ 5. The parallel reaction rate expression was fitted to data for 4-methyl-, 4-methoxy-, 2,6-dimethoxy-, and 3,4-dimethoxyphenol for pH 1-6. Beside accurately predicting rates for the calibrated conditions, the model predicts a sharp decline in rates at pH ≥ 6. Rates subsequently measured at pH 7 agreed well with those calculated a priori. Such predictions suggestthatthe proposed mechanism is robust and accurate. Rate constants were correlated with Hammett-type substituent parameters. Reaction products indicated both one- and two-electron pathways.

Redox Interactions of Cr(VI) and Substituted Phenols: Kinetic Investigation.

The kinetics of the reduction of Cr(V1) to Cr(II1) by substituted phenols in aqueous solution were studied over environmentally relevant ranges of reactant concentrations, pH, temperature, and ionic strength. At a fixed pH, the reaction was first order with respect to both the concentration of phenol reductant and the total concentration of monomeric Cr(V1). Reaction rates increased as much as 4 orders of magnitude from pH 5 to pH 1. The apparent reaction order with respect to [H+l varied between 0.2 and 2 over this same pH range, but also depended on the structure of the phenol. Comparison of the reactivities of 14 substituted phenols revealed a strong substituent effect. A t pH 2, rates for the 14 phenols spanned more than 5 orders of magnitude with reactivity generally increasing with the electron-donating character of the substituent (methoxy > methyl > chloro, aldehyde > nitro). Substituent effects are described by a linear correlation of the second-order rate constants ( ~ A ~ o H ) with the phenol half-wave potential (Elp). Representative reaction half-lives fall within the time scales of major environmental transport processes and suggest that the kinetics of these interactions are of significant concern in assessing sites contaminated with chromium and phenolic compounds.

High Methane Emissions from a Midlatitude Reservoir Draining an Agricultural Watershed

Reservoirs are a globally significant source of methane (CH4), although most measurements have been made in tropical and boreal systems draining undeveloped watersheds. To assess the magnitude of CH4 emissions from reservoirs in midlatitude agricultural regions, we measured CH4 and carbon dioxide (CO2) emission rates from William H. Harsha Lake (Ohio, U.S.A.), an agricultural impacted reservoir, over a 13 month period. The reservoir was a strong source of CH4 throughout the year, emitting on average 176 ± 36 mg C m(-2) d(-1), the highest reservoir CH4 emissions profile documented in the United States to date. Contrary to our initial hypothesis, the largest CH4 emissions were during summer stratified conditions, not during fall turnover. The river-reservoir transition zone emitted CH4 at rates an order of magnitude higher than the rest of the reservoir, and total carbon emissions (i.e., CH4 + CO2) were also greater at the transition zone, indicating that the river delta supported greater carbon mineralization rates than elsewhere. Midlatitude agricultural impacted reservoirs may be a larger source of CH4 to the atmosphere than currently recognized, particularly if river deltas are consistent CH4 hot spots. We estimate that CH4 emissions from agricultural reservoirs could be a significant component of anthropogenic CH4 emissions in the U.S.A.

Estimating Potential Increased Bladder Cancer Risk Due to Increased Bromide Concentrations in Sources of Disinfected Drinking Waters

Public water systems are increasingly facing higher bromide levels in their source waters from anthropogenic contamination through coal-fired power plants, conventional oil and gas extraction, textile mills, and hydraulic fracturing. Climate change is likely to exacerbate this in coming years. We estimate bladder cancer risk from potential increased bromide levels in source waters of disinfecting public drinking water systems in the United States. Bladder cancer is the health end point used by the United States Environmental Protection Agency (EPA) in its benefits analysis for regulating disinfection byproducts in drinking water. We use estimated increases in the mass of the four regulated trihalomethanes (THM4) concentrations (due to increased bromide incorporation) as the surrogate disinfection byproduct (DBP) occurrence metric for informing potential bladder cancer risk. We estimate potential increased excess lifetime bladder cancer risk as a function of increased source water bromide levels. Results based on data from 201 drinking water treatment plants indicate that a bromide increase of 50 μg/L could result in a potential increase of between 10(-3) and 10(-4) excess lifetime bladder cancer risk in populations served by roughly 90% of these plants.

Integrated data fusion and mining techniques for monitoring total organic carbon concentrations in a lake

Monitoring water quality on a near-real-time basis to address water resource management and public health concerns in coupled natural systems and the built environment is by no means an easy task. Total organic carbon (TOC) in surface waters is a known precursor of disinfection by-products in drinking water treatment such as total trihalomethanes (TTHMs), which are a suspected carcinogen and have been related to birth defects if water treatment plants cannot remove them. In this paper, an early warning system using integrated data fusion and mining (IDFM) techniques was proposed to estimate spatiotemporal distributions of TOC on a daily basis for monitoring water quality in a lake that serves as the source of a drinking water treatment plant. Landsat satellite images have high spatial resolution, but such application suffers from a long overpass interval of 16 days. On the other hand, coarse-resolution sensors with frequent revisit times, such as MODIS, are incapable of providing detailed water quality information because of low spatial resolution. This issue can be resolved by using data or sensor fusion techniques, such as IDFM, in which the high-spatial-resolution Landsat and the high-temporal-resolution MODIS images are fused and analysed by a suite of regression models to optimally produce synthetic images with both high spatial and temporal resolution. Analysis of the results using four statistical indices confirmed that the genetic programming model can accurately estimate the spatial and temporal variations of TOC concentrations in a small lake. The model entails a slight bias towards overestimating TOC, and it requires cloud-free input data for the lake. The IDFM efforts lead to the reconstruction of the spatiotemporal TOC distributions in a lake in support of healthy drinking water treatment.

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.

Comparing drinking water treatment costs to source water protection costs using time series analysis

We present a framework to compare water treatment costs to source water protection costs, an important knowledge gap for drinking water treatment plants (DWTPs). This trade-off helps to determine what incentives a DWTP has to invest in natural infrastructure or pollution reduction in the watershed rather than pay for treatment on site. To illustrate, we use daily observations from 2007 to 2011 for the Bob McEwen Water Treatment Plant, Clermont County, Ohio, to understand the relationship between treatment costs and water quality and operational variables (e.g., turbidity, total organic carbon [TOC], pool elevation, and production volume). Part of our contribution to understanding drinking water treatment costs is examining both long-run and short-run relationships using error correction models (ECMs). Treatment costs per 1000 gallons (per 3.79 m3) were based on chemical, pumping, and granular activated carbon costs. Results from the ECM suggest that a 1% decrease in turbidity decreases treatment costs by 0.02% immediately and an additional 0.1% over future days. Using mean values for the plant, a 1% decrease in turbidity leads to

Research Note Interferences due to Ozone-Scavenging Reagents in the GC-ECD Determination of Aldehydes and Ketones as the (2, 3, 4, 5, 6, -Pentafluorobenzyl) oximes

1123/year decrease in treatment costs. To compare these costs with source water protection costs, we use a polynomial distributed lag model to link total phosphorus loads, a source water quality parameter affected by land use changes, to turbidity at the plant. We find the costs for source water protection to reduce loads much greater than the reduction in treatment costs during these years. Although we find no incentive to protect source water in our case study, this framework can help DWTPs quantify the trade-offs.