Wastewater New York State Practice Exam 2026 - Free Wastewater Certification Practice Questions and Study Guide

The process referred to in the question is known as chlorine demand, which represents the difference between the amount of chlorine that is added to the water (the chlorine dose) and the amount of chlorine that remains in the water after a specific period of time (the chlorine residual). Chlorine demand is an important concept in water treatment as it helps in determining how much chlorine is required to achieve effective disinfection.

When chlorine is introduced into water, it reacts with various contaminants and organic materials present in the water. As a result, not all of the chlorine added is available to provide disinfection. The residual chlorine represents the amount of chlorine that remains available after these reactions.

Understanding chlorine demand is essential for water treatment operators to ensure that adequate chlorine is applied to achieve the desired disinfection levels while avoiding excess chlorine, which can lead to other water quality issues.

Other options, while related to chlorine use in water treatment, do not specifically describe the subtraction of chlorine residual from the chlorine dose in the same context as chlorine demand does.