Why is chemical oxygen demand higher than BOD?


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COD is always higher than BOD because chemical oxidation is easier than biological oxidation.

Which has the highest biological oxygen demand?

Oxygen use can also be measured per 100 gm of an organ to indicate concentrations of use; heart usage is highest, followed by the kidneys, brain, and liver. During exercise, the biochemical oxygen demand increases for active tissues including the heart and skeletal muscles.

What is chemical oxygen demand and biochemical oxygen demand of water?

The decay of organic matter in water is measured as biochemical or chemical oxygen demand. Oxygen demand is a measure of the amount of oxidizable substances in a water sample that can lower DO concentrations.

Is biological oxygen demand and biochemical oxygen demand same?

Biochemical oxygen demand (BOD, also called biological oxygen demand) is the amount of dissolved oxygen needed (i.e., demanded) by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period (Kaiser, 1998).

Which one is bigger BOD or COD?

BOD measures the amount of oxygen required by the aerobic organisms to decompose organic matter and COD measures the oxygen required to decompose organic and inorganic constituents present in the wastewater by chemical reaction. Hence, the value of COD is greater than BOD.

What are the advantages and disadvantages of the COD test compared to BOD?

The COD test has the advantage of not being subject to interference from toxic materials, as well as requiring only two or three hours for test completion, as opposed to five days for the BOD test.

What is chemical oxygen demand?

Chemical Oxygen Demand (COD) is a test that measures the amount of oxygen required to chemically oxidize the organic material and inorganic nutrients, such as Ammonia or Nitrate, present in water.

What does high BOD indicate?

The dissolved oxygen readings are usually in parts per million (ppm). Higher BOD indicates more oxygen is required, which is less for oxygen-demanding species to feed on, and signifies lower water quality. Inversely, low BOD means less oxygen is being removed from water, so water is generally purer.

What does Chemical Oxygen Demand indicate?

1.1 Chemical Oxygen Demand. COD is an indicative measurement of the amount of oxygen that can be consumed by reactions in a measured solution. It is an indicator of the contents of reducing substances in the water, which are organic, nitrite, sulfide, ferrous salts, etc., and the organic is dominant.

Why is COD determination preferred over biological oxygen demand determination?

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 are the limitations of the BOD test?

Limitations Of Test The method takes five days to perform and uses a discrete sample. The test has poor reproducibility and toxic chemicals can inhibit measurement. Short-term BOD determinations magnify errors and still require relatively long sample periods. The test is not suited for on-line, continuous measurement.

What is the disadvantage of COD?

Disadvantages of Cash on Delivery (COD) mode of payment The seller at this point will have already incurred transportation costs which accumulate to a loss for the e-commerce business. 2. The business representatives will be handling a lot of cash through the COD system unlike in the use of credit cards.

What is a high level of COD?

A higher COD in a sample indicates that it contains higher levels of oxidisable material. If this is the case, then the water will have reduced dissolved oxygen levels. Where this happens, the effects can be environmentally damaging to higher aquatic lifeforms.

Does high BOD mean pollution?

We can see that BOD is directly proportional to the amount of pollution. So, High BOD indicates highly polluted water. Hence, the correct answer is option (A).

Why a low BOD is important in wastewater treatment?

Generally, a higher BOD value indicates a higher level of water pollution, while a lower BOD value indicates less polluted, or cleaner water.

How does chemical oxygen demand affect water quality?

High chemical oxygen demand in water indicates greater levels of oxidizable organic matter and consequently, a lower amount of Dissolved Oxygen (DO). Critical DO depletion due to organic contamination can kill off aquatic life forms.

What are the advantages of COD over 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.

Is high chemical oxygen demand good?

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.

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 BOD and COD important?

COD and BOD tests are important because they help in the determination of the amount of waste in wastewater. This is important because the organic content in wastewater needs to be reduced before the wastewater is discharged.

What is importance of determining COD and BOD?

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.

Why 5 days are required for BOD?

BOD occurs in 2 general stages. While calculating the oxygen demand, the carbonaceous stage is taken into account. This stage is almost completed in 5 days, which means that most of the organic content of the sewage is oxidized under aerobic conditions in 5 days. Hence ,BOD for 5 days is calculated.

What are the necessary conditions for measuring BOD?

BOD measurement requires taking two samples at each site. One is tested immediately for dissolved oxygen, and the second is incubated in the dark at 20 C for 5 days and then tested for the amount of dissolved oxygen remaining.

Why is BOD test run in the dark?

The BOD test bottle is stoppered to ensure that the system is closed. b. Why is the test run in the dark (or in a black bottle)? The test run is done in the dark or in a black bottle to ensure there is no sunlight getting into the bottle.

Is COD risky?

With COD, there’s also a higher risk of delivery refusal. This can be especially disastrous when suppliers are transporting perishable goods. When this happens, suppliers lose profit on returned or spoiled goods and may have to pay shipping return fees.

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