Dive into the 2025 NY Wastewater Exam – Flush Away the Competition with Confidence!

The correct answer identifies that a decrease in dissolved oxygen (DO) concentration in the aeration tank is the first indicator of a higher than normal organic load being discharged into the sewer system. This decrease occurs because the organic material in the wastewater increases the demand for oxygen as microorganisms break it down through aerobic digestion. When there is a sudden influx of organic matter, the existing microorganisms may not be able to process it quickly enough, leading to a rapid consumption of oxygen and, consequently, a drop in DO levels. Monitoring DO is crucial, as low oxygen levels can impair the treatment process, harm aquatic life, and indicate potential issues that need to be addressed promptly.

While other indicators such as changes in pH levels, odors, or temperature may eventually manifest, they are not as immediate or directly linked to the initial impact of increased organic loading as a drop in DO concentration is.