Introduction

chemical oxygen demand (COD) is a measure of the amount of oxygen required to chemically break down organic matter in water. It’s a crucial parameter for assessing water quality evaluating waste water treatment efficiency and determining the environmental impact of organic pollutants.COD testing helps identify the level of organic insuring effective water management and pollution control

Objective:

  1. Identify the level of organic pollutants in water.
  2. Evaluating the effectiveness of wastewater treatment processes.
  3. water quality monitoring.

Reagents :

1. ferrous Ammonium Sulphate (FAS).

2. Sulphuric Acid (H2SO4)

3. Distilled water

4. Potassium dichromate ( K2Cr2O7)

5. Ferroin indicator

.6. Silver sulphate (Agso4)

7. Stone

Preparation of stock:

1. 0.1 N FAS (ferrous Ammonium sulphate)

2. 0.25 N K2Cr2O7 (potassium dichromate)

O.1 FAS

. FAS provides 1 equivalent per mole ,so it’s equivalent

Weight = 392.14g/equiv.

. For 1 lit (1000 ml ) of 0.1 N Solution

. O.1 N* 392.14 g/equiv = 39.21g

. For 100 ML

. 39.21/10 = 3.921g

Procedure

१. Take 3.92 g of ferrous Ammonium sulphate accurately.

2. In a 100 ml beaker add 70-80 ml distiiled water.

3. Slowly add 2ml of concentrated H2SO4 the water.

4. Stir the solution gently.

5. Add the FAS into the acidifaied water.

6. Stir until fully dissolved.

7. Transfer the solution into a 100 ml valumetric flask.

8. Rinse the beaker with distilled water and that in the flask.

9. make up the volume to 100 ml with distilled water.

10. mix throuly.

We collected 100 mL of grey water sample from a tank that accumulates wastewater from the girls’ hostel washroom. Following the procedure, we prepared two solutions: one using the grey water sample and another as a blank solution (without the grey water sample). The grey water sample solution will be used for analysis, while the blank solution serves as a control for comparison purposes.

proccedure:

  1. Add 20 mL water sample in COD flask( for blank sample add distilled water)
  2. Add 10 mL of 0.25 N K2Cr2O7 solution.
  3. Add 0.4 gm of Silver sulphate.
  4. Add 30 mL H2SO4.
  5. Put the flask in digester and attach condenser which has been set on 150 degree Celsius for 2 hours.
  6. After 2 hours .Let it cool.
  7. Add 150 ml distilled water through condenser.
  8. Add 3 – 4 drops of Ferroin Indicator.
  9. Titrate the sample with 0.1 N FAS solution.

Color change observed during Titration:

Calculation:

COD= (A-B)*N*8000/Volume of sample

Where,

A= Reading of blank sample

B= Reading of KHP sample

N= Normality of FAS solution

30/8/2025

SampleReadingCOD
Blank Sample 25.3
Dixit Sir 18.4276
Girls Hostel20.8180
Boys Hostel 19252

30/09/2025

SampleReadingCOD
Blank Sample25.3
Dixit Sir21.0180
Girls Hostel20220
Boys Hostel21.4164

30/10/2025

SampleReadingCOD
Blank Sample–
Dixit Sir320
Girls Hostel210
Boys Hostel280

30/11/2025

SampleReadingCOD
Blank sample 25 –
Dixit sir 19.5220
Girls Hostel18.2272
Boys Hostel21.5140

11/1/2026

Sample ReadingCOD
Blank Sample 25.5–
Dixit Sir19.2252
Girls Hostel 21.3168
Boys Hostel20220