While Chlorine Dioxide has been around and used in water disinfection for some 50 years, mostly in Europe, it has only recently seen renewed interest in municipal water treatment applications in the USA. The main reason it hasn’t been used more is price: it costs 5-10 times more than chlorine. The reason for the renewed interest is its efficacy.
Chlorine dioxide is a disinfectant that directly reacts with the cell wall of microorganisms. The reaction is not as dependent on time or concentration. Compared to chlorine, the chlorine dioxide concentration needed to effectively kill microorganisms is much lower and microorganisms cannot built up any resistance against chlorine dioxide. Also, chlorine dioxide remains in its molecular form in the pH range typically found in natural waters and it is far more effective in treating the water for cysts and controlling biofilms.
Since Chlorine dioxide does not react with ammonia, nitrogen, amines or other oxidizable organic matter, it generates fewer harmful byproducts. Chlorine dioxide does not produce THMs and produces only a small amount of total organic halide. The inorganic disinfection-by-products chlorite and chlorate are produced, but these can be quite easily be removed with the addition of a little ferrous sulfate. (NOTE: chlorite and chlorate can create problems for dialysis patients).
For the purpose of our application, Chlorine dioxide is about the only thing you can add to water with the hope that it will kill cryptosporidium. Some data as follows: 0.3 – 0.4 ppm of Chlorine dioxide completely deactivates tough Cryptosporidium oocysts in less than 20 minutes. Also, according to the Dept. of Microbiology and Immunology at the U. Arizona, in a report entitled Effects of ozone, chlorine dioxide, chlorine, and monochloramine on Crypto viability, ozone and chlorine dioxide more effectively inactivated oocysts than chlorine and monochloramine did. Exposure to 1.3 ppm of chlorine dioxide yielded 90% inactivation after 1 h, while 80 ppm of chlorine required approximately 90 min for 90% inactivation.
Cryptosporidium Inactivation with Chlorine Dioxide: “…is effective against viruses, fungi and algae over wide temperature and pH ranges. The use of chlorine dioxide reduces contact time 3 - 10 times over chlorine and 40 - 60 times over chloramines while being effective over a wide pH range. Chlorine dioxide is applied to the front end of a drinking water plant, where it disinfects the water and inactivates Cryptosporidium. The typical dosage is less than 2-ppm, because of limits in finished water.”
Common disinfectants against Cryptosporidium species: Chlorine dioxide 0.4 parts per million for 15 min.
However, Purified oocysts showed marked differences when using chlorine dioxide suggests that some strains of Crypto may be resistant to Chlorine Dioxide.
In water, chlorine dioxide is active as a biocide for at least 48 hours. For the pre- oxidation and reduction of organic substances, between 0.5 and 2 mg/L of chlorine dioxide is required at a contact time between 15 and 30 minutes. For post-disinfection, concentrations between 0.2 and 0.4 mg/L are applied. The residual byproduct concentration of chlorite is very low and there are no risks for human health.
While using chlorine dioxide as a disinfectant, one has to keep in mind that chlorine dioxide gas can escape from a watery solution containing chlorine dioxide. When disinfection takes place in a sealed space, this can be dangerous because when concentrations in air reach 10% or more, chlorine dioxide becomes explosive.
Like most any chlorine product, when the amount is too high it can cause skin irritations and burns. It will also burn your eyes. Chlorine dioxide gas can be absorbed by the skin, where it damages tissue and blood cells. Inhalation of chlorine dioxide gas causes coughing, a sore throat, headaches, lung edema and bronchio spasma. Chronical exposure to chlorine dioxide causes bronchitis. The health standard for chlorine dioxide is 0.1 ppm. For more info see: Chlorine Dioxide, Safety Sheet and EPA Guidance
Unlike chlorine, inactivation of pathogens is generally more rapid at pH 8 than at pH 6 but like chlorine the efficacy drops with temperature. For example, for inactivation of N. Gruberi cyst at pH 7, a CT (mg min/L) of 3.9 is required at 30C, and a CT of 15.5 is required at 5C.
The advantages of using Chlorine Dioxide include:
• More effective than chlorine, chloramines, and iodine against Cryptosporidium
• Oxidizes iron, manganese, sulfides.
• Controls taste and odours caused by algae and rotting vegetation, as well as phenolic compounds
• Under proper generation conditions (i.e. no excess chlorine), halogen-substituted Disinfection-By-Products are not formed
• Biocidal properties not affected by pH
• rovides residual for continuing protection
The disadvantages of using Chlorine Dioxide include:
• Forms chlorite and chlorate as by-products of generation and reactions.
• More expensive than chlorine
• Decomposes in sunlight
• It can go boom!
The chlorites can be reduced or removed by the addition of a little ferrous sulfate.
The only practical way to use Chlorine Dioxide in our application is to take advantage of off-the-shelf commercial products, typically designed for treating water in camping and hiking environments or industrial sanitization.
If you will be using surface water and can not boil, distill, or pasteurize, and do not have a filter with a minimum 2 micron absolute pore size, and ideally 1 micron, I would highly recommend getting some of these:
Chlorine dioxide tablets, such as Potable Aqua, $5 for a small bottle, or the Katadyn Micropur MP 1, which come in sealed foil bubble pack and have a 2-3 year shelf life. 30 tablets, with each tablet treating 1L. About $12.00
Klear Water is a one part chlorine dioxide liquid, allegedly the only one in existence, and the 2.7 oz bottle will treat 8.5G. Here are some test reports.
Aqua Mira is a small size, two part Chlorine dioxide treatment for 30 gallons. It is about $11 and is supposed to have a 4 year shelf life.
Another two part liquid product is called Purogene. Also called Oxine. The best prices for smaller bottles are here and a 16oz bottle ($13.80) will treat 640G. Or how about a gallon for $25?
Allegedly, Purogene has a 5 year shelf life because it is a stable chlorine dioxide carrying compound. To activate it a food grade acid (phosphoric, citric, ascorbic, lemon juice, etc) is added and allowed to react with it for 5 minutes to release chlorine dioxide before adding it to the raw water. As noted on one site, 1 oz. of Purogene per 30 gals makes the water safe to drink for five years or longer. Go here for a medical test report on Purogen and a USDA-like report here. Some marketing info follows:
OXINE AND PUROGENE: For years it has been known that chlorine dioxide gas is a powerful anti-microbial agent however this gas is toxic and unstable in an aqueous solution. Modern technology has overcome these problems with Oxine (North American name) and Purogene (European name). Today, stabilized chlorine dioxide (CLO2) is available in a concentrated stable form with very low toxicity.
As a powerful oxidant, stabilized CLO2 is virtually unaffected by organic load and hard water. These technical advances have resulted in the FDA (reference CFR 178-1010), EPA (registered for food and beverage contact surfaces), USDA (D-2, P-1, 3-D and G-5) and the majority of international authorities approving stabilized CLO2 as an acceptable sanitizer for numerous applications within the brewery, winery, soft drink, dairy and food (meat, fish, fruit and vegetable) processing plants.
ACTIVATION OF CLO2 CONCENTRATE: Since the ClO2 is in a stabilized form in concentrate, it must be "activated" before using. To manually activate Oxine add, in a well ventilated area, a food grade acid such as citric or phosphoric to lower the pH to below 4 pH. A Litmus paper test at 4 pH is a simple method to be sure of activating correctly. Activation can also be verified by a corresponding color change of the concentrate from clear to yellow/green. Keep stirred and let stand for 5 minutes before using. Any number of acids will activate the stabilized ClO2, however, food grade Citric or Phosphoric acid is recommended. Activated ClO2 has a half-life of approximately 48 hours under standard conditions.
STORAGE: Concentrated ClO2 can be stored in a dry, cool area away from acids for up to 3 years under standard conditions.
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