After bacteriological tests, the chlorine residual in the discharged water should be no greater than the feed water.

• A. no greater residual than the feed water
• B. equal to feed water
• C. zero
• D. twice the feed water

Answer: (A)

Chlorine residual shows how much disinfection power remains as water leaves the treatment point. After bacteriological tests prove the water is acceptable, the discharged water should not have a higher residual than the feed water because there’s no step after disinfection that would justify adding more chlorine to the effluent. Any higher residual would mean more chlorine is present than entering, which can lead to unnecessary chemical loading in the environment and potential taste/odor issues. So, the discharged water should have at most the same chlorine residual as the feed water (equal is possible, but it should not exceed it). For example, if the feed water carries 0.5 mg/L of free chlorine, the discharged water should be 0.5 mg/L or less.