It is expressed in milligrams per liter (mg/L) also referred to as ppm (parts per million), which indicates the mass of oxygen consumed per liter of solution.
The Chemical Oxygen Demand (COD) test uses a strong chemical oxidant in an acid solution and heat to oxidize organic carbon to CO2 and H2O.
Oxygen demand is determined by measuring the amount of oxidant consumed using titrimetric or photometric methods.
The test is not adversely affected by toxic substances, and test data is available in 1-1/2 to 3 hours, providing faster water quality assessment and process control.
Typical DIgestion Curves - COD vs. Time:
COD determinations made for process control purposes can be conducted in a shorter digestion time than specified in the procedure. For samples which are difficult to oxidize, the digestion time can be extended up to four hours if a blank is also run for the same period of time.
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