InTeGrate Modules and Courses >Renewable Energy and Environmental Sustainability > 11. Composting Toilets
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11. Composting Toilets

Maurice Crawford1 and Ben Cuker2

1Department of Natural Sciences, University of Maryland Eastern Shore

2Department of Marine and Environmental Sciences, Hampton University

Summary

Toilet use accounts for the largest use of water in single family homes. In 2016, the average US household toilet accounted for a quarter of a home's total indoor water. Compost toilets are one method that may be used to reduce water use and save energy. In this module, students will gain an understanding of flush toilets, composting toilets, and septic and wastewater treatment.

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Learning Goals

Students will be able to:

  1. Describe how a composting toilet functions in comparison to a flush toilet.
  2. Describe how a septic system functions.
  3. Evaluate water use differences between composting and flush toilets.

Context for Use

This module is for use in an undergraduate laboratory class with twenty to thirty students enrolled. It was developed for undergraduate non-science college majors who were enrolled in a general education science course at a four-year teaching college. The module may be used for science majors. The module can be completed in 1.5 to 2.0 hours.

This module was developed as part of a larger course and is the last module in the course. At this point, the students will have a good grasp of various conservation issues. Nonetheless, the module can be used independently in a different course (e.g., an environmental science lab).

Description and Teaching Materials

Link to student materials

To provide the students with hands-on composting experience, a worm bin ecosystem (i.e., vermicomposting) can be established. You will need to make it at the start of the semester. You can either make it yourself or have the students make one.

To make a worm bin:

  1. Purchase a plastic container with opaque sides to keep the bin dark; it should be about 10 gallons in volume. The one I used measured 9 inches tall, 15 inches across and about 11 1/2 inches deep.
  2. Drill quarter-inch holes in the lid and along the top edge of the bin, which will allow air in. I did not drill holes in the bottom of the container, but I also had to make sure the bin did not get too moist at the bottom or the worms would not be happy.
  3. I filled the bin about halfway up using material made from coconut husks. Following the instructions that came with the coconut husk material, I added water to get it moist. The coconut husks will quickly expand once they are moistened.
  4. I then mixed in about 500 red worms to the bin and let them sit there a day or two before I fed them.
  5. I fed the worms mostly banana peels, lettuce, and tea bags. As with any compost pile, do not add meat or dairy leftovers to the worm bin.
  6. Place the bin in the corner of a room away from the windows; the worms prefer temperatures between 12 to 25 degrees C. I usually fed them about a half cup of material, but make sure the previous material is well decomposed.
  7. When the bin's contents start looking very dark, harvest the worms by dumping the contents of the bin on a plastic sheet. Divide it up into cone-shaped piles about 6 inches in diameter. The worms avoid light, so by removing the top and the sides of the cone, you can get your compost. Once you are done, place the worms back in the bin with fresh bedding and food.

Structuring Class Time

Quiz & Discussion. This module is the last in the course and follows the module on Energy from Biofuels. Begin the class with a quiz from the prior week's module. Have students come to class with quiz questions, and select five students to read their questions aloud. Students may try to slide by on this by asking more "what is"-type questions than higher-order thinking questions. Here you will need to interject and encourage the students to think more analytically. After each student recites her/his question, pause for the appropriate time for their classmates to write answers. After all five questions have been completed, ask five different students how they answered the questions. This format allows focused discussion on the topic. Students have an opportunity to work through their understanding of the material. Also, the teacher gets feedback on the effectiveness of teaching materials and teacher delivery—what is clear and what is still muddy. Use the instructor-regulated discussion pedagogy as explained in the course overview for developing discussions of the current module.

Scaffolding Learning

It is important to help the students use what they learned in the earlier modules to gain a deeper understanding of this module. As the professor, you can help them apply what they have learned from previous modules, especially from the first module and the module on Energy from Biofuels. The opening quiz reinforces the scaffolding of learning and forces 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 class discussions.

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 quiz and discussion helps students become aware of 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. Having students think of questions for quiz and discussion will inform their approach to learning in general. Another strategy used in the course is requiring the students to apply basic science concepts to understanding a technology, and then requiring them to think about the application of that technology in the real world. In this particular module the students can research composting and sewage treatment at their college.

Systems - Thinking

A major theme of this course is that students see the various technologies in the context of the global system. This module on Composting Toilets provides an opportunity for the students to think about the effects of reducing water use through composting toilets but also to consider the conservation of matter and how matter is recycled. Because we can never create or destroy atoms, everything we think we throw away remains with us in one form or another. This includes the wastes generated by our bodies. These wastes are then recycled by biogeochemical processes.

Student Presentation. Each class should have one or two PowerPoint presentations by students, given either during the current module or at the beginning of the next module. This activity involves peer instruction.

  1. Present a case study where composting toilets have been used to improve sanitation in a developing nation.
  2. Present a case study where composting toilets have replaced or been used instead of flush toilets in a developed nation.
  3. Explain how composting toilets could be integrated into an agroecosystem.

Hands-on laboratory work. In this module, students will learn more about composting and the recycling of materials through use of a worm bin where students can monitor the environmental conditions of the compost bin (e.g. using a soil testing kit), the weight of the compost added, and the weight of the worms.

Please see the course overview to see how we suggest that you structure the class.

Teaching Notes and Tips

This module was used in an environmental science class with mostly non-science majors.

To start the module, have students read the papers by Pappas on why the world has a poop problem and DeOreo, et al. (2016), Residential End Uses of Water. This is a good introduction to the issues we have regarding human waste and how we use water. This can lead to discussions on sanitation and water conservation.

The students can start the class by discussing:

  • Where do they think the contents of the toilet that was flushed this morning went? What happens to the contents of a toilet in countries outside of the US?
  • The overall patterns of water use by fixture (see Figure 1 on p 5 of DeOreo, et al. (2016)) and why they think most of the water goes to toilet use.
  • How much water do we use each time we flush the toilet? Why do we flush perfectly good drinking water down the toilet? Is that a good use of resources? If every household on the planet had a flush toilet how much water would be needed?
  • What are some incentives that can be used to get people to conserve water? What are the reasons behind the reductions in water use between the 1999 and 2016 surveys?

The second paper I suggest they read is by Apul and Anand (2014), which provides an overview on composting toilets and is at a level that can be understood by most non-science majors. Overall it is a good paper but it barely mentions that too often thermophilic conditions are not reached in a composting toilet (see Hill et al (2013) and Tonner-Klank et al (2007)). The students can discuss:

  • The different types of composting toilets and under what conditions they may be used. Have them consider the goals of the organization installing the compost toilet, what is the organization trying to achieve?
  • The idea of composting human fecal matter is a difficult one because of the "yuck" factor. Consider having the students discuss this and what it would take for them to be comfortable with a composting toilet.
  • What incentives do students think could be used to encourage the use of compost toilets?

A third paper that may be assigned for reading is by Hill and Baldwin (2012) on the advantages of vermicomposting. This paper may be more of a challenge to read for non-science majors but makes important points regarding the advantages of vemicomposting and the limitations of composting toilet technology. The use of commercial compost toilets is fairly new in the US and the science suggests that some manufacturers are promising more than they actually deliver.

It is not expected that most institutions will have a composting toilet on campus, but they may be able to find one at nearby state or national park. Also, a tour of the local wastewater treatment plant would add value to the module. If that is not possible there is a link in the references below for a virtual tour of a wastewater treatment plant; others can be found on YouTube (e.g., City of Grand Island plant).

As an analog for a composting toilet, we use worm bins that compost food waste and transform it for use in gardens. The instructor will need to set up the worm bin at the start of the semester so that its ecosystem is fully developed.

Module Questions:

  1. If homes in your neighborhood were equipped with composting toilets, what would be the environmental benefits and disadvantages?
  2. What prevents the widespread adaptation of composting toilets in houses and other buildings?
  3. Suppose a city with a population of 100,000 decided it would be the first in the United States to convert to all composting toilets for houses, public buildings, businesses, etc. Detail the steps required to: obtain public acceptance, install, and maintain the composting toilets. Think through the entire process. Be sure to think about what new jobs this would create.

Assessment

Student assessment is based upon three different student activities: student-generated quizzes and discussion, student presentations, and module reports based upon laboratory and other work. In addition, there is a pre/post test that can provide further assessment. The assessment methods for this module can be found on the course assessment page.

Pre-post questions:

References and Resources

General:

Septic tanks:

Wastewater treatment:

Compost Toilets:

Worm bins:

Teaching Themes

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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 »