Development of chlorine dioxide-related by-product models for drinking water treatment.

Factorial experiments were conducted using source waters from seven drinking water treatment plants in Ontario, Canada to develop statistically based model equations capable of predicting chlorine dioxide consumption and chlorite and chlorate formation upon chlorine dioxide application. The equations address raw water quality and operational parameters including pH, temperature, chlorine dioxide concentration, reaction time and water organic content (as described by non-purgeable organic carbon x ultraviolet absorbance measured at 254 nm, NPOC x UV254). Terms describing two-factor interaction effects were also included, improving the accuracy of the predictive equations in fitting measured response concentrations as evaluated through internal and external validations. Nearly 80% of the predictions for chlorine dioxide consumption and chlorite formation were observed to be within 20% of the measured levels. Over 90% of the predicted chlorate levels were within +/- 0.1 mg/L of the measured levels. Chlorine dioxide concentration and NPOC x UV254 were key parameters when developing the predictive models.     

Evaluation of chlorite and chlorate genotoxicity using plant bioassays and in vitro DNA damage tests

In the last few years chlorine dioxide has been increasingly used for disinfecting drinking water in many countries. Although it does not react with humic substances, chlorine dioxide added to water is reduced primarily to chlorite and chlorate ions, compounds that are under investigation for their potential adverse effects on human health. The aim of this research was to study the genotoxicity of chlorite and chlorate and their mixtures. The end-points included two plant tests (chromosomal aberration test in Allium cepa and micronucleus assay in Tradescantia, carried out at different times of exposure) and two genotoxicity tests in human HepG2 cells (comet assay and cytokinesis-blocked micronucleus test). Preliminary toxicity tests were carried out for both plant and HepG2 assays. The results showed that chlorite and chlorate are able to induce chromosomal damage to plant systems, particularly chromosomal aberrations in A. cepa root tip cells, even at concentrations lower than the limit established by Italian normative law and WHO guidelines. In HepG2 cells increased DNA damage was only observed for chlorate at the lowest concentration. No increase in micronuclei frequency was detected in any of the samples tested in human HepG2 cells.     

Photodecomposition du bioxyde de chlore et des ions chlorite par irradiation U.V. en milieu aqueux—partie I. Sous-produits de reactionPhotodecomposition of chlorine dioxide and chlorite by U.V.-Irradiation—Part I. Photo-products

Literature data about the photochemistry of oxychlorine compounds in aqueous solutions (flash photolysis, pulse radiolysis, solar radiation) indicate that the products (ClO, Cl, O, O⁻,…) generated from the primary photochemical reactions of decomposition of chlorine dioxide and hypochlorite can then initiate complex reactions which lead to the formation of many secondary products (Cl₂O₂, Cl₂O₁, ClO⁻,…) and of chlorate, chloride and molecular oxygen as end-products (Table 1). The aim of this work was to study the photodecomposition of aqueous solutions of chlorine dioxide and chlorite in u.v. reactors equipped with low pressure mercury vapour lamps in order to show the effects of pH and of the initial concentrations on the nature of photoproducts and on the rate of photodecomposition of ClO₂ and ClO₂⁻. This paper presents the data obtained for the identification of photoproducts. The kinetics of photodecomposition will be presented in another paper (Part II).     

Technical note the pattern of ClO2 stabilized by Na2CO3/H2O2

In this paper, the existing patterns of carbonate and ClO2 in the so-called "stabilized chlorine dioxide" solution which is stabilized by stabilizers Na2CO3 and H2O2 are analyzed. Meanwhile, thermostability, UV absorption spectrum, specificity of the paper chromatogram, microstructure and ionic chromatogram of this solution were studied, and contrasted with pure NaClO2 and ClO2. The results show that ClO2 in "stabilized chlorine dioxide" solution exists in the form of chlorite ClO2-, carbonate exists in the form of bicarbonate. Therefore, it is considered that "stabilized chlorine dioxide" solution is mixed solution of ClO2- and HCO3-, its pH being 8.5.     

Disinfectant efficacy of chlorite and chlorine dioxide in drinking water biofilms

The drinking water industry is closely examining options to maintain disinfection in distribution systems. In particular this research compared the relative efficiency of the chlorite ion (ClO2-) to chlorine dioxide (ClO2) for biofilm control. Chlorite levels were selected for monitoring since they are typically observed in the distribution system as a by-product whenever chlorine dioxide is applied for primary or secondary disinfection. Previous research has reported the chlorite ion to be effective in mitigating nitrification in distribution systems. Annular reactors (ARs) containing polycarbonate and cast iron coupons were used to simulate water quality conditions in a distribution system. Following a 4 week acclimation period, individual ARs operated in parallel were dosed with high (0.25mg/l) and low (0.1mg/l) chlorite concentrations and with high (0.5 mg/l) and low (0.25mg/l) chlorine dioxide concentrations, as measured in the effluent of the AR. Another set of ARs that contained cast iron and polycarbonate coupons served as controls and did not receive any disinfection. The data presented herein show that the presence of chlorite at low concentration levels was not effective at reducing heterotrophic bacteria. Log reductions of attached heterotrophic bacteria for low and high chlorite ranged between 0.20 and 0.34. Chlorine dioxide had greater log reductions for attached heterotrophic bacteria ranging from 0.52 to 1.36 at the higher dose. The greatest log reduction in suspended heterotrophic bacteria was for high dose of ClO2 on either cast iron or polycarbonate coupons (1.77 and 1.55). These data indicate that it would be necessary to maintain a chlorine dioxide residual concentration in distribution systems for control of microbiological regrowth.     

Formation of disinfection by-products after pre-oxidation with chlorine dioxide or ferrate

The effect of pre-oxidation with chlorine dioxide (ClO₂) or ferrate (Fe(VI)) on the formation of disinfection by-products (DBPs) during chlorination or chloramination was tested with natural waters from 12 sources (9 surface waters, 1 groundwater, and 2 wastewater effluents). DBPs investigated included trihalomethanes (THM), chloral hydrate (CH), haloketones (HK), haloacetonitriles (HAN) and trichloronitromethane (TCNM), chlorite and chlorate. Chlorite and chlorate were found in the ClO₂-treated waters. Application of 1 mg/L ClO₂ ahead of chlorination reduced the formation potential for THM by up to 45% and the formation of HK, HAN and TCNM in most of the samples. The CH formation results were mixed. The formation of CH and HK was enhanced with low doses of Fe(VI) (1 mg/L as Fe), but was greatly reduced at higher doses (20 mg/L Fe). Fe(VI) reduced the formation of THM, HAN and TCNM in most of the samples. Reduced potential for the formation of NDMA was observed in most of the samples after both ClO₂ and Fe(VI) pre-oxidation.     

Photodecomposition du bioxyde de chlore et des ions chlorite par irradiation u.v. en milieu aqueux-partie II. Etude cinetiquePhotodecomposition of chlorine dioxide and chlorite by U.V.-Irradiation—Part II. Kinetic study

The decomposition of ClO₂ and ClO₂⁻ by u.v. radiation leads to the production of chlorate, chloride and oxygen as end-products via complex reactions which are initiated by the products generated by the primary reactions of photolysis (Buxton and Subhani, 1972a; Mialocq et al., 1973; Karpel Vel Leitner et al., 1992). As far as the rate of decomposition is concerned, Bowen and Cheung (1932) and Zika et al. (1985) have shown that the quantum yield of photodecomposition of chlorine dioxide (overall reaction) increases when the wavelength decreases [Zika et al. (1985): φ = 0.46 at 366 nm and 1.4 at 296.7 nm]. However, the values of the quantum yield of photodecomposition of ClO₂ and ClO₂⁻ at 253.7 nm as well as the quantum yields for the primary reactions of photolysis of ClO₂ and ClO₂⁻ at different wavelengths are not given in the literature.

The aim of this work was to study the kinetics of photodecomposition of chlorine dioxide and of chlorite by u.v. irradiation.     

Removal of chlorine dioxide disinfection by-products by ferrous salts

Chlorine dioxide when used as an effective disinfectant forms undesirable disinfection by-products, i.e. chlorite and chlorate ions. The aim of this research was to study the removal of these ions by ferrous ions in the presence or absence of oxygen. The efficiency of Fe+2 for ClO2- and ClO3- removal was followed by a determination of their initial and final concentrations, pH and delta Fe+2 consumed/delta ClO2- removed ratios. The optimal weight ratio of delta Fe+2 consumed/delta ClO2- removed for complete ClO2 removal was found to be close to the theoretical calculated value of 3.31. It was proved that ferrous salts can reduce chlorite ions to harmless Cl- ions. This method can be recommended as a part of ClO2 disinfection to ensure safe drinking water, with no harm to water consumers and to the environment.     

Photodecomposition du bioxyde de chlore et des ions chlorite par irradiation u.v. en milieu aqueux-partie II. Etude cinetique

The decomposition of ClO₂ and ClO₂⁻ by u.v. radiation leads to the production of chlorate, chloride and oxygen as end-products via complex reactions which are initiated by the products generated by the primary reactions of photolysis (Buxton and Subhani, 1972a; Mialocq et al., 1973; Karpel Vel Leitner et al., 1992). As far as the rate of decomposition is concerned, Bowen and Cheung (1932) and Zika et al. (1985) have shown that the quantum yield of photodecomposition of chlorine dioxide (overall reaction) increases when the wavelength decreases [Zika et al. (1985): φ = 0.46 at 366 nm and 1.4 at 296.7 nm]. However, the values of the quantum yield of photodecomposition of ClO₂ and ClO₂⁻ at 253.7 nm as well as the quantum yields for the primary reactions of photolysis of ClO₂ and ClO₂⁻ at different wavelengths are not given in the literature.The aim of this work was to study the kinetics of photodecomposition of chlorine dioxide and of chlorite by u.v. irradiation.     

Chlorine dioxide reactivity with proteins

Studies were conducted to evaluate chlorine dioxide reactivity with proteins and the role of these reactions in the inactivation of the bacterial virus f2 with chlorine dioxide. The effect of chlorine dioxide on the ability of f2 to specifically attach to its host Escherichia coli K13 was compared to the inactivation of virus during the initial seconds of contact time. At pH 7.2 and and 5°C, the virus was rapidly inactivated with 0.6 mg l⁻¹ of chlorine dioxide. Approximately 2 log units of inactivation were observed within 30 s. The loss of protein specific attachment function nearly paralleled intact virus inactivation with 1.2 log units of attachment inhibition occurring within 30 s. The inactivation of virus and the inhibition of specific attachment both increased with increasing pH and increasing disinfectant concentration.Inactivation of f2 was hypothesized to occur as the result of chlorine dioxide reacting with discrete chemical moieties in the viral protein. Cysteine, tyrosine and tryptophan reacted with chlorine dioxide within a time frame that could affect viral inactivation. In denatured f2 capsid protein monomers, these amino acids were almost totally degraded within 2 min by chlorine dioxide. Only tyrosine reacted with chlorine dioxide following treatment of the intact virion with disinfectant. Even though the degradation of tyrosine residues occurred at a much slower rate than the rate of virus inactivation, the protein component of f2 virus appeared to be the site of the lethal lesion produced by chlorine dioxide. These tyrosine reactions with chlorine dioxide appeared to alter the virus such that specific attachment was inhibited.     

The synthesis of activated chlorine in an electrodialyzer with a tube ceramic membrane and a titanium–dioxide–manganese anode

The article has investigated the impact of the design of an electrodialyzer with a little soluble titanium–dioxide–manganese anode and a ceramic membrane separating electrode spaces, on the concentration of chlorate–ions when producing sodium hydrochlorite. It has been shown that the location of the anode inside a ceramic membrane makes it possible to obtain sodium hypochlorite without an impurity of chlorite–ions.     

二氧化氯在饮用水处理中的应用研究

文章介绍了一个采用二氧化氯对饮用水处理的改进方案,能有效控制水中的三氯甲烷及亚氯酸盐的生成,该技术改善了的水质,降低了生产成本。     

Chlorine dioxide reactivity with nucleic acids

Studies were conducted with the bacterial virus f2 to determine the reactivity of chlorine dioxide with viral nucleic acid, and to evaluate the role of these reactions in the inactivation of virus with chloride dioxide. The effect of chlorine dioxide on naked infectious RNA was compared to the inactivation of intact virus and to infectious f2 RNA extracted from virus which was treated with chlorine dioxide. At pH 7.2 and 5°C, greater than 4 log units of virus inactivation were observed within 2 min of contact time. Almost no inactivation of infectious RNA extracted from chlorine dioxide treated virus was observed. Treatment of naked infectious RNA with chlorine dioxide yielded less than 1 log unit of inactivation after 5 min of contact time. The rate of inactivation both f2 virus and infectious RNA by chlorine dioxide increased with increasing pH.Inactivation of f2 infectious RNA was attributed to chlorine dioxide reactions with nucleotides. The reaction of chlorine dioxide within yeast RNA was uniquely associated with guanosine monophosphate (GMP). The reaction between chlorine dioxide and GMP may account for inactivation of naked f2 RNA. However, this reaction does not explain the inactivation of intact f2 virus, as the RNA within the treated virion remains infectious despite several log units of virus inactivation.     

二氧化氯消毒效果影响因素试验研究

通过对比实验,考察了二氧化氯、液氯和氯胺三种常用消毒剂对肠道菌的灭活效果,以及pH、温度、培养基稀释倍数等因素对二氧化氯消毒效果的影响.试验结果表明,二氧化氯消毒剂具有高效性和广谱性;pH值在6.0～9.0内变化,二氧化氯的消毒效果几乎不受影响;温度的升高会加强二氧化氯的灭菌效果;随着培养基稀释倍数的增加,粪肠球菌对二...     

Cinetiques et mecanismes de la degradation de la creatinine sous l'action de l'hypochloriteKinetics and mechanisms of hypochlorite oxidation of creatinine

An area of substantial interest in current research on chlorination is the formation, stability and nature of chloramines formed by the interaction of chlorine with nitrogen organic compounds of biological origin in natural water or swimming pool water. It is desirable to be able to predict the lifetime of these harmful compounds under various conditions. The research described here constitutes an effort to gather important baseline data regarding the rate of formation of creatinine chloramines, the stabilities of these products and their identities.

Some researchers have studied the effect of the presence of chlorinated creatinine compounds in swimming pool water. Lomas (1967), showed that the presence of urine in water allowed the formation of compounds which reacted with DPD like dichloramine. He reported that the presence of this apparent dichloramine could be due to a chlorine derivative of creatine and creatinine derived from urine. Hamence (1980) confirmed this work and found that urine and particularly creatinine were responsible for the apparent nitrogen trichloride. As a result of this work it was concluded that the DPD-fast titrimetric method of analysis did not determine nitrogen trichloride but other chlorine compounds, particularly those of chlorinated creatinine and creatine. We found it interesting to examine in this study, for a range of hypochlorite creatinine ratios and pHs, the kinetics and mechanisms of formation and decomposition of N-chlorocreatinines.

The hypochlorite oxidation of creatinine in aqueous solution has been investigated in the dark. The following of creatinine and chloramines concentrations by the DPD-fast titrimetric method and by their u.v. spectra confirmed Lomas' and Hamence's works. However we observed dichloramine formation (Fig. 4) when the molar ratio of hypochlorite and creatinine was sufficient to decompose all chlorinated creatinine forms. The creatinine determination (HPLC method) suggested that N-chlorocreatinines were formed rapidly at an initial stage. Then they were decomposed by an apparent first order reaction at pH 8. With equimolar (1:1 mmol) amounts of hypochlorite and creatinine at pH 8, it appeared that N-chlorocreatinines were decomposed by hydrolysis to regenerate creatinine. We observed then the formation of creatine, 1-methylhydantoin, chlorocreatinines and NH₂Cl (Fig. 3). When the molar ratio was greater, the N-chlorocreatinines decomposed completely to form carbon dioxide, chlorite ion and mineral chloramines (see Table 1).

The reaction in the initial stage should be considered as an electrophile substitution followed slowly by hydrolysis when pH remained around 8 (Scheme 2). If the addition of hypochlorite affects the amine group of the molecule, 1-methylhydantoin is produced (Scheme 3) with NH₂Cl. Reaction yield was about 10% of initial creatinine.

In acid aqueous solution, with a molar ratio of 3, we also obtained trichlorocreatinine. This reaction is due to the various form of creatinine after addition of proton on amino of N-H groups of the molecule. In these conditions N-chlororcreatinines remained stable in aqueous solution for many days. However in the presence of free chlorine, we observed the production of carbon dioxide and mineral chloramines. After 4 days the residual concentration of N-chlorocreatinines was half the initial value.

It appears that N-chlorocreatinines formed during the chlorination of natural or swimming pool water were relatively stable, leading to the increase of the combined chlorine level. This stability was a function of the molar ratio of hypochlorite and creatinine, and pH. However, since most of the difference types of water had a pH in the range of 6–9, there would be little effect of pH at ambient temperature.     

Chlorate and nitrate reduction pathways are separately induced in the perchlorate-respiring bacterium Dechlorosoma sp. KJ and the chlorate-respiring bacterium Pseudomonas sp. PDA

The effect of nitrate on perchlorate and chlorate reduction by perchlorate-respiring bacteria (PRB), and on chlorate reduction by chlorate-respiring bacteria (CRB), is not well understood, particularly with respect to the induction of pathways used to degrade these different chemicals. Based on kinetic data obtained in a series of batch tests, we determined that perchlorate respiratory enzymes were inducible (by chlorate or perchlorate) and separate from those used for denitrification by PRB strain Dechlorosoma sp. KJ. Aerobically grown cultures of KJ had lag times of greater than 0.3-2 days when transferred to a medium containing only perchlorate, chlorate, or nitrate as an electron acceptor. There were no lag times for transfers between identical media. Washed cells reduced very little nitrate (<10%) when grown only on chlorate or perchlorate. When grown on nitrate, they degraded little chlorate or perchlorate. The same lack of activity with these electron acceptors was also observed using cell extracts and methyl viologen as an electron carrier, indicating a lack of reactivity was not due to failure of the chemical to diffuse into the cell. Taken together, these results indicated that enzymes for perchlorate and nitrate reduction are separately expressed in strain KJ. The presence of small amounts of nitrate in contaminated groundwater may actually help to increase rates of perchlorate reduction once the nitrate is completely removed. When strain KJ was pre-grown on nitrate and perchlorate, perchlorate degradation (in the absence of nitrate) was more rapid compared to cells grown only on perchlorate. Pseudomonas sp. PDA was unable to degrade perchlorate or grow using nitrate, and the induction of enzymes necessary for chlorate respiration differed for strains KJ and PDA. While chlorate reductase and chlorite dismutase activity were induced in KJ by chlorate or perchlorate under anaerobic conditions, these two enzymes were constitutively expressed by PDA under anaerobic and aerobic conditions independent of the presence of chlorate. To our knowledge, this is the first report of constitutive expression of both chlorate reductase and chlorite dismutase in a bacterium.     

The impact of ferrous ion reduction of chlorite ion on drinking water process performance

The use of chlorine dioxide (ClO₂) as a primary disinfectant and pre-oxidant in drinking water treatment is being explored as an alternative to chlorine for reducing disinfection by-product formation and to assure compliance with United States Environmental Protection Agency's Stage 1 Disinfection/Disinfection By-Products Rule. However, the ClO₂ by-product chlorite ion (ClO₂⁻) is also regulated by the same regulation. Ferrous iron (Fe(II)) has been shown to effectively reduce chlorite ion to chloride ion (Cl⁻) and this study was conducted to evaluate the impact on overall treatment process performance due to the ferric hydroxide solids that form from the reaction. Ferrous iron application was explored at three different points in a pilot-scale water treatment system: pre-rapid mix, pre-settling and pre-filter. Chlorite ion concentrations were effectively reduced from 2 mg/L to less than 0.3 mg/L using an Fe(II) dose of approximately 6 mg/L for all trials. Fe(II) addition at the rapid mix caused no adverse effects and, in fact, allowed for reduction of the alum dose due to the newly formed ferric hydroxide acting as a supplemental coagulant. An increase of 241 and 247% of total suspended solids influent to the filter process was observed when Fe(II) was applied at the pre-settling and pre-filter locations. Pilot-scale filter runs during these trials were less than 2 h and never obtained true steady state conditions. Jar testing was performed to better understand the nature of the ferric hydroxide solids that are formed when Fe(II) was oxidized to Fe(III) and to explore the effectiveness of Fe(II) addition at intermediate stages in the flocculation process.     

ClO2消毒涉及毒性问题的探讨

对二氧化氯 Cl O2 消毒无机副产物亚氯酸盐 Cl O2 - 和氯酸盐 Cl O3- 来源进行了分析 ,高浓度的 Cl O2 、Cl O2 - 和 Cl O3- 的毒性主要与血液系统有关 ,在相当于人饮用 Cl O2 、Cl O2 - 和 Cl O3- 混合溶液 1 60倍的动物血液常规检测中未发现异常 ,Ames试验显示试验浓度的 Cl O2 、Cl O2 - 和 Cl O3-水溶液不具有致突变作用 .     

二氧化氯/混凝剂工艺处理含铁水的试验研究

通过向含铁水中投加二氧化氯和混凝剂,考察了二氧化氯对水中铁的去除效果及其影响因素。结果表明,二氧化氯投加量、原水pH、预氧化时间和混凝剂投加量对铁的去除效果均有较大的影响。当原水Fe2+浓度为5 mg/L时,二氧化氯最佳投加量为5 mg/L,最佳氧化时间为10 min,混凝剂的最佳投加量为1 mg/L,最佳pH值为7～9,对铁离子的去除率可达到94.0%。