What is the typical COD - to - CBOD ratio for domestic wastewater?

The typical COD to CBOD ratio for domestic wastewater is important for understanding the characteristics of wastewater and the degree of biodegradable organic matter present. The ratio indicates how much chemical oxygen demand (COD) is attributed to the biodegradable portion represented by carbonaceous biochemical oxygen demand (CBOD).

A standard ratio range of 1.9 to 2.2 is commonly observed in domestic wastewater. This means that for every unit of CBOD present, there are approximately 1.9 to 2.2 units of COD. The higher rates of COD relative to CBOD are often indicative of the presence of significant amounts of non-biodegradable organic materials in the wastewater, such as those found in households.

In practice, this ratio helps wastewater treatment facilities design and manage processes more effectively by understanding the balance between readily biodegradable material and overall organic loading present in the influent. A proper understanding of this ratio facilitates better predictions of treatment efficiency and the necessary operational adjustments needed to optimize biodegradation processes.

The other ranges do not reflect the characteristics of typical domestic wastewater, with either an overly simplistic interpretation of organic load or an unrealistic expectation of the types of wastes usually encountered.