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. Wwgw laboratory certification that a noncompliant sample was received and analyzed. Colorimetric analysis works because the two chromium ions absorb in the visible. Holding the vial by the cap in an empty sink, gently invert several times to mix the contents they will become very hot during mixing. The method relies on the release of oxygen from dichromate on heating which is consumed by carbon. Application this method may be used to analyze watersuspended sediment containing between 10 and 500 mgl chemical oxygen demand cod. Chemical oxygen demand cod is a quick, inexpensive means to determine organics in water. The design was evaluated using the closed reflux cod method 47. Although the quantity of ferroin indicator is not critical, use the same volume for all titrations. Green roof water monitoring report american society of. Selection of method the open reflux method b is suitable for a wide range of wastes where a large sample size is preferred. Miniaturized closed reflux, colorimetric method for the determination. Cod is the measurement of the amount of oxygen in water consumed for chemical oxidation of pollutants.
What is the standard procedure for analysing cod in waste. Measure cod of wastewater using closed reflux method. Milestone ethos one operator manual ma 3, rev002010. Scope and application chemical oxygen demand cod measures the oxygen equivalent of that portion of the organic. The closed reflux methods c and d are more economical in the use of metallic salt. Chemical oxygen demand cod closed reflux, titrimetric method mgl apha 5220 c 100 ml 3 days chemical oxygen demand cod closed reflux, colorimetric method mgl apha 5220 d 100 ml 3 days chloride, as cl ion chromatograph mgl apha 4110 100 ml 2 days. Chloride reacts with silver ion to precipitate silver chloride, and thus inhibits the catalytic activity of silver. Oxygen demand, chemical cod, colorimetric, dichromate oxidation parameter and code.
Odell inorganic chemistry branch chemistry research division. Colorimetric method 4 a4500ca standard method 20th 4500 cl c. Getting started with chemical oxygen demand requires just a few pieces of equipment. Musico selection of method open reflux method is suitable for a wide range of wastes where a large sample size is preferred. Cods of the synthetic samples containing varying cod and chloride concentrations were measured by closed reflux colorimetric method using three digestion solutions having different strengths. Brief method summary when a sample is digested, the dichromate ion oxidizes cod material in the sample. Miniaturized closed reflux, colorimetric method for the. 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. Both of these chromium species are colored and absorb in the visible region of the spectrum. Cod is a major indicator of the extent of organic compound removal. The closed reflux method we use magnetic stirrer to stir the samples for 10 minutes, then pipiette 2 ml of the sample and add into the reagent vials. Ammonia was measured using an ammoniaspecific electrode hach, loveland, co. Briefly, the digestion solution was prepared by mixing 2. Cod samples are prepared with a closedreflux digestion followed by analysis.
By john stone metals digestions, epa method 1664 oil and gr. 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. Cod was quantified according to a miniaturized closedreflux colorimetric method lapara et al. This results in the change of chromium from the hexavalent vi state to the trivalent iii state. Miniaturized closed reflux, colorimetric method for the determination of chemical oxygen demand. Carefully remove the cap of cod digestion reagent vial. 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. This means that the method may not be modified per part 6. Water technologychemical oxygen demand cod of sewage. Cod determination methods open reflux method closed reflux, titrimetric method closed reflux, colorimetric method. Principle when a sample is digested, the dichromate ion oxidizes cod material in the sample. It is based on the use of thermo orion test kits cat.
Place reflux flask in an ice bath and slowly add, with swirling, 25. The theoretical cod was considered to be the assigned cod value for each sample raposo et al. Cod levels which fall below this value are highly questionable because of the high chloride correction which must be made. To measure cod of wastewater using open reflux method. Cool to room temperature and titrate excess k2cr2o7with fas, using 0. Hach method 8000 for cod in wastewater is approved by the united states environmental protection agency usepa in title 40, chapter i, subchapter d, part 6. For these reasons, colorimetry is the most common method to measure cod.
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. Hach 8000 1979 chemical oxygen demand is considered a method defined parameter per the definition in the code of federal regulations, part 6. It is indicated in this study that a constant ratio of mercury sulphate can only prevent chloride interference up to a specific chloride concentration. While holding the vial at a 45 degree angle carefully pipet 2 ml sample into the vial. Besides, a modification of concentration and ratio of reagents was optimized to make the closed reflux colorimetric method suitable for complex substrates with cod levels ranging from 5 to 2500 g o 2 kg 1 ts. This method covers the determination of chemical oxygen demand cod in ground and surface waters, domestic. Oxygen demand, chemical cod, colorimetric, dichromate. The determination of chemical oxygen demand by semi. A colorimetric method for determining chemical oxygen.
Reactor digestion method usepa approved for reporting wastewater analysis. Determination of chemical oxygen demand in heterogeneous. This video explains cod in a simple and easy manner. When a sample is digested, the dichromate ion oxidizes cod material in the sample. Methods section 5220c and section 5220d reduce these waste problems but may be less accurate and less representative. Hydrogen peroxide interference in chemical oxygen demand. Modified procedure chemical oxygen demand cod cod determination in waterwastewater using closed reflux tritimetric method. The novel method, named solid dilution sd, is based on a. Chemical oxygen demand cod of a waste water sample youtube. The modified method, the potassium monochromate closed tube colorimetry with sodium bismuthate chloride removal kmccbi, generates the potassium dichromate on demand and eliminates mercury sulfate. The determination of chemical oxygen demand in waters and.
Total organic carbon by combustion infrared method. Chloride reacts with silver ion to precipitate silver chloride, and thus inhibits the catalytic activity of. The closed reflux colorimetric method used for cod employs potassium dichromate k 2 cr 2 o 7 as oxidant, requires only a small sample size, and produces minimal waste. Do the cod open reflux method and closed reflux method. Test method b micro cod by sealed digestion and spectrometry. Request pdf miniaturized closed reflux, colorimetric method for the determination of chemical oxygen demand the standard technique for the closed reflux.
The most widely used method for cod analysis is the closed reflux, colorimetric method with potassium dichromate k 2 cr 2 o 7 as an oxidation agent. An evaluation of the efficiency of miniaturized closed reflux, colorimetric method for the determination of chemical oxygen demand cod in various kinds of wastewater. Modified apha closedtube reflux colorimetric method for. Cod samples are prepared with a closedreflux digestion. 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. Thanks for a2a quora user the chemical oxygen demand cod test is commonly used to indirectly measure the amount of organic compounds in water. Test method a macro cod by reflux digestion and titration. The semi microanalysis procedure leads to a 60% reduction in sample volume and. Determinations can be made titrimetrically by several approved methods, or photometrically colorimetrically with epa method 410. Chemical oxygen demand cod closed reflux, colorimetric method. Colorimetry also makes measurement easy since all the analyst needs to do is digest the samples and let the instrument do the work. Samples with higher cod concentrations may be processed by appropriate dilution of the sample. The cv was found to be less than 2% for sdsmcrc method, which was much lower than the cv value for smort method around 10%. Cod assay solutions were prepared according to the closed reflux, colorimetric method of standard methods for the examination of water and wastewater.
Pdf miniaturized closed reflux, colorimetric method for. Cod closed reflux, colorimetric method composite glass 500 ml filter on site h 2 so 4 to ph closed reflux colorimetric method sdsmcrc. Does the temperature of the test vial affect results in. The method determines chemical oxygen demand see definitions, section 3. The chemical oxygen demand cod determines the amount of oxygen required for. Cod closed reflux, titrimetric 3 a3500cb standard method 20th 3500cr b. A cod test was conducted using closed reflux colorimetric method.
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