Hence, do analysis is a key test both in natural waters and water pollution control practice. The bod electrode method is suitable for determining the bod of water and wastewater. The quantity of organic matter or the demand of oxygen is calculated by determining how much oxidizing chemical was consumed during the test. Higher cod levels mean a greater amount of oxidizable organic material in the sample, which will reduce dissolved oxygen do levels. Test method a macro cod by reflux digestion and titration. Cod often is used as a measurement of pollutants in wastewater and natural waters. A chemical oxygen demand test is used to measure the amount of organic compounds in a water sample. The bod determination is an empirical test in which standardised laboratory procedures are used to determine the relative oxygen requirements of wastewaters, effluents and polluted. How does one measure the cod of wastewater in the presence. Chemical oxygen demand an overview sciencedirect topics. Chemical oxygen demand cod in wastewater i real tech water.
There are several methods for determination of chemical oxygen demand but the wet chemical method dichromate method is the most common method. The method determines chemical oxygen demand see definitions, section 3. The test for biochemical oxygen demand bod is a bioassay procedure that measures the oxygen consumed by bacteria. In environmental chemistry, the chemical oxygen demand cod test is commonly used to indirectly measure the amount of organic compounds in water.
Principle of chemical oxygen demand in dichromate method the organic matter in water oxidize with the strong oxidizing agent potassium dichromate under acidic conditions. Chemical oxygen demand cod test is a measure of the relative oxygen depletion effect of a waste contaminant. Cod test the chemical oxygen demand cod test uses a strong chemical oxidant in an acid solution and heat to oxidize organic carbon to co 2 and h 2 o. Prepare a new blank when the absorbance has changed by approximately 0. Chemical oxygen demand cod is the total amount of oxidisable organics biodegradable and nonbiodegradable and both dissolved and particulate, measured by the amount of oxygen in the form of oxidising agent required for the oxidation of organic matters by heating the sample in strong sulphuric acid containing potassium dichromate 14. In this case, the demand for oxygen will be high due to all the bacteria so the bod level will be. Biological oxygen demand 28 ps2829a the bod 5 test is used to measure the potential of wastewater and other waters to deplete the oxygen level of receiving waters. 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. 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. Introduction the organic matter present in sewage can be measured in number of ways. Performing cod testing the right way is important in determining wastewater treatment effectiveness and can help diagnose any problems in treatment.
It can be expressed in milligrams per liter mgl also referred to part. Associated identifiers there is no information about former or incorrectly used identifiers. Pdf the usefulness of the standard chemical oxygen demand cod test for water characterization is offset to some extent by its requirement for highly. It has been widely adopted as a measure of pollution effect. The test is also used to examine influents and effluents from wastewater processing facilities to compute the efficiency of operation of the treatment units. The quantity of oxidant consumed is expressed in terms of its oxygen equivalence. At the boiling point, the solubility of oxygen is zero. Throughout the booklet, the term chemical oxygen demand cod is used to express the amount of oxygen consumed during oxidation of a sample with hot acid dichromate solution under defined conditions. The higher value of chemical oxygen demand indicates the higher organic pollution in the water sample.
Determination of chemical oxygen demand of water hard. Methods chemical oxygen demand, method 5220 d, closed reflux, colorimetric method. It measures the capacity of water to consume oxygen during the. Method of sampling and test physical and chemical for water and wastewater, part 44. The term also refers to a chemical procedure for determining this amount. It can be expressed in milligrams per liter mgl also referred to part per million ppm which indicates the mass of oxygen consumed per liter solution. It measures the capacity of water to consume oxygen during the decomposition of organic matter and the oxidation of inorganic chemicals such as ammonia and nitrate. A chemical oxygen demand cod test is used to measure the amount of organic compounds in a water sample. The usefulness of the standard chemical oxygen demand cod test for water characterization is offset to some extent by its requirement for highly toxic or expensive cr, ag, and hg species.
Biochemical oxygen demand bod is the amount of dissolved oxygen needed i. Test method b micro cod by sealed digestion and spectrometry. Method of sampling and test physical and chemical for water and wastewater, part 58. Chemical oxygen demand testing is typically performed using a strong oxidizing chemical. Samples with higher cod concentrations may be processed by appropriate dilution of the sample. Only chemically digest able matter can be determined by the cod test. Chemical oxygen demand cod first revision name of standards organization. Also, it can be categorized in several ways such as biological. Oxygen demand is an important parameter for deter mining the amount of organic pollution in water. To determine the amount of pollution in a water stream to try to control and limit the amount of chemicals that can pollute the lakes and rivers if left in a final effluent or. Reagecons offering includes a comprehensive range of cod standards. Chemical oxygen demand cod is a critical waste treatment measurement in everything from municipal systems to food manufacturing waste streams.
Determination of chemical oxygen demand of wastewater. By definition, chemical oxygen demand is a measure of the oxygen equivalent of the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant. Chemical oxygen demand is an aggregate property of water, and no cas. Put the blank vial that is used in the test procedure into the instrument and record the absorbance value. During the fiveday period of a bod test, the bacteria oxidize mainly the soluble organic matter present in the water. In environmental chemistry, the chemical oxygen demand cod is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. If there is a large quantity of organic waste in the water supply, there will also be a lot of bacteria present working to decompose this waste. Organic matter is oxidized into carbon dioxide and water in an acidic condition. The chemical oxygen demand cod test is commonly used to indirectly measure the amount of organic compounds in water. The cod test only takes a few hours to complete, giving it a major advantage over the 5day bod test. While the bod test is performed by using a population of bacteria and other microorganisms to attempt to duplicate what would happen in a natural stream over a period of five days, the cod test uses a strong chemical oxidizing agent potassium dichromate or potassium permanganate to chemically oxidize the organic material in the.
This oxygen transaction is the source of the test s name, chemical oxygen demand. Chemical oxygen demand cod is used to determine the quantity of pollution in water after wastewater treatment. How to reduce chemical oxygen demand cod in wastewater. Understanding chemical oxygen demand test new delhi, may 1999 csmrs building, 4th floor, olof palme marg, hauz khas, new delhi 11 00 16 india tel. D biochemical oxygen demand bod is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. 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. Biochemical oxygen demand bod first revision name of standards organization. In essence a cod test determines the amount of carbon based materials by measuring the amount of oxygen the sample will react with. Rapid determination of the chemical oxygen demand of. Cod determination takes less time than the biological oxygen. Difference between bod and cod compare the difference. Most applications of cod determine the amount of organic pollutants found in surface water e. Closely related to biochemical oxygen demand bod, chemical oxygen demand cod is another important water quality parameter that industrial and municipal authorities should be familiar with to determine the best wastewater treatment methods for. Oxygen demand is a measure of the amount of oxidizable substances in a water sample that can lower do concentrations nemerow, 1974.
A measure of the oxygen equivalent of the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant, usually reported as cod as mg o2l. Pdf study of chemical oxygen demand cod in relation to. Other related analytical values are biochemical oxygen demand bod, total organic carbon toc, and total oxygen demand tod. The test is not subject to inhibition by toxic components that would be affected by tests that are dependent upon biochemical oxidation. Chemical oxygen demand cod is a second method of estimating how much oxygen would be depleted from a body of receiving water as a result of bacterial action. The result is usually expressed as milligrams of oxygen consumed. How to reduce chemical oxygen demand cod in wastewater written by aos treatment solutions on november 1, 2018. Pdf downscaling the chemical oxygen demand test researchgate. Biological oxygen demand bod is a measure of the oxygen used by microorganisms to decompose this waste. The cod test has been used for a very long time as one of the components of the method that water utilities use to charge dischargers for their part of the effluent.
Cod chemical oxygen demand cod is the most popular alternative test to bod for establishing the concentration of organic matter in wastewater samples. Chemical oxygen demand cod vs biological oxygen demand. While the bod test is performed by using a population of bacteria and other microorganisms to attempt to duplicate what would happen in a natural stream over a period of five days, the cod test uses a strong chemical oxidizing agent potassium. Chemical oxygen demand titrimetric, high level for saline waters analyte. Chemical oxygen demand cod vs biological oxygen demand bod. The chemical oxygen demand cod test is an empirical test that is a measure of the potential oxygen consumption of waste waters. The determination of chemical oxygen demand in waters and. Chemical oxygen demand test uses a strong chemical oxidant in an acid solution and heat to oxidize organic carbon to co2 and h2o. The key difference between bod and cod is that the bod is the oxygen demand of microorganisms to oxidize organic matter in the water under aerobic conditions while the cod is the oxygen demand to oxidize all the pollutants in the water chemically quality of a given water sample depends on some variable factors. It is based on the use of thermo orion test kits cat.
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