Dissolved oxygen refers to the level of free, noncompound oxygen present in water or other liquids. Hach 8000 1979 chemical oxygen demand is considered a methoddefined parameter per the definition in the code of federal regulations, part 6. The standard technique for the closed reflux, colorimetric analysis of chemical oxygen demand cod utilizes several hazardous compounds, including mercury, silver, chromium, and sulfuric acid. Genuine hach instruments, chemistries, methods and expertise from one source give you incomparable results. These methods have been revised and other procedures developed and are included in this booklet. Method 5220 c, or a closed reflux colorimetric method. Because of its unique chemical properties, the dichromate ion cr2o7. Cod samples are prepared with a closedreflux digestion. Chemical oxygen demand cod is a quick, inexpensive means to. Rather than biologically decomposeoxidize organic waste, we chemically decomposeoxidize organic waste.
A cod test can be used to easily quantify the amount of organics in water. A small scale 2 ml closedtube digestion procedure with mercury. Because of its unique chemical properties, the dichromate ion cr2o7 2 is the speci. A colorimetric method for determining chemical oxygen. Thanks for a2a quora user the chemical oxygen demand cod test is commonly used to indirectly measure the amount of organic compounds in water. Moreover, the results obtained in the determination of chemical oxygen demand following a closed reflux spectrophotometric method are compared with those obtained when a definitive analytical method is applied, in order to show the absence of direct interference from the matrix. The determination of chemical oxygen demand in waters and effluents 1 introduction methods for the determination of chemical oxygen demand have been previously published1, 2. This paper reports the development of an innovative sample preparation method for the determination of the chemical oxygen demand cod in heterogeneous solid or semisolid samples, with high suspended solids and cod concentrations, using an optimized closed reflux colorimetric method. Chemical oxygen demand chemistry physical sciences.
Chloride reacts with silver ion to precipitate silver chloride, and thus inhibits the catalytic activity of silver. 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. Glassware should consist of a 500 ml erlenmeyer flask or a 300 ml round bottom flask made of heatresistant glass connected to a 12 inch allihn condenser by means of a ground glass joint. The method relies on the release of oxygen from dichromate on heating which is consumed. Most types of organic matter are oxidized by a boiling mixture of chromic and sulfuric acids. Cod samples are prepared with a closedreflux digestion followed by analysis. There are two methods available for cod determination namely open reflux and closed. May 30, 2018 the analysis of total organic carbon toc by the american public health association apha closed tube reflux colorimetric method requires potassium dichromate k2cr2o7, silver sulfate agso4, and mercury hgso4 sulfate in addition to large volumes of both reagents and samples. Elimination of chloride interfer ence in the chemical oxygen demand test. All of these characteristics measured in entrance and in exit points are summarized in table table1 1. A modified method for the determination of chemical oxygen. Estimation of chemical oxygen demand in wastewater using.
After digestion, the remaining unreduced k 2 cr 2 o 7 is titrated with ferrous ammonium sulfate to determine the amount of k 2 cr 2 o 7 consumed and the oxidizable organic matter is calculated in. Chemical oxygen demand cod is an indicator of contamination that shows the amount of dissolved matter in water susceptible to being oxidized. Scope and application chemical oxygen demand cod measures the oxygen equivalent of that portion of the organic matter in a sample that is easily oxidised by a strong chemical oxidant. Modified apha closedtube reflux colorimetric method for toc. A new approach for chemical oxygen demand cod measurement. The determination of chemical oxygen demand in waters and effluents 2007 methods for the examination of waters and associated materials. Background on oxygen demand testing oxygen demand is an important parameter for deter.
Chemical oxygen demand cod is a critical waste treatment measurement in everything from municipal systems to food manufacturing waste streams. Cod samples are prepared with a closed reflux digestion followed by analysis. Since the use of mercury hg will be strictly restricted under the minamata convention on mercury, the feasibility of hgfree cod test by closed reflux, colorimetric method with excessive addition of silver sulfate ag 2 so 4 was discussed in this research. The amount of chemical oxygen demand determines the degree of water pollution by organic material. Determination of chemical oxygen demand in heterogeneous. The most commonly used detection method of cod is the closed reflux or colorimetric method, which requires several hours obtaining a measurement and use of costly, hazardous reagents. The novel method, named solid dilution sd, is based on a different technique of sample preparation. Dissolved oxygen probe ysi5000 do meter ysi5100 do meter ysi 59 do meter 5905 probe i 5210 b biochemical oxygen demand bodsoluble dissolved oxygen probe ysi5000 do meter ysi5100 do meter ysi 59 do meter 5905 probe i 5210 b chemical oxygen demand cod closed reflux colorimetric hach dr2010 uvvis spectrophotometer hach 8000.
The method determines chemical oxygen demand see definitions, section. Representation of pollution level of domestic and industrial wastewater, or contamination level of surface, ground, and. Standard operation procedure total chemical oxygen demand closed reflux, spectrophotometric method, cell test cat. For most people a complete understanding of the standard methods required to accurately complete critical wastewater analytical tests is not necessary. Representation of pollution level of domestic and industrial wastewater, or contamination level of surface, ground, and potable water.
Dec 01, 2015 chemical oxygen demand cod cod is an empiric laboratory assay which measures the amount of organic matter contained in a water sample. 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. Oxygen demand, chemical, total, i356185 cod in mgl. Demand chemical oxygen demand it is a measurement of the oxygen equivalent of the materials present in the wastewater that are subject for oxidation by a strong chemical oxidant, in this case, dichromate. Test method b micro cod by sealed digestion and spectrometry. A colorimetric method for determining chemical oxygen demand.
Modified apha closedtube reflux colorimetric method for. Closed reflux method closed reflux method has the cost advantage and it generates minimum of hazardous waste. The conventional method for measuring chemical oxygen demand requires sample preparation and pretreatment using chemicals. Determination of chemical oxygen demand in heterogeneous solid or semisolid samples using a novel method combining solid dilutions as a preparation step followed by optimized closed reflux and colorimetric measurement. Previously published methods equivalent method in this booklet. Samples with higher cod concentrations may be processed by appropriate dilution of the sample. Standard test methods for chemical oxygen demand dichromate. Determinations can be made titrimetrically by several approved methods, or photometrically colorimetrically with epa method 410. Pdf miniaturized closed reflux, colorimetric method for the. Rapid determination of chemical oxygen demand cod using.
A chemical oxygen demand cod test is used to measure the oxygen equivalent of the organic matter in a sample that is susceptible to oxidation by a strong chemical oxidant. Performing cod testing the right way is important in determining wastewater treatment effectiveness and can help diagnose any problems in treatment. Used to measure the organic strength of wastewaters same principle as bod but different execution. To eliminate a significant interference due to no2, add 10 mg sulfamic acid for each mg no2n present in the sample volume used. Chemical oxygen demand cod purpose using a standard colorimetric method to determine the chemical oxygen demand cod in water samples theory water samples in sealed tubes are heated in an oven in the presence of dichromate at 150c. The quantity of oxygen consumed is expressed in terms of its oxygen equivalent.
Oxygen demand and cod chemical oxygen demand cod is defined as the amount of specified oxidant that reacts with a sample under controlled conditions. Chemical oxygen demand cod cod is an empiric laboratory assay which measures the amount of organic matter contained in a water sample. However, a fundamental understanding of the theory behind and working knowledge of the basic procedures used for each test, and the answers to commonly asked questions about each test can be a valuable tool for anyone involved in generating. Chloride interference is an important problem of cod measurement for wastewaters containing low organic matter and high chloride concentrations. The determination of chemical oxygen demand in waters and. A modified method for the determination of chemical oxygen demand cod for samples with high salinity and low organics. Miniaturized closed reflux, colorimetric method for the determination. Feasibility of mercuryfree chemical oxygen demand cod. The chemistry of chemical oxygen demand chemical oxygen. Pdf the chemical oxygen demand cod is widely used as a surrogated measure for carbon bioavailability.
Hach s usepaapproved dichromate cod method is the most widely used chemical oxygen demand method in the world for npdes reporting and for easy process monitoring. Application this method may be used to analyze watersuspended sediment containing between 10 and 500 mgl chemical oxygen demand cod. The chemical oxygen demand cod determines the amount of oxygen required for. Each of hach s easytouse spectrophotometers and colorimeters give you. This results in the change of chromium from the hexavalent vi state to the trivalent iii state. After two hours, the tubes are removed from the oven, cooled, and measured. Brief method summary when a sample is digested, the dichromate ion oxidizes cod material in the sample.
The analysis of total organic carbon toc by the american public health association apha closedtube reflux colorimetric method requires potassium dichromate k 2 cr 2 o 7, silver sulfate agso 4, and mercury hgso 4 sulfate in addition to large volumes of both reagents and samples. Reflux titrimetric method, closed reflux colorimetric method. Test method a macro cod by reflux digestion and titration. Dec 28, 2015 dissolved oxygen demand do and chemical oxygen demand cod pdf 1. The quantity of oxidant consumed is expressed in terms of its oxygen equivalence. Chemical oxygen demand an overview sciencedirect topics. D dissolved oxygen demand and chemical oxygen demand chetan singh pundeer 12 ce 036 chetan singh pundeer 12 ce 036 1 2. May 23, 2010 chemical oxygen demand cod is used as a discharge standard parameter in wastewater treatment plant design, environmental modelling and many other applications. Pdf miniaturized closed reflux, colorimetric method for. Chemical oxygen demand cod closed reflux, colorimetric method. Hydrogen peroxide interference in chemical oxygen demand. Jul 01, 2000 read miniaturized closed reflux, colorimetric method for the determination of chemical oxygen demand, waste management on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. This method covers the determination of chemical oxygen demand cod in ground and surface waters, domestic.
Contents introduction chemical oxygen demand selection of methods interferences and limitations sampling and storage methods for cod analysis open reflux method closed reflux, titrimetric method closed reflux, colorimetric method reference 3. The novel method, named solid dilution sd, is based on a different technique of sample preparation, diluting. The method relies on the release of oxygen from dichromate on heating which is consumed by carbon associated with. By john stone metals digestions, epa method 1664 oil and gr. Dissolved oxygen demand do and chemical oxygen demand cod pdf. The chemistry of chemical oxygen demand by john stone chemical oxygen demand cod is a quick, inexpensive means to determine organics in water.
Chemical oxygen demand the chemical oxygen demand cod test is used to measure the oxygen equivalent of the amount of organic matter content of both wastewater and natural waters oxidizable by a strong chemical oxidizing agent in an acidic medium. Jun 05, 2012 this paper reports the development of an innovative sample preparation method for the determination of the chemical oxygen demand cod in heterogeneous solid or semisolid samples, with high suspended solids and cod concentrations, using an optimized closed reflux colorimetric method. Hydrogen peroxide interference in chemical oxygen demand during. Oxygen demand, chemical cod, colorimetric, dichromate oxidation parameter and code. Throughout the booklet, the term chemical oxygen demand cod is used to express the. Oxygen demand, chemical cod, colorimetric, dichromate oxidation. Sep 24, 2014 contents introduction chemical oxygen demand selection of methods interferences and limitations sampling and storage methods for cod analysis open reflux method closed reflux, titrimetric method closed reflux, colorimetric method reference 3. What is the standard procedure for analysing cod in waste. In waste water treatment plant, an important parameter, chemical oxygen demand is needed to be measured. Miniaturized closed reflux, colorimetric method for the. Any equivalent reflux apparatus may be substituted provided that a groundglass connection is used between the flask and the condenser. Chemical oxygen demand cod is used as a discharge standard parameter in wastewater treatment plant design, environmental modelling and many other applications. It is based on the use of thermo orion test kits cat.
Request pdf miniaturized closed reflux, colorimetric method for the determination of chemical oxygen demand the standard technique for the closed reflux. The conventional chemical oxygen demand cod test requires mercuric sulfate hgso 4 for masking chlorides cl. The closed reflux method 5220 c is economical in the use of metallic salt reagents, but requires homogenization of samples containing suspended solids to obtain reproducible results. This means that the method may not be modified per part 6. A sample is refluxed in strongly acid solution with a known excess of potassium dichromate k 2 cr 2 o 7.
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