It is used to indicate organic matter contamination and it helps in knowing overall organic load to the receiving body. There are two methods for COD determination. The first method: open reflux method is suitable for a wide range of wastes where large volume of sample is required (for samples with COD= 50 mg O2/L).
What is open reflux method for COD?
Methods for COD Analysis. 12. Open Reflux Method Principle: Most types of organic matter are oxidized by a boiling mixture of chromic and sulfuric acids. A sample is refluxed in strongly acid solution with a known excess of potassium dichromate (K2Cr2O7).
Which type of titration is involved in the determination of COD?
Titrimetric Method of COD
In the titration method for determining COD, the excess dichromate is reacted with a reducing agent, ferrous ammonium sulfate. As the ferrous ammonium sulfate (FAS) is added slowly, the excess dichromate is converted into its trivalent form.
Which method is used for COD?
The traditional chemical oxygen demand (COD) analysis method is the wet chemistry method. This involves a two hour digestion at high heat under acidic conditions in which potassium dichromate acts as the oxidant for any organic material present in a water sample.
Which indicator is used in determination of COD?
Using potassium dichromate
Most commonly, a 0.25 N solution of potassium dichromate is used for COD determination, although for samples with COD below 50 mg/L, a lower concentration of potassium dichromate is preferred.
What are the two methods of determining the COD value of a water sample?
There are two methods available for COD determination namely open reflux and closed reflux.
How is COD determined in wastewater?
What test methods are typically used to determine COD at water and wastewater laboratories? The most common test method is the colorimetric analysis after oxidizing the COD with acid and using indicator compounds, such as hexavalent dichromate.
What is the basis for the COD test?
Chemical oxygen demand (COD) is used to determine the quantity of pollution in water after wastewater treatment. The higher value of chemical oxygen demand indicates the higher organic pollution in the water sample. Only chemically digest able matter can be determined by the COD test.
What is the objective of COD test?
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.
Why is h2so4 used in COD test?
Chemical Oxygen Demand (COD) 1% Silver Sulphate in Sulphuric Acid (conc.) provides the primary and secondary digestion catalysts for oxidation of carbon during chemical oxidation.
Which instrument is used for determination of COD test?
COD Test Procedures
COD standards can also be purchased. A COD reactor/heating (150°C) block and a colorimeter are turned on so that both instruments are allowed to stabilize. Pre-prepared low-range (3-50 ppm) or high-range (20-1500 ppm) vials are selected for the COD test based on expected results.
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 and How Is It measured?
COD is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution, which in SI units is milligrams per liter (mg/L). A COD test can be used to easily quantify the amount of organics in water.
Why is COD preferred BOD?
COD is normally higher than BOD because more organic compounds can be chemically oxidised than biologically oxidised. This includes the chemical toxics to biological life, which can make COD tests very useful when testing industrial sewage as they will not be captured by BOD testing. Hence, COD is preferred over BOD.
Which catalyst is used in COD experiment?
Abstract. In this study, 10% CuO/Al2O3 catalyst was used in a catalytic wet-air oxidation process to remove chemical oxygen demand (COD) and color from experimentally designed wastewater containing lignin.
Why Ag2SO4 is used in COD?
The COD analysis uses silver sulfate (Ag2SO4) as a catalyst, mercury sulfate (Hg2SO4) to eliminate chloride interference, ferric ammonium sulfate ((NH4)2. Fe(SO4).
Why do we need to determine COD?
Chemical Oxygen Demand or COD is a measurement of the oxygen required to oxidize soluble and particulate organic matter in water. COD can be measured in rapidly or in real-time with Real Tech’s COD instruments to improve wastewater process control and plant efficiency.
Why COD measurement is necessary along with BOD test for waste water?
COD is the amount of oxygen required to chemically oxidize organic matter in your wastewater into inorganic matter. whereas BOD is the amount of oxygen required to biologically oxidize the organics in your sample, usually after 5 days or 21 days of incubation time, depending on the bioassay followed.
What is closed reflux method?
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. Applicable Concentration Range. 40 to 400 mg/L. Interferences. The most common interferent is the chloride ion.
What are the factors that affect COD?
The results reveal that three factors, i.e., water inflow concentration, gate opening size, and gate opening number, are the dominant factors of influence, and there are logarithmic relationships between the rate of change in COD concentration in the SCRRs and these factors.
What conclusion can be drawn from COD measurement?
Conclusion. COD and BOD tests are important because they help in the determination of the amount of waste in wastewater. This is important because the organic content in wastewater needs to be reduced before the wastewater is discharged.
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