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Chlorine dioxide (ClO2), an alternative disinfectant to chlorine, has been widely applied in water and wastewater disinfection. This paper aims at presenting an overview of the inactivation kinetics and mechanisms of ClO2 with viruses. The inactivation efficiencies vary greatly among different virus species. The inactivation rates for different serotypes within a family of viruses can differ by over 284%. Generally, to achieve a 4-log removal, the exposure doses, also being referred to as Ct values (mutiplying the concentration of ClO2 and contact time) vary in the range of 0.06–10 mg L−1 min. Inactivation kinetics of viruses show two phases: an initial rapid inactivation phase followed by a tailing phase. Inactivation rates of viruses increase as pH or temperature increases, but show different trends with increasing concentrations of dissolved organic matter (DOM). Both damages in viral proteins and in the 5′ noncoding region within the genome contribute to virus inactivation upon ClO2 disinfection.

The pathogenic free-living amoebae, Naegleria fowleri and Acanthamoeba polyphaga , are found in freshwater, soil, and unchlorinated or minimally chlorinated swimming pools. N. fowleri and A. polyphaga are becoming problematic as water leisure activities and drinking water are sources of infection. Chlorine dioxide (ClO 2 ) gas is a potent disinfectant that is relatively harmless to humans at the concentration used for disinfection. In this study, we examined the amoebicidal effects of ClO 2 gas on N. fowleri and A. polyphaga . These amoebae were exposed to ClO 2 gas from a ready-to-use product (0.36 ppmv/h) for 12, 24, 36, and 48 h. Microscopic examination showed that the viability of N. fowleri and A. polyphaga was effectively inhibited by treatment with ClO 2 gas in a time-dependent manner. The growth of N. fowleri and A. polyphaga exposed to ClO 2 gas for 36 h was completely inhibited. In both cases, the mRNA levels of their respective actin genes were significantly reduced following treatment with ClO 2 gas. ClO 2 gas has an amoebicidal effect on N. fowleri and A. polyphaga . Therefore, ClO 2 gas has been proposed as an effective agent for the prevention and control of pathogenic free-living amoeba contamination.

Effects of pre-treating pine kraft pulp kappa number 31.5 with peracetic acid (Paa) (0.33% and 0.66% as active oxygen based on oven-dried pulp) before O2-delignification were studied relative to the consumption of chlorine dioxide in a subsequent Elemental Chlorine Free (ECF) bleaching process. The study showed that such pre-treatment is an effective way to extend the delignification of the pine pulp and to reduce the consumption of chlorine dioxide required to bleach the pulp to a brightness of 87%. The reduction in chlorine dioxide required to bleach the pine pulp depended on the amount of Paa used for pre-treatment. Furthermore, the research showed that decreasing the kappa number of the pine pulp to approximately 7.5 units (with Paa pre-treatment and lengthening of O2-delignification process) caused an over-proportional reduction (by approximately 62.5%) in chlorine dioxide consumption to bleach the pulp to 87% brightness.

This work describes the effect of the hot chlorine dioxide delignification (D HT ) on the properties of bagasse fiber and the formation of AOX. The bagasse pulp was subjected to both D HT and normal temperature chlorine dioxide delignification (D 0 ), and the AOX contents in the effluent were determined respectively. The GC–MS results showed that the main components of the D 0 stage wastewater were chlorinated hydrocarbons and chlorinated diphenyls. In contrast, those AOXs in the D HT stage wastewater were very few. The GC–MS, ATR-FTIR, and XPS results showed the D HT process is more effective in the removal of the residual phenolic lignin and the hemicellulose-linked HexA compared with D 0 . Furthermore, in comparison, the AOX content could be reduced by 50% with D HT . The fully bleached pulp obtained via D HT E p D process has a higher brightness than that obtained by D 0 E p D, which provides a reliable theoretical basis for industrial application.

Background Chlorine dioxide has been promoted as an alternative for the prevention and treatment of COVID-19, especially in Peru, despite the lack of evidence to support its efficacy. This study aimed to evaluate the factors associated with chlorine dioxide consumption in the Peruvian population. Methods Analytical cross-sectional study. An adult Peruvian population was evaluated where chlorine dioxide consumption was divided into two groups according to the purpose of use: as prevention (individuals without COVID-19 history) and as treatment (individuals with COVID-19 history). The associated factors in each group were evaluated using Poisson regressions with the bootstrapping resampling method. Results Of 3610 participants included, 3213 reported no history of COVID-19, and 397 had been infected. The prevalence of chlorine dioxide consumption to prevent or treat COVID-19 was 8 and 16%, respectively. Factors either positively or negatively associated with chlorine dioxide consumption for prevention were male sex (aPR: 1.36; 95% CI: 1.09–1.71), being an adult or older adult (aPR: 0.54; 95% CI: 0.35–0.82), having a health sciences student within the family unit (aPR: 1.38; 95% CI: 1.02–1.87), using medical information as the main source of information of COVID-19 (aPR: 0.57; 95% CI: 0.40–0.80), having comorbidities for COVID-19 (aPR: 1.36; 95% CI: 1.01–1.82), considering COVID-19 dangerous and deadly (aPR: 0.57; 95% CI: 0.45–0.74), using medications (aPR: 1.59; 95% CI: 1.25–2.06) and plants to prevent COVID-19 (aPR: 1.69; 95% CI: 1.21–2.36), considering chlorine dioxide ineffective (aPR: 0.18; 95% CI: 0.18–0.24), and being uninformed of its efficacy (aPR: 0.21; 95% CI: 0.16–0.28). In addition, factors associated with chlorine dioxide consumption for treatment were considering COVID-19 dangerous and deadly (aPR: 0.56; 95% CI: 0.33–0.96), considering chlorine dioxide ineffective (aPR: 0.22; 95% CI: 0.12–0.42), and being uninformed of its efficacy (aPR: 0.15; 95% CI: 0.07–0.32). Conclusions The prevalence of chlorine dioxide consumption to treat COVID-19 was higher than prevent. It is important to apply information strategies, prioritizing population groups with certain characteristics that are associated with a higher consumption pattern.

Gaseous chlorine dioxide (ClO2) is a potent antimicrobial agent used to control microbial contamination in food and water. This study evaluates the bactericidal activity of gaseous ClO2 released from a sodium chlorite (NaClO2) pad against Campylobacter jejuni. Exposure to a low concentration (0.4 mg/L) of dissolved ClO2 for 2 h resulted in a >93% reduction of C. jejuni, highlighting the bacterium’s extreme sensitivity to gaseous ClO2. To elucidate the molecular mechanism of ClO2-induced bactericidal action, transcriptomic analysis was conducted using RNA sequencing (RNA-seq). The results indicate that C. jejuni responds to ClO2-induced oxidative stress by upregulating genes involved in reactive oxygen species (ROS) detoxification (sodB, ahpC, katA, msrP, and trxB), iron transport (ceuBCD, cfbpABC, and chuBCD), phosphate transport (pstSCAB), and DNA repair (rdgB and mutY). Reverse transcription-quantitative PCR (RT-qPCR) validated the increased expression of oxidative stress response genes but not general stress response genes (spoT, dnaK, and groES). These findings provide insights into the antimicrobial mechanism of ClO2, demonstrating that oxidative damage to essential cellular components results in bacterial cell death.

The objective of this study was to model the inactivation of Escherichia coli O157:H7 under varying relative humidity and gaseous ClO2 concentrations. E. coli was spot-inoculated onto baby-cut carrots and exposed to ClO2 gas at concentrations of 100 ppm, 200 ppm, and 300 ppm, within relative humidity ranges of 50 to 90%. The results demonstrate that the germicidal efficacy of gaseous ClO2 significantly increases with both ClO2 concentration and relative humidity increase (p < 0.05). Two different non-linear inactivation models, the Weibull model and the modified Chick model, were employed to describe the inactivation kinetics of E. coli. The modified Chick model, based on chemical reaction kinetics, proved more suitable (RMSE < 0.356) than the Weibull model (RMSE < 0.469). A multiple regression analysis was subsequently conducted, utilizing the modified Chick model to describe the inactivation of E. coli under varying relative humidity and ClO2 concentrations. At 50% relative humidity and 100 ppm ClO2 concentration, the inactivation rate constant of the modified Chick model was 1.04 × 10−3 min−1. The inactivation rate constant increased to 3.63 × 10−3 min−1 and 0.0668 min−1 as ClO2 gas concentration increased from 100 to 300 ppm and relative humidity increased from 50 to 90%, respectively. The model developed in this study describes the inactivation of E. coli as a function of relative humidity and ClO2 concentration (R2 of 0.985) and can be utilized by the food processing industry to design gaseous ClO2 processes for achieving desired levels of E. coli inactivation.

Background Recent randomized clinical trials suggest that the effect of using cetylpyridinium chloride (CPC) mouthwashes on the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral load in COVID-19 patients has been inconsistent. Additionally, no clinical study has investigated the effectiveness of on-demand aqueous chlorine dioxide mouthwash against COVID-19. Methods We performed a randomized, placebo-controlled, open-label clinical trial to assess for any effects of using mouthwash on the salivary SARS-CoV-2 viral load among asymptomatic to mildly symptomatic adult COVID-19-positive patients. Patients were randomized to receive either 20 mL of 0.05% CPC, 10 mL of 0.01% on-demand aqueous chlorine dioxide, or 20 mL of placebo mouthwash (purified water) in a 1:1:1 ratio. The primary endpoint was the cycle threshold (Ct) values employed for SARS-CoV-2 salivary viral load estimation. We used linear mixed-effects models to assess for any effect of the mouthwashes on SARS-CoV-2 salivary viral load. Results Of a total of 96 eligible participants enrolled from November 7, 2022, to January 19, 2023, 90 were accepted for the primary analysis. The use of 0.05% CPC mouthwash was not shown to be superior to placebo in change from baseline salivary Ct value at 30 min (difference vs. placebo, 0.640; 95% confidence interval [CI], -1.425 to 2.706; P  = 0.543); 2 h (difference vs. placebo, 1.158; 95% CI, -0.797 to 3.112; P  = 0.246); 4 h (difference vs. placebo, 1.283; 95% CI, -0.719 to 3.285; P  = 0.209); 10 h (difference vs. placebo, 0.304; 95% CI, -1.777 to 2.385; P  = 0.775); or 24 h (difference vs. placebo, 0.782; 95% CI, -1.195 to 2.759; P  = 0.438). The use of 0.01% on-demand aqueous chlorine dioxide mouthwash was also not shown to be superior to placebo in change from baseline salivary Ct value at 30 min (difference vs. placebo, 0.905; 95% CI, -1.079 to 2.888; P  = 0.371); 2 h (difference vs. placebo, 0.709; 95% CI, -1.275 to 2.693; P  = 0.483); 4 h (difference vs. placebo, 0.220; 95% CI, -1.787 to 2.226; P  = 0.830); 10 h (difference vs. placebo, 0.198; 95% CI, -1.901 to 2.296; P  = 0.854); or 24 h (difference vs. placebo, 0.784; 95% CI, -1.236 to 2.804; P  = 0.447). Conclusions In asymptomatic to mildly symptomatic adults with COVID-19, compared to placebo, the use of 0.05% CPC and 0.01% on-demand aqueous chlorine dioxide mouthwash did not lead to a significant reduction in SARS-CoV-2 salivary viral load. Future studies of the efficacy of CPC and on-demand aqueous chlorine dioxide mouthwash on the viral viability of SARS-CoV-2 should be conducted using different specimen types and in multiple populations and settings.

The influence of pre-treating Kappa number of 18.0 industrial birch kraft pulp with peracetic acid (Paa) before oxygen delignification (OD) was studied relative to the pulps’ level of delignification, yield, brightness, intrinsic viscosity (IV), FS-number, tear index (TI), and the consumption of chlorine dioxide (ClO2) in its subsequent Elemental Chlorine Free (ECF) bleaching. The study showed that such pretreatment is a way to extend the delignification of such pulp quite selectively in OD based on values of IV, FS-number, and TI, and to reduce significantly the consumption of ClO2 required to bleach this pulp to a brightness of 87%. This reduction depended on the amount of Paa used for pulp pretreatment. For example, when 0.33% and 0.66% as active oxygen (A.O.) of Paa were used, ClO2 consumption to bleach the pulp to 87% was lowered by 15.4% and 42.3%, respectively. As high as a 61.5% reduction in ClO2 consumption in its bleaching could be obtained using 0.66% as A.O. on pulp and change of time of OD. This result allows for a significant decrease in the chlorine passing to the filtrates from washing the pulp after the D0 and E stages to the pulp mill wastewater treatment plant.

Recently, ClO2-based oxidation has attracted increasing attention to micropollutant abatement, due to high oxidation potential, low disinfection byproduct (DBPs) formation, and easy technical implementation. However, the kinetics, reactive sites, activation methods, and degradation pathways involved are not fully understood. Therefore, we reviewed current literature on ClO2-based oxidation in micropollutant abatement. In direct ClO2 oxidation, the reactions of micropollutants with ClO2 followed second-order reaction kinetics (kapp = 10−3–106 M−1 s−1 at neutral pH). The kapp depends significantly on the molecular structures of the micropollutant and solution pH. The reactive sites of micropollutants start with certain functional groups with the highest electron densities including piperazine, sulfonyl amido, amino, aniline, pyrazolone, phenol groups, urea group, etc. The one-electron transfer was the dominant micropollutant degradation pathway, followed by indirect oxidation by superoxide anion radical (O2•−) or hydroxyl radical (•OH). In UV-activated ClO2 oxidation, the reactions of micropollutants followed the pseudo-first-order reaction kinetics with the rates of 1.3 × 10−4–12.9 s−1 at pH 7.0. Their degradation pathways include direct ClO2 oxidation, direct UV photolysis, ozonation, •OH-involved reaction, and reactive chlorine species (RCS)-involved reaction. Finally, we identified the research gaps and provided recommendations for further research. Therefore, this review gives a critical evaluation of ClO2-based oxidation in micropollutant abatement, and provides recommendations for further research.