In Fuel Cells, Some Hope for Urban Sanitation

SOPHIA LI

As more and more people around the world flock to cities, urban areas in developing nations are struggling to keep up with the human influx and the waste that people produce. In 2010 roughly 2.5 billion people lacked basic sanitation, according to the World Health Organization.

Energy Environ. Sci., 2012Microbes on the anodes (shown in green) break down the organic material in wastewater, producing carbon dioxide, protons and electrons.

A team of engineers has developed a tool that may prove to be a solution: fuel cells that harness a mix of microbes to clean wastewater while producing their own power. The technology is young, but it shows promise, said Hong Liu, an associate professor of biological and ecological engineering at Oregon State University who heads the team. The researchers’ fuel cells generate more power from waste than other, similar fuel cells, according to a recent article in the journal Energy and Environmental Science. If scaled up, the technology would even outpace the digesters that many treatment plants currently use to extract energy from wastewater, Dr. Liu said.

Wastewater itself contains more than nine times the energy that typical treatment plants currently use to clean it. The team aims to capture just enough to make the treatment process self-sustaining, she said.

So far, the researchers have built a modest contraption that they say has the potential to do just that. The fuel cell resembles a book, Dr. Liu said — quite a slim one, at half a centimeter thick. The current version holds roughly one cup of water.

The fuel cell consists of two electrodes: a platinum-coated cathode and an anode covered with several kinds of bacteria, Dr. Liu said. The microbes on the anode break down the organic material in wastewater, producing carbon dioxide, protons and electrons.

The electrons then flow through a wire to the fuel cell’s cathode, generating an electric current. There, at the cathode, the platinum coating jump-starts a chemical reaction that combines the electrons, the protons and oxygen in the air to make water. At the end of the process, the fuel cell has yielded water and carbon dioxide, ridding wastewater of some of its unwanted contents and generating electricity along the way.

The researchers hope to build a bigger system and reduce the cost of manufacturing the fuel cells, Dr. Liu said. She and her colleagues envision stacking the fuel cells together to make a unit of about 20 liters (about five gallons), large enough for them to test in areas that lack a central system for collecting sewage and treating wastewater. So far, groups in India, Malaysia and the Netherlands have contacted her about potential partnerships, she said.

“I don’t mind going anywhere, as long as I can help them make the treatment more efficient,” Dr. Liu said.

The group is focusing on building a treatment system that could be used in developing countries to clean relatively small amounts of wastewater — say, from a single factory or a group of homes, she said. If engineers improve the fuel cells to the point that they can produce electricity in addition to powering themselves, she believes that such a system could replace the digesters that cities’ treatment plants currently use.

“If the energy gain is really high, we can challenge the traditional way we treat wastewater,” Dr. Liu said.