Biochemical oxygen demand (BOD) is a measure of the amount of dissolved oxygen consumed by microorganisms during the decomposition of organic matter in water. It is a key indicator of organic pollution in aquatic systems.
Biochemical oxygen demand (BOD) quantifies the dissolved oxygen required by aerobic microorganisms to break down organic material present in a water sample over a specified period, typically five days at 20 degrees Celsius (BOD5). High BOD values indicate large amounts of organic pollution, which can deplete dissolved oxygen levels and harm aquatic life. Municipal wastewater typically has a BOD5 of 200-300 mg/L before treatment, while clean rivers usually have BOD values below 2 mg/L. BOD testing is a standard method used by environmental agencies to assess the effectiveness of wastewater treatment plants and to regulate effluent discharge permits. The test involves incubating a sealed water sample and measuring the decrease in dissolved oxygen concentration over the incubation period. BOD is closely related to chemical oxygen demand (COD), though COD measures total chemical oxidation rather than biological decomposition alone.