What is closed reflux method?
In the closed reflux method, ampules and culture tubes with premeasured reagents are used and then samples is placed in the tube and COD is determined. In this experiment, closed reflux method is used and samples with COD < 50 mg O2/L are tested.
How do you do the COD test?
The COD test uses a chemical (potassium dichromate in a 50% sulfuric acid solution) that “oxidizes” both organic (predominate) and inorganic substances in a wastewater sample, which results in a higher COD concentration than BOD concentration for the same wastewater sample since only organic compounds are consumed …
Is COD a method analysis?
The traditional chemical oxygen demand (COD) analysis method is the wet chemistry method. This involves a two hour digestion at high heat under acidic conditions in which potassium dichromate acts as the oxidant for any organic material present in a water sample.
What is the purpose of using HgSO4 and Ag2SO4 in the COD test?
The most general COD determination uses potassium dichromate (K2Cr2O7) in excess in an acidic medium with the aid of silver sulfate (Ag2SO4) as a catalyst, and mercuric sulfate (HgSO4) added to remove interference of chlorides.
How do you test water for COD?
There is a formula for calculating COD. Consider the formula for COD calculation: (a – b) X C X 8,000 / the volume of the sample in mL. Let “a” represent the titrant used for your sample expressed in mL. Let “b” represent the titrant used for your blank sample in mL.
Why do we use h2so4 in COD?
Chemical Oxygen Demand (COD) 1% Silver Sulphate in Sulphuric Acid (conc.) provides the primary and secondary digestion catalysts for oxidation of carbon during chemical oxidation.
How do you reduce COD in wastewater?
You can reduce COD and BOD by adding hydrogen peroxide to the wastewater solution. The hydrogen peroxide will chemically attack the organics in the wastewater, degrading them and reducing the measured COD and BOD.
Why is COD high?
Sources: COD increases as the concentration of organic material increases. It also increases if inorganic compounds susceptible to oxidation by the oxidant (typically dichromate) are present. Water with high COD typically contains high levels of decaying plant matter, human waste, or industrial effluent.
What is COD reactor?
Chemical Oxygen demand COD reactor Chemical oxygen demand (COD) test is commonly used to indirectly measure the number of organic compounds in water.
Why potassium dichromate is used in COD?
Currently, most COD tests use potassium dichromate as the oxidant. Potassium dichromate is a hexavalent chromium salt that is bright orange in color and is a very strong oxidant. Between 95-100% of organic material can be oxidized by dichromate.
Why do we use reflux method for determining COD?
Due to it higher oxidizing ability dichromate reflux method is preferred over other procedures using other oxidants (e.g. potassium permanganate). Oxidation of most organic compounds is up to 95-100% of the theoretical value.
Why is Sulphuric acid used in COD tests?
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