The oxygen consumed by microbes decomposing organic matter in water.
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Biochemical oxygen demand, BOD, is the amount of dissolved oxygen consumed by microorganisms as they decompose organic matter in a water sample. The standard test, BOD5, incubates a sample in the dark at 20 C for five days and measures the oxygen depletion. A high BOD indicates a large load of organic pollution, and the water can then support little aquatic life. Clean rivers typically have BOD below about 3 mg per L, while untreated sewage can exceed 200 mg per L. BOD is a key parameter in wastewater treatment design and regulation.
Key ideas: BOD5 is the oxygen consumed by microbes oxidizing organic matter in a sample over 5 days at 20 C in the dark, in mg per liter. Clean river water under 3 mg per liter, treated sewage effluent about 20, raw sewage about 200 to 400 and industrial wastes much more. Measure by difference in dissolved oxygen before and after incubation.
Common mistakes and connections: Mistake: viewing BOD as the amount of pollutant itself; it measures only biodegradable organic load. COD (chemical oxygen demand, dichromate oxidation) is higher because it oxidizes nearly all organics. Toxic wastes can give a falsely low BOD by killing microbes. Links to dissolved oxygen and eutrophication.
Oxygen consumption by microbes rises toward a limit. The standard BOD5 reading at 5 days, here about 8 mg per L, measures organic pollution. The interactive lesson shows this as a live animation or chart.
A river sample that loses 8 mg per L of oxygen over five days has a BOD5 of 8 mg per L.
The oxygen consumed by microbes decomposing organic matter in water.
Biochemical Oxygen Demand is a advanced topic in Biochemistry, Environment & Industry. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Biochemistry, Environment & Industry first: Air Quality Index, Water Pollution, Eutrophication.
The next topics in Biochemistry, Environment & Industry are Dissolved Oxygen and Heavy Metal Pollution.
Yes. The interactive lesson includes a self-check question on Biochemical Oxygen Demand, and the Biochemistry, Environment & Industry quiz draws on every topic in this area.
Biochemical Oxygen Demand is topic 81 of 127 in Biochemistry, Environment & Industry.
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