Turning Garbage into Energy! (GK-12 Challenge: A New Route Towards Reducing
Green House Gas Emissions and Developing Alternative Energy Technology by
Improving Urban Infrastructure)
Overview:
In this lesson students will learn how to make and quantify observations, design a
methane generating bio-reactor from garbage based on these observations, quantify
results using scientific instruments, and draw conclusions on their findings. The “big
ideas” this project will cover are microbiology (the idea that all living things are
composed of smaller living things; cells), alternative energy, and global warming from
green house gases.
Introduction and Background:
The video below may be used as introduction to the concept:
Modern Marvels: Landfill Bioreactors (http://www.youtube.com/watch?v=-fiEnVKXRA)
Below are some concepts needed for students to understand this process of converting
garbage to electricity.
Anaerobic Decomposition
The primary organisms involved are bacteria. Methanogensis is favored in anaerobic
environments where the primary electron acceptor, CO2, is produced from the
fermentation of various organic substrates. It does not occur, or is greatly inhibited, in
environments where electron acceptors such as oxygen, nitrate, and sulfate are readily
available. The complete process involves a complex mix of microbes, of which only a
few actually produce methane.
3 major groups of bacteria in anaerobic degradation are:
(1) Hydrolyzing-fermentative organisms
a. Produce powerful digestive enzymes which break down biopolymers, such
as starch, cellulose, proteins, and others. These are then fermented to form
hydrogen and carbon dioxide.
(2) Acetogens
a. Converts the above products to acetic acid
(3) Methanogens
a. Convert the acetic acid, hydrogen, and carbon dioxide to methane
i. Ammonia and hydrogen sulfide are also produced in the process
Methanogenesis is unique in that no single organism can completely convert a substrate
such as starch to methane. Instead it is the interaction of the bacterial groups described
above, comprising a complex microbial ecosystem, that results in the degradation of
complex organic compounds into end products (i.e. methane). The interrelationships of
the organisms establish thermodynamic conditions that favor methane formation.
Objectives:
The Students will:
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Gain experience in searching for scientific facts and observations from
literature reporting’s that are relevant and accurate
Learn how to design a methane bioreactor from garbage based on
observations/results
Learn creativity in solving a challenging problem
Understand the microbial ecosystem involved in the production of
methane
Be alerted to our current environmental issues (ie rise in green house
gases, need for alternative energy, etc.) and how these problems may be
alleviated and prevented.
Recognize the role and impact of engineers in society: converting a
negative into sometime positive
Arizona State Standards:
Strand 1:
Inquiry
Process
Strand 2:
History and
Nature of
Science
Strand 3: Science in
Personal and Social
Perspectives
Strand 4: Life
Science
Concept 1:
Observations,
Questions,
Hypothesis
Concept 1: History
of Science as a
Human Endeavor
PO4: Analyze the
use of technology
in science related
careers
Concept 1: Changes in
Environment
Concept 1: Structure
and Function of Living
Systems
Concept 2:
Scientific Testing
Concept 3: Analysis
and Conclusions
Concept 4:
Communication
Concept 2: Science and
Technology in Society
National Standards:
Concept A: Identify questions that can be answered through scientific investigations
Concept B: Transfer of energy
Concept E: Abilities of technical design
Materials/set-up:
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Methane Detector (Look at Amazon for some good deals on methane
detectors. They should preferably have a large range of methane detection.
Ours had a range of 100ppm to 900ppm)
Reactor Vessel (A single 2 Liter bottle works great or several 2 liter
bottles attached together)
Garbage (use inquiry to help students understand what kind of Garbage
would be best – see activity 1 and 2)
Manure
Dirt
Water
A place to store reactor for a long period of time
Heavily Sealed Zip lock bags
Assessment:
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Research activity – Completion of worksheet
Design activity – This activity will show how well students understood
microbial ecosystems, the production of methane from garbage, and what
factors influence methane production
Lesson Plan:
Pre-activity 1 (1st day time: 30 minutes)
Students will research the effects of Methane and Carbon Dioxide in the atmosphere. To
guide them in sorting out the relevant facts pertaining to these gases in the atmosphere
they will complete a worksheet while in the computer lab.
Here are some example questions (in italics) we had students answer in the computer lab:
What is heat capacity? What are the Heat Capacity’s of Methane and Carbon Dioxide? Write as
a ratio (be sure to be consistent with units)
What are the Sources/ Causes of Methane and Carbon Dioxide in the atmosphere?
What is Methane used for? Is it valuable?
What is a Methanogen?
How much methane is in the atmosphere?
How much CO2 is in the atmosphere?
Why is methane worse than CO2? Quantify your description (HINT: do they both have the same
green house effects? Which is worse? Why and by how much?)
Where does the Methane come from?
How can we reduce the production of methane from some of these sources of Methane?
(Be Creative: For example a methane tank attached to the stomachs of cows)
On this day, the students will also be asked to bring in various materials from their
garbage at home and put them in a sealable bag to let sit for several weeks.
Pre-activity 2 (2nd day time: 1 hour)
After several weeks, the students will take the sealed bags of garbage and make
observations about what is taking place and why some materials decompose and some do
not. The students will be given microscopes and hunt for miniature microorganisms in the
garbage. They will make observations in their notebooks and attempt to identify the
microorganisms.
Pre-activity 3 (3rd day time: 1 hour)
Students will design a bioreactor on paper. 8 groups of 4 students will be assigned for
each class. As a group of four, the students will come up with designs. One person in
each group will be designated the senior engineer and present the designs to three other
senior engineers. In this way, two major class groups will be formed and two final
designs per class will compete.
Activity
Students will build the bio reactor. For our experiments we added different amounts of
water with 1 cup of dirt, 1 cup of organic matter, and 1 cup of manure into a small
container (2 liter bottles worked well in our case). One particularly good design I saw a
student come up with is attaching 2 bottles together so they come together at the neck.
This way the bottle can be turned upside down then right side up again. This allows the
leachate (the sludge that tends to sink to the bottom) to become redistributed to the top of
the trash heap (similar to the design in an actual landfill reactor where the leachate was
pumped back to the top of the landfill). After 3 to 4 weeks, the methane concentration
will be measured using a methane detector. We created a separate “measuring tank” of
known volume to measure the methane concentration. This way the actual amount of
methane produced could be determined. If this approach is repeated, I recommend
coming up with a valve system to prevent the methane gas from escaping when
positioning the reactor vessel into the measurement vessel. It may also be best to only
take a single measurement after several weeks since taking multiple measurements
introduces uncontrolled variables. To add a competitive edge to the project a reward can
be given to the group that generates the most methane.