The chemistry of chemical oxygen demand chemical oxygen. Determinations can be made titrimetrically by several. What is the relationship between the cod and bod values in. The cod test only takes a few hours to complete, giving it a major advantage over the 5day bod test. Chemical oxygen demand cod is a quick, inexpensive means to determine organics in water. Samples are oxidised in a defined manner by refluxing with sulphuric acid and potassium dichromate. If you continue browsing the site, you agree to the use of cookies on this website. The cod test is often used to monitor water treatment plant efficiency. Most applications of cod determine the amount of organic pollutants found in surface water e. 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. These parameters reflect effect and material characteristics of one or more substances. H7 is the really bad boy solids content total suspended solids total dissolved solids.
Bod refers to the biochemical oxygen demand and cod is the chemical oxygen demand. Chemical oxygen demand cod is the amount of oxygen required to break down organic material, such as fecal matter, in wastewater. Estimation of chemical oxygen demand in wastewater using. Sulfite demand if there is a large demand for sulfite, adding large amounts will add tds to the boiler. Chemical oxygen demand is the amount of oxygen needed to oxidize the organic matter present in water.
The test for biochemical oxygen demand bod is a bioassay procedure that measures the oxygen consumed by bacteria. 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. 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. What is the difference in bod, bod5, cbod and nbod, i am. A chemical oxygen demand test is used to measure the amount of organic compounds in a water sample. Chemical control oxygen scavengers sulfite reacts with oxygen to form harmless salt others.
Cod samples are prepared with a closedreflux digestion. Biochemical oxygen demand definition, the oxygen required by aerobic organisms, as those in sewage, for metabolism. It can be expressed in milligrams per liter mgl also referred to part. Biochemical oxygen demand bod and chemical oxygen demand pdf. Chemical oxygen demand was developed as an alternative to the more lengthy bod analysis. The interference from nitrogenous demand can be prevented by an inhibitory chemical. Rather than biologically decomposeoxidize organic waste, we chemically decomposeoxidize organic waste. The standard method for indirect measurement of the amount of pollution that cannot be oxidized biologically in a sample of water. Difference between bod and cod compare the difference. Cod measurements are commonly made on samples of waste watersor of natural waters contaminated by domestic or industrial wastes. Chemical oxygen demand cod is a labortory test to give a. Also, it can be categorized in several ways such as biological. Chemical oxygen demand cod is a critical waste treatment measurement in everything from municipal systems to food manufacturing waste streams.
Used to measure the organic strength of wastewaters same principle as bod but different execution. Reagecons offering includes a comprehensive range of cod standards. Chemical oxygen demand cod is defined as the amount of a specified oxidant that reacts with the sample under controlled conditions. 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.
The water samples were analyzed weekly for several parameters, including chemical oxygen demand cod, ammonianitrogen nh. Bod, cod, toc and tod sum parameters in environmental. There are multiple methods to test for the cod of a solution or. 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.
Chemical oxygen demand cod is the amount of oxygen necessary to oxidize all of the organic carbon completely to co2 and h2o. This is important to trenchless operations because the efficient use of cod in sewer systems minimizes the impact of these materials on wastewater treatment facilities. Biochemical oxygen demand is the amount of oxygen required for microbial metabolism of organic compounds in water. Oxygen demand is a measure of the amount of oxidizable substances in a water sample that can lower do concentrations nemerow, 1974. How to reduce chemical oxygen demand cod in wastewater written by aos treatment solutions on november 1, 2018. Like the five day biochemical oxygen demand bod5 it. Note the distinction between this and the other oxygen demand test bod. Biochemical oxygen demand definition of biochemical. Cod is the amount of oxygen consumed when all materials present in a sample are fully oxidized. The carbohydrates cellulose, starch, sugars, proteins, petroleum hydrocarbons and other materials that comprise organic matter get into water from natural sources and from. The quantity of oxidant consumed is expressed in terms of its oxygen equivalence. Biochemical oxygen demand bod represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic oxygen is present conditions at a specified temperature. A cod test can be used to easily quantify the amount of organics in water.
Thus, cod is defined as the number of oxygen equivalents required to oxidize organic materials in water. Biochemical oxygen demand bod is a chemical procedure for determining 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. 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. Cod samples are prepared with a closedreflux digestion followed by analysis. Because oxygen demand is not a pollutant, it poses no.
Chemical oxygen demand thermo orion method codl00 and codh00 revision 5, 03252005 accepted by u. Chemical oxygen demand cod is a measure of the capacity of water to consume oxygen during the decomposition of organic matter and the oxidation of inorganic chemicals such as ammonia and nitrite. The most popular sum parameter in waste water analysis are the bod biochemical oxygen demand, cod chemical oxygen demand, tod total oxygen demand and toc total organic carbon. Chemical oxygen demand cod the amount of oxygen that is required for the chemical oxidation of the organic and inorganic chemicals present in the wastewater by utilising oxidising agents like potassium permanganate, potassium dichromate etc. The chemical oxygen demand cod test is commonly used to indirectly measure the amount of organic compounds in liquid waste. Chemical oxygen demand test uses a strong chemical oxidant in an acid solution and heat to oxidize organic carbon to co2 and h2o. 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. 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 determination of chemical oxygen demand in waters and. Chemical oxygen demand testing is used to determine the amount of oxidation that will occur and the amount of organic matter in a water sample. 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 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. The determination of chemical oxygen demand in waters and effluents 2007 methods for the examination of waters and associated materials this booklet contains guidance on methods for the determination of chemical oxygen demand using potassium dichromate solution, and notes for the disposal and recovery of selected reagents.
Organic matter is oxidized into carbon dioxide and water in an acidic condition. 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. Chemical oxygen demand an overview sciencedirect topics. Measurements that include nitrogenous demand generally are not useful for assessing the oxygen demand associated with organic material. It is also not necessarily a specific method defined parameter. Cod or chemical oxygen demand definition the laboratory people. The two most common parameters used to recognize the composition of wastewater are the biochemical oxygen demand bod and the chemical oxygen demand cod. The main difference between bod and cod is that bod is the amount of oxygen which is consumed by bacteria while decomposing organic matter under aerobic conditions whereas cod is the amount of oxygen required for the chemical oxidation of total organic matter in. Older references may express the units as parts per million ppm. Biochemical oxygen demand bod and chemical oxygen demand pdf slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. The chemical oxygen demand test procedure is based on the chemical decomposition of organic and inorganic contaminants, dissolved or suspended in water.
Performing cod testing the right way is important in determining wastewater treatment effectiveness and can help diagnose any problems in treatment. It is expressed in milligramsgrams per liter, which indicates the mass of oxygen consumed per liter of solution. To determine and measure of oxygen requirement of the sample waste water through chemical oxygen demand cod process. Chemical oxygen demand is a measure of the oxygen required to oxidize all organic material present into water and carbon dioxide, and thus a measure of the amount of organic material within a substance 7. The quantity of organic matter or the demand of oxygen is calculated by determining how much oxidizing chemical was consumed during the test. Epa on march 31, 2005 for wastewater compliance monitoring. However, both analysis methods have restrictions such as being tigris of. A special chemical is added to kill the autotrophic bacteria so nitrification is inhibited so that only the oxidation of cod occurs. Finding excessive levels of one or more of these parameters can serve as an early warning of potential pollution problems. This demand occurs over some variable period of time depending on temperature, nutrient concentrations, and the enzymes available to indigenous microbial populations. 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.
Chemical oxygen demand cod is often used to measure organic matter in wastewater, treated effluent, and receiving waters. Oxygen demand biochemical oxygen demand chemical oxygen demand indicator organisms fecal coliform escherichia coli e coli 0157. 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 rajasekharan, 2015. The chemical oxygen demand cod is a measure of water and wastewater quality. The chemical oxygen demand cod test is commonly used to indirectly measure the amount of organic compounds in water. Biochemical oxygen demand bod is the amount of oxygen, expressed in mgl or parts per million ppm, that bacteria take from water when they oxidize organic matter.
The chemistry of chemical oxygen demand by john stone chemical oxygen demand cod is a quick, inexpensive means to determine organics in water. 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. Chemical oxygen demand cod is a measure of the capacity of water to consume oxygen during the decomposition of organic matter and the. Chemical oxygen demand testing is typically performed using a strong oxidizing chemical. Cod or chemical oxygen demand definition the laboratory. It measures the capacity of water to consume oxygen during the. In this regard, chemical oxygen demand cod is a parameter that could be useful for evaluation of waste biodegradability and also for evaluating the mass or the energetic balance of the process. Although cod measures more than organic constituents, the organic fraction usually predominates and is the constituent of interest.
Chemical oxygen demand cod does not differentiate between biologically available and inert organic matter, and it is a measure of the total quantity of oxygen required to oxidize all organic. Chemical oxygen demand does not differentiate between biologically available and inert organic matter, and it is a measure of the total quantity of oxygen required to oxidize all organic material into carbon dioxide and water. Chemical oxygen demand analysis of anaerobic digester. A chemical oxygen demand cod test is used to measure the amount of organic compounds in a water sample. Difference between bod and cod definition, test method.