Biochemical Oxygen Demand (BOD), is defined as a chemical procedure for determining the quantity of oxygen needed by organisms to break down the organic material in wastewater. Organic matter such as dead plants, leaves, food waste present in water, the bacteria start breaking down these waste materials.
This is considered as the standard method for measuring BOD. It is recognized by Environmental Protection Agency (EPA) U.S. This analysis is carried out by taking 300ml incubation bottles containing buffered dilution water which is heavily dosed with seed microorganisms and kept in the darkroom at 20° Celsius for pentad (5-days). The 5-days time is due to avoid DO (Diluted Oxygen) production exerted by photosynthesis. To measure carbonaceous BOD (cBOD), a nitrification inhibitor should be added after adding dilution water to the sample, and as a result, nitrogenous BOD (nBOD) is exhibited.
Unseeded- BOD5 = [(D0-D5)]/P
Seeded- BOD5 = [(D0-D5)-(B0-B5)f]/P
D5- DO after 5-days incubation.
B0-diluted seed sample after preparation.
B5- Diluted seed sample after 5 days incubation.
F- Seed volume in dilution solution to seed volume in BOD Test.
D0- Is the dissolved oxygen.
P- P represent the Decimal dilution factor.
In this method, keep the sample in a tightly packed container which is fitted with a pressure sensor. Generally, adding lithium hydroxide to the container above the sample level. Compared to the above method ( method for dilution) this is simple and doesn't need dilution of the sample and no need of seeding, and also this method allows to read the values of BOD directly.
Some of the alternative methods include Biosensor, software sensor, a fluorescent Redox indicator, and titration and so on.
There are many problems which lead to some disturbances in the measurement; they are either due to dirty BOD bottles and DI water or due to bad seed and bubbles and so on. Some measures that should be taken into account while performing the measurements are provided below:
Safety and hygiene
Manometric is an accurate, handy method for the determination of BOD. The results obtained after conducting the technique show that there will be some deviation between BOD7measured by manometric and titration method.
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