Chemical Oxygen Demand Calculation

COD Formula:

\[ COD = \frac{(blank - sample) \times normality \times 8}{weight} \]

Blank Titration (mL):

Sample Titration (mL):

Normality of Ferrous Ammonium Sulfate:

Sample Volume (for liquid samples):

Chemical Oxygen Demand (COD):

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1. What is Chemical Oxygen Demand (COD)?

Chemical Oxygen Demand (COD) is a measure of the amount of oxygen required to chemically oxidize organic and inorganic matter in water. It's an important water quality parameter that indicates the degree of pollution in water bodies.

2. How Does the Calculator Work?

The calculator uses the standard COD formula:

\[ COD = \frac{(blank - sample) \times normality \times 8}{weight} \]

Where:

\( blank \) — Titration value for blank (mL)
\( sample \) — Titration value for sample (mL)
\( normality \) — Normality of ferrous ammonium sulfate (N)
\( weight \) — Sample volume (mL)
8 — Conversion factor (milliequivalent weight of oxygen, mg/meq)

Explanation: The difference between blank and sample titration represents the amount of oxidizable material in the sample. The normality and sample volume normalize the result to mg/L.

3. Importance of COD Measurement

Details: COD is crucial for assessing water quality, monitoring wastewater treatment efficiency, and ensuring compliance with environmental regulations. It provides a rapid alternative to BOD (Biochemical Oxygen Demand) testing.

4. Using the Calculator

Tips: Enter all titration values in mL, normality of the titrant, and sample volume. Ensure all values are positive numbers and sample volume is greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between COD and BOD?
A: COD measures all chemically oxidizable material, while BOD only measures biologically oxidizable material. COD is faster (hours vs. days) but less specific to organic pollution.

Q2: What are typical COD values?
A: Clean surface water: 10-30 mg/L, Raw sewage: 250-1000 mg/L, Industrial wastewater: up to 100,000 mg/L. Discharge limits vary by location and industry.

Q3: Why is the blank titration important?
A: The blank accounts for any oxidizable material in the reagents and ensures the result reflects only the sample's oxygen demand.

Q4: What are limitations of COD testing?
A: Doesn't distinguish between biodegradable and non-biodegradable matter. Some compounds (like chloride) can interfere with the test.

Q5: How should samples be prepared?
A: Samples should be well-mixed and representative. Highly contaminated samples may need dilution. Follow standard methods for preservation and analysis.