Engineer builds low-cost device to purify human waste, make compost and generate electricity

August 8th, 2012 in Technology / Energy & Green Tech

(Phys.org) -- Caitlyn Shea Butler, a civil engineering professor at the University of Massachusetts Amherst, has designed and is now field-testing a new “green latrine” that purifies human waste, turning it into compost for farming and generating electricity.Her multipurpose invention is called a “Microbial Fuel Cell Latrine.”



Butler traveled to Ghana in May to install a pilot version of her device. Working with graduate students Cynthia Castro and Joe Goodwill, collaborators Mark Henderson and Brad Rogers from Arizona State University, and residents of thesmall village of Agona Nyakrom, they installed the first working model of her Microbial Fuel Cell Latrine.


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.

“This is a centralized resource that will benefit the whole community,” says Butler.

Butler’s latrine works like a battery. It has an anode and a cathode and is similar to a where a fuel, for example hydrogen, is oxidized at the anode, and an oxidant, such as oxygen, is reduced at the cathode. In this case, the organic waste matter is the fuel and nitrate is the oxidant. 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 assisted by bacteria on the anode surface and uses 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 oxidation, or nitrification. In Butler’s latrine, nitrification takes place thanks to 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.

Butler says, “My research objectives focus on developing energy-efficient treatment strategies for both water and wastewater treatment. I examine bioelectrochemical 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 & Melinda Gates Foundation in this collaborative project between engineers from UMass Amherst and Arizona State.

Provided by University of Massachusetts Amherst

"Engineer builds low-cost device to purify human waste, make compost and generate electricity." August 8th, 2012. http://phys.org/news/2012-08-low-cost-device-purify-human-compost.html