Tennessee Wastewater Operator Practice Exam

Which scenario would likely cause an increased chlorine demand?

1. High ammonia concentration

2. Low pH levels

3. Optimal chlorine levels

4. Stable temperature

The correct answer is: High ammonia concentration

A high ammonia concentration in wastewater is known to significantly increase chlorine demand. This occurs because chlorine reacts with ammonia to form chloramines, which are less effective as disinfectants than free chlorine. When ammonia is present in elevated levels, more chlorine is required to achieve the desired disinfection level, as a portion of the chlorine will be consumed in reacting with the ammonia instead of being available for pathogen removal. Low pH levels can also affect chlorine efficacy, often requiring more chlorine for disinfection, but the specific scenario of high ammonia concentration is the primary driver for increased chlorine demand. Optimal chlorine levels aim to ensure enough chlorine is available for effective disinfection without excessive demand from contaminants. Similarly, stable temperature conditions generally support consistent chlorine reactions and do not inherently increase demand.