Sewage Lab: The Effects of Biodegradable waste on Dissolved Oxygen
Abstract:
write short (3 sentences) summary of the purpose of the this lab, what you did and the results.
Introduction:
Answer the following questions in 1 paragraph:
1.
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6.
What is Sewage?
What are decomposers?
What gas is taken in and which gas is given off by microorganisms (bacteria)?
What is dissolved oxygen? Do polluted water have a lot of dissolved oxygen?
What are the steps of water treatment of sewage water?
What happens at each step?
The purpose of this lab is to investigate the influence which biodegradable wastes have on the amount
of dissolved oxygen consumed by decomposers in an aquatic environment. The yeast will represent the
decomposers (i.e. bacteria), and the milk is the biodegradable waste material/sewage (i.e. leachate).
Will increasing the amount of sewage added to a water system affect the amount of dissolved oxygen in
the system? We hypothesize that if we increase the amount of sewage in the water system, then the
dissolve oxygen in the system will ___________ . This will be indicated by the amount of time that it
takes for the methylene blue to change color.
Materials and Procedure:
3 test tubes, pipette, yeast mixture, methylene blue, saran wrap, test tube rack, water, milk
1.
2.
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4.
Place the three test on the test tube rack.
The correct amounts of milk and water to each of the test tubes, according to table 1.
Check to make sure the height of the liquids in all the test tubes is about equal.
Add 3 drops of methylene blue to each test tube to act as an indicator of the levels of dissolved
oxygen.
a. Blue = dissolved oxygen
b. Yellow = dissolved carbon dioxide
5. Place the cap on the test tubes, and invert 7 times, to mix the methylene blue into the solutions.
6. The timer should dictate the start of the next portion, because you will start timing right as you
add the yeast. Do NOT add the yeast until you have written down a start time!
7. Add ½ a teaspoon of yeast (decomposers) to each solution and put the cap on each test tube.
Make sure that the amounts of yeast are the same that go into each test tube.
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Begin timing.
Observe when the mixture turns completely yellow (except for the top layer).
Record the time in Table 2 below.
After 15 minutes stop observing the test tubes.
Clean out your test tubes (WITHOUT MAKING a MESS!!!) at the back sinkso the next group can
use them.
13. Complete the results and Discussion.
Data:
Table 1: Drop of liquid (milk or water added)
Test Tube
1
2
3
Milk Drops
Water Drops
37
15
3
0
22
34
Table 2: Color Change times and observations
Test Tube
Time (in minutes) it took for the contents
to turn from blue to white/colorless
Observations
Does the top of each test tube remain
blue? Why?
1
2
3
Results:
Graph the results of the number of drops of milk vs. the time in minutes it took for the color to change
(line graph).
Discussion:
Answer the following questions in paragraph form.
1. What happened to the amount of dissolved oxygen in the water as more “sewage” (milk) was
added to it?
2. What effects would dumping raw sewage into a river have on the dissolved oxygen levels?
3. Could aquatic plants be used for phytoremediation? Why?
4. What step in the water treatment process do you think removes bacteria?