BOD (Biochemical Oxygen Demand) Calculator

Biochemical Oxygen Demand (BOD) measures how much oxygen microorganisms consume when breaking down organic matter in water — a standard indicator of water pollution and treatment effectiveness. Enter your initial and final dissolved oxygen readings for both the diluted sample and blank control, along with the dilution factor, sample volume, and test duration (BOD3, BOD5, BOD7, or BOD20). The BOD Calculator returns your BOD value in mg/L, oxygen consumed, blank correction, and a pollution level classification.

mg/L

Dissolved oxygen at start of test

mg/L

Dissolved oxygen after 5 days

mg/L

Initial DO of control sample

mg/L

Final DO of control sample

Fraction of sample volume to total bottle volume

mL

Volume of sample used

Standard test duration

Results

BOD Value

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Oxygen Consumed

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Blank Correction

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Pollution Level

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Frequently Asked Questions

What is BOD and why is it important?

Biochemical Oxygen Demand (BOD) measures the amount of oxygen required by bacteria to decompose organic matter in water. It's a key indicator of water pollution and is essential for wastewater treatment monitoring.

What does BOD5 mean?

BOD5 refers to the biochemical oxygen demand measured over 5 days at 20°C. This is the standard test duration used worldwide for water quality assessment and regulatory compliance.

How do I interpret BOD results?

Generally, BOD values below 3 mg/L indicate clean water, 3-5 mg/L is moderately polluted, 5-15 mg/L is heavily polluted, and above 15 mg/L indicates severe pollution requiring immediate treatment.

Why is dilution necessary in BOD testing?

Dilution ensures there's enough dissolved oxygen in the sample bottle to support bacterial activity throughout the test period. Without proper dilution, oxygen would be depleted too quickly, giving inaccurate results.

What is the blank correction in BOD testing?

The blank correction accounts for oxygen consumption by bacteria naturally present in the dilution water. This ensures the measured BOD reflects only the oxygen demand from the sample itself.

What factors can affect BOD test accuracy?

Temperature, pH, presence of toxic substances, bacterial seed quality, and proper sample handling all affect BOD accuracy. Tests must be conducted under standardized conditions at 20°C in darkness.

How does BOD relate to wastewater treatment?

BOD helps operators monitor treatment efficiency, determine oxygen requirements for aeration systems, and ensure effluent meets discharge standards. It's also used to calculate organic loading rates.