Chemical Oxygen Demand (COD) Calculator

To calculate Chemical Oxygen Demand (COD) using this calculator, input Initial Concentration of Dichromate Solution, Volume of Sample, Volume of Blank, Volume of FAS used for titration, and Molarity of FAS.

Select appropriate Sample Volume units and click Calculate to determine the COD Value in mg/L. The calculator also provides the Percentage Removal when comparing initial and final COD values.

How to Calculate Chemical Oxygen Demand?

To calculate Chemical Oxygen Demand, first prepare a sample with Potassium Dichromate and Sulfuric Acid. After digestion, titrate with Ferrous Ammonium Sulfate (FAS) until the endpoint.

Calculate using the difference between Blank and Sample titration volumes, considering the Normality of FAS and Sample Volume. Multiply by the Equivalence Factor (8000) to convert to mg/L oxygen demand. For COD Removal Efficiency, compare initial and final values.

Formula for Chemical Oxygen Demand Calculation

Basic COD Formula:

COD (mg/L) = (V1 - V2) × N × 8000 / S
where:
V1 = Volume of FAS used for blank (mL)
V2 = Volume of FAS used for sample (mL)
N = Normality of FAS
S = Sample volume (mL)
8000 = Milliequivalent weight of O₂ × 1000

FAS Normality:

N = (Volume of K₂Cr₂O₇ × Normality of K₂Cr₂O₇) / Volume of FAS
where:
Volume of K₂Cr₂O₇ = Volume used in titration
Normality of K₂Cr₂O₇ = 0.25N (standard)

COD Removal Efficiency:

Removal (%) = ((Initial COD - Final COD) / Initial COD) × 100
where:
Initial COD = Starting COD value
Final COD = Ending COD value

Example 1: Wastewater Sample

• Sample Volume = 20 mL
• Blank FAS = 25 mL
• Sample FAS = 15 mL
• FAS Normality = 0.25
• Calculated COD = 400 mg/L
• Sample Type = Raw Wastewater

Example 2: Industrial Effluent

• Sample Volume = 10 mL
• Blank FAS = 30 mL
• Sample FAS = 10 mL
• FAS Normality = 0.25
• Calculated COD = 800 mg/L
• Sample Type = Industrial Waste

Example 3: Treated Water

• Sample Volume = 25 mL
• Blank FAS = 20 mL
• Sample FAS = 18 mL
• FAS Normality = 0.1
• Calculated COD = 64 mg/L
• Sample Type = Treated Effluent

Example 4: High Strength Waste

• Sample Volume = 5 mL
• Blank FAS = 25 mL
• Sample FAS = 5 mL
• FAS Normality = 0.25
• Calculated COD = 1600 mg/L
• Sample Type = Concentrated Waste

Example 5: Treatment Efficiency

• Initial COD = 500 mg/L
• Final COD = 50 mg/L
• Removal Efficiency = 90%
• Treatment Type = Biological Treatment
• Sample Type = Process Monitoring

What is Chemical Oxygen Demand?

Chemical Oxygen Demand (COD) is a key Water Quality Parameter that measures the amount of Oxygen required to chemically oxidize Organic Matter in water. This test uses Potassium Dichromate as a strong oxidizing agent under Acidic Conditions. The COD Value indicates the total quantity of Oxygen required to oxidize all Organic Compounds to Carbon Dioxide and Water.