Because most samples of wastewater will have a BOD higher that the amount of oxygen available in the BOD bottle during the incubation period, the samples must be diluted . This dilution is done by adding dilution water to the sample in the BOD bottle. ... If the final DO is too low, the BOD cannot be determined.
How many days are required for BOD measurement and why?
Measuring biochemical oxygen demand requires taking two measurements. One is measured immediately for dissolved oxygen (initial), and the second is incubated in the lab for 5 days and then tested for the amount of dissolved oxygen remaining (final).
Why is BOD measured for 5 days?
The standard oxidation (or incubation) test period for BOD is 5 days at 20 degrees Celsius (°C) (BOD5). The BOD5 value has been used and reported for many applications, most commonly to indicate the effects of sewage and other organic wastes on dissolved oxygen in surface waters (see TECHNICAL NOTE).
Why is BOD5 important?
The BOD5 indicates how much dissolved oxygen (mg / l) is needed in a given time for the biological degradation of the organic wastewater constituents . This value is an important parameter for the assessment of the degree of pollution that wastewater represents for the environment (receiving water).
Why do we calculate BOD?
The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at 20 °C and is often used as a surrogate of the degree of organic pollution of water. BOD reduction is used as a gauge of the effectiveness of wastewater treatment plants.
What is a good BOD level?
A BOD level of 1-2 ppm is considered very good. There will not be much organic waste present in the water supply. A water supply with a BOD level of 3-5 ppm is considered moderately clean.
What is BOD formula?
BOD = biochemical oxygen demand, mg/L . When seed is added, seed control tests must be done to determine the amount of oxygen depleted by the seed. Calculation of BOD includes a correction factor for seed as expressed by Equation 2. where: IDO = initial D.O. of diluted sample, mg/L.
Why is COD higher than BOD?
COD stands for ‘Chemical Oxygen Demand’ where BOD stands for Biochemical Oxygen Demand. ... COD is normally higher than BOD because more organic compounds can be chemically oxidised than biologically oxidised .
How is BOD removed from wastewater?
Some BOD is removed in the septic tank by anaerobic digestion and by solids which settle to the bottom of the septic tank, but much of the BOD present in sewage (especially detergents and oils) flows to the leaching field. ... The bacteria in a healthy biomat also digest most of the remaining BOD in the sewage.
What happens when BOD is high?
The greater the BOD, the more rapidly oxygen is depleted in the stream. This means less oxygen is available to higher forms of aquatic life. The consequences of high BOD are the same as those for low dissolved oxygen: aquatic organisms become stressed, suffocate, and die .
What is BOD and its importance?
The biological oxygen demand (BOD) is also called biochemical oxygen demand. The BOD refers to the amount of oxygen required for the biotic degradation of organic matter in bodies of water . The BOD is a pollution parameter mainly to asses the quality of effluent or wastewater. ... The significance of BOD is very clear.
What causes high COD in wastewater?
COD increases as the concentration of organic material increases . It also increases if inorganic compounds susceptible to oxidation by the oxidant (typically dichromate) are present. Water with high COD typically contains high levels of decaying plant matter, human waste, or industrial effluent.
Why is BOD value important in wastewater treatment?
The BOD is an important parameter for assessing water quality. It deals with the amount of oxygen consumption (mg O 2 L − 1 ) by aerobic biological organisms to oxidize organic compounds . Sewage with high BOD can cause a decrease in oxygen of receiving waters, which in turn can cause the death of some organism.
What is BOD Toppr?
BOD refers to the dissolved oxygen that the microorganisms like bacteria need to oxidize, means to break down inorganic and organic matter in water. It is a measure of water quality.
What is BOD value?
Biochemical oxygen demand (BOD) represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature. When you look at water in a lake the one thing you don’t see is oxygen.
