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COD stands for ‘Chemical Oxygen Demand’ where BOD stands for Biochemical Oxygen Demand. COD is normally higher than BOD because more organic compounds can be chemically oxidised than biologically oxidised.
What causes high 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.
Why is COD value high?
The higher the COD value, the more serious the pollution of organic matter by water. The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g., lakes and rivers) or wastewater (Davidson, 2001; Sara and Goncaloglu, 2008).
How is COD BOD ratio calculated?
To establish the COD:BOD ratio for your wastewater, simply have both COD and BOD run on several wastewater samples. Divide the COD concentration by the BOD concentration for each sample and average the results.
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 BOD and COD in sewage?
Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) are two of the most important parameters to characterise (measure the degree of pollution) of wastewater. BOD, the biological demand for oxygen a source of water has, is the amount of oxygen used by microorganisms to break down organic substances.
What is BOD COD ratio?
BOD (Biochemical oxygen demand) is the pollution index of any water sample. BOD : COD (Chemical oxygen demand) ratio using the formulated seed comes in the range of 0.7-0.8 whereas that using BODSEED comes in the ratio of 0.5-0.6. The ultimate BOD (UBOD) was also performed by exceeding the 3-day dilution BOD test.
Why is COD preferred over the body?
COD uses strong chemicals to oxidize organic matter. Generally, COD is preferred to BOD for process control measurements because results are more reproducible and are available in just two hours rather than five days.
What does COD mean in wastewater?
5 Chemical oxygen demand (COD) The COD is the estimate of oxygen required for the portion of organic matter in wastewater that is subjected to oxidation and also the amount of oxygen consumed by organic matter from boiling acid potassium dichromate solution.
How is BOD removed from wastewater?
Some BOD is removed in the septic tank by anaerobic digestion and by solids which settle to the bottom of the septic tank, but much of the BOD present in sewage (especially detergents and oils) flows to the leaching field. The bacteria in a healthy biomat also digest most of the remaining BOD in the sewage.
How do you remove COD and BOD from water?
There are different options for Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD) removal: A first option is biological purification where the polluting components are removed by means of bacteria. Sometimes, an alternative is the use of ultrafiltration to separate the polluting components.
Is BOD always less than COD?
BOD express the total organic load that can be decomposed biologically in presence of oxygen (thus aerobically). COD express the total organic load that can be decomposed chemically (thus more drastically). Based on that, it derives that always BOD is less or equal to COD.
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.
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 1500 Sulphate mg/l 1500.
Does aeration reduce COD?
Aeration should help reduce the COD in 2 ways. First it may evaporate some volatiles like hexane. Second it will add oxygen to the water speeding up any biological oxidation of the less volatile organics by the bacteria (microbial growth). It will actually increase the COD very quickly.
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 BOD limit?
For drinking water BOD has to be less than 5 mg/L and for treated wastewater to be disposed of in the water bodies it is 30 mg/L, 100 mg/L if treated waste water is discharged into the sewerage system in India.
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.
Which is better BOD or COD?
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.
What is the COD of drinking water?
The COD is the amount of oxygen consumed to chemically oxidize organic water contaminants to inorganic end products. The COD is often measured using a strong oxidant (e.g. potassium dichromate, potassium iodate, potassium permanganate) under acidic conditions.
What does high BOD indicate?
BOD indicates the amount of putrescible organic matter present in water. Therefore, a low BOD is an indicator of good quality water, while a high BOD indicates polluted water. Dissolved oxygen (DO) is consumed by bacteria when large amounts of organic matter from sewage or other discharges are present in the water.
What is the relationship between COD and do?
Typically, the average BOD result is divided by the average COD result to find a “conversion factor” between the two parameters. One would then multiply their COD results by this factor to estimate BOD. COD values are almost always higher than BOD values for the same sample.
What is BOD COD and do?
The biochemical oxygen demand (BOD) represents the amount of dissolved oxygen (DO) consumed by biological organisms when they decompose organic matter in water. The chemical oxygen demand (COD) is the amount of oxygen consumed when the water sample is chemically oxidised.
