Calculation method for COD in wastewater

Data can be obtained directly using a COD tester! ! !

Experimental measurements show that national standards specify this; it’s the potassium dichromate oxidation method

It’s specified in the national standards, including the analysis methods and criteria; LZ, please take a look first before asking further questions!

Those on the 1st floor need to explain the situation: There are two methods for testing COD in wastewater using experimental approaches: the potassium permanganate method and the potassium dichromate method. It can also be measured directly using a COD meter.

Determination of Chemical Oxygen Demand (COD) in Industrial Wastewater 1 Subject Matter and Scope of Application This method specifies the principles, instruments, reagent preparation, operational procedures, and result calculation for determining chemical oxygen demand in industrial wastewater. This method is suitable for water samples with a chemical oxygen demand value higher than 50 mg/L. 2 Principle: The water sample is placed in a solution of sulfuric acid, phosphoric acid, and silver sulfate; it is then nitrated with potassium dichromate for 10 minutes. The excess potassium dichromate is titrated using ammonium ferrous sulfate, with ferroin as an indicator. The chemical oxygen demand in the water sample is calculated based on the amount of potassium dichromate consumed, and it is expressed in mg/L of oxygen. 3 Instruments 3.1 All-glass reflux apparatus with a 500 mL Erlenmeyer flask. 3.2 10 mL burette. 3.3 Heating device: electric heating plate or rheostatic furnace. 4 Reagents 4.1 Potassium dichromate standard solution: c(1/5K2Cr2O7) = 0.25 mol/L 4.2 Ammonium ferrous sulfate standard solution: c = 0.25 mol/L 4.3 Sulfuric acid–phosphoric acid–silver sulfate solution: Dissolve 10 g of silver sulfate in 500 mL of concentrated sulfuric acid and 500 mL of concentrated phosphoric acid. 4.4 Test ferroin indicator solution: Weigh 1.485 g of o-phenanthroline and 0.695 g of ferrous sulfate, dissolve them in water, dilute to 100 mL, mix well, and transfer to a brown bottle. 4.5 Chemically pure mercuric sulfate. 5 Operating Steps 5.1 Take 5 mL of the well-mixed water sample (or an appropriate amount of the sample diluted to 10 mL) and place it in a 500 mL ground-mouthed reflux conical flask. Add exactly 5.0 mL of 0.25 mol/L potassium dichromate standard solution, then slowly add 25 mL of sulfuric acid–phosphoric acid–silver sulfate solution. Gently shake the flask to ensure uniform distribution of the solution. Heat under reflux for 10 minutes; after cooling, rinse the mouth of the reflux condenser with 100 mL of distilled water. Remove the conical flask, allow it to cool again, add 3 drops of ferroin, and titrate using 0.2500 mol/L ammonium ferrous sulfate. The end point is reached when the color changes from yellow to blue-green to red and then fades. If the solution turns green after heating and shows a high oxygen consumption, it should be diluted before taking another sample. Record the amount of ammonium ferrous sulfate used, using distilled water as a blank (V0). 5.2 If the chloride ion concentration in the wastewater exceeds 30 mg/L, 0.2000 g of mercuric sulfate should be added first. 6 Result Calculation Chemical Oxygen Demand COD (mg/L) = (V1-V0)*C*8*1000/V

The COD in wastewater is determined through testing; it cannot be obtained solely through mathematical calculations.

Chemical oxygen demand refers to the amount of oxidation consumed by reducing substances in water by strong oxidizing agents, expressed as an amount of oxygen in mg/L. There is no fixed formula for it.

It was determined through experimentation; there is no calculation formula