Biochemical oxygen demand

Biochemical oxygen demand (BOD) measures the dissolved oxygen microorganisms consume while decomposing biodegradable organic matter in water. It is commonly reported as the oxygen consumed during a specified incubation period.

Dissolved oxygen: Dissolved oxygen is molecular oxygen present in water and available to aquatic organisms and chemical reactions. BOD is calculated from the decrease in dissolved oxygen during incubation.
Wastewater treatment: Wastewater treatment removes contaminants from used water through physical, chemical, and biological processes. Treatment plants track BOD to evaluate how much biodegradable pollution remains.
Hypoxia (environmental): Environmental hypoxia is a condition in which water contains too little dissolved oxygen to support many aquatic organisms. High BOD can deplete dissolved oxygen until hypoxic conditions develop.
Total organic carbon: Total organic carbon measures the amount of carbon bound in organic compounds in a water sample. It measures organic carbon directly, while BOD measures oxygen consumed during biodegradation.
Five-day biochemical oxygen demand: Five-day biochemical oxygen demand is the oxygen consumed by a water sample during five days of incubation under specified conditions. This standard test duration gives many reported BOD values their familiar form, BOD₅.
Activated sludge: Activated sludge is a suspended microbial community used to biologically treat wastewater. Its microbes reduce wastewater BOD by consuming organic matter.
Eutrophication: Eutrophication is nutrient enrichment that stimulates excessive biological growth in an aquatic ecosystem. Algal growth and subsequent decomposition can raise BOD and lower oxygen.
Theoretical oxygen demand: Theoretical oxygen demand is the oxygen required to completely oxidize a substance, calculated from its chemical composition. It predicts complete oxidation rather than measuring microbial consumption under test conditions.
Nitrification: Nitrification is the microbial oxidation of ammonia to nitrite and then nitrate. Nitrifying microbes can consume oxygen during a BOD test, adding nitrogenous demand.
Effluent: Effluent is liquid discharged from a facility or treatment process into the environment or another system. Effluent BOD indicates the residual oxygen demand released by a discharge.

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