Tag: biology

Biological Oxygen Demand (BOD) in simple terms is the amount of oxygen that would be used by the decomposing bacteria to decompose or break down the organic compounds in the water body. The increase in the BOD reflects that the concentration of the organic mass is tremendous and so a large amount of oxygen would be claimed by the bacteria. This results in the deficiency of the dissolved oxygen in the water and adversely affects the aquatic life due to hypoxia. So, the BOD can be defined as the measurement of the rate of oxygen utilization by a unit volume of water over a period of time.

Discharge of untreated sewage into streams which contains high quantity of nutrients induce the disproportionate growth of algae causing eutrophication which results into depletion of dissolved oxygen in the water. The continuous flow of sewage reduces the self-purification capacity of the water body. The condition of hypoxia arises due to depletion of oxygen. Increase in temperature favours the eutrophication and algal bloom is the cause of eutrophication. Depletion of oxygen is the adverse effect of the eutrophication.

Biological Oxygen Demand indicates the increase in presence of organic matter in the water body. High BOD indicates the great amount of organic matter. The dissolved oxygen in water is consumed by bacteria to decompose the organic matter of sewage or other discharges thereby depleting the oxygen of the water body. The decrease in oxygen can kill the aquatic life in water body.

The microorganisms in polluted bodies use dissolved oxygen to metabolise organic matter in polluted waters. This is called biochemicalical oxygen demand. The more organic matter in sewage and polluted bodies, greater the BOD and hence less oxygen is left availble tor higher animals like fishes.

• BOD is the Biological Oxygen Demand that is created when there is an excessive quantity of the organic matter in the water body and its decomposition is initiated by the decomposing bacteria. More the amount of organic waste, the higher will be the BOD and so more will be pollution in the water body. 
• This causes an extreme reduction in the dissolved oxygen and suffocates the aquatic animals. 
• Distillery effluent is rich in organic waste left from alcoholic fermentation and it has the highest BOD. 

The concentration of the organic waste and its subsequent decomposition determines the BOD of the water. If the organic concentration is high, there will be high BOD because more dissolved oxygen will be used to breakdown the organic mass by the bacteria. So, high BOD marks high pollution. Distilled water has no content of the organic substances as it has been treated and filtered. Unpolluted water pond will not have polluted source of organic mass but the existing organisms die and their dead bodies contribute to a little raised BOD. Highly polluted water will show a very high value of BOD as it will take a lot of dissolved oxygen to breakdown the organic mass in water body. So, distilled water is least polluted, followed by unpolluted pond water and then highly polluted pond water.

A large quantity of urban sewage will have a large amount of organic and inorganic material. Due to this, the decomposition of the organic mass will initiate the use of dissolved oxygen and so, the DO of receiving water body decreases. This will cause increase in the biological oxygen demand (BOD) by the decomposing bacteria. As the DO decreases, the aquatic animals will suffocate and die. Also, the inorganic nutrients, as well as the decomposed nutrients, will cause lush growth of algae, causing algal bloom over the surface of the water, which will further decrease the DO by not allowing the mixing of atmospheric oxygen.

The BOD test measures the amount of dissolved oxygen in the water that is used up due to the breakdown of organic pollutants, such as sewage, in a certain number of days. Raw sewage has a BOD of forty to 150 milligrams per litre, whereas drinking water has a BOD of less than 0.5 milligrams per litre. The BOD indicates the content of oxygen needed to decompose organic compounds in wastewater by bacteria.

Biological Oxygen Demand (BOD) is a measure of the oxygen used by microorganisms to decompose this waste. This results in a high BOD level. When BOD levels are high, dissolved oxygen levels decrease because the oxygen that is available in the water is being consumed by the bacteria.

A river with an inflow of domestic sewage rich in organic waste will reduce the dissolved oxygen (DO). The organic waste will increase biological oxygen demand of the river thus depleting the O2 content and may result in the death of fish due to lack of oxygen.