Water sanitation part 3b: Oxidizers used for water sanitation

In a previous article, the common oxidizers were discussed that are used for water sanitation. These included chlorine gas, chlorine dioxide, calcium hypochlorite, sodium hypochlorite, ozone and activated peroxygen. In this article, the focus will be on other types of sanitizing systems used for irrigation water, how they work and their advantages and disadvantages. These sanitizing systems include: copper ionization, ultraviolet radiation, heat treatment and slow sand filtration.

by Lance Lawson

Copper Ionization: A copper ionization system consists of two copper electrodes that are positioned parallel to each other inside a pipe. As water flows over these electrodes through the pipe, an electrical current is applied between these electrodes, which displaces copper ions from one of the electrodes. The copper ions are carried away and then they firmly attach to pathogens, disrupting their cell walls, and thereby killing them. Copper ions also attach to the organic matter present in the water. Ideally free copper should be applied at rates of 0.5-1.0 ppm Cu to reduce water-borne pathogens and 1-2 ppm Cu to reduce algae.

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.

Copper ionization used for sanitizing water in a greenhouse.
Source: http://www.karobv.nl

Diagram showing how a copper ionization system works.
Source: http://www.ecosmarte.com

Advantages of copper ionization include: the residual copper in the water can still kill pathogens after water has passed through copper ionization, the system is easy to use, and it is safe for workers. It requires a moderate initial investment, but has low operating costs, which include the electricity to run the system and annual replacement of copper electrodes. It is ideal where water flow rates are high as there is no minimal contact time with water required. Although some copper is bound up in organic matter, it is not as critical as with other sanitation systems, making it acceptable for recycled water. Copper application rates required to control pathogens are low enough that it should not cause phytotoxicity in plants.

As stated, recycled or pond water still needs to be filtered to remove the organic matter that copper ions would bind to. Maintain water pH below 7.0 to keep copper from forming precipitates. The electrical conductivity (E.C.) of the water is important because as it changes, so does the copper output from an electrode. For example, the higher the E.C. of the irrigation water, the more electrical current the water carries, which results in higher release of copper ions. If the water source has changes from well water to rain water, which has zero E.C., then copper ion release is very low and will not control pathogens. It is best to use a copper ionization system that automatically adjusts the copper output based on changes in the E.C. of the water.

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