Biological Oxygen Demand
The determination of the Biochemical Oxygen Demand or Biological Oxygen Demand (BOD) estimates the amount of biodegradable organic matter that is present in polluted waters, effluents and polluted waters.The BOD considers the amount the amount of dissolved oxygen that are consumed by bacteria, while analysing the oxidation of these materials.
In addition, Dissolved oxygen is necessary for the life of the Aquatic flora and fauna.
And the BOD test is a measure of the impact the effluent water has on the ecosystem and water bodies. This test is often requires in discharge permits, as it is a means of assessing the degree of water pollution.
Two methods are widely in use for BOD measurement: the dilution method and the manometric method:
• Dilution method
This is a standard method. for instance, the APHA standard methods 5210B from the American Public Health Association describes in detail this protocol. First a dilute solution is got by adding inorganic nutrients and buffer salts to the purified water, microbial seed is put on bases of the requirement.
For instance. If the sample does not show the presence of sufficient bacteria in other words, if compounds of toxic bacteria are produce, then the addition of microbial seed becomes necessary.
Therefore, Dilution water is useful to make different variations of sample water. Specific BOD bottles show filling to the top, capping and sealing. the bottles incubate for 5 days at. 20°C .
Dissolved oxygen levels are usually measure before and after 5-day incubation period, the results of the 5 days after the incubation period after correction of the dilution and blank factor, gives the BOD value and the results expresses in mg/L of dissolved oxygen.
• Manometric method
In this test, a manometer is fixes itself in the bottle that contains the undiluted sample. The drop of air pressure in the bottle measuring continuously and this directly complies to the amount of oxygen by the sample, comparing to the dilution method this method is simple and easy and no dilution involves and the measurements are continuously monitor.
However, BOD can sometimes show a false report if there is the presence of toxic or poor seeding material in the water samples. Therefore, it recommends to regularly use a glucose – glutamic acid (GGA) solution as a standard check solution. The oxygen uptake of this solution should be 198 +/- 30.5 mg/L.
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