BOD - Biological Oxygen Demand

The biological oxygen demand (BOD), also called biochemical oxygen demand, refers to the amount of oxygen required for the biotic degradation of organic matter in bodies of water. It serves as a pollution parameter to assess the quality of effluent or wastewater. Untreated wastewater typically has high oxygen demand.

The decomposition of organic substrates is carried out by microorganisms, primarily aerobic bacteria that consume dissolved oxygen to produce energy. When substantial organic material is present, the oxygen demand increases correspondingly, potentially depleting oxygen needed by plants and animals in the water.

Authorities regulate BOD levels to protect public health and water quality. High BOD can indicate fecal contamination or organic carbon from various sources, which may affect human health and industrial operations.

BOD is measured through standardized empirical methods: samples are kept at 20 degrees C in darkness for five days, then oxygen content is measured and compared to original values. For high BOD situations, samples may be diluted to prevent oxygen depletion during testing. Drinking water should have a BOD well below 1 mg/l after five days, while acceptable wastewater from treatment plants should have approximately 20 mg/l.

Because these are empirical tests, BOD gives no absolute results but provides good comparative data among samples, though it cannot detect anaerobic bacteria like sulfur-reducing bacteria.