Research progress and trends of gaseous chlorine dioxide application technology

Release time:

2023-06-20

Yi Ying, Wu Jinhui, Hao Limei, Qi Jiancheng

( Institute of Health Equipment, Academy of Military Medical Sciences, Tianjin 300161, China)

In 1811, British scientist Humphrey Davy discovered chlorine dioxide (ClO2). Since its discovery, researchers have been conducting uninterrupted research on chlorine dioxide, including physical, chemical, toxicological properties, absorption spectroscopy, and application techniques in various fields. Chlorine dioxide is a strong oxidizing agent with a redox potential of 0.95 V when typical single-electron transfer occurs to form chlorite (ClO-2). When 1 mol of ClO2 is reduced to chloride ion (Cl-), 5 mol of electron transfer occurs, so its available chlorine content is 263% (52.6%×5), and the oxidizing capacity is 2.63 times that of Cl2. Chlorine dioxide is often used as a disinfectant due to its strong oxidizing properties, and is recognized as a highly effective, broad-spectrum disinfectant that can kill almost all microorganisms, including bacterial propagules, bacterial spores, fungi, mycobacteria, and viruses.

Chlorine dioxide is soluble in water, and basically maintains an indissociative form in aqueous solution, which can effectively destroy trace organic pollutants in water, such as benzopyrene, quinone, chloroform, carbon tetrachloride, phenol, chlorophenol, cyanide, etc., and does not undergo chlorination reaction when oxidizing organic matter, and does not generate carcinogenic trihalomethanes (THMs). Therefore, chlorine dioxide has long been used as a disinfectant in solution form, especially in drinking water treatment. The boiling point of chlorine dioxide is 9.9~11°C, and its gas color is related to concentration, which is yellow-green to orange-red at room temperature, and has good diffusion and penetration characteristics. Using the gaseous and disinfection characteristics of chlorine dioxide, foreign countries began to study the disinfection technology of gas chlorine dioxide in 1999, and achieved many satisfactory research results, so that the gas chlorine dioxide disinfection technology has developed rapidly. In 2006, relevant research reports began to appear in China, which have been used for disinfection and preservation of fruits and vegetables, disinfection of space and object surfaces and removal of formaldehyde pollution, etc., following the pace of foreign technology development, but there are still some problems and deficiencies in related fields. In this paper, the research progress of gas chlorine dioxide application technology at home and abroad is reviewed, and the existing problems in this research field are proposed, in order to objectively and comprehensively introduce the development status of this technology, and provide reference for promoting the research and application of gas chlorine dioxide application technology in China.

1. Disinfection of gas chlorine dioxide space and object surface

Gas disinfectants have good diffusion and penetration, and have strong advantages in the disinfection of space and object surfaces. Due to the complexity of the surface of objects in the space, the traditional disinfection methods such as spraying and wiping no longer meet the needs of comprehensive disinfection, such as it is not easy to achieve the disinfection of surfaces such as the inside of semi-closed objects and the bottom of equipment. The commonly used formaldehyde fumigation and disinfection has the problem of time-consuming and laborious, and formaldehyde was clearly listed as a carcinogen by the World Health Organization in 2004, and its use has been banned in many developed countries such as Europe and the United States, which has promoted the gas chlorine dioxide to the historical stage. In particular, in 2001, the U.S. Environmental Protection Agency (USEPA) evaluated the disinfection effect of gas chlorine dioxide on the entire building such as the Senate office building and the Brentwood Post Office Sorting Center in Washington, D.C., which was suspected of being contaminated by anthrax, making the gas chlorine dioxide space disinfection technology widely concerned and recognized. In 2006, the commercial gas chlorine dioxide disinfection machine of ClorDiSys Company in the United States was approved by USEPA, which made the gas chlorine dioxide disinfection machine embark on the road of commercial promotion. In 2007, the National Sanitation Foundation (NSF) revised the NSF/ANSI 49 standard to designate that the gas chlorine dioxide can replace formaldehyde for the sterilization of biological safety cabinets. In 2008, with the support of the U.S. Department of Defense, Wood et al. developed a large-scale vehicle-mounted gas chlorine dioxide disinfection system, which aims to disinfect the entire 9912 m3 building, providing a technical reserve for the overall disinfection of large buildings in the United States to deal with anthrax-like mail incidents. In 2015, during the Ebola epidemic in West Africa, American scholars explored the feasibility of gas chlorine dioxide disinfection of Ebovirus, Doona et al. applied the portable gas chlorine dioxide sterilizer developed by the Natick Soldier Center in the United States to the sterilization of Ebola-contaminated medical devices, Lowe and other studies showed that gas chlorine dioxide is ineffective in disinfecting the surface of objects containing blood dirt, such as using gas chlorine dioxide for disinfection, the surface must be cleaned manually. From 2003 to 2016, domestic and foreign research institutions evaluated the disinfection effect of gas chlorine dioxide on different spaces and object surfaces, and some of the main research results are listed in Table 1, showing that gas chlorine dioxide can achieve thorough and rapid disinfection of biosafety laboratories and their internal equipment, hospitals, general laboratories, ambulances, libraries, restaurants and other objects.

From the results of Table 1, it can be seen that when gas chlorine dioxide is used for high-level disinfection or sterilization, it requires a higher concentration and a longer disinfection time, while when it is used to disinfect ordinary indoor environments such as libraries, it can be exposed for a long time at concentrations lower than 8h weighted concentration values (0.28 mg/m3) to achieve the purpose of eliminating common indoor bacteria. When killing bacterial spores, a high relative humidity is required, which should generally not be less than 60% RH. The high relative humidity can wet the outer wall of the spores and expand it to facilitate the adhesion and penetration of gas chlorine dioxide, while the high humidity environment increases the risk of corrosion of gas chlorine dioxide. Therefore, when gas chlorine dioxide is applied to the high level of disinfection or sterilization of spaces and surfaces, the material compatibility of gas chlorine dioxide needs to be considered. USEPA has conducted a systematic experimental study on the compatibility of commonly used electronic equipment and common materials in laboratories and other indoor laboratories with gas chlorine dioxide, and the results show that the compatible metals include stainless steel (304SS, 316SS), hard aluminum with oxidation treatment on the surface, etc., and commonly used plastics include polyvinyl chloride, polyoxymethylene, polytetrafluoroethylene, etc., which provides guiding information for the application of gas chlorine dioxide.

Compared with gas disinfectants such as formaldehyde and ethylene oxide, the disinfection effect of gas chlorine dioxide is greatly affected by the properties of the surface materials of objects. USEPA has published a large number of experimental results to illustrate the effect of building materials on disinfection effectiveness when gas chlorine dioxide is used to disinfect buildings; Li et al. and Wang Yanqiu et al. studied the killing effect of gaseous chlorine dioxide on the surface of atrophic Bacillus spores of common materials in biosafety laboratories. Some of the results of the above studies are listed in Table 2, and the results show that gas chlorine dioxide can effectively kill microorganisms on the surface of various materials, but the sterilization effect on complex porous surfaces such as cloth and wood is poor, and the sterilization effect on dense structural surfaces such as stainless steel, glass, and plastic is also significantly different, and the material factors on the surface of objects need to be considered in disinfection applications.

2. Gas chlorine dioxide keeps fruits and vegetables fresh

Gas chlorine dioxide can be applied to the surface disinfection of fruits, vegetables, cereals and other foods to prolong the storage period and improve safety. The Department of Food Science at Purdue University in the United States started the first in this research field, and the research team represented by Y. HAN, followed by the B.S.M. Mahmoud and V. Trinetta teams, has achieved very comprehensive research results.

In addition to the evaluation of disinfection effectiveness listed in Table 3, foreign scholars have also conducted research on some related issues. Y.HAN ET AL. OBTAINED A RESPONSE SURFACE MODEL OF ESCHERICHIA COLI ON THE SURFACE OF GREEN PEPPER TREATED WITH GAS CHLORINE DIOXIDE, AND THE RESULTS SHOWED THAT THE CONCENTRATION OF GAS CHLORINE DIOXIDE WAS THE MOST IMPORTANT INFLUENCING FACTOR, WHILE THE TEMPERATURE WAS THE MOST MINOR INFLUENCING FACTOR, AND THE CONCENTRATION AND RELATIVE HUMIDITY HAD A SYNERGISTIC EFFECT. Y.HAN et al. also compared the bactericidal effects of one-time injection and continuous flow of gas chlorine dioxide on the surface of strawberry Escherichia coli and Listeria monocytogenes, and the results showed that a bactericidal value of >5 was obtained by one-time injection of 4 mg/L for 30 min and 3 mg/L for 10 min. Also from the Department of Food Science of Purdue University, Trinetta et al. conducted a research and evaluation on the residue problem of gas chlorine dioxide disinfection that the industry is concerned about, and investigated the chemical residue levels of seven kinds of fruits and vegetables such as tomatoes, oranges, apples, strawberries, lettuce, alfalfa and cantaloupe after disinfection (including chlorine dioxide, chlorite, chlorate, chloride, etc.), except for lettuce and alfalfa, two leafy vegetables, which had higher residues, there were no obvious residues. Arango et al. quantified chlorine dioxide consumption in the process of sterilizing strawberries by monitoring the concentration of gas chlorine dioxide. YounsukLee et al. studied the diffusion rate factor of gaseous chlorine dioxide in air and the degradation rate under dark, UVA, fluorescent lamp, etc., which provided a methodological basis for quantifying the amount of gaseous chlorine dioxide used in the application process.

Since 2005, there has been a literature on the application of gas chlorine dioxide in food disinfection and preservation, Fu Maorun et al. studied the effect of gas chlorine dioxide on the endogenous hormone content of red grapes during storage, and believed that gas chlorine dioxide is conducive to preservation and delays aging and shedding. After returning from a visit to Purdue University, Hu Shuangqi from the School of Chemical Engineering and Environment of North University of China led a team to study the bactericidal effect of gas chlorine dioxide on Salmonella, Staphylococcus aureus, Escherichia coli, Listeria monocytogenes and saprophytic yeast on the surface of fruits and vegetables such as cantaloupe, grapes, apples, and jujubes, and the sterilization rate could reach more than 99%. The bactericidal effect of gas chlorine dioxide on Aspergillus flavus and Bacillus subtilis on tartary buckwheat, sweet buckwheat, oats, corn and other cereals was evaluated, and it was shown that gas chlorine dioxide had a good effect on preventing mildew of grains, and it was considered that gas chlorine dioxide had a better bactericidal effect on smaller grains. The explosive characteristics and photodegradation law of gaseous chlorine dioxide were studied, which provided a scientific basis for the application of gaseous chlorine dioxide in the field of food safety in China.

3. Gas chlorine dioxide removes formaldehyde

Decoration pollution directly endangers human health, especially when the formaldehyde exceeds the standard and causes leukemia and other accidents, it is common in the mainstream news media, and it is more and more concerned by families and society, so the removal of decoration pollution has formed a large-scale industry. In addition to physical methods such as ventilation, ultraviolet irradiation, and activated carbon adsorption, oxidants can also be used to react with formaldehyde to achieve the purpose of removal. The gas chlorine dioxide is a gas at room temperature, which has strong oxidizing properties, and can react with formaldehyde to form formic acid and further deepen the reaction until carbon dioxide and water are formed. Since 2003, domestic researchers have discussed the efficiency and influencing factors of formaldehyde removal by gas chlorine dioxide. Zheng et al. showed that when the volatilization rate of gas chlorine dioxide reached 7.4 mg/h, the formaldehyde with a volatilization rate of 4.48 mg/h could be completely removed. Deng Feiying simulated the formaldehyde concentration exceeding the standard by 6 times, 4 times and 2 times, and treated it with different concentrations of gas chlorine dioxide, and obtained the optimal release rate of gas chlorine dioxide under different conditions. Kang Zhijuan's study showed that the removal of formaldehyde at concentrations of 0.5, 0.3 and 0.15 mg/m3 required gas chlorine dioxide at concentrations of 0.9, 0.6 and 0.4 mg/m3, respectively. Cheng Jin showed that the gas chlorine dioxide at concentrations of 12.5 mg/m3 and 5.0 mg/m3 acted on formaldehyde at concentrations of 2.0 mg/m3 and 0.5mg/m3 for 40 min, respectively, and the removal rates were 64% and 84.6%, respectively. Yunhong et al. studied the removal rate of formaldehyde from slow-release gas chlorine dioxide on wood-based panels, and the effect of gas chlorine dioxide with a release rate of 2.3 mg/h for 9 days reduced the formaldehyde emission of particleboard and MDF by 49.2% and 52.5%, respectively.

The human exposure limit of gas chlorine dioxide is 0.3 mg/m3 (8h weighted concentration), which means that it can achieve human-machine coexistence, which is in line with the characteristics of the slow release of formaldehyde in the middle and late stages of decoration materials. The slow-release rate of gas chlorine dioxide can be controlled through the gas chlorine dioxide sustained-release device or the gel-like sustained-release agent, which is convenient to use. Biocide System's commercial indoor air purification box uses a gas chlorine dioxide slow-release gel for the removal of organic substances such as formaldehyde and benzene in the room, which is popular in China.

4. There is a problem

After ten years of accumulation, many research results have been achieved in domestic research on gas chlorine dioxide, which basically follow the technical level of European and American countries, but there are still some problems.

4.1 Small research team

Domestic researchers of gas chlorine dioxide mainly include the team represented by Hu Shuangqi and Jin Riya of North University of China and the team represented by Qi Jiancheng and Wu Jinhui of the Academy of Military Medical Sciences. North University of China focuses on the field of food safety, while the Academy of Military Medical Sciences focuses on the field of biosecurity, and has not formed more research teams that can concentrate on the results, and has failed to form a research hotspot.

4.2 Lack of basic research

The domestic research results mainly focus on the application of technology research, that is, the evaluation of the disinfection effect of different objects, but there is a lack of relevant basic research. For example, the mechanism of gas chlorine dioxide disinfection; Kinetic model of reactor for gas-solid reaction to prepare gas chlorine dioxide, reactor life detection method; Quality variation, disinfection by-products and residues of gaseous chlorine dioxide for disinfection of fruits, vegetables and grains; The influence of organic matter and covering on the surface of the object on the disinfection effect, etc.

4.3 Less equipment support

The two teams of North University of China and the Academy of Military Medical Sciences each have their own self-developed gas chlorine dioxide generation equipment, compared with the liquid-liquid reaction type of North University of China, the generated gas contains a small amount of chlorine components; The Academy of Military Medical Sciences is a gas-solid reaction type, and the gas produced is pure chlorine dioxide except for nitrogen. Both have their advantages and disadvantages, but neither has formed a commercial product for promotion. In addition, there is a lack of accurate on-line concentration detection devices for application studies at very low concentrations (<0.28 mg/m3). In the disinfection application scenario that is not suitable for the installation of on-line concentration monitoring devices, a reliable chemical indicator card will be very valuable, and the CD-CHECK of ClorDiSys company in the United States is such a product, and there is still no relevant research report in China.

4.4 Absence of national standards

Among the five national standards for chlorine dioxide that have been promulgated and implemented, all of them are related to chlorine dioxide solutions rather than gas chlorine dioxide, including GB 26366-2010 "Hygienic Standard for Chlorine Dioxide Disinfectants", which also emphasizes the application of solution form. As another form of chlorine dioxide disinfectant, gaseous chlorine dioxide has shown superiority and applicability, and should be included in relevant standards, or national standards for the application of gaseous chlorine dioxide in different fields should be drafted.

5. Development trend

Through the analysis of domestic and foreign literature, gas chlorine dioxide has more research foundation support in the fields of space and object surface disinfection, food disinfection and preservation, and formaldehyde removal, which has its advantages and good promotion prospects. Especially in the disinfection of space and object surfaces, it is easier to promote because it does not involve sensitive issues such as food safety and health hazards.

In the field of biosafety, the competitive technology of gas chlorine dioxide is vaporized hydrogen peroxide, both of which have their own advantages and disadvantages, the reactants of gas chlorine dioxide are chemical dangerous goods when prepared on site, and vaporized hydrogen peroxide cannot penetrate the high-efficiency air filter, so both have their own applicable occasions. Among them, gas chlorine dioxide is more suitable for the overall disinfection of the laboratory, including laboratory ventilation ducts and laboratory internal equipment.

Another important application scenario for gaseous chlorine dioxide is the overall disinfection of biopharmaceutical workshops. With the transfer of part of the industrial chain of global biopharmaceutical enterprises from developed countries and regions such as Europe, America and Japan to developing countries such as China and India, as well as China's support for the biopharmaceutical field, large-scale biopharmaceutical clean workshops have sprung up. Responsible companies have basically abandoned the formaldehyde fumigation method, and the same competition with gas chlorine dioxide is vaporized hydrogen peroxide, and as mentioned above, gas chlorine dioxide is more suitable for one-time overall disinfection of very large spaces, including pre-production sterilization and product conversion room sterilization, etc., which has huge market prospects.

Because gas chlorine dioxide has good diffusion characteristics and material compatibility, it is suitable for the disinfection of precision equipment containing electronic, optical and other components and complex structures, and with the upgrading of informatization, more and more precision equipment is put into use in the army, and gas chlorine dioxide will make a great difference in the elimination of biological warfare agent pollution in precision equipment.

In the field of medical and health care, the gas chlorine dioxide should be further promoted. First of all, gas chlorine dioxide can be used for disinfection of special parts such as infectious disease wards, burn wards, and clean operating departments; Secondly, chlorine dioxide, a very low-concentration gas, can also be used for human-machine coexistence air purification in ordinary clinics and wards; Thirdly, gas chlorine dioxide can be used for the disinfection or sterilization of medical devices, such as the Academy of Military Medical Sciences applies gas chlorine dioxide to the high-level disinfection of digestive endoscopes, and Doona in the United States uses gas chlorine dioxide for portable sterilization of surgical instruments.

Gas chlorine dioxide is a safe, broad-spectrum and efficient gas disinfectant, and it is believed that with the investment of more researchers and funds, it will be more widely recognized and further improve the technical level of disinfection in China.

*Source: Chinese Journal of Sterilization, Vol. 34, No. 4, 2017

Key words:

Application of chlorine dioxide disinfectant in food processing

Research on the killing effect of chlorine dioxide disinfectant on bacteria and viruses and its application in poultry breeding