[Greenbuilding] ... device to purify human waste, make compost and generate electricity

[sanjay jain]

http://www.umass.edu/loop/content/engineer-builds-low-cost-device-purify-human-waste-make-compost-and-generate-electricity

Caitlyn Shea Butler, assistant professor in Civil and Environmental Engineering, 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 believes her inexpensive green latrine can be deployed 
throughout places such as rural Africa, transforming the way human waste is treated in areas where sanitation facilities are poor or 
nonexistent. At the same time, the device can play a key role in 
preventing waterborne diseases, including diarrhea. 
 
“You get a lot out of this system,” says 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.”
 
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.
 
She says the pilot model can immediately address two issues faced 
by the village. First, 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 
prevents that from happening.
 
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 fuel cell 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.
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