How to measure the oxygen consumption in water

The detection of oxygen consumption in drinking water in the laboratory is of great significance for water quality monitoring. How to measure the oxygen consumption in water in the laboratory?

According to GB/T 5750.7-2006 "Standard test methods for drinking water - Comprehensive indicators of organic matter", the potassium permanganate titration method is used to determine the amount of suspended solids and organic and inorganic substances that can be oxidized by potassium permanganate in water.

Principle: Potassium permanganate oxidizes reducing substances in acidic solutions, and excess potassium permanganate is reduced with oxalic acid. Oxygen consumption expressed as O2 based on potassium permanganate consumption

Scope of application: This method is applicable to the determination of oxygen consumption in drinking water and its source water with a chloride mass concentration below 300mg/L (calculated as Cl -). The minimum detectable concentration of this method (when taking 100mL of water sample) is 0.05mg/L, and the maximum detectable oxygen consumption is 5.0mg/L (calculated as O2).

Instruments: electric constant temperature water bath, conical flask, burette

Reagents: sulfuric acid (1+3), sodium oxalate standard solution (c=0.01000mol/L), potassium permanganate standard solution (c=0.01000mol/L)

Analysis steps:

1. Pre treatment of conical flask: Add 1mL of sulfuric acid solution (1+3) and a small amount of potassium permanganate standard solution to a 250mL conical flask. Boil for a few minutes, remove the conical flask and titrate with sodium oxalate standard solution until it turns slightly red. Discard the solution.

2. Take 100mL of well mixed water sample and place it in the treated conical flask mentioned above. Add 5mL of sulfuric acid solution (1+3). Add 10.00mL of potassium permanganate standard solution using a burette.

3. Place the conical flask in a boiling water bath and place it accurately for 30 minutes. If the red color significantly decreases during the heating process, the water sample must be diluted and redone.

4. Remove the conical flask, add 10.00mL of sodium oxalate standard solution while hot, shake thoroughly, and let the red color fade away.

5. On a white background, drop potassium permanganate standard solution into the burette until the solution turns slightly red, which is the endpoint. Record the amount V1

6. Add 10.00mL of sodium oxalate standard solution to the water sample titrated to the endpoint while hot (70-80 ℃). Immediately titrate with potassium permanganate standard titration solution until it turns slightly red, and record V2. If the concentration of potassium permanganate standard solution is accurate to 0.01000mol/L, the amount used for titration should be 10.00mL. Otherwise, a correction factor K can be calculated, as shown in the formula: K=

7. If the water sample is diluted with pure water, take another 100mL of pure water and titrate it according to the above measurement steps. Record the consumption of potassium permanganate standard solution V0