Chlorine is a water-soluble chemical disinfectant that is commonly used for microbial disinfection because it is effective, economical, and approved by the Environmental Protection Agency (EPA) for water treatment (EPA, 2017). Chlorine-based compounds have been used as ‘primary’ disinfectants for drinking water, wastewater, and agricultural irrigation water (Figure 1) for decades. Primary disinfection kills or inactivates bacteria, viruses, and other potentially harmful organisms. Chlorine is also an effective ‘secondary’ disinfectant for prevention of bacterial and fungal growth or re-growth in distribution systems. Secondary disinfection provides long-lasting, residual water treatment as the water moves through pipes, including irrigation pipes and sprinklers with prolonged retention times (Schwankl et al., 2012). In general, chlorine can be applied to irrigation water in three forms: (1) as solid calcium hypochlorite [Ca(OCl)2], (2) as liquid sodium hypochlorite (NaOCl, or common bleach), or (3) as gaseous chlorine (Cl2) (USDA NRCS; Schwankl et al., 2012). Each form of chlorine varies in concentrations of ‘available’ chlorine, levels of effectiveness, characteristics, and advantages. It is therefore important to understandt hese differences before deciding on a chlorine treatment method for your agricultural irrigation water.
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