The TDS is the sum of all dissolved solids which included COD also. Thus TDS should be higher than COD. Sir, COD should include acid digestion of all the organics and inorganic compounds (Dissolved and suspended) in water or wastewater. Hence, COD should be greater that TDS.
What is BOD COD and TDS?
These parameters reflect effect and material characteristics of one or more substances. The most popular sum parameter in waste water analysis are the BOD (biochemical oxygen demand), COD (chemical oxygen demand), TOD (total oxygen demand) and TOC (total organic carbon).
What is COD formula?
COD as mg/l of oxygen consumed =(A-B) x Normality of FAS x 8000 / ml.
Why does COD increase in water?
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 does COD affect water quality?
When treated wastewater is discharged into the environment, it can introduce pollution in the form of organic content to receiving waters. High levels of wastewater COD indicate concentrations of organics that can deplete dissolved oxygen in the water, leading to negative environmental and regulatory consequences.
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.
How is COD measured?
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 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.
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 test 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 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 is a high COD level?
Higher COD levels mean a greater amount of oxidizable organic material in the sample, which will reduce dissolved oxygen (DO) levels.
What causes COD to decrease?
in your research COD decreases with increasing time because the bacteria in the water will grow and degrade the organic matters in your water sample.
What is COD level in water?
COD is a measure of the oxygen equivalent of the organic matter in a water sample that is susceptible to oxidation by a strong chemical oxidant. COD is widely used as a measure of the susceptibility to oxidation of the organic and inorganic materials present in water bodies and in the municipal and industrial wastes.
What is the COD value of drinking water?
According to standards of Central Pollution Control Board, permissible value of BOD is 30 mg/l and COD is 250 mg/l. Hope this helps, it mentions standards for India relating to different uses.
How do you reduce 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 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 a good BOD level?
1-2 ppm
A BOD level of 1-2 ppm is considered very good. There will not be much organic waste present in the water supply. A water supply with a BOD level of 3-5 ppm is considered moderately clean.
What is BOD limit?
As per the World Health Organisation, a limit of less than 5.0 mg/l is ideal for water bodies. At this limit BOD will not cause any harmful impacts on the human body, wastewater sewage must have BOD around 80 ppm and COD 200 ppm for discharge.
Why K2Cr2O7 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 glass beads are used in COD?
Test for Chemical Oxygen Demand:
Add some glass beads to prevent the solution from bumping into the flask while heating.
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