Which chlorination method is the most effective for field water treatment and preferred for large-scale systems, with 65-70% chlorine?

• A. Chlorine Gas
• B. Bleach
• C. Ozone
• D. High-test calcium hypochlorite

Answer: (D)

In field water treatment and large-scale systems, you want a disinfectant form that combines high available chlorine with practical handling, storage, and dosing. High-test calcium hypochlorite fits that need because it contains about 65–70% available chlorine in a dry solid. That high concentration lets you dose effectively with relatively small, simple feeders and ships and stores more safely and easily than gases or dilute liquids. Chlorine gas, while very effective, requires specialized equipment, gas handling safety, and robust leak control, which is impractical for widespread field operations. Household bleach is convenient but usually only around 5–8% chlorine, so you’d need huge volumes to reach the same disinfection dose, plus it can degrade with storage. Ozone isn’t a chlorine-based disinfectant at all and needs an expensive, complex generator with its own set of operating demands. So, the solid high-test calcium hypochlorite provides the best balance for large-scale field use with the specified chlorine content.