Microbiological Fact Sheet

Description 5-Day Biochemical Oxygen Demand (BOD) Test
Method SM5210B
Method Summary The sample of water, or an appropriate dilution, is combined with a working bacterial seed solution and incubated for five days at 20ÂșC without exposure to light. The reduction in dissolved oxygen concentration during the incubation period yields a measure of the carbonaceous and nitrogenous biochemical oxygen demand.

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Scope and Application The most useful application of this test is to measure the waste load pre- and post-wastewater treatment plant in order to determine the removal efficiency of a treatment system. The BOD or carbonaceous BOD (CBOD) can be utilized to determine the degree to which a waste stream will contribute to the pollution of environmental waters through the depravation of oxygen to existing organisms.
BOD and CBOD Wastewater from sewage treatment plants often contains organic materials that are decomposed by microorganisms, which use oxygen in the process. The amount of oxygen consumed by these organisms in breaking down the waste is known as the biochemical oxygen demand or BOD. BOD measures the amount of oxygen consumed by microorganisms in decomposing organic matter in stream water. BOD also measures the chemical oxidation of inorganic matter (i.e., the extraction of oxygen from water via chemical reaction). A test is used to measure the amount of oxygen consumed by these organisms during a specified period of time (5 days at 20 C). The rate of oxygen consumption in a stream is affected by a number of variables: temperature, pH, the presence of certain kinds of microorganisms, and the type of organic and inorganic material in the water. BOD directly affects the amount of dissolved oxygen in rivers and streams. 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. Sources of BOD include leaves and woody debris; dead plants and animals; animal manure; effluents from pulp and paper mills, wastewater treatment plants, feedlots, and food-processing plants; failing septic systems; and urban storm water runoff. CBOD or carbonaceous biochemical oxygen demand measures the same depletion using a nitrification inhibitor. It is an indicator of the demand created only by carbon compounds because micro-organisms are inhibited from utilizing nitrogen metabolism.
Result Interpretation BOD mg/L = Depletion of dissolved oxygen per liter of sample CBOD mg/L = Depletion of dissolved oxygen per liter of sample due to carbonaceous compounds (excluding nitrogenous).

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