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10. Energy from Biofuels

Benjamin Cuker, Hampton University
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This unit explores the historic, current, and potential use of biomass for the production of energy. Various bio fuels are introduced, and students are reminded of the role of biomass in the development of civilization prior to the era of fossil fuel exploitation.

Learning Goals

Students will be able to:

  1. Recount the history of the use of biofuels during the course of human cultural development, including the impact on forests and whales.
  2. List and explain the impacts of biofuels on human health and air quality.
  3. Distinguish between alcohol fermentation and methane production from feedstocks, noting the different underlying biological processes and approaches to production.
  4. Evaluate the production of alcohol from sugar cane and corn, including the economics, energy efficiency, and ecological impact of each feedstock.
  5. Use data collected from experimentation to determine how different feedstocks determine the biofuels produced under anaerobic conditions.
  6. Use published data to evaluate the efficacy of using land for biofuel production versus solar-electric production.

Context for Use

This unit is developed for use by college students at all levels. A good background in high school level science and history is sufficient for understanding the concepts. The readings and illustrations provide the basis for classroom discussions that work best for sections of twenty-five or fewer students. The module fits well with a course in environmental science or more specialized offerings such as a class in alternative energy.

Description and Teaching Materials

Student materials page

Be sure to read the very detailed section developed for the students. It is strongly suggested that the students also read the unit prior to attending the class: Energy from Biofuels.

Structuring your classroom time

1. Quiz & Discussion. I like to begin class with the quiz, as it promotes timely arrival. Ask five different students to read a question they brought for the quiz. This should be based upon the material from the last class. If you are going in the suggested order, these questions should all be from the module, Hybrid and Electric Cars. After each student recites her/his question, pause for the appropriate time for classmates to write answers. After all five questions have been completed, then ask five different students how they answered. When you and the class have reached consensus on what constitutes a correct answer, have the students mark their quizzes. The question-asking and the quiz- grading times offer opportunities for mini-lectures to clarify a point and for focused discussion on the topic. I suggest having the students write their answers on the opposite side of the paper where they wrote their quiz and discussion questions. That way you will have just one piece of paper with a grade on it from each student. Remember that you are the one in control of the questions. If a student asks a poor question, you might ask them to offer an alternative question, or you may decide ad hoc to modify the question so it is better.

Here are examples of ways to handle poor questions. Ashley asks, "What year was the first electric car produced in the United States?" You might say, "OK Ashley, it is interesting to have that fact in mind, but can you build a better question that puts that time frame in context?" If Ashley succeeds in improving the question, provide praise and go forward. If Ashley cannot find her way to a better question, you could then say, "How about asking what three different ways that automobiles were powered in 1900?" Or, "The electric automobile preceded the gasoline powered car, but by the 1920s gasoline all but replaced electricity as the source of power. What are three reasons that gasoline engines won the market?" Sometimes students will come up with seemingly bizarre questions. Hesitate before rejecting those offerings, as it may be interesting to see where the classmates go with their answers. Warning: just because a student offers a question, it does not mean he or she knows the correct response! How to deal with student answers? Often the student asked to provide an answer will have it wrong, at least in part. Rather than providing the answer yourself, first ask other students for their responses. If nobody got it right you might consider asking for a substitute question.

After completing the quiz process, I suggest moving on to the discussion phase. The students should all have brought four questions based upon the readings/videos assigned for the new material (that day's module — Energy from Biofuels). Use the instructor-regulated discussion pedagogy as explained in the course overview for conducting this exercise. The length of this phase will depend on how much time you need for the rest of that day's activities. If possible, each student should have had the opportunity to ask or answer a question during this exercise. As with the quizzes, rely first on other students to produce an acceptable answer, rather than simply jumping in yourself.

Scaffolding Learning — It is important to help students use what they learned in the preceding modules to build deeper understanding of this module. The student readings reference important concepts from the module on Electricity, Work, and Power. As the professor, you can help them make the connections. Near the end of the readings students are asked to think about the efficiency of using a field to produce a crop for biofuel production versus photovoltaic electricity production. The unit used for comparing biofuels and photovoltaics is the kilowatt, which they learned about in the first module. If taught in the suggested order, the module preceding this one is on Hybrid and Electric Cars. Point out that most of the interest in biofuels today stems from their use in transportation where vehicles like cars, trucks, ships, and aircraft must carry their fuel with them and cannot be tethered to the electrical grid. The opening quiz reinforces the scaffolding of learning. It forces the students to revisit the previous module twice, once during their studies when they review for the quiz and formulate the quiz questions, and again when they participate in the quiz process in class.

Metacognition — The flipped-classroom structure advocated for this course facilitates the development of metacognition by the students, directly involving them in the learning process. The use of student-generated questions for the quiz, discussion, and post-student presentation interactions is an important strategy in teaching the students about how they learn and understand the material. This is a big departure from the simple memorizing of terms and concepts that characterized much of their earlier education. You are teaching them a new way to approach their studies that if mastered, will inform their approach to learning in general. Another metacognitive strategy used in the course is requiring the students to apply basic science concepts to understand a technology, and then requiring them to think about the application of that technology in the real world. The portion of the exercise that has them create biofuels from sugar and vegetable manure moves along those lines. The Energy from Biofuels module also offers students the opportunity to use their senses of smell and taste to better understand the topic. They can smell and taste the ethanol they create with fermentation, and smell the sulfides produced as consequence of anaerobic digestion.

Systems Thinking — This module provides an opportunity to teach about negative and positive feedbacks. The fermentation of sugars to produce alcohol is done by yeast. The process stops at around 18% ethanol. Ethanol is a waste product that essentially poisons the yeast. Ask the students if this is a positive or negative feedback. Biofuel crops grow a bit faster at higher levels of atmospheric CO2. As more biofuels are burned, more CO2 enters the atmosphere, promoting more plant growth. This is an example of a positive feedback.

2. Student Presentation — Remember you must give the students at least one week to prepare their PowerPoints! We suggest following the quiz/discussion with a short (10- minute) student presentation on a topic in the module. It is good to choose questions for the student presentations that go beyond the provided readings. We like to require that all the students in the class write two questions to be asked about the presentation. The next portion of the class should be devoted to one or more student presentations. We suggest that if you have Blackboard or a similar teaching aid, you have your students post their PowerPoints in a discussion group so they may be reviewed by all the students. This activity involves peer instruction. Potential student presentation questions:

1. Producing ethanol for biofuels initially results in a solution that is about 15–20% alcohol dissolved in water. Explain how solar energy could be used in the process of distillation to isolate isolate and collect the alcohol so it could be used as a biofuel. Present case studies of such plants that might be in operation.

2. Present a case study where energy is being generated from garbage. Discuss the pros and cons.

3. Sugar and corn are widely used feedstocks for biofuel production. Present three others and explain the process used to create biofuels from each.

3. Hands-on activity — The remaining class time (assuming a three-hour lab setting) should be used for the hands-on laboratory work. Caution: these experiments will produce vessels under pressure. Plastic soda bottles will tend to crack around the neck in a harmless way to relieve the pressure. Do not make bombs!

Disclaimer: Make sure to follow your local institutional guidelines with regard to safety in setting up this sort of chemical reaction, which may include the requirement that the materials be stored in a fume hood. If you do not feel comfortable knowing you can conduct the experiment safely, you should not attempt it.

A hands-on experiment is described using simple materials to make reactors for alcohol and methane production. Handout for biofuels lab (Microsoft Word 2007 (.docx) 24kB Oct31 17) Materials needed are: twenty-four 1-liter soda bottles, sugar, flour (whole grain is best), tap water, yeast, rotting vegetable material, or manure from cows, sheep, or horses. A hygrometer for testing alcohol concentration will be needed to quantify production differences. I suggest using the soda bottles as reactor vessels. Cap the bottle tightly and incubate at room temperature. Students can test alcohol concentration with the hygrometer, smell it, and drink it (depends on campus policies).

For methane generation, the rotting veggies should be put in a blender to make for easy pouring through a funnel into the bottles. Handling the manure will require imagination, gloves, and a special attitude. Again, place compost or manure in tightly sealed containers. When the containers are opened in a few days the students will smell hydrogen sulfide. This stinks like rotten eggs. They are not smelling the methane, which is odorless.

Be sure to ask students about the nature of the gas that is pressurizing the bottles in each case. Help them understand the difference between alcohol fermentation and methanogenesis.

Teaching Notes and Tips

The hands-on aspect of this unit requires that students set up the incubation one day and then take observations and measurements some days later, as the biological processes will take time to do their work. Consider having the students be part of the experimental design. They may want to test incubation results using different levels of substrate (amounts of sugar for example), and different temperatures.


The assessment methods for this module can be found on the course assessment page. It is essentially what was provided in the web space for the course overview. Below are selected Pre/Post Test questions. One approach is to have the students take the pretest for all the modules at the beginning of the class, and then to administer it again at the end of the class to document advancement in learning.

Pre-Post Questions: Energy from Biofuels

References and Resources

The following references provide good background information for the various biofuels discussed in the unit.

Solid waste to biogas:

Landfill gas recovery:

Biofuel using cellulose as feedstock:

Switchgrass for feedstock:

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These materials are part of a collection of classroom-tested modules and courses developed by InTeGrate. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »