Chemical Oxygen Demand (COD)

Chemical symbol/abbreviations:

COD

Form commonly found in stormwater:

Residual food and beverage waste from cans/bottles, antifreeze, emulsified oils.

Solubility in water:

Most forms of COD are water soluble

Adverse human impacts:

High levels of COD in water often correlate with threats to human health including toxic algae blooms bacteria from organic wastes and seafood contamination.[ii]

Adverse impacts on the environment:

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

Stormwater Treatment to Remove COD

Background:

Chemical oxygen demand (COD) is often used to measure organic matter in wastewater, treated effluent, and receiving waters. Although COD measures more than organic constituents, the organic fraction usually predominates and is the constituent of interest.[vii] Chemical oxygen demand was developed as an alternative to the more lengthy BOD analysis.

Sources of COD in stormwater are varied. However, soluble organic compounds are most likely to contribute to escalated COD concentrations. Residual food waste from bottles and cans, antifreeze, emulsified oils are all high in COD and are common sources of COD for industrial stormwater. A typical COD concentration for soda and beer is about 100,000 mg/L.

U.S. EPA recommended water quality criteria:

None. Dissolved oxygen water quality criteria depend upon natural stream temperature and dissolved oxygen level.[i]

Appendices

[i] U.S. EPA, National Recommended Water Quality Criteria, http://www.epa.gov/waterscience/criteria/wqctable/index.html#U (last visited July 7, 2010).

[ii] See National Science & Tech. Council, An Assessment of Coastal Hypoxia and Eutrophication in U.S. Waters, 2 (2003) available at http://oceanservice.noaa.gov/outreach/pdfs/coastalhypoxia.pdf.

[iii] Ambient Aquatic Life Water Quality Criteria for Dissolved Oxygen (Saltwater): Cape Cod to Cape Hatteras, 65 Fed. Reg. 71317, 71318 (Nov. 30, 2000).

[iv] Ecological Society of America, Hypoxia http://www.esa.org/education_diversity/pdfDocs/hypoxia.pdf (last visited Aug. 11, 2010).

[v] Ecological Society of America, supra.

[vi] Standard Methods, 5-14(Andrew Eaton, et al. eds., 21st ed. 2005).

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