BOD

Biochemical Oxygen Demand also known as BOD, provides testers with an indication of how much biodegradable waste is present in a water source. Biodegradable wastes are wastes that can be broken down by nature. This biodegradable waste is broken down as aerobic bacteria feed on it. Aerobic bacteria are bacteria that use oxygen. The more oxygen that these aerobic bacteria use the less is available for other aquatic life. A high amount of BOD means that the water source has a lot of bacteria. Having a lot of bacteria present in a water source is not a good thing because bacteria use oxygen as they eat and breakdown biodegradable wastes.

Testing for BOD

Chemical tests are performed in order to indicate how much biodegradable waste is present in a water source. The test is usually performed five days after the samples are taken. BOD is a more accurate test than Dissolved Oxygen known as DO because it gives an image of the water quality by including the long-term effects of biodegradable wastes on Dissolved Oxygen (DO). In addition, DO tests only show the DO level at the time the test was performed.

BOD Levels and What They Mean

BOD Levels	Significance/Meaning
1-2 (mg/L)	Super clean water with little biodegradable waste
3-5 (mg/L)	Fairly clean water with some biodegradable waste
6-9 (mg/L)	A lot of bacteria and biodegradable waste present
10 (mg/L) and above	Very bad water quality with lots of bacteria and biodegradable waste present

Results

The lower the amount of BOD, the healthier the water source is because it has little amounts of bacteria and biodegradable waste. The results are shown in the table below:

Site	Amount of BOD
1	0 (mg/L)
2	17 (mg/L)
3	2 (mg/L)

Based on the results above the North Channel of the Chicago River has a low amount of BOD. This means that there is little biodegradable waste and bacteria present. There must have been an error that occurred at the second site due to the fact that the value (17) is out of place. This could have happened due to a mix up on the procedure or the place that the sample was taken from.

Influences

Humans have a negative influence on BOD. The use of fertilizers (agricultural runoff), which are high in nitrates and phosphates can cause algae and other aquatic plants to grow at a rapid pace. As a result, not a lot of sunlight can get into the water causing these plants to die fast. Thus the bacteria is in charge of breaking down these dead plants. They go though this process using oxygen to decompose the waste. Since there is a lot of waste in the form of dead aquatic plants the bacteria have to use more oxygen to decompose the large amount of waste. The bacteria are using up too much oxygen and as a result they lower the oxygen present in water. Thus other aquatic life don’t have enough oxygen and die. The water source will usually tend to have an odor.
Waste from industries and salt used to melt ice from streets also have devastating
effects .Runoff from industries stir up the organic wastes trapped in the bed of the body of water. As a result similar effects such as the ones listed above can occur.
Humans should use less fertilizer in general to prevent the problems listed. They also should plant trees close to bodies of water to absorb runoff. As a result, the runoff would not reach the body of water. In addition, the height of bridges over bodies of water should be increased to prevent salt from getting into the water. If humans apply some of these changes they can keep bodies of water clean.