Dr. Caitlyn Butler of the Civil and Environmental Engineering Department journeyed to Ghana in late May to install a pilot version of her new “green latrine,” which is the first privy anywhere capable of purifying human waste, turning it into healthy compost for farming, and generating electricity. Her multipurpose invention is called a “Microbial Fuel Cell Larine.” Butler envisions that her inexpensive green latrine can be deployed throughout rural Africa.
If so, it will transform the way human waste is treated in areas where sanitation facilities are in poor working order or nonexistent, and helping to prevent some of Africa’s deadliest waterborne diseases, including diarrhea.
“This would be a centralized resource for the whole community,” explains Butler. “Its purpose is a combination of removing the harmful components of human waste and generating electricity for the villagers.”
In Ghana, Butler worked with her two graduate students, Cynthia Castro and Joe Goodwill, collaborators Mark Henderson and Brad Rogers from Arizona State University, and many residents of the small farming village of Agona Nyakrom to install the first working model of her Microbial Fuel Cell Larine in the field. Together they proved that it takes a whole village to raise a good latrine, and in turn the whole village will benefit.
“You get a lot or resources out of this system,” notes Butler. “The latrine produces electricity. It makes compost. And you protect the ground water source. So you get a lot back for a small investment.”
In the long term, when her latrine is deployed more widely, it will address two persistent problems throughout the developing world.
The first problem is that, when human waste leaches into underground water, deadly pathogens that cause waterborne diseases such as diarrhea spread throughout the aquifer. High nitrogen concentrations contained in the waste can also damage healthy water systems as well as cause nitrate-poisoning in infants and the elderly. Butler’s microbial latrine would neutralize all those issues.
The second problem is that many rural areas of Africa have limited electricity, and Butler’s fuel cell would generate enough electricity to power a light within the latrine, thus allowing villagers access throughout the night.
Since Butler’s latrine is in essence a battery, it has an anode and a cathode, like all batteries. After solid wastes are first filtered in a composting chamber, dissolved waste organic matter is oxidized in an anode chamber. The oxidation of organic matter is facilitated by bacteria that reside on the anode surface and use the anode as an electron acceptor to complete their metabolic reaction. Electrons released in this biological process are conveyed through a load-bearing circuit, producing electricity, to the cathode compartment. There a different community of bacteria uses the cathode as an electron donor, capturing the energy from the electrons, to reduce harmful nitrates in the waste stream.
The primary nitrogen compound found in human waste is ammonium, which can be broken down by the oxidation of ammonium, or nitrification. In Butler’s latrine, nitrification is facilitated by bacteria living in an intermediate chamber that separates the anode and cathode chambers. The result is effluent water that is quite low in organic matter and nutrients, minimizing pathogen persistence in the environment.
As Butler has written about her research specialty, “My research objectives focus on developing energy-efficient treatment strategies for both water and wastewater treatment. I examine bioelectrochemcial systems where biofilms, capable of using either an anode as an electron acceptor or cathode as an electron donor, remediate environmental pollutants, and concurrently produce electricity.”
Butler’s project and her Ghana trip were funded by a $100,000 grant from the Grand Challenges Exploration program supported by the Bill & Linda Gates Foundation in this collaborative project between engineers from UMass Amherst and Arizona State. (July 2012)