Bridging the GAPs: Approaches to Treating Water On Farms

Other Factors to Consider

There are several additional factors to consider when using chlorine. Availability of chlorine in the chosen form may limit grower’s options. For example, in many cases chlorine gas may not be as available as the solid or liquid form of chlorine. Employee safety is another key factor. Like many pesticides, use of the chemical may require operator certifications and use may need to be accounted for through recordkeeping. The chlorine injection method is also another factor to consider, taking into account infrastructure and cost of equipment. Implementation of treatment systems will be covered in a later section.

Sources of Chlorine

The primary forms of chlorine include sodium hypochlorite (NaOCl), calcium hypochlorite [Ca(OCl)2], and chlorine gas (Cl2). Sodium hypochlorite is available in the liquid form at 5.25, which is household bleach, 12.75, or 15% concentrations. (Keep in mind that 1% is equal to 10,000 ppm.) Calcium hypochlorite is another form, which is a solid at 65 or 68% and is usually sold as a powder or tablets; however, it does not dissolve readily (especially in cold water). Undissolved particles can injure fruits and vegetables. In order to prevent this from occurring, the powder or tablets are first dissolved in a small amount of water before adding it to the tank. If using tablets for continuous, slow release of chlorine, ensure that the tablets are placed where water circulates well around them. Chlorine gas comes in pressurized gas cylinders. This is the most dangerous form to work with and should be handled cautiously according to the label instruction. Chlorine dioxide is another form and may have residual sodium that could harm or cause plant injury.

Advantages and disadvantages

Chlorine is the most widely used sanitizer and disinfectant throughout the food industry. It is a cost-effective option and, for growers of produce, has been shown to be effective against plant pathogens and preventing clogged emitters by preventing the formation of biofilms. However, growers must take into account factors that impact chlorine’s activity, including pH and organic load of the irrigation water, which can significantly fluctuate. The use of chlorine for irrigation water has not been established by the National Organic Program, as its current approval is limited to postharvest washing. While chlorine is effective against a broad spectrum of bacteria and some viruses, as a comparison, it is less effective against parasites, such Cryptosporidium or Cyclospora. In addition, as with any chemical such as a pesticide, worker safety is important, particularly in the instance of the formation of by-products, such trihalomethanes.


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