Application of chlorine dioxide disinfectants in environmental disinfection

Chlorine dioxide, as a fourth-generation disinfectant for aquaculture, not only significantly reduces the number of pathogenic microorganisms in the water but also does not harm plankton, thus disinfecting and oxygenating the water. Stable chlorine dioxide is non-irritating, does not harm aquatic organisms, and improves water quality. Compared with other control drugs, it has advantages such as short sterilization time and fewer side effects. It has significant efficacy against hemorrhagic septicemia, gill rot, red skin disease, enteritis, and saprolegniasis in fish, and vibriosis and viruses in shrimp. In recent years, it has been rapidly adopted in coastal aquaculture areas such as Hainan, Guangdong, Shandong, Hebei, and Liaoning, and is gradually penetrating inland freshwater aquaculture areas.

In aquaculture, disinfection of the water is an essential measure to prevent diseases in aquatic animals. Currently, chlorine-based disinfectants are commonly used, such as bleaching powder, sodium dichloroisocyanurate, and trichloroisocyanuric acid. While these chlorine-based disinfectants are effective at killing pathogens in the water, the available chlorine reacts with the water to form various halogenated compounds, producing non-volatile chlorinated organic compounds such as trihalomethanes. Trihalomethanes have been identified as carcinogens. In the 1980s, another class of non-volatile chlorination disinfection byproducts were discovered, including halohexanoic acid, dichlorohexanoic acid, and trichlorohexanoic acid. Their carcinogenic risk is 50 to 100 times that of trihalomethanes, polluting natural and groundwater and threatening human health. Furthermore, chlorine-based disinfectants react with ammonia in the water to produce chloramines, which have almost no inactivation effect on pathogens in the water. Furthermore, chlorinated chlorine at concentrations of 0.05–1.2 mg/L is toxic to aquatic organisms, and chlorine-based disinfectants are significantly affected by pH and suspended solids in the water. When the pH is high and there are many suspended solids, chlorine-based disinfectants are almost ineffective for disinfection without increasing the concentration, wasting disinfectant and polluting the water. Long-term use of chlorine-based disinfectants can also lead to drug resistance in pathogens. ClO₂ is suitable as a disinfectant for aquaculture because:

First, stable ClO₂ requires a small dosage. Compared to commonly used disinfectants such as quicklime, bleaching powder, sodium dichloroisocyanurate, trichloroisocyanuric acid, and bromochlorohydantoin, stable ClO₂ requires a much smaller dosage, reducing the workload for operators. According to available information, when using stable ClO₂ to prevent infectious diseases in aquatic animals, a concentration of 0.1–0.2 mg/L applied to the entire pond each time is sufficient to achieve good results. When using stable ClO₂ to treat diseases in aquatic animals, only 0.2–0.3 mg/L is needed, applied twice with a one-day interval.

Secondly, stable ClO₂ has a superior disinfection effect. Because stable ClO₂ possesses extremely strong oxidizing power, it can kill various bacteria, viruses, molds, fungi, algae, and bacterial spores even in the presence of suspended solids in the water, even with relatively small doses. According to data, stable ClO₂, especially at low concentrations, has a stronger diffusion rate and penetration capacity in water than chlorine. Under the same conditions, 5 mg/L chlorine gas achieves a 90% sterilization rate after 5 minutes, while 2 mg/L ClO₂ can kill 100% of various microorganisms in just 30 seconds. Stable ClO₂ maintains a strong bactericidal ability over a wide pH range, while chlorine gas cannot. Furthermore, because stable ClO₂ does not react with ammonia and amines, its bactericidal effect is unaffected by the concentration of ammonia and amines in the water.

Thirdly, stable ClO₂ leaves no residue or harmful substances after its action. When disinfecting with chlorine-based agents such as chlorine gas, chlorine reacts with organic matter in water to produce trihalomethanes (THMs), such as CHCl₃ and other organohalogenated compounds, which are known carcinogens. However, the products of stable ClO₂ are water, sodium chloride, trace amounts of CO₂ , and small amounts of sugars, with no substances harmful to human health. Furthermore, chlorine dioxide can remove excess inorganic pollutants such as Fe2+, Mn2+, S2−, and CN−, as well as organic pollutants such as phenols and humic substances from water . Stable ClO₂ can oxidize carcinogenic organic compounds, such as benzopyrene, into non-carcinogenic substances. Stable ClO₂ also has a strong removal effect on odor compounds such as musty and fishy smells.

Fourth, stable ClO₂ has a high safe concentration, making it unlikely to cause poisoning in aquatic animals due to excessive use. Experiments using fish, shrimp, and crab fry have shown that stable ClO₂ is a low-toxicity substance. Furthermore, toxicological experiments conducted on mice have indicated that stable ClO₂ is practically non-toxic.

Fifth, stable ClO₂ is very convenient to use. If using a stable ClO₂ solution to soak aquatic animals, simply add the required amount of drug to the water and stir well. If using a stable ClO₂ solution to spray the entire aquatic animal rearing pond, you can also directly dilute the required amount of stable ClO2 _in a small amount of water and then spray it evenly throughout the pond.

Chlorine dioxide is an oxidizing agent and does not undergo chlorination. Therefore, it does not have the toxic side effects of chlorinating agents. Its safety performance has been classified as A1 by the World Health Organization, making it an internationally recognized ideal alternative to chlorine-based disinfectants. It not only serves as a highly effective bactericidal disinfectant, controlling the transmission of pathogenic microorganisms and effectively preventing the occurrence and spread of infectious diseases in aquaculture, but also has excellent water purification effects. It can increase dissolved oxygen in the aquatic environment while reducing chemical oxygen demand (COD) and ammonia nitrogen levels, thus reducing eutrophication and improving the overall productivity of fishponds.