Basic Wastewater Operator Practice Exam

Which condition increases chlorine demand in wastewater treatment?

1. High flow

2. Low flow

3. A decrease in organic matter

4. An increase in organic matter

The correct answer is: An increase in organic matter

Chlorine demand in wastewater treatment is significantly influenced by the presence of organic matter. When there is an increase in organic matter in the wastewater, the chlorine used for disinfection must not only kill pathogens but also react with the organic compounds present. This reaction reduces the amount of chlorine available for effective disinfection, thereby increasing the overall chlorine demand. Organic matter serves as a substrate for microbial life, and its presence indicates a higher concentration of biodegradable materials that can consume chlorine. Consequently, more chlorine is required to achieve the same level of disinfection, leading to an increase in chlorine demand. In contrast, other factors such as flow rates or a decrease in organic matter typically do not impact chlorine demand in the same way. High or low flow conditions can affect contact time and dilution but do not directly influence the demand created by organic material. Similarly, reducing the organic matter would lower chlorine demand, as there are fewer compounds for chlorine to react with before addressing pathogens.