An advantage of using ozone treatment is....

• A. It is easy to feed
• B. It is noncorrosive in small doses
• C. Its by-products are biodegradable
• D. It improves coagulation

Answer: (D)

Ozone pretreatment helps the downstream removal steps by altering the organic matter in the water. When ozone oxidizes natural organic matter and color-causing compounds, it breaks large, complex molecules into smaller, more easily destabilized fragments. These smaller fragments respond better to coagulation and flocculation, allowing the coagulant to form larger, heavier flocs that settle more readily. In practice, this means better overall removal of organic material and turbidity during the coagulation/sedimentation phase, which is a clear advantage of using ozone.

Other options aren’t as accurate. Feeding ozone requires specialized equipment and control, so it isn’t simply “easy.” Ozone can be reactive with materials, so it isn’t generally considered noncorrosive in small doses. By-products of ozonation aren’t guaranteed to be easily biodegradable, and while ozone provides strong disinfection, the question focuses on coagulation improvement, which is the most direct benefit.