Oxidizers used for water sanitation

In part 2, Premier Tech discussed the importance of “preparing” irrigation water for sanitation. This involved removal of total suspended solids, reduction of biofilm in pipes and tanks and consideration of water pH and electrical conductivity. All these factors influence the application rate and efficacy of a sanitizing agent. Now in this final part, they discuss different types of sanitizing agents, how they work and some of the advantages and disadvantages of each. As many have found, there is not one system that works best for all growers. This article will focus on oxidizing agents used to sanitize greenhouse irrigation water and the second half, which will be in the next Grower Services Newsletter, will focus on other methods to sanitize water.

by Lance Lawson

Oxidizing agents: Oxidizing agents are added to irrigation water to kill pathogens by direct exposure to the agent for a specified length of time. The length of exposure required to kill pathogens depends on the pathogen itself, its inoculum structure, the type and concentration of the oxidizing agent and biological load in the water.

An advantage of most oxidizing agents is that there is residual product that persists in the water. Therefore, if the ‘sanitized’ irrigation water becomes re-contaminated with a pathogen before reaching the crop, it can control the pathogen. Oxidizing agents work well, but are often ‘used up’ in organic media components, such as peat, bark, compost and coir as well as algae, plant debris, biofilm and of course, pathogens. It is critical that water is filtered and cleaned in order for an oxidizing agent to effectively control pathogens in water. Also consider that oxidizers react and bind with iron, manganese, boron and other metals found in the water, also reducing their efficacy.

The most common oxidizing agents used to clean irrigation water will be discussed in the following chart below. These are chlorine gas, chlorine dioxide, calcium hypochlorite, sodium hypochlorite, ozone and activated peroxygen.

Chlorine gas cylinders supply the chlorine gas that is injected into the irrigation water to sanitize it. Source: Premier Tech Horticulture.

Chlorine dioxide generator for greenhouse water sanitation.
Source: http://aquapulsechemicals.com/products.html.

Ozone Generator for water sanitation.
Source: http://www.climatecontrol.com

These oxidizing agents all have their own advantages and disadvantages. Whether you consider cost, residual effects, environmental hazards, worker safety, etc., not one system meets all these criteria. In the next edition of the Grower Services Newsletter, we will continue presenting the remaining types of water sanitation methods that are currently offered today to sanitize irrigation water for plants.

References

Konjoian, P. 2011. Chlorine Dioxide in Horticulture: A Technology Review. Greenhouse Grower March 17, 2011
Powell, C.C. 2001. "Are Your Plants Drinking Dirty Water?" Grower Talks 79(7)
http://hort.ifas.ufl.edu/yprc/resources/water/pdfs/Water%20Quality%20Series%20from%20GMPro.pdf
http://pnwhandbooks.org/plantdisease/pesticide-articles/treating-irrigation-water-eliminate-water-molds
Newman, S.E. 2004. "Disinfecting Irrigation Water for Disease Management." 20th Annual Conference on Pest Management on Ornamentals – Society of American Florist Meeting (San Jose, CA).

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