Frequently Asked Questions about Chlorine Dioxide
Is chlorine dioxide (ClO2) the same as chlorine (Cl2)?
No. While chlorine dioxide has chlorine in its name, its chemistry is dramatically different from chlorine. One of the most important properties of chlorine dioxide that sets it apart from chlorine is its behavior when placed in water. Chlorine hydrolyzes, or reacts, when placed in water to form hypochlorous and hydrochloric acids. Chlorine dioxide does not hydrolyze and remains a truly dissolved gas in water. Chlorine is an effective biocide only in systems where pH is less than 8, whereas chlorine dioxide retains its useful oxidative and biocidal properties throughout a broad pH range (2 to 10 pH). Chlorine dioxide has a lower oxidative potential than chlorine but has 2.5 times the capacity, making it a more effective disinfectant. Additionally, chlorine dioxide does not chlorinate organics to form disinfection by products such as THMs and HAAs.
Can I purchase chlorine dioxide in package containers?
No. Chlorine dioxide cannot be compressed like chlorine gas and must be generated at the point of application using “generation” equipment. In some applications, like oil and gas, this on-site generation is actually desirable as it minimizes storage and transportation of large volumes of highly volatile chemicals.
Is chlorine dioxide safe for use in my application?
Chlorine dioxide has been used safely in industrial and municipal applications for over 70 years. It is being used in a growing number of industries due to its highly selective oxidizing properties, which result in a lower dosage requirement. Chlorine dioxide has gained wide acceptance in the oil and gas industry for use in water treatment. Like many chemicals, there are safety concerns when using chlorine dioxide. However, ADOX Water Technologies works with partners who have extensive training and an understanding of the chlorine dioxide chemistry. The knowledgeable partners are critical in the selection of the generation technology and have experience with applications in the field, which allow for a safe and effective chlorine dioxide treatment program.
Where is chlorine dioxide typically used?
Chlorine dioxide is used in municipal water plants to disinfect potable water and in wastewater treatment plants for oxidation and odor control. It is used in food and beverage plants for hard surface sanitation and fruit and vegetable processing. It is also used in cooling towers and hospitals for legionella control, rendering plants for odor control, and in oil and gas water treatment as a biocide, among other common uses. In many instances, chlorine dioxide is replacing chlorine gas or bleach to meet higher performance standards or regulatory requirements. Chlorine dioxide is used to disinfect potable water around the world and is approved for use by the Environmental Protection Agency (EPA) and the World Health Organization (WHO).
Is it complicated to generate chlorine dioxide on-site?
No. Chlorine dioxide is generated with the proper equipment selection and training of operation personnel. The process is simple enough for general industrial operations, and automation can simplify operations further. With the right application partner, on-site generation is relatively simplistic. Chlorine dioxide allows for precise, customized treatment with options for data gathering and remote operation. By ensuring proper equipment design and training of personnel, effective treatment can be ensured.
How does chlorine dioxide work and can bacteria become resistant to it?
No. Chlorine dioxide kills bacteria by attacking their critical cell physiological functions, including the disruption of protein synthesis. It also alters the permeability of the outer cell membrane. Chlorine dioxide diffuses through the protective layer of the cell and inactivates pathogens from the inside out. It prohibits both anaerobic and aerobic bacteria from developing resistance and eliminates the need to alternate biocide treatments. Sulfate-reducing bacteria (SRBs) and acid-producing bacteria (APBs) are especially vulnerable to chlorine dioxide oxidation. Not only is chlorine dioxide an effective biocide, its oxidizing properties will also destroy hydrogen sulfide (H2S) and iron sulfide (FeS) contaminants in water systems.
Is chlorine dioxide effective in oil fields?
Yes. Chlorine dioxide has been used safely in industrial and municipal applications for over 70 years. The selective oxidizing chemistry of chlorine dioxide is a highly effective biocide, well suited for oil and gas disinfection applications. It provides unique advantages over some traditional biocides in that water can be treated precisely to limit the amount of chemical used while providing the ability to confirm kills in real time. This minimizes the total amount of biocide applied.
Can chlorine dioxide be generated from simple salt electrolysis?
No. Salt electrolysis in an undivided electrochemical cell leads exclusively to the production of sodium hypochlorite. Chlorine dioxide generation from brine electrolysis may be theoretically possible, but it would require multiple stages of specialized electrolysis combined with chemical processing to get some measureable chlorine dioxide along with many unwanted by-products. Therefore, chlorine dioxide generation starting with brine is probably not commercially or economically feasible today. Research papers* indicate that there is an analytical limitation when attempting to detect chlorine dioxide in the presence of a brine solution, resulting in a false positive for chlorine dioxide.
Chlorine dioxide must be produced commercially via the chemical reduction of sodium chlorate in acidic medium for large-scale processes, such as the bleaching of pulp for paper production or via sodium chlorite in smaller-scale chlorine dioxide production, such as those used in oil and gas water treatment. The sodium chlorite feedstock is produced in a two-step chemical process involving chlorine dioxide generation from an integrated chlorate-acid based generation unit, followed by chlorine dioxide reaction with hydrogen peroxide and caustic to produce sodium chlorite.
It is commercially impossible to produce measureable quantities of chlorine dioxide from simple brine electrolysis used today to make bleach.
* Measuring Oxidant Species in Electrolyzed Salt Brine Solutions, by Gordon et al., Journal AWWA, October 2002.