BIOLOGICAL OXYGEN DEMAND

Biological Oxygen Demand (BOD) is one of the most common measures of pollutant organic material in water. BOD indicates the amount of putrescible organic matter present in water. Therefore, a low BOD is an indicator of good quality water, while a high BOD indicates polluted water. Dissolved oxygen (DO) is consumed by bacteria when large amounts of organic matter from sewage or other discharges are present in the water. DO is the actual amount of oxygen available in dissolved form in the water. When the DO drops below a certain level, the life forms in that water are unable to continue at a normal rate. The decrease in the oxygen supply in the water has a negative effect on the fish and other aquatic life. Fish kills and an invasion and growth of certain types of weeds can cause dramatic changes in a stream or other body of water. Energy is derived from the oxidation process. BOD specifies the strength of sewage. In sewage treatment, to say that the BOD has been reduced from 500 to 50 indicates that there has been a 90 percent reduction.

The BOD test serves an important function in stream pollution-control activities. It is a bioassay procedure that measures the amount of oxygen consumed by living organisms while they are utilizing the organic matter present in waste, under conditions similar in nature. The other traditional tests or indicators for water quality are chemical oxygen demand (COD) and pH.

For results of the BOD test to be accurate, much care must be taken in the actual process. For example, additional air cannot be introduced. Temperature must be 20°C, which is the usual temperature of bodies of water in nature. A five-day BOD test is used in environmental monitoring. This test is utilized as a means of stating what level of contamination from pollutants is entering a body of water. In other words, this test measures the oxygen requirements of the bacteria and other organisms as they feed upon and bring about the decomposition of organic matter. Time and temperature, as well as plant life in the water, will have an effect on the test. High BOD burdens or loads are added to wastewater by food processing plants, dairy plants, canneries, distilleries and similar operations, and they are discharged into streams and other bodies of water.

Mark G. Robson

(see also: Ambient Water Quality; Dissolved Oxygen; Ecosystems; Water Quality )

Bibliography

Shelton, T. (1991). Interpreting Drinking Water Quality Analysis—What Do the Numbers Mean? New Brunswick, NJ: Rutgers Cooperative Extension.

Wallace, R. (2000). Maxcy-Rosenau-Last Public Health and Preventive Medicine. Stamford, CT: Appleton & Lange.

Oxygen Demand, Biochemical

Biochemical oxygen demand (BOD) is a measure of how much organic pollution is in water. The BOD test measures the amount of dissolved oxygen in 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 liter, whereas drinking water has a BOD of less than 0.5 milligrams per liter.

Engineers and scientists measure the BOD of a lake or river to see how healthy the water is. The lower the BOD, the healthier the water. Water needs to have oxygen in it to support aquatic life such as fish and plants. Oxygen in the water is replenished from the atmosphere through aeration, but if it is used up faster than it is replenished, the water becomes anaerobic (or hypoxic)—existing in the deficiency or absence of free oxygen. Anaerobic water cannot support life.

see also Fresh Kills; Hypoxia; Water Treatment.

Bibliography

peavey, howard s.; rowe, donald r.; and tchobanoglous, george. (1985). environmental engineering. new york: mcgraw-hill.

Julie Hutchins Cairn

biochemical oxygen demand (BOD) The amount of oxygen taken up by microorganisms that decompose organic waste matter in water. It is therefore used as a measure of the amount of certain types of organic pollutant in water. BOD is calculated by keeping a sample of water containing a known amount of oxygen for five days at 20°C. The oxygen content is measured again after this time. A high BOD indicates the presence of a large number of microorganisms, which suggests a high level of pollution.

biochemical oxygen demand (biological oxygen demand, BOD) An indicator of the pollution of water by organic matter where the decomposition of the organic matter by micro-organisms depletes the water of dissolved oxygen. It is measured as the mass (mg) of oxygen per litre of water that is taken up when a sample of water containing a known amount of oxygen is kept in darkness at 20°C, usually for five days (when the result is described as the BOD₅).

biological oxygen demand (BOD, biochemical oxygen demand) An indicator of the polluting capacity of an effluent where pollution is caused by the take-up of dissolved oxygen by micro-organisms that decompose the organic material present in the effluent. It is measured as the weight (mg) of oxygen used by one litre of sample effluent stored in darkness at 20°C for five days.

biological oxygen demand (BOD, biochemical oxygen demand) An indicator of the polluting capacity of an effluent where pollution is caused by the take-up of dissolved oxygen by micro-organisms that decompose the organic material present in the effluent. It is measured as the weight (mg) of oxygen used by one litre of sample effluent stored in darkness at 20°C for five days.

biological oxygen demand (BOD, biochemical oxygen demand) Indicator of the polluting capacity of an effluent, where pollution is caused by the take-up of dissolved oxygen by micro-organisms that decompose the organic material present in the effluent. It is measured as the weight (mg) of oxygen used by 1 litre of sample effluent stored in darkness at 20°C for five days.

biological oxygen demand (BOD) A way of assessing bacterial contamination of water, milk, etc. by micro‐organisms which take up oxygen for their metabolism.

biochemical oxygen demand See BIOLOGICAL OXYGEN DEMAND.

biochemical oxygen demand See biological oxygen demand.

biochemical oxygen demand See BIOLOGICAL OXYGEN DEMAND.

biological oxygen demand See BIOCHEMICAL OXYGEN DEMAND.

biochemical oxygen demand: see sewerage.