Water Treatment MCQ with answer and solution

Concept

Breakpoint chlorination involves adding sufficient chlorine to oxidize all impurities and establish a free chlorine residual.

Step-by-step solution

1. Understand the breakpoint chlorination curve where chlorine is added to water containing ammonia and organics. 2. Initially, chloramines and chloro-organics are formed, and destruction of these compounds occurs as the breakpoint is approached. 3. At the breakpoint, all impurities are oxidized. 4. Beyond this point, additional chlorine remains uncombined in the water as free available chlorine.

Explanation

Breakpoint chlorination is the point in chlorination where all the chlorine-demanding substances (like ammonia, organics, and reducing agents) have been completely oxidized, and any chlorine added beyond this point appears as free available residual chlorine. Free residual chlorine provides active disinfection protection in the water distribution system.

Why the other options are wrong

A: Alkalinity is consumed or affected by chlorination, not ensured by it. B: Complete oxidation of organics happens *at* and before the breakpoint, but the primary definitive *ensured* output parameter measured for safety is free residual chlorine. C: Taste removal can occur during the process, but the specific engineering definition and guarantee of breakpoint chlorination is free residual chlorine.

Shortcut

Remember 'Breakpoint = Free residual chlorine achieved'.

Common mistake

Confusing breakpoint chlorination with simply adding enough chlorine to kill bacteria without reaching the breakpoint (combined residual only).