• Afif Sani

Biological Oxygen Demand (BOD)

Updated: Sep 20

What is BOD?

Biochemical oxygen demand (BOD) testing is used to determine the relative oxygen requirements of :

  • Wastewaters

  • Effluents

  • Polluted Waters

The BOD test is and indirect measurement of organic matter by calculating the change in dissolved oxygen (DO) concentration caused by microorganisms as they degrade organic matter in a sample held in a stoppered bottle incubated in the dark at 20oC for 3 or 5 days.

At SaniChem, our analysts measure DO before and after incubation, and compute BOD using the difference between DO measurements.

Since initial DO is determined shortly after dilution, all oxygen uptake occurring after this measurement is included in BOD measurements.

Why is BOD measurement important?

BOD tests is generally used to measure waste loadings for treatment plants and in assessing the plants’ BOD removal efficiency.

BOD testing determines the molecular oxygen used during a specified incubation period to:

  • Biochemically degrade organic material (carbonaceous demand)

  • Oxidize inorganic material

  • Oxidize reduced forms of nitrogen (nitrogenous demand)

How is BOD Calculated?

At SaniChem we use the standard APHA method to calculate BOD5 using the formula below


D1: DO of diluted sample immediately after preparation, mg/L

D2: DO of diluted sample after 5 days incubation at 20oC, mg/L

S: Oxygen uptake of seed [∆DO/mL Seed suspension added per bottle (S=0 if samples are unseeded)]

Vs: Volume of seed in respective test bottle, mL

P: decimal volumetric fraction of sample used; 1/P = dilution factor

What causes high BOD?

BOD is highly correlated with pollution levels. High BOD is usually caused by high levels of organic pollution due to inadequately treated wastewater and/or high nitrate levels, which produce elevated plant growth.

What is the difference between chemical oxygen demand and biological oxygen demand?

BOD measures the amount of oxygen required by microorganism to breakdown organic material, whereas Chemical Oxygen Demand (COD) is the amount of oxygen required to breakdown organic material via oxidation.

Click here to learn more about COD

BOD is an indirect representation of the amount of biodegradable organic matter while COD is and indirect representation of the amount of biodegradable and non-biodegradable organic matter.

COD does not differentiate between biologically available and inert organic matter. Because of this, COD value is always higher than BOD value (about 1.3 to 1.5 times higher)

BOD test requires a minimum of 5 day incubation period whereas COD test is a rapid test which only requires 2 hours digestion.

Contact us for more information BOD testing in Malaysia.


1. YOUNG, J.C. 1973. Chemical methods for nitrification control. J. Water Pollut. Control Fed. 45:637

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