By Austin Lai, Yuhgene Liu and Miranda Mitchell
Any farmer, gardener or sustainability-minded citizen who composts organic matter might notice that their compost pile generates a substantial amount of heat over the course of a few weeks to months. However, the concept of capitalizing on the thermal energy generated from these compost piles to produce electricity is novel and has only recently become a topic of investigation on college campuses. Few college campuses provide access to small-scale, interactive compost systems for educational purposes, which substantially increase student awareness and knowledge about composting as a waste management practice through hands-on composting demonstrations.
In 2017, three Emory students, Austin Lai (20C), Yuhgene Liu (18C), and Miranda Mitchell (16OX, 18C, 19RSPH), set out to address these educational and scientific gaps by researching compost-to-electricity potential on Emory’s campus. The Biology, Chemistry and Environmental Science majors met through Emory’s first student-run research fellowship, the Translational Research and Innovation (TRAIN) Fellowship, housed in the University Provost’s Office, with faculty advisors from the Department of Chemistry, the Department of Biology and the Goizueta School of Business.
Due to its interdisciplinary nature, the TRAIN Fellowship is unique in its ability to foster collaborations across Emory’s various undergraduate programs and departments. The program is aimed at producing projects focused on translating scientific research into industry applications. Through financial support from the Office of Sustainability’s General Sustainability and Social Justice Incentives Fund, Austin, Yuhgene and Miranda were able to develop a compost-to-electricity system prototype using a residential-grade, compost tumbler mounted with a thermoelectric generator.
The system uses a wheel-shaped compost bin, to allow for easy homogenization of the compost material through rotating the composter, as well as a copper pipe to be heated up one side, by the heat generated from the compost, and cooled on the other side with a tray of ice-water.
The concept is that the copper (or other metal) atoms at the heated end (facing the compost) of the copper pipe semiconductor would have more energy than the electrons at the colder end (in the ice tray). This gradient in energy levels makes it favorable for electrons to move towards the colder end, thereby accumulating a negative charge where the electrons build up.
In effect, the heated end would experience a loss of electrons and become positively charged. Under these charge-separating conditions, the system would produce a voltage much like a battery. To maintain the flow of electrons, the temperature gradient must be maintained. A steady heat supply from the compost is enough to initialize electron movement. The other end of the metal is doused in the water tray; the high specific heat of water would act to hinder temperature equalization by creating a lower limit heat sink. Semiconductor plates were also glued to cover the base of the bread tin with thermally conductive glue. These plates were then connected to a voltage regulator and a USB port.
The students were able to maintain an average of 5 volts of electricity, with a maximum of 8 volts of electric charge from their first experimental trial with this prototype. With 5 volts, you can charge an iPhone overtime, as well as other electronics such as Bluetooth headphones. The student researchers are excited to continue their project and implement it at Kaldi’s at the Depot Education Garden in the Spring. They hope to create a functional demonstration for other students, sustainability classes and clubs interested in learning more.
If you would like to lend a hand and get involved in this project, please email Miranda Mitchell at firstname.lastname@example.org the subject line: “Compost-To-Electricity Spring 2019.”