Because the BOD
Biochemical oxygen demand
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.
Full Answer
Is COD test enough for wastewater treatment?
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.
What is cod testing?
Guide to Chemical Oxygen Demand (COD) Testing May 2017 Chemical oxygen demand (COD) is a critical waste treatment measurement in everything from municipal systems to food manufacturing waste streams. Performing COD testing the right way is important in determining wastewater treatment effectiveness and can help diagnose any problems in treatment.
What are the most common techniques for cod wastewater removal?
Two of the most common techniques for COD wastewater removal are: 1 Wastewater separation (coagulation and flocculation) 2 COD removal by microbial action. More ...
What is a good Cod and BOD ratio for wastewater?
For example, food processing wastewater will generally have a COD:BOD ratio of ~2:1, while textile wastewater that can contain dyes will often have a much higher COD:BOD ratio of ~5:1. To establish the COD:BOD ratio for your wastewater, simply have both COD and BOD run on several wastewater samples.
How does wastewater reduce COD?
What is a COD test?
What is the oxidant in COD?
How long does it take to do a BOD test?
Why is BOD important in wastewater?
How does COD compare to BOD?
Why is colorimetry used for COD?
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About this website
How do you test COD in wastewater?
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 the average COD in sewage?
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 does COD measure in wastewater treatment?
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.
Why do we test COD in water?
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.
What is the limit of COD?
According to standards of Central Pollution Control Board, permissible value of BOD is 30 mg/l and COD is 250 mg/l.
How do you maintain COD and BOD?
These are the best practices for reducing BOD and TSS that facility managers should know:Focus on removing TSS from wastewater first. ... Get a properly sized EQ tank. ... Control the pH of the waste stream. ... Install a modern plate pack DAF made of stainless steel or plastic. ... Use a regenerative turbine air dissolution pump.More items...•
How COD is determined?
A typical determination of the COD is to introduce an excess of the dichromate ion. After the reaction is completed the excess amount of dichromate is measured by titration with ferrous ammonium sulfate. COD is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen consumed per liter of solution.
Why should you measure COD of 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.
How is COD calculated?
There is a formula for calculating COD. Consider the formula for COD calculation: (a - b) X C X 8,000 / the volume of the sample in mL. Let "a" represent the titrant used for your sample expressed in mL. Let "b" represent the titrant used for your blank sample in mL.
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.
What is COD analysis?
COD analysis is used as an indirect measure of pollutants (organics) in a water sample. It is an important parameter in water quality analysis, helping to reduce risk to humans and the environment. COD is an excellent way of monitoring the efficiency of water treatment plants.
Why do we measure BOD and COD?
Answer: Both COD and BOD test methods aim to give an indication of the amount of pollution in a water sample. COD is the amount of oxygen required to chemically breakdown the pollutants whereas BOD is the amount of oxygen required to do this biologically through micro-organisms.
Calculation of Chemical Oxygen Demand (C.O.D)
Calculation of Chemical Oxygen Demand (C.O.D). Apparatus: . Round bottom flask, water condenser, Burette, Pipette,Heating mantle.
Determination of chemical oxygen demand of water
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Determination of Chemical Oxygen Demand of Wastewater
COD determination takes less time than the Biological Oxygen Demand test. COD is recommended where the polluted water has toxicity and organic matter can’t be determined by biological oxygen demand and useful in water effluent treatment plants.
How does wastewater reduce COD?
Wastewater facilities reduce COD and BOD by using these same microbes under controlled conditions. These facilities aerate chambers injected with specialized bacteria that can break down the organic matter in an environment that does not harm natural waters. A reduction in BOD is used in these facilities as a benchmark for treatment effectiveness.
What is a COD test?
Chemical oxygen demand (COD) is an indirect measurement of the amount of organic matter in a sample. With this test, you can measure virtually all organic compounds that can be digested by a digestion reagent.
What is the oxidant 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.
How long does it take to do a BOD test?
Since a BOD test takes five days to complete, COD is used to monitor the treatment process in day-to-day operations. The COD test takes only a few hours to complete. If BOD were always used, treated wastewater would need to be held, and a problem with the treatment process wouldn’t be detected until five days later!
Why is BOD important in wastewater?
As gauges of organic matter in a sample, BOD and COD are critical in wastewater for determining the amount of waste in the water. Waste that's high in organic matter requires treatment to reduce the amount of organic waste before discharging into receiving waters.
How does COD compare to BOD?
COD contrasts with biochemical oxygen demand (BOD), which relies on the use of microorganisms to break down the organic material in the sample by aerobic respiration over the course of a set incuba tion period (typically five days). BOD and COD correlate with one another in virtually all samples, but BOD is always lower than COD as ...
Why is colorimetry used for COD?
Colorimetry also makes measurement easy since all the analyst needs to do is digest the samples and let the instrument do the work. For these reasons, colorimetry is the most common method to measure COD.
How long does a COD test take?
The COD test only takes a few hours to complete, giving it a major advantage over the 5-day BOD test. Wastewater treatment system personnel can use COD as an almost real-time operational adjustment parameter.
Why are a COD reactor and a colorimeter turned on?
A COD reactor/heating (150°C) block and a colorimeter are turned on so that both instruments are allowed to stabilize.
What is organics in wastewater?
Organics ? A determination of the concentration of carbon-based (i.e., organic) compounds aimed at establishing the relative “strength” of wastewater (e.g., Bio chemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), and Oil and Grease (O&G)).
How to determine final BOD?
After dilution, the resulting difference between the initial and final DO reading simply has to be multiplied by the dilution factor to determine the final BOD result. For example: 1.0 mL of a full strength wastewater sample added to 9.0 mL of DI water results in a 0.1 dilution of the wastewater. The DO concentration (mg/L) reduction must then be multiplied by 10 to determine the final BOD concentration.
What is the effect of increased water use and process wastewater generation?
This increased water use and process wastewater generation requires more efficient removal of by-products and pollutants that allows for effluent discharge within established environmental regulatory limits.
What is the purpose of analytical tests?
Analytical tests aimed at establishing the concentration (typically in mg/L or ppm) of organic (i.e., carbon-containing) matter have traditionally been used to determine the relative "streng th" of a wastewater sample. Today there are four common laboratory tests used to determine the gross amount of organic matter (i.e., concentrations > 1.0 mg/L) in wastewater:
When was the Clean Water Act created?
Since the implementation of the Clean Water Act and subsequent creation of the United States Environmental Protection Agency (USEPA) in the early 1970s, industrial, institutional and commercial entities have been required to continually improve the quality of their process wastewater effluent discharges.
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.
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 is aerobic COD removal?
Aerobic COD removal is ideal for wastewater with COD < 3000 mg/L.
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.
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 floculation in water treatment?
Flocculation uses a chemical polymer (flocculating agent) to precipitate the clumped particles out of the water by forming larger particles , or flocs. The flocs then undergo the sedimentation process in wastewater treatment by being deposited into a sedimentation tank for further treatment prior to disposal.
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.
When is it necessary to measure BOD or COD in the influent water?
For compliance, it’s necessary to measure BOD or COD in the influent water as it enters the plant, before mechanical screening processes and at the end of the treatment at the discharge point.
What is COD in 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 is the difference between COD and BOD?
COD describes the amount of oxygen required to chemically break down pollutants, while BOD indicates the amount of oxygen required to breakdown organic pollutants biologically with microorganisms.
What does TOC measure?
TOC measures organic carbon but different organic carbons will generate different oxygen demand. Measuring TOC alone will not necessarily indicate how much oxygen will be consumed by the organics in the environment. For example, oxalic acid and ethanol produce identical TOC results. However, due to different oxidation states, ...
What happens when wastewater is discharged into the environment?
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 most missed step in COD analysis?
The most missed step by customers in the COD analysis is the reagent vital inversion step. After the digestion and before the vial is fully cooled, the vial must be inverted several times. This returns any condensation to the reacted sample. Do not invert the vial again immediately before inserting the vial into the instrument. It is necessary to allow time for undissolved particles to settle to the bottom and out of the light path of the digital instrument.
How to determine oxygen demand?
When selecting a method for analyzing oxygen demand, it’s important to consider the following: 1 Specific testing application 2 Oxidant that will be used 3 Completion time 4 Accuracy and precision of the measurement
Why Hach?
I know I must sometimes seem to be a walking/talking/never ending advertisement for Hach. If you think that I don't blame you. The fact is, Hach is the vendor I use as often as possible for my lab work. I like their equipment and their solutions.
Range of COD Reagents Available
There are five COD ranges that I use from Hach, tabulated below. The actual method used to test for COD, using Hach's TNT chemistry, is identical other than the sample volume used. So pay attention to that.
Hach COD TNT Interferences
Chloride is the primary interference in this test method and results in a positive interference. Each COD vial contains mercuric sulfate that will eliminate chloride interference to a maximum of 10,000 mg/L Cl–.
One Final Note on Interferences
I do a lot of work with hydrogen peroxide. A hydrogen peroxide residual in a sample to be tested for COD will "falsely" increase the COD. Therefore, the hydrogen peroxide residual must be removed before running the COD test. Opposite to the impact hydrogen peroxide has on COD, is the impact it has on the biochemical oxygen demand (5-day BOD) test.
What to do if COD is elevated in wastewater?
Action: If COD is elevated in wastewater, treatment methods such as aerobic and anaerobic biological treatment, filtration, coagulation and flocculation should be used to remove organic and inorganic material.
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 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.
How long does it take to complete the Bod5 test?
Due to the length of time required to complete the BOD5 test (five days), BOD results provide historical data only and do not facilitate rapid water quality assessment for optimal process control. The often highly variable chemical composition ...
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 do a TOC?
The TOC test can take several minutes to several hours to complete, and information obtained from a TOC analysis is less useful than information obtained from the BOD5 or the COD analysis. The TOC test does not differentiate between compounds with the same number of carbon atoms in different stages of oxidation and will thus produce different oxygen demand results. Because BOD5 and COD tests directly measure the amount of oxygen required to stabilize a waste sample, results reflect the original oxidation state of the chemical pollutants. The relationship between BOD5, COD, and TOC is shown below.
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 ...
Is the COD/BOD ratio variable?
COD/BOD ratios can be highly variable. The more variable the ratio values, as in, the higher the COD/BOD ratio, the greater the percentage of slowly biodegradable and non-biodegradable material in the sample. And that means the BOD5 test will give a lower value than is truly representative of the oxygen demand in the sample.
What is a cod test?
COD measures how much DO is consumed by the oxidation of organic matter and inorganic compounds such as ammonia or nitrite under controlled conditions. COD testing typically involves digestion of the water sample in a sealed vial with potassium dichromate and sulfuric acid at 150C for 2 hours.
Why is COD analysis more commonly performed?
Of the two tests, COD analysis is more commonly performed as it takes less time and is more replicable. Furthermore, treatment operators can quickly react to changes in oxygen demand and modify treatment processes appropriately.
Why do plant engineers use a COD/BOD ratio?
The COD value may be used as justification for BOD removal from a plant permit.
How does wastewater reduce COD?
Wastewater facilities reduce COD and BOD by using these same microbes under controlled conditions. These facilities aerate chambers injected with specialized bacteria that can break down the organic matter in an environment that does not harm natural waters. A reduction in BOD is used in these facilities as a benchmark for treatment effectiveness.
What is a COD test?
Chemical oxygen demand (COD) is an indirect measurement of the amount of organic matter in a sample. With this test, you can measure virtually all organic compounds that can be digested by a digestion reagent.
What is the oxidant 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.
How long does it take to do a BOD test?
Since a BOD test takes five days to complete, COD is used to monitor the treatment process in day-to-day operations. The COD test takes only a few hours to complete. If BOD were always used, treated wastewater would need to be held, and a problem with the treatment process wouldn’t be detected until five days later!
Why is BOD important in wastewater?
As gauges of organic matter in a sample, BOD and COD are critical in wastewater for determining the amount of waste in the water. Waste that's high in organic matter requires treatment to reduce the amount of organic waste before discharging into receiving waters.
How does COD compare to BOD?
COD contrasts with biochemical oxygen demand (BOD), which relies on the use of microorganisms to break down the organic material in the sample by aerobic respiration over the course of a set incuba tion period (typically five days). BOD and COD correlate with one another in virtually all samples, but BOD is always lower than COD as ...
Why is colorimetry used for COD?
Colorimetry also makes measurement easy since all the analyst needs to do is digest the samples and let the instrument do the work. For these reasons, colorimetry is the most common method to measure COD.