The amount of dissolved oxygen used up by aerobic microorganisms to decompose the organic matters present in a sample of water is termed Biochemical Oxygen Demand or Biological Oxygen Demand (BOD). BOD and DO are inversely proportional to each other i.e a decline in DO levels reflects a high level of BOD.
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What is the relationship between do BOD and COD?
The only relation between COD & BOD is – COD > BOD. For most industrial process waste water, community sewage, drains and even some hetrogeneous sources, COD/BOD ratio has been found to be in a defined range and hence, COD result gives more or less BOD value range for such identifiable waste water.
What is biochemical oxygen demand BOD levels?
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.
How is biological oxygen demand measured?
The test for biochemical oxygen demand (BOD) is a bioassay procedure that measures the oxygen consumed by bacteria from the decomposition of organic matter (Sawyer and McCarty, 1978). The change in DO concentration is measured over a given period of time in water samples at a specified temperature.
Which is better COD or BOD?
COD is normally higher than BOD because more organic compounds can be chemically oxidised than biologically oxidised. This includes chemicals toxic to biological life, which can make COD tests very useful when testing industrial sewage as they will not be captured by BOD testing.
Why is COD always higher than BOD?
always COD is higher about 5 times than BOD because its comprises both Organic and inorganic Pollutants while BOD is only for Organic Pollutants. Dear brother, Simply BOD indicates the biodegradable organic matter (OM) while COD represents both biodegradable and non-biodegradable OM in water.
How does BOD and COD reduce in water?
You can reduce COD and BOD by adding hydrogen peroxide to the wastewater solution. The hydrogen peroxide will chemically attack the organics in the wastewater, degrading them and reducing the measured COD and BOD.
Is biological oxygen demand and biochemical oxygen demand same?
Biochemical oxygen demand (BOD, also called biological oxygen demand) is the amount of dissolved oxygen needed (i.e., demanded) by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period (Kaiser, 1998).
What causes high BOD in water?
Sources: BOD represents the amount of organic matter in a water supply; therefore, it increases when decaying plants, human or animal waste, and other organic compounds are added to water.
Why is BOD important in water quality?
The BOD is an important parameter for assessing water quality. It deals with the amount of oxygen consumption (mg O2 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 the BOD value of pure water?
UPLOAD PHOTO AND GET THE ANSWER NOW! Solution : A pure water would have about 1 ppm value. A water supply with BOD level of 3.5 ppm is moderately clean, and water with a BOD level of 6.9 ppm is considered as polluted water.
Why is BOD calculated?
The BOD test measures the strength of the wastewater by measuring the amount of oxygen used by the bacteria as they stabilize the organic matter under controlled conditions of time and temperature.
Why COD is higher than BOD in waste water?
The COD test uses a chemical (potassium dichromate in a 50% sulfuric acid solution) that “oxidizes” both organic (predominate) and inorganic substances in a wastewater sample, which results in a higher COD concentration than BOD concentration for the same wastewater sample since only organic compounds are consumed …
Why is BOD done for 5 days?
BOD occurs in 2 general stages. While calculating the oxygen demand, the carbonaceous stage is taken into account. This stage is almost completed in 5 days, which means that most of the organic content of the sewage is oxidized under aerobic conditions in 5 days. Hence ,BOD for 5 days is calculated.
What happens if 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.
How do you reduce BOD in water?
- Focus on removing TSS from wastewater first.
- Get a properly sized EQ tank.
- Control the pH of the waste stream.
- Install a modern plate pack DAF made of stainless steel or plastic.
- Use a regenerative turbine air dissolution pump.
What does high BOD indicate?
The dissolved oxygen readings are usually in parts per million (ppm). Higher BOD indicates more oxygen is required, which is less for oxygen-demanding species to feed on, and signifies lower water quality. Inversely, low BOD means less oxygen is being removed from water, so water is generally purer.
How is BOD related to water pollution?
So, the higher the amount of organic pollutants in the water, the higher oxygen is required by the bacteria and this oxygen required by the bacteria is known as BOD. So, the amount of pollution in a water body is directly proportional to the BOD.
Does BOD increase with temperature?
The BOD removal rate in the bioreactor increased when the temperature increased from 20 degrees C to 30 degrees C, 40 degrees C, and 50 degrees C, but it decreased when the temperature increased from 50 degrees C to 60 degrees C. Higher temperature enhanced the endogenous respiration of microbes in the bioreactor.
What is the minimum value of BOD in polluted water?
Clean water has BOD value less than 5 ppm. Polluted water has BOD value higher than 10 ppm.
How many days BOD is measured Why?
The BOD is an empirical test to determine the molecular oxygen used during a specified incubation period (usually five days), for the biochemical degradation of organic matter (carbonaceous demand) and the oxygen used to oxidise inorganic matter (e.g., sulphides and ferrous iron).
Why is BOD test run in the dark?
Bubbles in a BOD bottle also invalidate that bottle’s DO measurement. Algae in a BOD sample and left out on a lab bench exposed to sunlight can be a source of bubbles. Always put the BOD bottle in a dark incubator soon after the initial DO is measured and the bottle sealed.
What are the limitations of BOD test?
Limitations Of Test The method takes five days to perform and uses a discrete sample. The test has poor reproducibility and toxic chemicals can inhibit measurement. Short-term BOD determinations magnify errors and still require relatively long sample periods. The test is not suited for on-line, continuous measurement.
Does BOD increase with time?
Both BOD and COD is increasing with time. Join ResearchGate to ask questions, get input, and advance your work.
How do you increase BOD in water?
Organic loading is occurrence of excess organic matter inside water due to sewage disposal and eutrophication. This leads to an increase in biological oxygen demand (BOD) for putrefaction. Explosive multiplication of alga leads to algal bloom.