What primarily determines the strength of sewage?

The primary strength of sewage is determined by Biological Oxygen Demand (BOD). BOD is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in sewage. This measurement provides insight into the degree of pollution found in the sewage and indicates the organic material present, which is crucial for understanding its potential impact on receiving waters.

When BOD is high, it reflects high levels of biodegradable organic material, which is a significant concern for water quality because it can lead to oxygen depletion in aquatic ecosystems. Managing and treating sewage with high BOD levels is essential for environmental protection and ensuring that ecosystems are not adversely affected by nutrient loading.

Other factors like pH levels, Chemical Oxygen Demand (COD), and suspended solids do provide important information about the sewage, but they do not give as direct a measure of the organic strength as BOD does. pH informs about the acidity or alkalinity of the effluent, COD measures the total amount of oxygen required to oxidize both biodegradable and non-biodegradable substances, and suspended solids quantify the solid particles in the water. However, BOD is the primary determinant of sewage strength due to its direct relationship with organic contamination.