FAQ's Chlorine Dioxide
Is chlorine dioxide the same as chlorine?
How is ClO2 used in water treatment applications? How does it work?
Does ClO2 have any uses other than municipal water treatment?
How does the use of ClO2 affect the environment?
Why should I use ClO2 instead of chlorine for water treatment?
Is ClO2 toxic?
Is ClO2 a commodity chemical?
How is ClO2 made?
Is ClO2 expensive?
Can ClO2 be stored safely?
While chlorine dioxide (ClO2) has chlorine in its name, chlorine dioxide's chemistry is radically different than that of chlorine. One atom can make all the difference in the world. The difference between chlorine and ClO2 stems from their dissimilar chemical structure--and this is what accounts for their distinct chemical behaviors.
Similarly, hydrogen is an explosive gas. But when combined with oxygen, it becomes dihydrogen oxide--commonly known as water.
At present in North America, ClO2 is used principally as a primary disinfectant for surface waters with odor and taste problems. It is an effective biocide at concentrations as low as 0.1 ppm and over a wide pH range. ClO2 penetrates the bacteria cell wall and reacts with vital amino acids in the cytoplasm of the cell to kill the organism. The by-product of this reaction is chlorite. Of importance is that toxicological studies have shown that ClO2's disinfection by-product, chlorite, poses no significant adverse risk to human health.
Chlorine dioxide is used extensively as a bleaching agent in the pulp and paper industry. In fact, in order to minimize the environmental effects of the bleaching process, ClO2 is rapidly becoming the chemical of choice. Chlorine dioxide is also being used as a disinfectant agent in the food industry for fruit and vegetable washing, flume water disinfection, meat and poultry disinfection, food process equipment sanitizing water and for odor control. In industrial processes, ClO2 is used in industrial water treatment (cooling systems/towers), ammonia plants, pulp mills (slime control, paper machines), oil fields, scrubbing systems/odor control, textile bleaching and the electronic industry. Chlorine dioxide is also being applied to medical wastes.
Chlorine dioxide is environmentally friendly and in fact is a pollution protection technology that protects the environment and human health from bacteria and by-products formed from other disinfection methods. For example, in the pulp and paper industry the use of ClO2 has virtually eliminated dioxin in mill waste water and has led to a significant improvement in the aquatic eco-system.
It should first be noted that both chlorine and chlorine dioxide are powerful and effective disinfectant agents. Chlorine has been and continues to be a very effective disinfectant which is responsible for making and keeping drinking water safe for people around the world. In the instances in which the drinking water source is surface water, which contains organic materials, ClO2 offers the following benefits. First, ClO2 functions via an oxidative rather than chlorinating reaction. This virtually eliminates the formation of chlorinated organic compounds which are suspected to increase cancer risk. Second, ClO2 is generated on site, thereby eliminating the need for site storage of chlorine and/or transportation thereof.
Fifty years of worker experience has demonstrated that ClO2 is a safe compound when handled properly. World-wide, nearly 4.5 million pounds per day (pounds into kg ?) of chlorine dioxide are used in the production of pulp and paper. However, as with any and all disinfectant chemicals, if handled improperly, or consumed internally or absorbed or subjected to prolonged exposure, ClO2 can be toxic. However, it is also this toxicity that makes ClO2 a good water disinfectant agent.
Pure chlorine dioxide cannot be purchased in solid, liquid or gaseous form. In fact, because ClO2 is such a highly effective and reactive chemical, transportation of ClO2 is not permitted. Chlorine dioxide must be produced and used at the point of application. Chlorine dioxide generators are automated and user friendly.
Chlorine dioxide may be prepared chemically from either sodium chlorite or sodium chlorate or generated electrochemically.
The cost of chlorine dioxide is dependent on the cost of the precursor chemicals-sodium chlorite or sodium chlorate-and the chemicals required to convert these chemicals into ClO2. The cost of ClO2 will also depend on the generation method employed. When compared to the cost of chlorine, the cost of ClO2 is higher. However in those instances in which chlorine is not the preferred regulatory or environmental alternative, ClO2 is a very attractive alternative. The capital equipment costs of generating ClO2 are also far less than that of other alternatives like ozone which can also be used for water treatment.
Solutions of approximately 1% ClO2 (10 g/L) may safely be stored at 5°C for several months, with little change in concentration, provided that the solution has no gas space and is protected from light.