ClO2 Solution Research Articles

Effect of chlorine dioxide (ClO2) combined with different oxygen permeability package treatments on postharvest antioxidant activity and storage life of ‘Liaofeng’ grapes

To enhance the storage quality of ‘Liaofeng’ grapes, this research employed chlorine dioxide in collaboration with different package of preservative bags to explore its preservative effect on ‘Liaofeng’ grapes. After fumigating the grapes with 300 mg L−1 ClO2 solution, the control group was packaged in unpacked and PE bags, while the treatment group was packaged in three kinds of bags with different oxygen permeability, and stored in 4 °C and relative humidity controlled at 90%–95% for 90 days. The results showed that ClO2-GB package treatment significantly delayed the decline of grape hardness (P < 0.05), and decreased the weight loss, threshing, decay and peduncle browning index after storage for 90 days. ClO2-GB package treatment not only diminishes the levels of soluble solids content, titrable acidity, ascorbic acid and glutathione but also effectively suppresses the respiration rate in fruits. The contents of total phenols, flavonoids, anthocyanins and reduced glutathione after ClO2-GB treatment were significantly higher than those in unpackaged group (P < 0.05), and curbed the increase in relative electrical conductivity and malondialdehyde concentration. In comparison to ClO2-YTB and ClO2-YB treatments, ClO2-GB treatment demonstrated superior efficacy in modulating the antioxidant metabolism of grapes. It notably elevated the enzymatic activities of catalase, superoxide dismutase, ascorbate peroxidase, and glutathione reductase, while inhibiting the activities of peroxidase and polyphenol oxidase. The quality assessment of ‘Liaofeng’ grapes after 90 d storage period, conducted through principal component analysis (PCA), yielded the following ranking: ClO2-GB > ClO2-YB > ClO2-YTB > ClO2-PE > ClO2. This suggests that 300 mg L−1 ClO2 fumigation combined with different package treatments was more beneficial to the storage of ‘Liaofeng’ grape. ClO2-GB package treatment emerged as the most advantageous.

Study on corrosion inhibition of carbon steel by imidazolylium-based ionic liquids in chlorine dioxide water disinfection

Chlorine dioxide (ClO2), recognized for its high efficiency, broad-spectrum capabilities, and safety, is extensively utilized in water disinfection processes. Possessing strong oxidizing properties, prolonged exposure to ClO2 can lead to irreversible corrosion of metals. To mitigate the ClO2-induced corrosion on steel, the corrosion inhibition performance and underlying mechanism of BMIMAc and BMIMBr on 20 steel and Q235 steel in ClO2 solutions ranging from 2.5 to 10 mg/L is systematically studied by static weightlessness experiments, potentiodynamic polarization curve experiments, SEM, EDS, DFT calculations, and MD simulation. The findings demonstrate that both ionic liquids significantly impede corrosion, where BMIMAc outperforms BMIMBr in terms of corrosion inhibition efficacy. These inhibitors exhibit effective adsorption onto the carbon steel surface, conforming to the Langmuir isotherm model. Both ionic liquids are cathodic inhibitors. They can adsorb on the metal surface in an approximately parallel manner and their imidazole ring can form a coordination bond with the metal, leading to the formation of an adsorbent membrane that prevents further contact of the metal with ClO2, thus reducing the degree of oxidation and retarding the corrosion process.

Elicitation as a Process of Enhancing Bioactive Compounds Concentration in Sprouts

During growth, plants produce bioactive compounds—secondary metabolites. Their concentration can be stimulated by the presence of a stressful factor—an elicitor. Since chlorine dioxide is commonly used in water plants to disinfect drinking water, its application as a plant elicitor seems to be very attractive. The aim of this work was to investigate the influence of a new elicitor, ClO2, on the quality of seeds and bioactive compounds of sprouts. Elicitation of radish and broccoli seeds using ClO2 solutions did not significantly reduce their germination percentage (GP remained over 90%). Radish sprouts sprouted from seeds elicited in chlorine dioxide solutions with concentrations up to 800 ppm did not differ statistically significantly in terms of polyphenol content. Sprouts which were grown in the presence of ClO2 contained significantly fewer polyphenolic compounds. Elicitation of broccoli seeds in 800–1000 ppm ClO2 solutions causes an increase in total phenolic content and concentration of ascorbic acid in sprouts. Elicitation in chlorine dioxide solutions not only increased concentrations of selected bioactive compounds but also improved the microbiological quality of sprouts.

A pilot study comparing the disinfecting effects of commercialized stable ClO2 solution (free of activation) with conventional H2O2 on dental unit waterlines in the dental practice setting.

Disinfection of dental unit waterlines (DUWLs) plays a key role in control and prevention of nosocomial infection in a dental clinic. The most conventional disinfectant is hydrogen peroxide (H2O2), while chlorine dioxide (ClO2) has been considered however was limited by the "activation" procedures. With the availability of commercialized stable ClO2 solution (free of activation), direct application of ClO2 in the dental practice became possible. This study was designed to compare the disinfecting effects of stable 5 ppm of ClO2 solution with conventional 0.24% of H2O2 on DUWLs in dental practice. Studies of colony-forming units (CFUs), confocal laser scanning microscopy (CLSM) and scanning electron microscope (SEM) were employed for evaluation. In CFUs studies, we found that the efficiency of ClO2 was no less than those of H2O2. In the morphological studies, the stronger disinfecting effects of ClO2 was verified by both CLSM and SEM studies for removal and prevention of biofilm. Importantly, ClO2 solution achieved a better disinfecting efficiency not only at the surface of bacterial biofilm, but also, it has penetrating effects, presented disinfecting effects from the surface to the bottom of the biofilm. This pilot study provided evidence regarding the efficiency of stable ClO2 solution on disinfection of DUWLs in the dental practice setting. Application of stable ClO2 solution in dental practice is therefore become possible.

Possibility of safe, easy and lower cost substrate disinfection with chlorine dioxide in Hypsizygus ulmarius cultivation

The mushroom Hypsizygus ulmarius exhibits economic, biological and medicinal benefits. The aim of this research was to advance solutions with low cost, simple disinfection procedures that are technically applicable for the cultivation of the H. ulmarius. In the study, the H. ulmarius growing substrates was treated chlorine dioxide (ClO2) alone, fungicide alone and ClO2 combinated with a fungicide or stream sterilization and measured the cultivation parameters. Moreover, the effect of these treatments on the nutritional content of H. ulmarius was also evaluated. The results reveal that, among the ten experimental tested treatments, the most efficient method was the disinfection by soaking in 5 ppm of ClO2 solution for 40 min was the most efficient method. This treatment prevented substrate contamination by harmful microorganisms. It also permitted a shorter cultivation cycle from inoculation to the first flush (34.1 ± 0.6 days) and enhanced the mushroom yield and biological efficiency (304.8 ± 12.3 gkg−1 and 89.7 ± 3.6%, respectively). The nutritional analysis indicated that H. ulmarius exhibited 13.5 ± 0.1–18.7 ± 0.1 g100 g−1 of protein, 7.6 ± 0.3–10.3 ± 0.1 g 100 g−1 of ash, 2.6 ± 0.2–4.3 ± 0.3 g100 g−1 of fat, 69.6 ± 0.6–73.5 ± 0.2 g 100 g−1 of total carbonhydrates, and 372.2 ± 0.8–391.1 kcal 100 g−1 of energy (on a dry weight basis). The findings of this study suggest that, disinfection with ClO2, is a convenient and affordable method, that can replace autoclave sterilization in preparing the growing substrates in H. ulmarius cultivation.

Inactivation of Salmonella Newport on blueberries by treatment with chlorine dioxide gas and its effect on blueberry qualities

The purpose of this study was to use chlorine dioxide (ClO2) gas to inactivate Salmonella Newport on blueberries and observe quality changes of blueberries as affected by the treatment. Blueberries inoculated with S. Newport were treated with ClO2 gas for 10 h ClO2 gas was generated from either 1 or 2 mL of ClO2 solution dropped in a sealed container and the container was hold at 12 °C or 25 °C. Within 30 min, Salmonella populations on blueberries treated with ClO2 gas, regardless of treatment temperature and amount of ClO2 solution, reduced below the detection limit (1.7 log CFU/sample) and the organism was eliminated within 30 min when 1 mL of ClO2 solution was used to generate gas at 25 °C. After the ClO2 gas treatment, blueberries were analyzed with an electronic eye. Color of untreated and ClO2-gas treated blueberries are composed of 12 and 11 color codes, respectively. Out of the color codes, 7 codes of both blueberries in control and treatment groups are the same. ClO2 gas treatment did not cause significant changes in Hunter's L, a, and b-value of blueberries. Hardness (g) of blueberries treated with ClO2 gas for 30 min significantly increased; however final values were not significantly different from the values of untreated ones. As a result of this study, the ClO2 gas successfully reduced S. Newport on blueberries without significant changes in their color and hardness.

Lignin Degradation via Chlorine Dioxide at Room Temperature: Chemical Groups and Structural Characterization

Lignin degradation is an effective means of achieving the high-value application of lignin, but degradation usually requires the use of high temperatures and harsh reaction-conditions. This study describes a green, mild approach for the degradation of lignin, in which chlorine dioxide (ClO2) was used for the oxidative degradation of lignin (IL) in an acidic aqueous suspension at room temperature. The optimal process conditions were: 30 mL of ClO2 solution (2.5 mg·L-1), pH 4.5 and 3 h. The FT-IR, NMR (1H NMR, 2D-HSQC and 31P NMR), XPS and GPC analyses indicated that lignin could be degraded by ClO2 relatively well at room temperature, to form quinones and muconic acids. Additionally, DIL was reduced to substances with a high phenolic-hydroxyl (OH) content (RDIL) under the presence of NaBH4, which further confirmed the composition of DIL and which can be applied to the development of lignin-based phenolic resins, providing a reference for the further modification as well as the utilization of DIL.

The Anticancer Potential of Chlorine Dioxide in Small-Cell Lung Cancer Cells.

Background Chlorine dioxide (ClO2) is an effective disinfectant consisting of oxygen, chloride, and potassium. Because of its high oxidative capacity, ClO2 exerts antimicrobial, antiviral, and antifungal effects. However, its anticancer effects remain to be elucidated. Methodology The anticancer activity of CIO2 was assessed on DMS114 small-cell lung cancer (SCLC) cells and human umbilical vein endothelial cells (HUVEC) as control by WST-1, Annexin V, cell cycle analysis, and acridine orange staining. We for the first time investigated the possible therapeutic effects of long-term stabilized ClO2 solution (LTSCD). Results Our preliminary findings showed that LTSCD significantly inhibited the proliferation of SCLC cells (p < 0.01) with less toxicity in HUVEC cells. Additionally, LTSCD induced apoptotic cell death in SCLC cells through nuclear blebbing and vacuolar formation. However, LTSCD treatment did not induce cell cycle arrest in both cell lines. Conclusions LTSCD can be a therapeutic potential for the treatment of SCLC. However, further investigations are required to assess the LTSCD-induced cell death in SCLC both in vitro and in vivo.

Chlorine dioxide alleviates the yellowing process of broccoli by regulating chlorophyll degrading enzyme activity and gene expression

During the postharvest storage of broccoli, yellowing becomes a problem that affects the nutritional value and market value of broccoli. The aim of this study was to investigate the effect of chlorine dioxide (ClO2) on chlorophyll degradation in postharvest broccoli. Broccoli heads were immersed in 100 mg L−1 ClO2 solution and then stored at 4°C for 25 days. The results showed that postharvest ClO2 treatment delayed the yellowing of broccoli, suppressed weight loss and relative electrical conductivity, and increased total soluble solid content, indicating that ClO2 treatment could delay the decline of broccoli quality. At the same time, ClO2 treatment also reduced the loss of chlorophyll content and suppressed chlorophyllase (CLH), pheophyllase (PPH) and pheophyllase a oxygenase (PAO) activity, which in turn inhibited the expression of BoCLH1, BoCLH2, BoCLH3, BoPPH, and BoPAO. In summary, the results indicated that ClO2 treatment could delay the yellowing rate and maintain the commercial value of broccoli during storage. Novelty impact statement Chlorine dioxide (ClO2) treatment can delay yellowing and maintain the commercial value of broccoli. ClO2 treatment inhibited chlorophyll degrading enzyme activity in harvested broccoli. ClO2 treatment can downregulate the expression of chlorophyll degradation gene in harvested broccoli.

Antimicrobial activities of a combination of chlorine dioxide gas and heat against Xanthomonas campestris and Salmonella enterica on cabbage, chili pepper, and radish seeds

We developed a short-time treatment to inactivate Xanthomonas campestris and Salmonella enterica on cabbage, chili pepper, and radish seeds by a combination of chlorine dioxide (ClO2) gas and heat. ClO2 gas was evaporated from a mixed solution which contained hydrochloric acid (1 N) and sodium chlorite (100,000 ppm) (ClO2 solution). To produce ClO2 gas (3,000 ppm) in an 1.8 L airtight container, a standard curve indicating the amount of ClO2 solution and time needed to produce desired concentrations was constructed (y = 5758.3x; R2 = 0.9981). The influence of simultaneous treatment with ClO2 gas (3,000 ppm) and heat (70 °C at 85% relative humidity [RH]) on seed germination rates was determined. It was found that the germination rates of cabbage, chili pepper, and radish seeds were not significantly (P > 0.05) changed after 30, 20, and 60 min of treatment, respectively. The antimicrobial effects of the combined treatment against X. campestris and S. enterica on cabbage, chili pepper, and radish seeds were determined. When 3,000 ppm of ClO2 gas were applied at 70 °C and 85% RH for 10 min, the populations of X. campestris (initial populations: 6.2–6.4 log CFU/g) on seeds were reduced by > 4.4 log CFU/g regardless of seed type. The initial populations of S. enterica (6.3–6.5 log CFU/g) on cabbage and chili pepper seeds treated for 10 min was reduced by > 5.3 log CFU/g. However, populations on radish seeds decreased only by 2.5 log CFU/g. The lower lethality against S. enterica on radish seeds, revealed by field-emission scanning microscopy to have a rougher surface than do cabbage and chili pepper seeds, is attributed in part to inhibited access of ClO2 gas to cells in protected areas. Our findings provide useful information when developing more efficacious methods to decontaminate vegetable seeds using a combination of ClO2 gas and heat.

Aqueous chlorine dioxide generated with organic acids have higher antimicrobial efficacy than those generated with inorganic acids

Chlorine dioxide (ClO2) is commonly generated by mixing sodium chlorite and acid. This study aimed to evaluate how acid affects the release kinetics and antimicrobial property of ClO2. Solutions made with weak acids released ClO2 more slowly and had higher stability than those made with hydrochloric acid. Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes were treated with 1, 2.5, and 5 ppm ClO2 for 3 or 5 min. Lettuce inoculated with the pathogenic bacteria were treated with 2.5 and 5 ppm ClO2 for 5 min. The effects of peptone load at 0.01% and 0.02% on the antimicrobial efficacy of ClO2 were investigated in S. Typhimurium cell suspensions. The contribution of acids alone at the pH of the ClO2 solutions to bacterial reduction was also evaluated. The 2.5 ppm ClO2 solutions made with citric acid, lactic acid, and malic acid showed higher reductions in all three bacteria than ClO2 made with hydrochloric acid and sodium bisulfate. The 5 ppm ClO2 solutions produced with organic acids reduced populations of all bacterial strains from 7 log CFU/mL to undetectable level in 3 min, except S. Typhimurium treated by ClO2 produced with lactic acid. On inoculated Romaine lettuce model, 5 ppm ClO2 produced with lactic acid and malic acid resulted in the highest reduction of E. coli O157:H7, S. Typhimurium, and L. monocytogenes of approximately 1.4, 1.7, and 2.4 log CFU/g, respectively. The antimicrobial efficacy of ClO2 made with HCl and NaHSO4 were affected by 0.01% and 0.02% peptone load, respectively. Food-grade organic acids produced aqueous ClO2 solutions with stronger antimicrobial properties than inorganic acids. The acids alone at the pH of ClO2 did not show significant bacterial reductions.

Bactericidal and Fungicidal Efficacy of Chlorine Dioxide in Various Workspaces

Previously, we demonstrated the virucidal efficacy of low concentration chlorine dioxide (ClO2) gas in room settings. The purpose of these studies was to evaluate novel ClO2 formats as potential biocidal interventions for real world congregate settings and air systems. Three types of studies were conducted to determine the efficacy of ClO2 in reducing bacteria and mold in various workspaces: hard and soft surfaces (gymnasium & equipment), aerosol (in-room), and within a laboratory environment. The study demonstrated that ClO2 was highly effective against both bacteria and mold with reduction ranging from 85.0% - > 99.4% for bacteria and >99.4% for yeast and mold. Treatments on hard and soft surfaces (gymnasiums and sports equipment), reduced bacteria by an average of 90% - 95%. The following treatments were applied overnight: 1) hard surface spraying with dilute ClO2 solutions, 2) carpet and tumbling treatments with powdered ClO2 releasing impregnates, and 3) HVAC treatment and overall room deodorization with low dose ClO2 gas from controlled releasing sachets. The in-room study treating air with a ClO2 filtration media also indicated significant air and surface room efficacy, with an average of 94% reduction in bacteria after 24-hour, and 99.4% reduction in mold after 24-hours. In a related air study, a biological combination of Raoultella terrigena and Staphylococcus aureus was injected as a bio-aerosol into a 4-inch diameter pipe with air flowing at approximately 1200 ft/min. Dry ClO2 gas was introduced into the air flow to achieve an effective concentration of 5 or 10 ppmv. Air samples were collected at sampling ports downstream from the fan at 10, 22, 55 and 100 ft along the pipe and used to evaluate changes in airborne bacteria and mold. Testing was conducted in a laboratory setting at ambient conditions. The data showed ClO2 gas reduced viable organisms at both gas concentrations, and indicated that reductions were higher for 10 ppmv concentration, and longer pipe runs. In a final study, laboratory application of gaseous chlorine dioxide was tested. Low gas release filter testing demonstrated significant surface reductions of airborne bacteria with an overall average 99.4% reduction in the 24-hour testing period. Higher gas treatments of a class II biological cabinet reduced bacillus spores on steel coupons throughout cabinet by 6 log. ClO2 was effective as a bactericidal and fungicidal treatment providing significant reduction in both surface and air. Novel product delivery forms may be useful for rapidly disinfecting air and solid surfaces in complex congregate settings.

Chlorine dioxide gas generation using rotating packed bed for air disinfection in a hospital

Chlorine dioxide (ClO2) has proven its efficiency as a fumigant toward bacteria and viruses. However, it still has challenges on its portability and simplicity of ClO2 generation to meet the demand for disinfection in public and medical sectors. In this study, ClO2 stripping process via a rotating packed bed (RPB) from the commercial ClO2 solution was developed to a non-chemical-reaction ClO2 generation for air sterilization in a hospital. The ClO2 stripping efficiency (η) and the volumetric liquid mass-transfer coefficient (KLa) were examined under various operating variables, such as initial liquid concentration (CLi), rotational speed (ω), gas-to-liquid flow rate ratio (QG/QL), and liquid flow rate (QL). The results indicated that the gaseous ClO2 can be rapidly and continuously generated via stripping using RPB with η varied above 97% in the certain range of CLi (100–2000 mg/L) and QL (0.04–0.250 L/min). The overall KLa depends on the change of QL and ω, varied from 0.009 s−1 to 0.027 s−1. The output concentration of gaseous ClO2 (CG) can be adjusted from around 10 ppm to over 1000 ppm based on the established prediction model and controlling CLi, QL, QG, and ω. The results of the on-site disinfection test in the Mycobacterium Tuberculosis Laboratory in a hospital have shown effective elimination of all sites of E. coli and 2 of 5 sites of G. stearothermophilus with a CT value at the gas monitoring point of 642 ppm-h and humidity of 81%.

Shelf-Life of Half-Shell Mussel (Mytilus edulis) as Affected by Pullulan, Acidic Electrolyzed Water, and Stable Chlorine Dioxide Combined Ice-Glazing during Frozen Storage.

Mussel (Mytilus edulis) is an economic shellfish with a high nutritional value. Due to the high amount of protein and fat, fresh mussels are susceptible to spoilage during storage. In the present study, how a combination of pullulan, acidic electrolyzed water (AEW), and stable chlorine dioxide (ClO2) ice-glazing treatments affect the quality of mussels was investigated during 90 days of frozen storage. The results indicate that the combined glazing treatment effectively maintained the mussel muscle quality during storage mainly due to its air barrier actions. Mussel samples coated with AEW and ClO2 showed lower aerobic plate counts than other groups, resulting from the strong antibacterial action of AEW and ClO2. After 90 days of frozen storage, the mussel glazed with a combination of AEW, ClO2, and pullulan solutions showed better texture properties, higher content of myofibrillar proteins, higher Ca2+-ATPase activity, and more SH groups than the other glazing treatments. The water-holding capacity and SEM observations showed that the pullulan glazing efficiently inhibited the physical damage caused by the frozen and long-term storage, which mainly contributed to the high amount of hydrophilic hydroxyl groups in the muscle tissues. The present study supports the use of a combination of cryoprotectants for extending the shelf-life of frozen mussel products during long-term storage.

Fate of Salmonella Typhimurium and Listeria monocytogenes on Whole Papaya during Storage and Antimicrobial Efficiency of Aqueous Chlorine Dioxide Generated with HCl, Malic Acid or Lactic Acid on Whole Papaya.

Papaya-associated foodborne illness outbreaks have been frequently reported worldwide. The goal of this study was to evaluate the behavior of Salmonella Typhimurium and Listeria monocytogenes on whole papaya during storage and sanitizing process. Fresh green papayas were inoculated with approximately 7 log CFU of S. Typhimurium and L. monocytogenes and stored at 21 or 7 °C for 14 days. Bacteria counts were determined on day 0, 1, 7, 10 and 14. Fresh green papayas inoculated with approximately 8 log CFU of the bacteria were treated for 5 min with 2.5, 5 and 10 ppm aqueous chlorine dioxide (ClO2). The ClO2 solutions were generated by mixing sodium chlorite with an acid, which was HCl, lactic acid or malic acid. The detection limit of the enumeration method was 2.40 log CFU per papaya. At the end of storage period, S. Typhimurium and L. monocytogenes grew by 1.88 and 1.24 log CFU on papayas at 21 °C, respectively. Both bacteria maintained their initial population at inoculation on papayas stored at 7 °C. Higher concentrations of ClO2 reduced more bacteria on papaya. 10 ppm ClO2, regardless the acid used to generate the solutions, inactivated S. Typhimurium to undetectable level on papaya. 10 ppm ClO2 generated with HCl, lactic acid and malic acid reduced L. monocytogenes by 4.40, 6.54 and 8.04 log CFU on papaya, respectively. Overall, ClO2 generated with malic acid showed significantly higher bacterial reduction than ClO2 generated with HCl or lactic acid. These results indicate there is a risk of survival and growth for S. Typhimurium and L. monocytogenes on papaya at commercial storage conditions. Aqueous ClO2 generated with malic acid shows effectiveness in inactivating the pathogenic bacteria on papaya.

Antimicrobial activity of ClO2 gas against Salmonella Enteritidis on almonds

Nuts, including almonds, are occasionally contaminated with Salmonella spp. In this study, we used chlorine dioxide (ClO2) gas to inactivate S. enterica subsp. Enterica serovar Enteritidis on almonds. Almonds inoculated with a single strain of S. Enteritidis (8.95 log cfu/mL) were exposed to ClO2 gas generated from 1.0 or 1.5 mL ClO2 solution in a sealed container at 50 or 60 °C (43% relative humidity) for up to 10 h. The concentration of ClO2 gas peaked at 354–510 and 750–786 ppm within 0.5 h upon deposition of 1.0 and 1.5 mL of aqueous ClO2, respectively, and gradually decreased thereafter. Population of S. Enteritidis on almonds treated at 50 °C decreased to 1.70–2.32 log cfu/sample within 1 h of exposure to ClO2 gas and decreased to below the detection limit (1.7 log cfu/sample) at all ClO2 concentrations after 8 h. At 60 °C, the microbial population fell below the detection limit within 1 h, regardless of the volume of ClO2 solution supplied. Microbial survival on almonds treated with ClO2 gas and stored at 12 or 25 °C was observed for up to 8 weeks and the organism was not recovered from the almonds treated for 10 h and stored at 12 °C for 2–8 weeks. The lightness (L value) and redness (a value) of almonds treated for 10 h were not changed by ClO2 gas treatment, but yellowness (b value) increased. Results showed that Salmonella on almonds was successfully inactivated by ClO2 gas treatment and the microbial survival did not occur during storage.

Low chlorine impurity might be beneficial in chlorine dioxide disinfection

Chlorine dioxide (ClO2) is a prevalently used disinfectant alternative to chlorine, due to its effectiveness in pathogen inactivation and low yields of organic halogenated disinfection byproducts (DBPs). However, during ClO2 generation, chlorine is inevitably introduced into the obtained ClO2 solution as an “impurity”, which could compromise the merits of ClO2 disinfection. In this study, drinking water disinfection with ClO2 containing 0‒25% chlorine impurity (i.e., at Cl2 to ClO2 mass ratios of 0‒25%) was simulated, and the effect of chlorine impurity on the DBP formation and developmental toxicity of the finished water was evaluated. With increasing the chlorine impurity in ClO2, the chlorite level kept decreasing and the chlorate level gradually increased; meanwhile, an unexpected trend from decline to rise was observed for the total organic halogenated DBPs, with the minimum level appearing at 5% chlorine impurity. To unravel the mechanisms for the variations of organic halogenated DBPs with chlorine impurity, a quantitative kinetic model was developed to simulate the formation of chlorinated, brominated, and iodinated DBPs in the ClO2-disinfected drinking water. The modeling results indicated that reactions involving iodide accounted for the decrease of organic halogenated DBPs at a relatively low chlorine impurity level. In accordance with DBP formation, ClO2 with 5% chlorine impurity generated less toxic drinking water than pure ClO2, while significantly higher developmental toxicity was induced until the chlorine impurity reached 25%. For E. coli inactivation, the presence of chlorine impurity enhanced the disinfection efficiency due to a synergistic effect of ClO2 and chlorine. Therefore, disinfection practices with ClO2 containing low chlorine impurity (e.g., <10%) might be favored (i.e., there is no need to eliminate low chlorine impurity in the ClO2 solution), while those containing high chlorine impurity should be concerned.

Kinetic model of a carboxymethylcellulose-agar hydrogel for long-acting and slow-release of chlorine dioxide with a modification of Fick’s diffusion law

A long-acting and slow-release material for chlorine dioxide, based on bagasse pulp (BP) was prepared with a superabsorbent resin as the slow-release substrate and agar as the cross-linking agent. The stable ClO2 solution and the acidic activator were locked into the network structure of the superabsorbent resin, which was prepared with a carboxymethyl cellulose made from bagasse pulp. Because of the network structure of the resin, the diffusion resistance was greatly increased, and the effective release time was up to 2 months. The mechanism for the release process of the ClO2 was explored, and a kinetic model was established based on modified Fick’s diffusion law. The results showed that the release process was a diffusion-controlled process. When compared with a zero-order kinetic model and a Higuchi model, the new established model had better fitting results, and it more fully reflected the release patterns and characteristics of the ClO2.

Antimicrobial activity of gaseous chlorine dioxide against Aspergillus flavus on green coffee beans

The aim of this study was to use chlorine dioxide (ClO2) gas to inactivate Aspergillus flavus on green coffee beans. Green coffee beans inoculated with A. flavus were exposed to ClO2 gas generated from 0.75, 1, 1.25, or 1.5 mL of ClO2 solution in a sealed container at 25 or 50 °C (100% relative humidity [RH]) for up to 10 h. Numbers of A. flavus on beans treated at 25 °C decreased by 1.1–2.2 log cfu/bean within 1 h of exposure to ClO2 and decreased to below the detection limit (≤1.0 log cfu/bean) at all ClO2 concentrations after 10 h. At 50 °C, the microbial population reached the detection limit within 0.5 h regardless of the ClO2 solution concentration. Beans exposed to gas for 10 h at 25 °C were stored for 14 days under conditions of 43, 75, or 100% RH and 4, 12, or 25 °C. At 4 °C, visible mold growth was not established regardless of RH. After 12 days, mold was observed only at 25 °C. At 100% RH, beans stored under the same conditions without ClO2 gas treatment showed mold formation at 13 and 4 days at 12 and 25 °C, respectively.

Effects of chlorine dioxide on the germination, oxidative metabolism and growth of barley seedlings (Hordeum vulgare L.)

The effects of chlorine dioxide, ClO2, on the germination, oxidative metabolism and growth of barley seedlings were investigated. Barley seeds were separately treated with 0, 500, 1000 and 2000 mg.L−1 ClO2 solutions. Differences in the percentage of seed germination were observed in treatments with 1000 and 2000 mg.L−1 ClO2 solutions only. However, 1000 and 2000 mg.L−1 ClO2 significantly decreased the germination percentage. No significant difference in the MDA content, electrolyte leakage and amount of chlorophyll was observed in seedlings germinated from seeds treated with 0, 500 and 1000 mg.L−1 of ClO2. Similarly, POD and CAT activities showed no significant differences in seedlings germinated from seeds treated with 0 and 500 mg.L−1 while with 1000 mg.L−1 ClO2 there was an increase of these activities. Although there was no significant difference in the above ground part fresh weight between barley seedlings in which seeds were treated with distilled water and ClO2, the fresh weight of barley roots in which seeds were treated with ClO2 was significantly higher than that of control. The total length of barley roots and the number of roots were also increased. The lignin content of barley roots was markly reduced. Staining with Evans blue indicated that barley roots were not obviously damaged. Furtherly, the stimulation of the cell membrane H+-ATPase activity and root activity were observed to be induced by ClO2.