What is BOD and COD in water treatment?
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.
What causes high COD in wastewater?
Sources: 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.Mar 14, 2020
What is COD in drinking water?
Chemical oxygen demand (COD) is the amount of dissolved oxygen that must be present in water to oxidize chemical organic materials, like petroleum. COD is used to gauge the short-term impact wastewater effluents will have on the oxygen levels of receiving waters.
What COD means?
COD is defined as the amount of oxygen equivalents consumed in the chemical oxidation of organic matter by strong oxidant (e.g., potassium dichromate).
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).
How can COD be removed from water?
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 the acceptable range of COD in drinking water?
Ltd. According to standards of Central Pollution Control Board, permissible value of BOD is 30 mg/l and COD is 250 mg/l.
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.
How much COD water should I drink?
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.Oct 8, 2018
How does COD affect water quality?
The chemical oxygen demand (COD) is a measure of water and wastewater quality. 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 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. The chemical oxygen demand can be measured using different methods, direct or indirect.Aug 11, 2017
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 COD in wastewater?
Background: Chemical oxygen demand (COD) is often used to measure organic matter in wastewater, treated effluent, and receiving waters. Although COD measures more than organic constituents, the organic fraction usually predominates and is the constituent of interest.
What are the sources of COD in stormwater?
Sources of COD in stormwater are varied. However, soluble organic compounds are most likely to contribute to escalated COD concentrations. Residual food waste from bottles and cans, antifreeze, emulsified oils are all high in COD and are common sources of COD for industrial stormwater.
How to reduce COD in wastewater?
There are various proven methods for COD reduction in wastewater management. Two of the most common techniques for COD wastewater removal are: 1 Wastewater separation (coagulation and flocculation) 2 COD removal by microbial action.
What is the best way to remove COD from sewage?
Another efficient technique for COD removal is to introduce bacteria or microorganisms that break down organic compounds present in the wastewater. Microbes in sewage treatment can be aerobic or anaerobic.
Why is chemical oxygen demand important in wastewater treatment?
A key benefit of knowing the chemical oxygen demand in wastewater treatment is that it helps industrial and municipal clients determine the best method for treatment and the most effective structure for their wastewater treatment facility.
How long does it take to get a COD test?
The common technique uses COD vials for measurement and results are typically achieved within 2 – 3 hours.
What does high oxygen demand mean in water?
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 is the chemical oxygen demand?
What Is Chemical Oxygen Demand? Chemical Oxygen Demand (COD) is the amount of oxygen required to oxidize all soluble and insoluble organic compounds present in a volume of water. COD value is usually expressed in milligrams per liter of water (mg/L).
What is COD in water?
The chemical oxygen demand (COD) is a measure of water and wastewater quality . 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. The COD is the amount of oxygen consumed ...
What is the purpose of the COD test?
Therefore, the COD test can be used to measure the strength of wastes that are too toxic for the BOD test. Some organic molecules (e.g., benzene, pyridine) are relatively resistant to dichromate oxidation and may give a falsely low COD.
What is COD in water?
Chemical Oxygen Demand or COD is a measurement of the oxygen required to oxidize soluble and particulate organic matter in water. COD can be measured in real-time with our COD sensors to improve wastewater process control and plant efficiency.
Why is chemical oxygen demand important?
Chemical Oxygen Demand is an important water quality parameter because, similar to BOD, it provides an index to assess the effect discharged wastewater will have on the receiving environment. 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. The COD test is often used as an alternate to BOD due to shorter length of testing time.
How much COD is removed from wastewater?
How to reduce COD in wastewater. Primary and secondary treatments remove around 75-85% COD, but the hard-to-treat COD remains. Typically, legislation for COD discharge is from below 120 mg/L in the EU to below 50 mg/L in China and therefore in order to meet regulatory standards, additional treatment is often required.
What is the purpose of a COD test?
A COD test can be used to decipher the level of organics in water. Regulators enforce limits on the maximum amount of COD allowed in wastewater before it enters the environment and the local utility provider stipulates levels for effluent going ...
Is COD biodegradable?
COD can be split into two types – non-biodegradable and biodegradable. The Nyex™ processes specialise in the non- biodegradable category, as the biodegradable type tend to be broken down using a simple biological treatment process.
What is COD in water?
Chemical Oxygen Demand (COD) is a parameter of water quality used to determine the concentration of organic matter in a water supply.1 COD represents the amount of oxygen needed to allow a strong oxidant to oxidise all the organic matter in the sample. However, the strong oxidants used in COD tests do not discriminate between inorganic and organic compounds; some inorganics will be oxidised while some organics will remain intact.2 Despite its inability to measure the absolute organic carbon concentration perfectly, COD is often sufficient for wastewater treatment applications. These tests also only take a matter of hours rather than days ( Biological Oxygen Demand, or BOD, levels take around five days to measure) and generally provide enough information about water quality to be useful in wastewater treatment. In addition, COD can be used in toxic wastes that would otherwise kill the bacteria used in BOD testing.2
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.
Why is it important to monitor COD?
It is important to monitor COD because it reflects the level of pollution and contamination present in a water sample. In wastewater treatment, organic compounds can react with chlorine-containing disinfectants in the final steps of treatment to form THM’s. This is a major problem due to the carcinogenic nature of THM’s.
How long does it take to measure BOD?
These tests also only take a matter of hours rather than days ( Biological Oxygen Demand, or BOD, levels take around five days to measure) and generally provide enough information about water quality to be useful in wastewater treatment.
How to reduce COD in water?
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.
Why is COD important?
COD is an extremely important element of water quality. It helps to assess the effect that wastewater will have on the environment that it’s being released into. 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.
What is BOD5 in wastewater?
Typically, municipal wastewater treatment plants will use BOD5 as a measure of the organic concentration into, and through, the wastewater plant. Industrial wastewater systems will more often use COD to measure the organic concentration moving through the treatment plant. In my experience, I see TOC being used much less often (rarely) ...
How long does it take to test for organics in wastewater?
The often highly variable chemical composition and strength of industrial wastewater requires a much more rapid method for measuring the organic concentration, hence the use of the two hour COD test or, in some plants, the 30 minute TOC analysis.
What is the purpose of a wastewater test?
The test measures only the approximate amount of oxygen that will be required (absorbed or consumed) by a wastewater when it is exposed to air or oxygen for an extended period of time. Toxic substances in the wastewater inhibit or even prevent bacterial growth and, therefore, oxidation of the organic matter.
What is the BOD5 test?
The BOD5 test measures the oxygen consumed by microorganisms as they oxidize (consume or eat) the soluble organic matter in the wastewater. But the BOD5 test is a somewhat unreliable means of determining the amount of organic matter present in water. The test measures only the approximate amount of oxygen that will be required ...
