Introduction:

Objective of COD:

1. To understand how polluted the water is due to organic waste.
2. To regularly observe and control the quality of water.
3. To support proper treament of wastewater.

Reagents:

1. Ferrous Amonnium Sulphate (FAS)
2. Potassium Dichromate (K₂Cr₂O₇)
3. Sulphuric Acid (H₂SO₄)
4. Silver Sulphate (Ag₂SO₄)
5. Ferroin Indicator
6. Distilled Water
7. Stone

Preparation of Stock Solution:

0.1 N Ferrous Ammonium Sulphate (FAS)

Equivalent weight of FAS = 392.14 g/equiv

For 1 L of 0.1 N solution:
0.1 × 392.14 = 39.21 g

For 100 mL:
39.21 / 10 = 3.921 g

Preparation Steps:

1. Weigh 3.92 g FAS accurately
2. Take 70–80 mL distilled water in a beaker
3. Add 2 mL concentrated H₂SO₄ slowly
4. Add FAS to the acidified water
5. Stir until dissolved
6. Transfer to 100 mL volumetric flask
7. Rinse beaker and add washings
8. Make up volume to 100 mL
9. Mix thoroughly

0.25 N Potassium Dichromate (K₂Cr₂O₇) was used as standard oxidizing solution.

Sample Collection:

100 mL grey water samples were collected from hostel wastewater tanks. setups were prepared:

• Sample solution (with grey water)
• Blank solution (distilled water only)

The blank acts as a control for COD calculation.

Procedure:

1. Titrate with 0.1 N FAS
2. Take 20 mL water sample in COD flask (distilled water for blank)
3. Add 10 mL of 0.25 N K₂Cr₂O₇
4. Add 0.4 g Silver sulphate
5. Add 30 mL concentrated H₂SO₄
6. Place flask in COD digester with condenser at 150°C for 2 hours
7. Allow to cool
8. Add 150 mL distilled water through condenser
9. Add 3–4 drops Ferroin indicator

Calculation:

COD (mg/L) = (A − B) × N × 8000 / V

Where:
A = Blank reading
B = Sample reading
N = Normality of FAS
V = Volume of sample (mL)

Sample	Reading	Cod
Blank Sample	25.5	_
Dixit Sir’s House sample	19.2	252
Girls Hostel	21.3	168
Boys Hostel	20.0	220

Conclusion:

COD analysis showed varying organic pollution levels in hostel wastewater. Higher COD values indicate greater organic load and need for treatment before discharge. The experiment provided practical understanding of wastewater analysis, titration techniques, and environmental monitoring.