Texas Wastewater Class B Practice Exam

What is the minimum total combined residual of chlorine required in the contact chamber after 20 minutes?

1. 0.5 mg/L

2. 1.0 mg/L

3. 1.5 mg/L

4. 2.0 mg/L

The correct answer is: 1.0 mg/L

The minimum total combined residual of chlorine required in the contact chamber after 20 minutes is 1.0 mg/L. This requirement is designed to ensure that effective disinfection occurs to eliminate pathogens in the wastewater being treated. A residual level of 1.0 mg/L after 20 minutes ensures that sufficient chlorine remains in the water to effectively neutralize harmful microorganisms, thereby protecting public health and the environment. Higher levels of residual chlorine may lead to issues such as chlorine toxicity, which is detrimental to aquatic life, while too low of a level could result in insufficient disinfection and an increased risk of disease transmission. It is essential to maintain a balance, which is why the standard of 1.0 mg/L is established as the minimum for effective treatment during the specified contact time. This standard reflects best practices in wastewater treatment to achieve optimal safety and compliance with health regulations.