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.
Why is a COD test preferred over a BOD test?
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.
Why COD is used instead of BOD?
As because COD can be estimated within two hours compare to BOD that takes for five days incubation. COD method is faster analysis than BOD.
Why COD is a better measure of organic carbon than BOD?
The COD test uses a chemical (potassium dichromate in a 50% sulfuric acid solution) that “oxidizes” both organic (predominate) and inorganic substances in a wastewater sample, which results in a higher COD concentration than BOD concentration for the same wastewater sample since only organic compounds are consumed
What are the advantages of COD?
Nutrition. Cod is a low-fat source of protein, making it an excellent choice for people who would like to reduce their fat intake and improve their heart health. Cod also contains a significant amount of iodine, which is an important mineral for thyroid function.
What are the limitations of 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.
Is COD always higher than BOD?
COD stands for Chemical Oxygen Demand, and it is the amount of oxygen that will be consumed by the chemical break down of both organic and inorganic compounds. As such, COD will always be higher than BOD.
What is the significance of 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 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 limitation of COD test?
One of the main limitations of the COD test is its inability to differentiate between biodegradable and biologically inert organic matter on its own. The use of chemicals such as chromium and strong acids produce hazardous liquid waste, which requires careful disposal.
Which is better BOD or COD?
COD is always higher than BOD because chemical oxidation is easier than biological oxidation.
Why is COD important in wastewater?
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.
Why COD test is important?
The COD test is often used to monitor water treatment plant efficiency. This test is based on the fact that a strong oxidizing agent, under acidic conditions, can fully oxidize almost any organic compound to carbon dioxide.
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.
Why is BOD sample kept in darkness?
In one bottle of each pair, the concentration of dissolved oxygen is determined (e.g. by means of an oxygen probe) immediately after mixing. The other bottle is stored for n days at 20°C in the dark (to prevent photochemical reactions).
Why is the BOD test run for 3 5 days?
Legend has it that the 5-day BOD (Biological Oxygen Demand) test was developed in England. Sewage was dumped in a river and it took five days for it to reach the ocean, hence the five-day incubation requirement in the BOD method.
Can BOD be equal to COD?
If the content of organic matter is more more the value of BOD.In general COD is always more than BOD. BOD (Biochemical oxyen demand) – The amount of oxygen required by micro-organisms to degrade the organic matter and can be calculated as BOD of diluted and Undiluted samples.
What is the ratio of COD to BOD?
0.3 to 0.8
Typical values for the ratio of BOD/COD for untreated municipal wastewater are in the range from 0.3 to 0.8 (see in table 3). If the BOD/COD ratio for untreated wastewater is 0.5 or greater, the waste is considered to be easily treatable by biological means.
What happens to the quality of water if the COD is too high?
When the COD levels are higher, there is a greater demand for oxygen. This means that there is likely more oxidizable organic material in water with high COD levels. This also means that there are reduced Dissolved Oxygen (DO) concentrations in wastewater with high COD levels.
Why is BOD important in water quality?
The BOD is an important parameter for assessing water quality. It deals with the amount of oxygen consumption (mg O2 L− 1) by aerobic biological organisms to oxidize organic compounds. Sewage with high BOD can cause a decrease in oxygen of receiving waters, which in turn can cause the death of some organism.
What happens if BOD is high?
The greater the BOD, the more rapidly oxygen is depleted in the stream. This means less oxygen is available to higher forms of aquatic life. The consequences of high BOD are the same as those for low dissolved oxygen: aquatic organisms become stressed, suffocate, and die.
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