Tennessee Wastewater Operator Practice Exam

What is the required contact time for disinfecting with ozone?

1. 5-10 minutes

2. 10-30 minutes

3. 30-60 minutes

4. 1-2 hours

The correct answer is: 10-30 minutes

The required contact time for disinfecting with ozone is often cited as being in the range of 10 to 30 minutes. This timeframe is crucial because ozone is a powerful oxidizing agent that effectively kills bacteria, viruses, and other pathogens by disrupting their cellular structures. The necessary contact time allows ozone to penetrate and interact with these microorganisms, ensuring that disinfection is thorough and effective. Factors such as the concentration of ozone used, the specific type of pathogens present, and the environmental conditions can influence the exact contact time needed for effective disinfection. However, the 10 to 30 minutes range is a standard guideline widely accepted in the wastewater treatment industry to achieve the desired level of microbial inactivation. The other timeframes listed, such as 5-10 minutes, 30-60 minutes, or 1-2 hours, do not align with the commonly recommended practices for ozone disinfection. While shorter times may not provide sufficient exposure for effective disinfection, longer contact times may be unnecessary and inefficient for practical operations. Therefore, the 10-30 minutes range represents a balance between efficacy and operational feasibility in ozone disinfection applications.