BOD Incubator- Determination of Biological Oxygen Demand

April 21st, 2014 by Acmas Leave a reply »

BOD incubator is the most versatile and reliable low temperature Incubator which is designed to maintain at 20°C, necessary for Biological Oxygen Demand/Biochemical Oxygen Demand (BOD) determination. BOD incubators provide controlled temperature conditions for accelerated tests and exposures.  The biological oxygen demand (BOD) is an empirical test in which standardized laboratory procedures are used to determine the relative oxygen requirements of microbes in waste waters, effluents, and polluted waters and in simple words,.

It is a chemical process that determines how fast biological organisms use up oxygen in a body of water or it measures the oxygen required for the biochemical degradation of organic material (carbonaceous demand) and the oxygen used to oxidize inorganic materials, such as sulfides and ferrous iron  The seeding and dilution procedures provide an estimate of the BOD at pH 6.5 to 7.5.

Overview of BOD Methodology

Biochemical oxygen demand (BOD), sometimes referred to as Biological Oxygen Demand, is a quantitative expression of microbes ability to deplete the oxygen content of a waste water. This depletion takes place due to the microbes consuming organic matter in the water via aerobic respiration. This type of respiration uses oxygen as an electron acceptor, and the organic material being consumed provides the energy source. This organic matter also undergoes oxidation without the aid of microbes, which can be measured using the Chemical Oxygen Demand (COD) procedure.

The method consists of placing a sample in a full, airtight bottle and incubating the bottle under specified conditions for a specific time. Dissolved Oxygen (DO) (amount of oxygen present in water body) is measured initially and after incubation. The BOD is computed from the difference between the initial and final DO.

High levels of BOD in streams cause the dissolved oxygen (DO) content of the water to drop. It is this DO that fish, and zooplankton use to survive. If DO drops to below a critical level the ecology of the stream could begin to die off as well. This condition can lead to an increase in anaerobic bacteria (species that can live in the absence of oxygen) that leads to the production of foul-smelling and possibly toxic gases. These gases may include methane, hydrogen sulfide, and ammonia. If this water were to enter into groundwater sources one can imagine the potential problems with toxicity to humans.

Factors affecting the BOD

Some factors may affect the accuracy and precision of BOD measurements. Such as

  • Soluble versus particulate organics,
  • Settle able and float able solids,
  • Oxidation of reduced iron and sulfur compounds, or
  • Lack of mixing
  • Oxidation of reduced forms of nitrogen, such as ammonia and organic nitrogen, can be mediated by microorganisms and exert nitrogenous demand. Nitrogenous demand historically has been considered as an interfering factor in the determination of BOD, and the inclusion of ammonia in the dilution water contributes an external source of nitrogenous demand. The interference from nitrogenous demand can now be prevented by an inhibitory chemical (If an inhibiting chemical is not used, the oxygen demand measured is the sum of carbonaceous and nitrogenous demands).

BOD and Water Pollution

Biological Oxygen Demand (BOD) is one of the most common measures of pollutant organic material in water. BOD indicates the amount of pollutants present in water. Therefore, a low BOD is an indicator of good quality water, while a high BOD indicates polluted water. Dissolved oxygen (DO) is consumed by bacteria when large amounts of organic matter from sewage or other discharges are present in the water. DO is the actual amount of oxygen available in dissolved form in the water. When the DO drops below a certain level, the life forms in that water are unable to continue at a normal rate. The decrease in the oxygen supply in the water has a negative effect on the aquatic life.

The BOD test serves an important function in stream pollution-control activities. It is a bioassay procedure that measures the amount of oxygen consumed by living organisms while they are utilizing the organic matter present in waste, under conditions similar in nature. The other traditional tests or indicators for water quality are Chemical Oxygen Demand (COD) and pH.


  • In measuring waste loadings to treatment plants and in evaluating the BOD-removal efficiency of such treatment systems.
  • It measures the molecular oxygen utilized during a specified incubation period for the biochemical degradation of organic material (carbonaceous demand) and the oxygen used to oxidize inorganic material such as sulfides and ferrous iron.
  • It measures the amount of oxygen used to oxidize reduced forms of nitrogen (nitrogenous demand) unless their oxidation is prevented by an inhibitor.

Safety Guidelines

  • Do not cover the shelves of the incubator with aluminum foil. It may cause temperature control malfunction or an obstruction of air circulation.
  • Control the temperature of incubator regularly to avoid any error.
  • While performing test BOD bottles should be closed in BOD incubator.
  • BOD incubators are not designed to store eating and drinking materials and cosmetics too.
  • Flammable substances are not permitted to be stored.

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