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What is Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD)?

What is Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD)?


Chemican oxygen demand (COD) and biochemical oxygen demand (BOD) – a slightly more refined measure of water quality constituents than COD – measures the amount of oxygen that would be required to fully break down the organic components that can be biologically degraded in water. COD and BOD are measured in mg oxygen/L of water. COD is always equal to or greater BOD. The ratio of BOD to COD is the percent of the organic materials in water that can be degraded by natural micro-organisms in the environment. Dissolved oxygen (DO) is a measure of oxygen dissolved in water.

What causes high COD/BOD in stormwater runoff?

High COD/BOD levels in stormwater runoff are cause by the residual food and beverage waste from cans/bottles, antifreeze, and emulsified oils from industrial food processing and agricultural activities. As most forms of COD are water soluble, this pollutant spreads easily via stormwater to waterways.

Why should COD/BOD be reduced in industrial stormwater runoff?

COD / BOD should be removed from stormwater because high levels in waterways often correlate with threats to human and wildlife health through toxic algae blooms, and bacteria from organic wastes and seafood contamination. 

High COD / BOD levels also decrease the amount of dissolved oxygen available for aquatic organisms. Low (generally under 3 mg/L) levels of dissolved oxygen, or “hypoxia,” causes reduced cell functioning, disrupts circulatory fluid balance in aquatic species and can result in death of individual organisms, as well as large “dead zones” in the waterbody. Hypoxic water can also release pollutants stored in sediment.

How is COD/BOD reduced in industrial stormwater runoff?

In most applications, chemical oxygen demand (COD) and biochemical oxygen demand (BOD) can be reduced using passive media filtration and/or polishing. BOQU offers enhanced and advanced stormwater treatment systems to remove COD. The Aquip passive media filter and the Purus polisher combined offer an advanced level of COD removal from stormwater prior to discharge to help facilities meet benchmarks or NALs. Learn more about our stormwater media filtration.

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