What determines the level of organic contamination in water, particularly from sewage?

The level of organic contamination in water, especially from sources like sewage, is primarily measured by Biochemical Oxygen Demand (BOD). BOD quantifies the amount of oxygen that microorganisms will consume while decomposing organic matter in the water. When sewage or organic waste is present, microorganisms thrive and their oxygen consumption increases, indicating a higher level of contamination from organic materials.

BOD is particularly useful for assessing the degree of organic pollution in water bodies and is widely used in wastewater treatment processes to gauge the effectiveness of treatment methods. A higher BOD value signifies a greater level of organic pollution, which can lead to environmental issues such as oxygen depletion in aquatic systems.

In contrast, Chemical Oxygen Demand (COD) measures the total quantity of chemicals in the water required to oxidize both organic and inorganic substances. While COD can provide information about water quality, it does not specifically isolate organic contamination like BOD does. Turbidity testing assesses the clarity of water based on suspended solids, and color testing involves the visual aspects of water quality but does not directly indicate the level of organic contamination. Thus, BOD is the most relevant parameter for determining organic pollution, especially from sewage.