CHLORINE DIOXIDE DISINFECTION OF PRODUCE WASHWATER
WHAT IS CHLORINE DIOXIDE (ClO2)?
Chlorine dioxide (ClO2) is a gas that can be used for water disinfection. To date, only uncut and unpeeled produce can be contacted with ClO2. Chlorine dioxide has been given a USDA 3-D approval for washing fruits and vegetables to be used as ingredients of meat and poultry products.1 Chlorine dioxide is normally made at the point of use (on-site). Chlorine dioxide can be made by mixing sodium chlorite (NaClO2) with hydrochloric acid (HCl). Bio-Cide International's (BCI) product, PurogeneTM, produces chlorine dioxide when combined with low pH (acidic) water or weak acids.
Some benefits of chlorine dioxide disinfection include longer shelf-life of produce, minimal equipment corrosion, significantly less water use, reduced chemical costs, and reduced packinghouse sanitation costs.
HOW DOES ClO2 WORK?
The sanitation of wastewater with chlorine dioxide is caused by oxidation. It undergoes oxidation to affect the reproduction and metabolism of microorganisms. This results in disinfected water and produce surfaces through a reduction of pathogen populations. Chlorine dioxide has over two and a half times the oxidation power of chlorine.
A microorganism is any yeast, mold, bacteria, protozoa, or virus. A pathogen is a disease or injury causing microorganism. Pathogens of interest in the fresh produce industry include E. coli, Cyclospora, Salmonella, and Hepatitis. A cyst is a protective coating for a dormant microorganism, and an ova is a female germ that is capable of reproducing.
Chlorine dioxide will cause suspended particles in solution to attract each other, allowing them to be easily filtered. Because of this, "cloudy" water is readily cleaned by chlorine dioxide along with a filter.
HOW EFFECTIVE IS ClO2?
Chlorine dioxide is effective against a variety of pathogens, but has limitations. Mold and yeast spores are reduced 80 to 99% by chlorine dioxide concentrations of 0.75 to 5 ppm (parts per million) in water. Bacteria and viruses are also greatly reduced with the use of chlorine dioxide. Chlorine dioxide is effective as a USDA P-1 bactericide.1 One specific pathogen of interest, the cryptosproidium oocyst, is effectively destroyed with chlorine dioxide. However, most cysts and ova must be removed by filtration. A 5 micron filter will significantly reduce spores and cysts.
WHAT CONDITIONS ARE BEST?
In order for chlorine dioxide to be effective, the treated water must be filtered before treatment to reduce the amount of organic material.
Chlorine dioxide effectiveness is relatively unaffected by pH. Little is published about the affect of temperature variation when using chlorine dioxide, but it works well at normal or ambient air temperatures. Temperatures above 100 0F are not recommended.
Chlorine dioxide's effectiveness is reduced by iron and manganese content. Iron may be present in water at many produce operations. Solutions containing either of these two metals should be filtered before disinfection.
WHERE IS ClO2 ADDED?
Chlorine dioxide is effective and safe at concentrations of 0.5 to 5 ppm in solution. The maximum allowable concentration for contacting produce with chlorine dioxide solution is 5 ppm. This level has been chosen by the NFPA (National Food Processors Association) and The FDA (Food and Drug Administration).
Chlorine dioxide solutions are injected with commercially available equipment into a produce dump tank or water reservoir. Dump tanks usually have a chemical concentration of 0.5 to 5 ppm and a contact time of 3 minutes. After the dump tank or reservoir, spray bars rinse the product with a potable water rinse.
Chlorine dioxide can not be stored or transported because it is unstable at normal conditions and explosive under pressure. Chlorine dioxide must not be used in combination with equipment made of wood. Great amounts of organic substances, such as wood, may cause explosions when contacted with chlorine dioxide. Chlorine dioxide solutions should be handled with protective clothing and glasses. Shower and eyewash stations should be near the generating area.
Although it is not storable in its normal form, one company (BCI) offers a storable and transportable form of chlorine dioxide called PurogeneTM. Upon mixing with acid activator, purogene produces ClO2 at the levels that are not explosive and are safe to use. However, the activated PurogeneTM solution must be diluted within 10 to 15 minutes of the mixing with the acid, to avoid accumulation of ClO2 to toxic levels. For this reason it is best to perform activation in well-ventilated areas. If the gas escapes, it is easily identified by its greenish-yellow color and its characteristic of settling on the floor. Avoid inhalation of this gas.
PurogeneTM should be transported only in the unactivated form and in well-labeled containers that are supplied by distributors. PurogeneTM is quite safe to store when stored in its original container and away from direct sunlight, chlorine, phosphorus, and flammables. Drying of PurogeneTM on wood products or organics should be avoided.
HOW DO I CONTROL MY DOSAGE?
It is important to have a method for monitoring the amount of chlorine dioxide entering the water system. The only safe way to dose chlorine dioxide solutions is with automatic controls or semi-automatic controls. (Several companies that distribute automatic controls and chemicals are listed at the end of this article.)
Surface debris must be removed before treating with chemical disinfectants.
Due to the corrosiveness of hydrochloric acid (one of the ingredients of chlorine dioxide), the generating equipment lines must be checked at least twice per week. Periodic checks should also be made by emergency service personnel. Leaks must be repaired immediately. Employee training for handling chlorine dioxide solution is provided by most distributors.
ARE CHLORINE DIOXIDE, SODIUM CHLORITE, AND HYDROCHLORIC ACID HEALTH HAZARDS?
Chlorine dioxide is mildly corrosive to equipment. It must be dosed so that high concentrations in air will be avoided. Automatic metering devices greatly reduce the amount of gas in the air. Chlorine dioxide gas is labeled as a toxin on the Material Safety Data Sheet (MSDS, available from any company that sells a chemical).2 It is also an irritant to the respiratory system at concentrations over 45 ppm in air. It will burn skin and eyes on contact; flush the exposed area with water for 15 minutes and seek medical advice.
Federal exposure limits of chlorine dioxide are published in the MSDS. Chlorine dioxide and is regulated, with air exposure limits of 0.1 ppm long term (> 8 hours) and 0.3 ppm short term (< 15 minutes). Monitors for off-gases are available from most chlorine dioxide equipment generators.
Sodium chlorite is also a toxin and an irritant. Even short term exposure can cause difficulty breathing and severe skin and eye irritation. Sodium chlorite should be stored in an easily identifiable container. It should be kept away from acids, flammable materials, cyanides, metals, oxidizing materials, and metal salts.2
Hydrochloric acid is toxic and corrosive. Short term exposure will cause lung, skin, and eye irritation. It should also be stored in an easily identifiable container. It should be kept away from bases, flammable materials, halogens, halo carbons, cyanides, metals, oxidizing materials, and metal salts. The exposure limit is only 5 ppm in water.2
Although THMs (trihalomethanes) and chloro-organics are not easily formed by chlorine dioxide, some harmful by-products are. By-products chlorate and chlorite are toxic. Their reaction products may cause anti-thyroid activity or hemolytic anemia.
HOW DO I IDENTIFY CHLORINE DIOXIDE, SODIUM CHLORITE, AND HYDROCHLORIC ACID?
As a gas, chlorine dioxide has a yellow-green color and is heavier than air. It is soluble (up to 2900 ppm in water) and colorless in water solution, but it can be identified by a swimming pool odor (Do not taste chemicals for identification!). Chlorine dioxide may cause foaming on the surface of circulated water, particularily in the prescence of organic matter.
The chemicals that make up chlorine dioxide can also be easily identified by the user. Sodium chlorite is a white crystalline powder. One of its physical characteristics is its ability to absorb moisture. The other component of chlorine dioxide, hydrochloric acid, is a colorless liquid. It should not be inhaled or identified by smell. It has a pH of 2 and the density is very similar to water.
WHERE DO I DISPOSE OF TREATED WASTEWATER, UNUSED CHEMICALS, OR SPILLED CHEMICALS?
Chlorine dioxide should be disposed in accordance with all applicable regulations. Small quantities (< 10 gal) are relatively non-toxic to aquatic life2 and can be flushed into a sewer with water.2 If large quantities (> 10 gal) of concentrated chlorine dioxide solutions are spilled, contact the MiDEQ hotline at 800-292-4706. Do not drain large amounts chlorine dioxide solution into surface or groundwater sources. The solution should be contained and neutralized with sodium bisulfite or sodium thiosulfate. Another option is to dispose of the material at an authorized chemical disposal site or class I landfill. Spill areas should be flushed with ample amounts of water. PurogeneTM solutions must be flushed before they are dried because the dry form is flammable.
WHAT WILL I NEED TO BUY?
Specific equipment is required to generate and mix chlorine dioxide on-site. This equipment is readily available from numerous companies.* Each chlorine dioxide company uses slightly different methods of mixing the chemical with water. Monitors are a necessity to avoid overdosing. Proper operation and maintenance procedures must be followed for safety, and equipment should be examined frequently.
Chlorine Dioxide Food Application Summary1
WHERE CAN I PURCHASE CHLORINE DIOXIDE GENERATING CHEMICALS AND EQUIPMENT?
Chlorine dioxide equipment and information can be obtained from the following companies. These companies were chosen only for reference. This article is not intended to be an advertisement nor provide a product recommendation. Many other companies exist that make and sell similar products.
Aldrich Chemical Co.