Biochemical Oxygen Demand (BOD)

Definition - What does Biochemical Oxygen Demand (BOD) mean?

Biochemical oxygen demand (BOD) is a chemical procedure for determining the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period.

Organic matter oxidizes as it decays, producing CO2 which, in the presence of water, can be very corrosive to iron and steel substrates. Therefore, BOD is one way assess the corrosive potential of water.

Corrosionpedia explains Biochemical Oxygen Demand (BOD)

Biochemical oxygen demand is a measure of the quantity of oxygen used by microorganisms (e.g., aerobic bacteria) in the oxidation of organic matter. For example, wastewater from sewage treatment plants often contains organic materials that are decomposed by microorganisms, which use oxygen in the process. The amount of oxygen consumed by these organisms in breaking down the waste is known as the biochemical oxygen demand (BOD). The term also refers to a chemical procedure for determining this amount.

BOD is affected by the same factors that affect dissolved oxygen. Generally, when BOD levels are high, there is a decline in dissolved oxygen levels. This is because the demand for oxygen by the bacteria is high and they are taking that oxygen from the oxygen dissolved in the water.

The BOD test is one of the most basic tests used in the wastewater field. The BOD test is carried out by determining the dissolved oxygen on the wastewater or a diluted mixture at the beginning of the test period, incubating the wastewater mixture at 68°F (20°C), and determining the dissolved oxygen at the end of five days. The difference in dissolved oxygen between the initial measurement and the fifth day's measurement represents the biochemical oxygen demand.

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