When the influent load to a wastewater treatment plant changes rapidly, which test is most effective for control purposes?

When the influent load to a wastewater treatment plant changes rapidly, measuring Chemical Oxygen Demand (COD) is particularly effective for control purposes. This is because COD provides a quick and comprehensive indication of the organic pollution level present in the wastewater, reflecting how much oxygen is needed to chemically oxidize the organic and inorganic matter in the sample.

COD testing offers a faster turnaround time compared to Biological Oxygen Demand (BOD), allowing operators to respond more swiftly to changes in influent conditions. This rapid assessment is crucial in managing treatment processes and ensuring compliance with discharge permits, especially in situations where load fluctuations may impact treatment efficiency and effluent quality.

In contrast, while Total Solids gives an indication of the concentration of solids in the wastewater, it doesn't directly measure the organic pollution. Dissolved Oxygen (DO) levels are essential for evaluating aerobic biological processes, but they may not adequately reflect sudden load changes. BOD, although important for understanding biodegradable organic matter, typically requires a longer incubation period (usually five days) to yield results, making it less suitable for immediate control actions when rapid changes occur. COD’s quicker and broader analysis makes it the preferred choice in these scenarios.