The concentrations of COD observed in surface waters range from 20 mg/l O2 or less in unpolluted waters to greater than 200 mg/l O2 in waters receiving effluents. Industrial wastewaters may have COD values ranging from 100 mg/l O2 to 60,000 mg/ O2.
What is the acceptable range of COD in drinking water?
According to standards of Central Pollution Control Board, permissible value of BOD is 30 mg/l and COD is 250 mg/l .
What is a good COD level?
BMS have recorded average ratios of 2-3 mg/l COD to 1 mg/l BOD over its 30 years of business. 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.
Is High COD in water good?
IMPORTANCE OF COD FOR WASTEWATER
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 the limit of COD?
| Parameter Unit Maximum permissible limit | Chemical Oxygen Demand (COD) mg/l 120 | Biochemical Oxygen Demand (BOD 5 ) mg/l 40 | Chloride mg/l 750 | Sulphate mg/l 750 |
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Why is COD higher than BOD?
COD is normally higher than BOD because more organic compounds can be chemically oxidised than biologically oxidised . This includes chemicals toxic to biological life, which can make COD tests very useful when testing industrial sewage as they will not be captured by BOD testing.
How do you treat high COD?
One way to reduce COD in water is to use coagulants and flocculants to bind sludge together . Once they are bound into big enough masses that they can be easily filtered out and deposited into a sedimentation tank for removal. This method does however rely on the use of chemicals, and requires high reoccurring cost.
What is COD & BOD in water?
COD or Chemical Oxygen Demand is the total measurement of all chemicals (organics & in-organics) in the water / waste water; BOD is a measure of, the amount of oxygen that require for the bacteria to degrade the organic components present in water / waste water.
Why does COD increase in water?
All Answers (5) It may be due the presence of interfering agents like NH 4 + ,NO 3 – , Cl – , in the sample . These got oxidised by the K 2 Cr 2 O 7 in strongly acidic medium (H 2 SO 4 ) and hence an alteration comes in the COD value (increased COD). The nitrogenous ions and chlorides are common in organic wastes.
What causes COD 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.
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 so important?
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 . ... Compared to off-line measurement this method is much quicker providing an easier way to analyse the chemical oxygen demand.
How do you test for COD in water?
What test methods are typically used to determine COD at water and wastewater laboratories? The most common test method is the colorimetric analysis after oxidizing the COD with acid and using indicator compounds, such as hexavalent dichromate .
What is COD value?
In environmental chemistry, the chemical oxygen demand (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 litre (mg/L).
How is COD calculated?
Chemical oxygen demand, or COD, is a test that measures the amount of organic compounds in water. ... 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.
Which is greater ThOD or COD?
Explanation: ThOD mostly greater than COD . BOD u = 0.9ThOD, ThOD > BOD.
