Full Answer
Why is cod testing important for wastewater treatment?
Performing COD testing the right way is important in determining wastewater treatment effectiveness and can help diagnose any problems in treatment. In this blog, we’ll cover what chemical oxygen demand is, how to test it, and how to get the best equipment for your tests.
How long does it take to determine COD in wastewater?
While COD is a common parameter for wastewater utilities to monitor within the plant, the 3-hour time requirement for the standard dichromate COD test makes it unsuitable for use as an influent and effluent monitor. peCOD is a new method of COD determination that solves this challenge, providing a COD result in less than 12 minutes.
How to reduce Cod in wastewater?
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: Wastewater separation (coagulation and flocculation)
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 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 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.
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 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.
How do you reduce high 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.
How do you test for COD?
The most common test method is the colorimetric analysis after oxidizing the COD with acid and using indicator compounds, such as hexavalent dichromate. In some instances, however, there are compounds that will interfere with the colorimetric analysis, and titration is required to determine COD levels.
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.
What is COD level?
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.
Why is it important to determine COD in wastewater treatment?
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.
What is COD analysis?
Chemical Oxygen Demand (COD) analysis is a measurement of the oxygen-depletion capacity of a water sample contaminated with organic waste matter. Specifically, it measures the equivalent amount of oxygen required to chemically oxidize organic compounds in water.
What is COD and BOD test?
COD stands for 'Chemical Oxygen Demand' where BOD stands for Biochemical Oxygen Demand. It is a test of the amount of oxygen required to oxidise organic matter in a sewage sample by chemical oxidation with a powerful oxidising agent such Potassium Dichromate.
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 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 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 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 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.
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.
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.
How to compare plant B and plant A?
Simply looking at the difference in concentration between the two plants would lead us to believe that Plant B contributes a much higher amount of organics (four times as much) into the sewer. However, we need to take into account that Plant A is a large industrial manufacturer that discharges 1,000,000 gallons of wastewater per day (1.0 MGD), while Plants B is a much smaller facility only discharging 50,000 gallons each day (0.05 MGD). Plugging these values into the loadings formula gives the following results:
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.
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 long does it take to get a COD test?
COD is expressed in mg/L, which indicates the mass of oxygen consumed per liter of solution. The COD test only requires 2-3 hours, while the Biochemical (or Biological) Oxygen Demand (BOD) test requires 5 days. It measures all organic contaminants, including those that are not biodegradable.
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.
How to measure COD?
The COD is often measured using a strong oxidant (e.g. potassium dichromate, potassium iodate, potassium permanganate) under acidic conditions. A known excess amount of the oxidant is added to the sample. Once oxidation is complete, the concentration of organics in the sample is calculated by measuring the amount of oxidant remaining in the solution. This is usually done by titration, using an indicator solution. COD is expressed in mg/L, which indicates the mass of oxygen consumed per liter of solution.
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 relationship between BOD and COD?
It measures all organic contaminants, including those that are not biodegradable. There is a relationship between BOD and COD for each specific sample , but it must be established empirically. COD test results can then be used to estimate the BOD of a given sample.
How do wastewater treatment plants work?
Wastewater treatment plants are highly dependent on biological processes to break down the wide variety of organics stemming from both sanitary sewage and industrial process effluents. Upon initial plant design, all aspects of the expected influent waste are taken into account, and ultimately determine the appropriate combination and configuration of treatment processes. The expected BOD, COD, and TOC are crucial in this determination, as they are directly related to the microbes’ ability to thrive in their appropriate treatment process. If the microbes are not supplied with enough organics (or ‘food’), a die-off will occur impacting overall treatment performance. If the microbes are supplied with too much organic matter, they will propagate beyond the intended design parameters and cause numerous plant challenges such as clogging, stagnation, odor events, and decreased effluent quality.
What is the difference between COD and COD?
Samples containing higher concentrations of organic matter provide more ‘food’ for microbes, resulting in greater microbiological activity, leading to greater oxygen depletion. COD is a similar measure of organic matter and oxygen demand; however,the method of oxygen depletion is through chemical oxidation reactions as opposed to biological ...
What is TOC in wastewater?
TOC is a common parameter that utilities use to monitor for changes in organic load. However, studies have shown that this test is not sufficient for determining the full impact of complex organics on treatment. Organics with similar amount of carbon may have vastly differing molecular structures; therefore COD provides insight into the oxygen demand, and reactivity, of the wastewater load. While COD is a common parameter for wastewater utilities to monitor within the plant, the 3-hour time requirement for the standard dichromate COD test makes it unsuitable for use as an influent and effluent monitor. peCOD is a new method of COD determination that solves this challenge, providing a COD result in less than 12 minutes. This allows the utilities to be proactive and fine-tune their treatment processes based on the actual organic load at any given time. In addition, the oxidation potential of the peCOD chemistry is double that of the dichromate method, which indicates that it is more suitable for detecting and quantifying oxygen demand of complex organic molecules.
How do BOD5 and COD complement each other?
Oxygen demand, BOD5 and COD can give an indication as to the oxidizability or reactivity of the organics. TOC and DOC quantify the amount of carbon in the organics. By comparing these two aspects, insight can be gained on the overall ‘oxidation state’ of the organics.
What is Pecod monitoring?
Treatment plants, both municipal and industrial, rely on their monitoring tools to provide optimal treatment and benefit greatly from having as many of these tools available as possible. PeCOD is the tool which can deliver the COD results quickly, effectively, and with the greatest ability to detect changes. It is simple to operate in any environment, 24/7, and a low cost for investment.
What is a pecd?
Photoelectrochemical Oxygen Demand (peCOD) is a novel technique for determining COD that eliminates the hazardous chemicals and delivers a result within 5 minutes for water samples. A 2014 study by Dalhouise University highlights peCOD as an excellent opportunity for drinking water utilities to address NOM removal with a green, easy-to-use method that can be directly implemented in the plant either in portable, benchtop, or online configurations. peCOD has already proved invaluable to numerous utilities through its ability to monitor for DBP formation, optimize coagulation processes, and identify deficiency in a treatment process quicker than other common measures. An ASTM International method for peCOD, D8084, was released in 2017 and confirmed the applicability of peCOD to drinking water treatment, showing an MDL for the test of 0.7 mg/L.
What are the challenges of wastewater treatment?
After a treatment plant becomes operational, one of the greatest challenges faced is keeping up with constantly increasing wastewater loads in growing areas . Plant design typically includes a factor accounting for expected growth in the service area, however it can be quite difficult to estimate industrial expansion and subsequent increases in industrial wastewater. In the case of process effluents, the challenge is not only in determining the increase in volume, but also the increase in organic load and oxygen demand. As industrial activity in a service area develops, it is in the hands of the treatment plant and municipality to determine the changes in wastewater volume/quality and make adjustments to the treatment processes to account for it.
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.
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 ...
How does COD affect the environment?
Reducing COD levels positively affects the environment by reducing the amount of contamination which enters our water supplies. It also helps organisations avoid fines from utilities or regulatory bodies.
Is COD a biodegradable substance?
COD can be split into two types – non-biodegradable and biodegradable.
Can Nyex treated wastewater be reused?
Because of the lack of dosing chemicals in the process, Nyex™ treated wastewater can also be safely reclaimed and reused for other purposes within the business, saving money and addressing high water demands in times of shrinking supplies.
Why is COD testing important?
Performing COD testing the right way is important in determining wastewater treatment effectiveness and can help diagnose any problems in treatment. In this blog, we’ll cover what chemical oxygen demand is, how to test it, and how to get the best equipment for your tests.
How does COD measure organic matter?
As mentioned before, COD measures organic matter by using a chemical oxidant. It’s critical that a strong enough oxidant is used to react with virtually all organic material in the sample. Historically, potassium permanganate filled this role, but it was found to be inconsistent in its ability to oxidize all the organic matter in a wide variety of waste samples.
What is Chemical Oxygen Demand?
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!
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.
What is the purpose of COD in wastewater?
Chemical Oxygen Demand (COD) is another indirect methodology that is used to establish the levels of organic contamination in wastewater. However, chemical oxidation is used during this test which breaks down the contamination in the water and then measures the oxygen that is exhausted in the process.
How long does it take to determine the oxygen demand in a biochemical effluent?
The SOR declares, “The demand due to the quantity of carbonaceous biochemical oxygen demanding matter in the effluent must be determined in accordance with a five-day biochemical oxygen demand test with nitrification inhibition.” [34]
How does a TOC analyzer work?
All TOC analyzers function by oxidizing organic matter to CO 2, which can then be measured using conductivity methods or non-dispersive infrared detection (NDIR). [45] Different methodologies of sample oxidation include combustion, UV persulfate and supercritical water oxidation (SCWO). [45]
What is the oxygen demand in a BOD test?
The oxygen demand from the BOD test is generally a combination of carbonaceous biochemical oxygen demand (CBOD) and nitrogenous biochemical oxygen demand (NBOD), which takes place due to the decomposition of ammonia or other nitrogen-based compounds.
What are the most commonly used parameters for organic contamination?
Thus, the concept of ‘sum parameters’ is applied to group together numerous compounds with similar qualities into a single category: BOD, COD and TOC are the most commonly used for organic contamination.
Which countries use BOD to test TOC correlations?
However, some countries, including the US and India, know the value in other testing parameters and are permitting the application of BOD to TOC correlations.
Why are wastewater discharge regulations becoming more stringent?
Wastewater discharge regulations are becoming more stringent as the public continues to push for human health and environmental protection. This has led to the development and use of varying monitoring methods. The need for powerful identification methods for contaminants is crucial to preventing ha. Wastewater discharge regulations are becoming ...