Chlorate Concentrations Research Articles

Rapid determination of chlorate and perchlorate in tea by ion exchange chromatography-tandem mass spectrometry

Ion exchange chromatography-tandem mass spectrometry (IEC-MS/MS) has recently become the preferred method for detecting ionic substances in tea. In this study, an IEC-MS/MS method was developed for the rapid determination of chlorate and perchlorate residues in tea samples. The optimal sample extraction process, pretreatment column, and chromatographic and mass spectrometric conditions were systematically investigated. In the optimal process, the tea samples were ultrasonically extracted with methanol-water (13∶7, v/v), and a PRiME HLB SPE column was used to purify the sample extract. An AceChrom Hybri-A IEC column (150 mm×2.1 mm, 5.0 μm) was used for separation, and 100 mmol/L ammonium acetate-acetonitrile (40∶60, v/v) was used as the mobile phase for isocratic elution. The flow rate was 0.3 mL/min, the column temperature was 40 ℃, and the injection volume was 5.0 μL. The mass spectrometric data were collected in negative electrospray ionization mode combined with multiple reaction monitoring (MRM) mode to achieve the rapid and accurate separation and qualitative analysis of the desired chemical components. Quantification was performed using the internal standard (IS) method. The measurement results showed a good linear relationship when the mass concentrations of chlorate and perchlorate were between 2.00-200 and 1.00-100 μg/L, respectively, with correlation coefficients (r2) greater than 0.9990. The average recoveries of chlorate and perchlorate at three spiked levels of low, medium, and high ranged from 88.54% to 97.25% with relative standard deviations (RSDs, n=7) of 3.2%-5.2%. The limits of detection for chlorate and perchlorate were 12.0 and 8.0 μg/kg, respectively, while the limits of quantification were 40.0 and 26.6 μg/kg, respectively. The results of tests conducted to assess the linearity, specificity, accuracy, precision, and applicability of the method to the analysis of chlorate and perchlorate in 15 tea samples collected from a local market demonstrated its validity for the routine analysis of tea samples. The proposed method is simple, rapid, sensitive, and accurate, and can meet requirements for the rapid screening and quantitative analysis of residual trace chlorate and perchlorate in large quantities of tea samples.

Evaluating the effectiveness of minimum chlorate technologies employed by manufacturers of skim milk powder from both microbiological quality and chemical residue perspectives

Dairy processors in the Republic of Ireland have adopted chlorine-free chemicals for cleaning and chlorine gas for water disinfection as a means of minimizing chlorate residue in dairy products. For these "minimum chlorate technologies" to be satisfactory, they must be able to deliver product with acceptable levels of bacteria as well as minimum levels of chlorate and other chlorine-based residues. To establish the effectiveness of these technologies, sampling was conducted across the skim milk powder (SMP) manufacturing chain in 3 separate milk processing sites. Across the 3 sites a total of 11 different batches of SMP were sampled in duplicate from the whole milk silo through the manufacturing process to the powder product; yielding a total of 137 samples. Samples were tested for chlorate, perchlorate and trichloromethane alongside a suite of microbiological plate count tests including total bacteria, thermophilic bacteria, thermoduric bacteria and both mesophilic and thermophilic spore-forming bacteria. Chlorate was detected at reportable levels (≥0.01 mg/kg) in 9 of 22 SMP samples analyzed; resulting in a mean chlorate concentration 0.0183 mg/kg. Bacteria were ubiquitous across all samples analyzed with spore-forming bacteria counts ranging from 1.30 to 2.33 log cfu/g in SMP.

Perchlorate and chlorate in aquatic products from Shenzhen, China, and their implications for human exposure

Perchlorate and chlorate are chemically stable species with high solubility and are widely distributed in various foods. Dietary intake is considered to be the main route of human exposure to these chemicals. Aquatic products are an important component of residents' daily diets. However, there is still a lack of a complete research report on perchlorate and chlorate contamination in aquatic products. Thus, this study investigated the concentration of perchlorate and chlorate in shellfish, freshwater fish, freshwater shrimp, sea fish, and sea shrimp from Shenzhen and assessed human exposure risks. The detection frequency of chlorate was low, and the incidence of perchlorate was significantly lower than previous studies, demonstrating a substantial reduction in perchlorate contamination in Shenzhen waters. However, certain samples exhibited relatively elevated concentrations. The highest concentration of chlorate (43.1 µg kg−1) and perchlorate (14,865 µg kg−1) were both found in sea shrimp. Notably, the 95th percentile estimated daily intake (EDI) value of perchlorate derived from sea shrimp and shellfish surpassed the reference dose (RfD), while the EDI values of chlorate were all below the RfD. Therefore, Shenzhen residents are advised to consume sea shrimp and shellfish with caution to minimize the possible health risks linked to perchlorate and chlorate exposure.

Bioremediation of Chlorate and Chromium in Soil Columns Using Contaminated Site Native Culture

AbstractChlorate and hexavalent chromium (chromate) are both widely used in different industries, and the improper waste management in the past left many sites with elevated concentrations in groundwater that pose potential risk to human and/or ecological health. Bioremediation is a sustainable management solution that can reduce both of these contaminants to less toxic species. In our earlier microcosms experiments, we have demonstrated that native microorganisms collected from a site contaminated with chlorate and chromate can lower the concentration of these chemicals in groundwater to acceptable regulatory levels provided sufficient electron donor, nitrogen, and phosphorous are provided. In this study, continuous flow column experiments were performed using soil from the site impacted by both chlorate and chromate in the Province of Manitoba (Canada) and synthetic groundwater amended with acetate, nitrogen, and phosphorous. The objective was to evaluate at a bench scale possibility of in‐situ groundwater treatment. Concentrations of chromate and chlorate measured in the columns' effluent water dropped by 86% and 96%, respectively. However, increased biomass and precipitation of trivalent chromium reduced the water flow rate in the columns, a concern for implementing this method as a long‐term in‐situ remediation solution.

Occurrence and exposure assessment of chlorate and perchlorate in food and drinking water from Fujian, China

Exposure to chlorate and perchlorate can cause significant health problems because of the sustained inhibition of iodine uptake by the thyroid. This study analyzed the contamination characteristics of chlorate and perchlorate in food and drinking water and assessed the exposure of the population in Fujian, China. A total of 679 samples, including 661 food samples belonging to 14 types and 18 drinking water samples, were analyzed by modified liquid chromatography–tandem mass spectrometry. The detection rates of chlorate and perchlorate in food was 38.8% and 90.6%, respectively, and the detection rates of chlorate and perchlorate in drinking water was 100%. The maximum concentration of chlorate and perchlorate in food was 2480 μg/kg of Agaricus blazei Murill and 4550 μg/kg of Chinese prickly ash, whereas the maximum concentration in drinking water was 83.3 and 5.67 μg/kg, respectively. The mean dietary exposure to chlorate and perchlorate for infants was below the tolerable daily intake recommended by EFSA. The average daily dose of chlorate and perchlorate for infants was 15.6 and 1.06 μg/kg, respectively, with drinking water and infant formula being the main routes of exposure. The average daily dose of chlorate in adults was 4.31 μg/kg, with drinking water, edible fungi, meat, vegetables, and milk being the main exposure routes. The mean dietary exposure and average daily dose of perchlorate for adults were 0.440 and 2.49 μg/kg, respectively, with cereals, spices, vegetables, marine fish, eggs, and milk being the main routes of exposure. Therefore, risk reduction and regulation are necessary.

The dissolution of gold in chloride media under ambient conditions-a re-assessment of mechanisms

This study has shown that the use of methods that measure the initial rates of dissolution of gold using iron(III) as the oxidant under ambient conditions can be deceptive in that, in the absence of efficient methods to re-oxidize iron(II) to iron(III), the rates rapidly decrease with time resulting in predictable poor recoveries. Nevertheless, the results obtained have confirmed that gold(I) is the main product of dissolution with iron(III) as the oxidant and that the initial rate increases parabolically with increasing chloride concentration, is proportional to the square root of the iron(III) concentration and is independent of the acidity. These observations are consistent with the effects of chloride and acid concentrations on the anodic dissolution of gold. The mixed potential model of oxidative dissolution was shown to be operative in this system.The rate of homogeneous re-oxidation of iron(II) to iron(III) by dissolved oxygen under ambient conditions is too slow to be of value in sustaining the high potentials required. On the other hand, the use of low concentrations of chlorate have been shown to be effective in sustaining the reaction as a result of the generation of small quantities of chlorine by oxidation of chloride.

Purified Chlorine Dioxide as an Alternative to Chlorine Disinfection to Minimize Chlorate Formation During Postharvest Produce Washing.

The washwater used to wash produce within postharvest washing facilities frequently contains high chlorine concentrations to prevent pathogen cross-contamination. To address concerns regarding the formation and uptake of chlorate (ClO3-) into produce, this study evaluated whether switching to chlorine dioxide (ClO2) could reduce chlorate concentrations within the produce. Because ClO2 exhibits lower disinfectant demand than chlorine, substantially lower concentrations can be applied. However, ClO3- can form through several pathways, particularly by reactions between ClO2 and the chlorine used to generate ClO2 via reaction with chlorite (ClO2-) or chlorine that forms when ClO2 reacts with produce. This study demonstrates that purging ClO2 from the chlorine and ClO2- mixture used for its generation through a trap containing ClO2- can scavenge chlorine, substantially reducing ClO3- concentrations in ClO2 stock solutions. Addition of low concentrations of ammonia to the produce washwater further reduced ClO3- formation by binding the chlorine produced by ClO2 reactions with produce as inactive chloramines without scavenging ClO2. While chlorate concentrations in lettuce, kale, and broccoli exceeded regulatory guidelines during treatment with chlorine, ClO3- concentrations were below regulatory guidelines for each of these vegetables when treated with ClO2 together with these two purification measures. Switching to purified ClO2 also reduced the concentrations of lipid-bound oleic acid chlorohydrins and protein-bound chlorotyrosines, which are exemplars of halogenated byproducts formed from disinfectant reactions with biomolecules within produce.

Perchlorate and chlorate assessment in drinking water in northern Chilean cities

Perchlorate and chlorate are endocrine disruptors considered emerging contaminants (ECs). Both oxyanions are commonly associated with anthropogenic contamination from fertilizers, pesticides, explosives, and disinfection byproducts. However, the soils of the Atacama Desert are the most extensive natural reservoirs of perchlorate in the world, compromising drinking water sources in northern Chile. Field campaigns were carried (2014–2018) to assess the presence of these ECs in the water supply networks of twelve Chilean cities. Additionally, the occurrence of perchlorate, chlorate and other anions typically observed in drinking water matrices of the Atacama Desert (i.e., nitrate, chloride, sulfate) was evaluated using a Spearman correlation analysis to determine predictors for perchlorate and chlorate. High concentrations of perchlorate (up to 114.48 μg L−1) and chlorate (up to 9650 μg L−1) were found in three northern cities. Spatial heterogeneities were observed in the physicochemical properties and anion concentrations of the water supply network. Spearman correlation analysis indicated that nitrate, chloride, and sulfate were not useful predictors for the presence of perchlorate and chlorate in drinking water in Chile. Hence, this study highlights the need to establish systematic monitoring, regulation, and treatment for these EC of drinking water sources in northern Chilean cities for public health protection.

Generation, toxicity, and reduction of chlorinated byproducts: Overcome bottlenecks of electrochemical advanced oxidation technology to treat high chloride wastewater

Electrochemical advanced oxidation process (EAOP) is recommended for high-strength refractory organics wastewater treatment, but the accompanying chlorinated byproduct generation becomes a bottleneck that limits the application of this technology to actual wastewater. In this study, we applied EAOP (0.4-40 mA cm−2) to treat ultrafiltration effluent of an actual landfill leachate, and quantitatively assessed the toxicities of the dominant chlorinated byproducts in EAOP-treated effluent. Considering both toxic effect and dose, it followed the order: active chlorine > chlorate > perchlorate > organochlorines. The toxic active chlorine could spontaneously decompose by settling. And secondary bioreactor originally serving for denitrification could be used to reduce perchlorate and chlorate. The effects of residual active chlorine and extra carbon addition on simultaneous denitrification, perchlorate, and chlorate reduction were investigated. It seemed that 20 mg of active chlorine was an acceptable level to bioactivity, and sufficient electron donors favored the removal of chlorate and perchlorate. Pseudomonas was identified as an active chlorine tolerant chlorate-reducing bacteria. And Thauera was responsible for perchlorate reduction under the conditions of sufficient carbon source supply. Our results confirmed that the perchlorate and chlorate concentrations in the effluent below their health advisory levels were achievable, solving the issue of toxic chlorinated byproduct generation during EAOP. This study provided a solution to realistic application of EAOP to treat high chloride wastewater.

Combined leaching of Carlin-type gold deposit in Guizhou by potassium chlorate and bleaching powder

Cyanidation has been considered an effective process for extracting gold from gold-bearing ores for over 100 years. However, this process also has several disadvantages including it being toxic, inefficient, and unsuitable for leaching gold from carbonaceous gold ores containing organic and inorganic carbons. Moreover, it is not feasible for the extraction of gold from refractory gold ores , which are increasingly being used.Therefore, there is an urgent need to find an environmentally friendly and efficient leaching method to improve the extraction rate of gold from refractory gold ores. This study discusses using potassium chlorate and bleaching powder for combined leaching of refractory gold ore. Compared with other leaching methods, this method does not require the pre-oxidizing of the refractory gold ore. Moreover, the optimal reaction temperature required for the reaction is lower, thus achieving efficient and environmentally friendly leaching of refractory gold ore. To improve on the method, we used response surface methodology (RSM). RSM can quickly determine the quadratic function connection between the response value and each component and optimize the experimental settings to precisely forecast the experimental findings, saving a significant amount of time and money.This study presents a response surface approach based on a thermodynamic analysis of gold-bearing mineral oxidation to analyze the primary composite design experiment. The response surface model uses four components and three levels of potassium chlorate concentration, bleaching powder addition, reaction temperature, and reaction pH. The model gives 0.16 mol l−1 potassium chlorate, 37.5 g bleaching powder, 25 °C reaction temperature, and reaction pH of 13 as the optimal conditions for leaching gold using potassium chlorate and bleaching powder. Under these conditions, the gold leaching rate can reach 90.84%. In addition, the following parameters influence combined gold leaching in decreasing order: bleaching powder dose, reaction temperature, potassium chlorate concentration, and reaction pH.The results show that potassium chlorate and bleaching powder combined is advantageous for leaching of Carlin-type gold ore in Guizhou. It provides a high leaching rate. There is no need for pre-oxidation of gold ore. It is a simple inexpensive process that can be operated at a low optimum reaction temperature. Thus, it is a feasible method in industrial applications and provides a new way for gold leaching.

Monitoring of On-Site generated Hypochlorite for Water Disinfection

The aim of this study was to better evaluate the impact of on-site electro-generated hypochlorite for water disinfection. For this venture, the daily variability of hypochlorite-generating systems and their performance to produce low disinfection by-products during the formation of hypochlorite were observed. Seven on-site electro-generated hypochlorite installations, were selected at different swimming pool facilities in Switzerland. Active chlorine (AC), the two disinfection by-products chlorate (ClO3-) and perchlorate (ClO4-), and the pH were monitored over several hours. All monitored installations produced significant concentrations of chlorate, related to the measured active chlorine concentration. The median chlorate concentrations ranged between 1.4 to 76.9 µg ClO3-/mg AC during daily monitoring. Perchlorates have been detected only in the installations of one brand that generated concentrations up to 34.9 µg ClO4-/mg AC. For all installations, pH was lower than expected with a median pH of 9.6. Some samples presented even surprisingly acidic pH leading to possible sample degradation. This study clearly shows the weakness of a one-shot sampling to evaluate the quality of on-site electro-generated hypochlorite systems, due to high daily process variations. Additionally, the evaluation of the influence of three process parameters has pointed out that including chlorate aspects during the optimisation stage of on-site generated hypochlorite may significantly reduce chlorate contamination during water disinfection.

Determination of chlorate and perchlorate in pangasius samples by liquid chromatography tandem mass spectrometry (LC-MS/MS)

The LC-ESI-MS/MS method has been successfully developed for determination of chlorate and perchlorate in pangasius samples. Residues of chlorate and perchlorate in the sample were extracted with a methanolic solution acidified with 1% formic acid. Then, the extract was cleaned with C18 powder, used a normal phase column to separate chlorate and perchlorate, and quantified on an LC-ESI-MS/MS instrument. The method was validated for good specificity, linear calibration curve in the range of 0.0005 - 0.015 mg/L; the limit of quantification (LOQ) was 0.005 mg/kg; the recovery and relative standard deviation was from 91 to 109% and from 6.4 to 9.5% respectively and all met the requirements of SANTE. The method was applied to the real analysis, a total of 427 pangasius fillet samples collected from seafood processing companies. There were 76 samples were detected chlorate equivalent to 18%. The concentration of chlorate ranged from 0.43 to 253 mg/kg.  

Hydrogen-Chlorate Electric Power Source: Feasibility of the Device, Discharge Characteristics and Modes of Operation.

A power source based on the current-generating reaction of aqueous chlorate-to-chloride reduction by molecular hydrogen would provide as much as 1150 Wh per 1 L of reagent storage (for a combination of 700 atm compressed hydrogen and saturated aqueous solution of lithium chlorate) at room temperature, but direct electroreduction of chlorate only proceeds with unacceptably high overvoltages, even for the most catalytically active electrodes. In the present study, we experimentally demonstrated that this process can be performed via redox-mediator catalysis by intermediate products of chlorate reduction, owing to their participation in homogeneous com- and disproportionation reactions. A series of current–voltage and discharge characteristics were measured for hydrogen-chlorate membrane–electrode assembly (MEA) cells at various concentrations of chlorate and sulfuric acid under operando spectrophotometric monitoring of the electrolyte composition during the discharge. We established that chlorine dioxide (ClO2) is the key intermediate product; its fraction in the electrolyte solution increases progressively, up to its maximum, equal to 0.4–0.6 of the initial amount of chlorate anions, whereas the ClO2 amount decreases gradually to a zero value in the later stage. In most discharge experiments, the Faradaic yield exceeded 90% (maximal value: 99%), providing approximately 48% chemical energy storage-to-electricity conversion efficiency at maximal power of the discharge (max value: 402 mW/cm2). These results support prospect of a hydrogen-chlorate flow current generator as a highly specific energy-capacity source for airless media.

Health risk assessment of perchlorate and chlorate in red swamp crayfish (Procambarus clarkii) in China

Perchlorate and chlorate are both strong oxidants and thyroid toxicants that are widely distributed in soil, water and human foods. The red swamp crayfish (Procambarus clarkii) is a common aquatic organism that is popular in Chinese culinary dishes. Dietary intake is the main route of human exposure to perchlorate and chlorate, though the health risks of crayfish consumption are unknown. Thus, this study investigated the quantities of perchlorate and chlorate in red swap crayfish from sampling sites in five provinces located near the Yangtze River in China, along with the associated health risks of consuming this species. Perchlorate was detected in 55.6–100 % of crayfish samples in each sampling location, and chlorate was found in 100 % of samples cross all sites. Concentrations of perchlorate in crayfish from upstream provinces (Hubei, Hunan and Jiangxi) were higher than those from downstream provinces (Anhui and Jiangsu). Perchlorate and chlorate concentrations were positively correlated in crayfish, suggesting that chlorate may be a degradation byproduct of perchlorate. The quantities of both pollutants in hepatopancreas tissue were higher than in muscle tissues (p < 0.05), such that we do not recommend ingesting crayfish hepatopancreas. Hazard quotient (HQ) values for chlorate in crayfish were <1 across all provinces, suggesting no potential health risk of chlorate exposure through crayfish consumption. However, perchlorate concentrations in crayfish from the Jiangxi province had an associated HQ value >1, suggesting potential risks for human health. These results will be useful in informing mitigation measures aimed at reducing perchlorate exposure associated with crayfish consumption.

E-peroxone process of a chlorinated compound: Oxidant species, degradation pathway and phytotoxicity

An electro-peroxone (EP) process was conducted in an up-flow bubble column reactor with BDD electrodes. The efficiency of the process was tested in the 4-Chlorophenol (4-CPh) mineralization and compared with that attained by single treatments like ozonation (O3) and electro-oxidation (EO). At [TOC]o= 56 mg·L−1, pHo= 7.0, T = 293 K, j = 0.06 A·cm−2, t = 120 min, the oxidation power decreased in the following order EP>EO>O3, and the TOC removed was, in the same order, 100%> 93%> 40%. The calculated synergy coefficient was 0.31, while the mineralization current efficiency percentage (MCE%) and the energy consumption (EC) were 12.24% and 11.48%, 2.84 and 2.31 kW·h−1, for EP and EO, respectively. The germination percentage of Lactuca sativa, was 100%, 30% and 20%, at the end of EP, EO and O3, respectively. This indicates that phytotoxicity, was only eliminated with EP. Based on the by-products, e.g. aromatic compounds (4-chlorocatechol, catechol, phenol, p-benzoquinone, hydroquinone) and carboxylic acids (maleic, formic, fumaric, succinic, oxalic, malonic and acetic acids) identified by UHPLC-UV/DAD and the changes of the concentration of chloride ion (Cl-), hypochlorite, chlorite, chlorate and perchlorate, a reaction pathway was proposed for the 4-CPh mineralization by the E-peroxone process. It was demonstrated that under the studied conditions both, hydrogen peroxide and ozone, are produced during EO. At the end of EO, H2O2, carboxylic acids and perhaps persulfates, are responsible for the phytotoxicity of the solution.

Sensor Data Fusion as an Alternative for Monitoring Chlorate in Electrochlorination Applications

As chlorate concentrations have been found to be harmful to human and animal health, governments are increasingly demanding strict control of the chlorate concentration in drinking water. Since there are no chlorate sensors available, the current solution is sampling and laboratory analysis. This is costly and time consuming. The aim of this work was to investigate Sensor Data Fusion (SDF) as an alternative approach, with a focus on chlorate formation in the electrochlorination process, and design an observer for the real-time estimation of chlorate. The pH, temperature and UV-a absorption were measured in real time. A reduced-order nonlinear model was derived, and it was found to be detectable. An Extended Kalman Filter (EKF), based on this model, was then used to estimate the chlorate formation. The EKF algorithm was verified experimentally and was found to be capable of accurately estimating chlorate concentrations in real time. Electrochlorination is an emerging and efficient method of disinfecting drinking water. Soft sensing of chlorate concentrations, as proposed in this paper, may help to better control and manage the process of electrochlorination.

Comparison of Disinfection By-Product Formation and Distribution during Breakpoint Chlorination and Chlorine-Based Disinfection in Drinking Water

Breakpoint chlorination (BC) and disinfection with chlorine-based disinfectant are widely used procedures in drinking water production. Both involve dosing chlorine into the raw water, where it can react with organic compounds, forming disinfection by-products (DBPs) of health concern. However, technological parameters (e.g., contact time, chlorine dosage, and bromide to residual free chlorine ratio) of the two chlorination procedures are different, which can lead to differences in DBP formation. To better understand this, a year-long sampling campaign was carried out at three waterworks in Hungary, where both BC and chlorine disinfection are used. To confirm the results of the field sampling, bench-scale experiments were carried out, investigating the impact of (a) bromide concentration in raw water, (b) residual free chlorine (bromide to residual chlorine ratio), and (c) contact time on DBP formation. The measured DBPs were trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and chlorate. During BC, the DBPs were formed in higher concentration, with the exception of one waterwork having elevated bromide content in the raw water. Bromine substitution factors (BSFs) were significantly higher during disinfection than BC in both field and laboratory experiments. After BC, the chlorate concentration range was 0.15–1.1 mg/L, and 96% of the samples exceeded the European Union (EU) parametric value (0.25 mg/L), whereas disinfection contributed only slightly. Granular activated carbon (GAC) filters used to remove DBPs in waterworks were exhausted after 6–8 months of use, first for those chlorinated THMs, which are generated predominantly during BC. The biological activity of the filters started to increase after 3–6 months of operation. This activity helps to remove the biodegradable compounds, such as disubstituted haloacetic acid (DHAAs) and HANs, even if the adsorption capacity of the GAC filters are low.

Multi-angle comparison of UV/chlorine, UV/monochloramine, and UV/chlorine dioxide processes for water treatment and reuse

Advanced oxidation processes (AOPs) have been increasingly studied and practiced for micropollutant abatement in drinking water treatment and potable water reuse. This study conducted the multi-angle comparison of the UV/chlorine, UV/monochloramine (UV/NH2Cl), and UV/chlorine dioxide (UV/ClO2) AOPs with respect to reactive species generation, micropollutant degradation, byproduct formation, and toxicity change. The concentrations of radicals (HO·, Cl·, and ClO·) generated in the three AOPs followed the order of UV/chlorine > UV/NH2Cl > UV/ClO2 at an oxidant dose of 70 μM, an irradiation wavelength of 254 nm, and a pH of 7.5. The concentration of ozone generated in the UV/ClO2 AOP was higher than that in the UV/chlorine AOP, while ozone was not generated in the UV/NH2Cl AOP. The effects of pH (pH 6.0, 7.5, and 9.0) and UV wavelength (254 nm, 285 nm, and 300 nm) on the three AOPs were evaluated and compared. Using the radical and ozone concentrations determined in this study, the pseudo-first-order degradation rate constants of 24 micropollutants by the three AOPs were predicted and compared. When the three AOPs were used to treat the water containing the same concentration of natural organic matter, the formation of total organic chlorine (TOCl) and the organic byproduct-associated toxicity followed the same order of UV/chlorine > UV/NH2Cl > UV/ClO2. On the contrary, the inorganic byproduct-associated toxicity followed the order of UV/ClO2 > UV/chlorine > UV/NH2Cl, due to the high concentrations of chlorite and chlorate formed in the UV/ClO2 AOP. Findings in this study offer fundamental information useful for the selection and operation of AOPs for micropollutant abatement in drinking water treatment and potable water reuse.

Application of nanofiltration for the removal of chlorate from skim milk

Chlorate has emerged as a residue of concern within the food and beverage sector, associated with chlorine sanitiser usage for sanitation in industrial food production and is of particular concern due to the adverse health effects of chlorate exposure. This study assessed a nanofiltration approach for the removal of chlorate from skim milk. The chlorate content of skim milk was decreased by up to 62.3 ± 2.6% per unit of dry matter (DM) when concentrating from 9 to 18% DM at both lab and pilot-scale. Chlorate had a rejection efficiency of 38.8 ± 8.1%, which was lower than calcium, potassium, and lactose at 97.7 ± 0.3%, 64 ± 3.0%, and 98 ± 0.3% respectively. In contrast, a comparative reverse osmosis membrane demonstrated a chlorate rejection of 98 ± 0.5%, identifying applications in chlorate free process water production.

The Photochemical Chlorate-Iodide Clock Reaction.

Mixing iodide and perchloric acid solutions with an excess of chlorate inside a diode-array spectrophotometer led to the observation of an abrupt decrease of the absorbance at the 215 nm isosbestic point after an induction period. The clock time decreases by increasing the initial concentrations of chlorate and acid, but increasing the initial iodide concentration has an opposite effect. The proposed mechanism simulates the experimental results and considers the interaction of UV light with iodide, producing iodine and triiodide ion. The autocatalytic core of this mechanism is the same as that employed to explain the autocatalytic behavior of chlorine dioxide-iodine reaction, but considering H2IO+ as the reactive species rather than HOI, being a more realistic mechanism for acid conditions.