A Sierran Lake. Photo©CLCase

Biology 101

Water Pollution Study

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Sewage, or wastewater, includes all the water from a household that is used to washing and toilet wastes, Rainwater flowing into street drains and industrial wastes does not usually enter the sewage system. Sewage is mostly water and contains little particulate matter, perhaps 0.03%. but contains up to 350 ppm of biodegradation organic matter called biochemical oxygen demand (BOD),

Eutrophication is caused by an overabundance of nutrients in a body of water. Additional nutrients can cause dense growths of algae called algal blooms. Once eutrophication results in blooms of algae or cyanobacteria, the eventual effect is the same as the addition of biodegradable organism matter. In the short run, these algae and cyanobacteria produce oxygen. However, they eventually die and are degraded by bacteria. During the degradation process, the oxygen in the water is used up, which may kill fish and other animals. Undegraded remnants of organic matter settles to the bottom and hasten the filling of a lake.

Biochemical Oxygen Demand
An important concept in sewage treatment, biochemical oxygen demand (BOD) is a measure of the biologically degradable organic matter in water. BOD is determined by the amount of oxygen required by bacteria to metabolize the organic matter. The more oxygen that is used up as bacteria degrade the organic matter, the greater the BOD, which is usually expressed in milligrams of oxygen per liter of water, The amount of oxygen that normally can be dissolved in water is only about 10 ml/l; typically BOD values may be twenty times this amount. If this wastewater enters a lake, bacteria in the lake begin to consume the organic matter responsible for the high BOD, rapidly depleting the oxygen in the lake water.

From the S.F. Chronicle

In this study, you can specify the following characteristics:

A. The kind of body of water:

1. Large pond
2. Large lake
3. Slow-moving river
4. Fast-moving river

B. The water temperature in degrees Celsius

C. The rate of dumping of waste in parts per millons (ppm)/day.

D. The type of treatment of the waste

1. None
2. Primary
3. Secondary
4. Tertiary


Run the program and answer the following questions in your Lab Report.
For Question 1, run the experiment on each body of water keeping all other variables (type of treatment, temperature, and dumping rate) constant: Record your results in Table 2.
1. Which type of waterway is harmed least by receiving sewage? How can you tell?

For Question 2, run the experiment using different types of treatment keeping the other variables (body of water, temperature, and dumping rate) constant. Record your results in Table 2.
2. Which type of sewage was least harmful? How can you tell?

For Question 3, keep the body of water constant and change one of the other variables.
3. Design your own experiment using POLUT. What variable did you consider (e.g., temperature, dumping rate, type of treatment)? Which condition in Table 2 is your control? What is your conclusion? (Attach the graph from POLUT and show where it substantiates your conclusions.)