Significance: Biochemical Oxygen Demand (BOD) is defined as the requirement or demands for oxygen that matter, organic and chemical, places on water during the decay process or during chemical reactions. In other words, BOD is the measurement of how much stress is being placed on the dissolved oxygen system of a river or waterway.
When organic matter is present, then BOD is present in the waterway. When the organic matter breaks down, it reduces the abundant supply of dissolved oxygen in the water.
There are many ways that organic matter can exist in a waterway. Such examples include runoff from a farm, falling leaves, decomposing logs and/or floating logs, untreated sewage, and other industrial wastes that distribute chemicals into the air and into the soil and ultimately run into waterways.
When testing for BOD, the first step is to collect equal amounts of water from the research waterway and dilute each of the samples (usually 2 or 3 equal sized containers) with the exact same amount of distilled water. Next, one of the samples, BOD1, is tested for dissolved oxygen content. The remaining samples are placed in foil (to keep out all light) and placed in a safe dark area where they will stay undisturbed for five days, BOD5, to seven days, BOD7, depending upon the test and time available. Then the dissolved oxygen test for BOD5 or BOD7 is subtracted from the first dissolved oxygen test for BOD1, to give the result of the Biochemical Oxygen Demand test. This is a comparison of Dissolved Oxygen on the first day subtracted from the Dissolved Oxygen on the final day that provides the result of the BOD test.
After testing is complete, it will indicate the condition of the research area. If high amounts of BOD exist, then the waterway is poor; but if it has a low BOD, the waterway is ideal for survival. To keep the BOD low, individuals and organizations must watch what is discharged into the waterways surrounding them. The health of all organisms, including humans, depends upon the health of our waterways. It is a serious issue to think about.
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