What does Biochemical Oxygen Demand (BOD) indicate?

Biochemical Oxygen Demand (BOD) is a critical measure that indicates the strength of sewage by assessing the amount of oxygen that microorganisms need to decompose organic matter in water over a specified period, typically five days at a temperature of 20°C. A higher BOD value signifies a higher concentration of organic pollutants in the water, indicating that the sewage is stronger or more loaded with biodegradable material. This is essential for evaluating the potential impact of wastewater on receiving waters and for designing effective wastewater treatment systems.

In contrast, measuring sewage volume or the temperature of sewage does not provide information about its organic content or strength. The purity of water refers more to the absence of contaminants and pollutants rather than a direct measure of organic matter decomposition demands. Therefore, the importance of BOD lies specifically in its ability to gauge the organic pollution strength in sewage.