Method summary An aliquot of the sample is digested for two hours at 150°C in the presence of dichromate and sulfuric acid. The resulting solution is titrated to a colored endpoint with ferroin indicator or read on a spectrophotometer at an appropriate wavelength.
How do you do the COD test?
Test for Chemical Oxygen Demand:
- Take 10 ml of sample into a round bottom reflex flask.
- Add some glass beads to prevent the solution from bumping into the flask while heating.
- Add 1 ml of Mercury sulfate (HgSO4) solution to the flask and mix by swirling the flask.
- Add 5 ml of Potassium dichromate (K2Cr2O7) solution.
Why do we perform COD?
COD is a water quality measure used not only to determine the amount of biologically active substances such as bacteria but also biologically inactive organic matter in water [8]. It is an important and rapidly measured variable for characterizing water bodies, sewage, industrial wastes, and treatment plant effluents.
How long does a COD test take?
This is usually done by titration, using an indicator solution. COD is expressed in mg/L, which indicates the mass of oxygen consumed per liter of solution. The COD test only requires 2-3 hours, while the Biochemical (or Biological) Oxygen Demand (BOD) test requires 5 days.
What is the limit of COD?
The chemical oxygen demand (COD) concentration in a treated effluent, if observed to be persistently greater than 250 mg/l before disposal to any receiving body (public sewer, land for irrigation, inland surface water and marine coastal areas), such industrial units are required to identify chemicals causing the same.
What is COD and How Is It measured?
COD is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution, which in SI units is milligrams per liter (mg/L). A COD test can be used to easily quantify the amount of organics in water.
How do you make COD standard solution?
Preparation of a COD standard solution:
Dissolve 0.851 g of potassium hydrogen phthalate in a calibrated or conformity-checked 100-ml volumetric flask and make up to the mark with dilution solution. The stock solution prepared according to this procedure has a concentration of 10 000 mg/l COD and 20 g/l Cl–.
Why Sulphuric acid is used 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.
What chemicals are used in COD?
COD is measured via a laboratory assay in which a sample is incubated with a strong chemical oxidant for a specified time interval and at constant temperature (usually 2 h at 150°C). The most commonly used oxidant is potassium dichromate, which is used in combination with boiling sulphuric acid.
Why COD is important in water treatment?
In wastewater treatment, the Chemical Oxygen Demand (COD) is an important measurement for the amount of oxygen that is required to break down pollutants (organic substances) in water. The chemical oxygen demand can be measured using different methods, direct or indirect.
What is a good COD level?
Influent COD in normal domestic sewage is therefore generally 600 – 900 mg/l and it is then treated to at least 75 -100 mg/l before discharge to minimise pollution potential.
What happens if COD is high?
Higher COD levels mean a greater amount of oxidizable organic material in the sample, which will reduce dissolved oxygen (DO) levels. A reduction in DO can lead to anaerobic conditions, which is deleterious to higher aquatic life forms.
What is COD value?
The COD value indicates the amount of oxygen which is needed for the oxidation of all organic substances in water in mg/l or g/m3. The COD (Chemical Oxygen Demand) is closely related to the laboratory standard method named Dichromate-Method.
What is BOD and COD limit?
According to standards of Central Pollution Control Board, permissible value of BOD is 30 mg/l and COD is 250 mg/l.
Why is COD high in wastewater?
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.
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How is COD load calculated?
BOD (or COD) load: Units: kg/day
This is simply done by multiplying the BOD in mg/l by the daily effluent volume in cubic metres (m3) and dividing the product by 1000.
How do you treat 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.
Which indicator is used in COD test?
potassium dichromate
Using potassium dichromate
. Most commonly, a 0.25 N solution of potassium dichromate is used for COD determination, although for samples with COD below 50 mg/L, a lower concentration of potassium dichromate is preferred.
Is code for COD test?
IS 3025
IS 3025 (Part 58): Method of Sampling and Test (Physical and Chemical) for Water and Wastewater, Part 58: Chemical Oxygen Demand (COD) First Revision)
What is COD reagent?
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.
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