Environmental Engineering Professor Caitlyn Butler from the University of Massachusetts Amherst has designed and developed a green pit latrine that can purify domestic waste for a small village of subsistence farmers in Africa, while also churning it into healthy compost for their fields, and turning it into enough carbon-neutral electricity to provide some lighting in the village. The multipurpose new invention is called a Microbial Fuel Cell Pit Latrine. Dr. Butler will travel to Ghana this May to install a pilot latrine in one village. But her long-term goal is the deployment of her inexpensive privies throughout the developing world.
“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 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 such as diarrhea and typhoid 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 latrine would generate enough electricity to supplement the supply in a village. Using this technology in place of a conventional pit latrine in a village of 100 people could power up to ten 45-Watt incandescent lights for over five hours every evening, or even longer if energy-efficient light bulbs are used.
Unlike most brand new technologies, Butler’s green latrine will go to work almost immediately. This May Butler, UMass graduate students Cynthia Castro and Joe Goodwill, and co-PIs Mark Henderson and Brad Rogers from an Arizona State University organization called GlobalResolve will visit a small rural community in Ghana and build their first Microbial Fuel Cell Pit Latrine in the field. GlobalResolve works with a range of partners to develop sustainable technologies and programs in the areas of energy, clean water, and local economic development for rural communities in the developing world.
“We will be installing a pilot latrine in that one village, but there is the potential to continue expanding their deployment throughout the surrounding region,” says Butler. “Our goal is that our technology can be adapted to existing latrines, which makes the cost very inexpensive. In addition, none of the materials are expensive.”
Butler’s research project, entitled “Bioelectricty Generation from Domestic Waste: The Microbial Fuel Cell Pit Latrine,” is being funded by a one-year, $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.
The simple elegance of Butler’s latrine is that it’s a waste-treatment device that also transforms biochemical energy into sustainable electricity.
Since Butler’s pit 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.
“You get a lot or resources out of this system,” notes Butler. “You get electricity out of it. You get compost. And you get a healthy ground water source. So you get a lot back for a small investment.” (February 2012)
