A Less Wasteful Way to Deal with Wastewater

Published by MIT

An Israeli company aims to commercialize microbial fuel-cell technology.

Tuesday, July 5, 2011

By Matthew Kalman

An Israeli company called Emefcy has developed a process that promises to decrease the energy drain of wastewater treatment. This week, Energy Technology Ventures—a joint venture between GE, NRG Energy, and ConocoPhillips—invested in the company, marking the venture's first-ever investment in a non-U.S. company.

Conventional wastewater treatment consumes 2 percent of global power capacity, some 80,000 megawatts, at a cost of $40 billion per year.

Using conventional microbial fuel-cell technology and its own proprietary engineering, Emefcy harvests energy from wastewater, generating enough to power the entire treatment process. In the treatment of particularly carbon-rich industrial wastewater, the company says, the process produces excess electricity that can be fed back into the grid at a profit.

In microbial fuel cells, naturally occurring microorganisms oxidize wastewater. An anode and cathode, placed a critical distance apart in the water, create an electrical circuit from the electrons gained from this oxidation.

Ely Cohen, Emefcy's vice president of marketing, says the company's process reduces the total cost of wastewater treatment by 30 to 40 percent by eliminating spending on energy, and also reduces the amount of sludge that must be trucked away afterward by up to 80 percent.

Traditional wastewater treatment involves forcing air through the water to aerate it. This is also important to the activity of the microbial cells. Emefcy exposes more wastewater to air but without the energy-intensive process of pumping air through water. Instead, the wastewater flows through a "biogenic reactor" made of tubes 1.7 meters in diameter and four meters high. Inside the tubes, water and air flow alongside each other separated by a membrane.

"The reactor is split into two areas," says Emefcy CEO Eytan Levy. "In one area there is a lot of wastewater but there is no air. In the other area there is air but no wastewater. These two areas are separated by a membrane wall and both areas are connected to an electrically-conductive surface on which the bacteria grows."

The electrons produced by the bacteria flow towards the oxygen in the air through nanowires made of naturally-occurring hair-like projections found on the surface of the microbes. "Under these reactor conditions the bacteria develop the ability to convert these pili to become electrically conductive and it behaves just like a metallic wire," says Levy.

The electrodes used are made of a coated plastic, which makes them cheaper, and easier to maintain.

Each stack can process 10 cubic meters of wastewater a day, and has a planned lifespan of 15 years. Stacks can be added on a modular basis, avoiding the need for a large up-front investment in infrastructure. Emefcy hope to begin industrial production this month, with first sales targeted for early 2012.

Itamar Willner, a professor at the Institute of Chemistry at the Hebrew University, and author of a recent review of biofuel cell technology in the journal Fuel Cells, says using microbial fuel cells for the decontamination of wastewater remains "a challenge."

"There is a tremendous difference between a demo system and upscaling to thousands of tons of wastewater, and a difference between artificially contaminated water used for laboratory testing and the real world, where you have different waste and different materials," says Willner.

Lital Alfonta, an assistant professor in the Department of Biotechnology Engineering at Ben-Gurion University, who develops genetically engineered microbial fuel cells, says there has been growing excitement at international conferences over the progress made by Emefcy.

"They use very cheap materials that still give them the highest possible power output," says Alfonta. "They also immensely improved the approach by stacking their electrodes, giving a much higher surface area."

But Alfonta says that 80 percent of the energy generated by the microbes is lost in the process, because the electrons never reach the electrodes. She is researching whether the microbes can be genetically engineered to improve the efficiency of the electron transfer between the microorganism and the fuel cell's electrode.

For the moment, Emefcy will be content if its stacks prove to be energy-neutral, with a little surplus from the industrial wastewater treatment.

"If you're an organization that's looking for renewable energy, don't come to us," says Cohen. "Go to wind. Go to solar. If you have a wastewater problem, come to us and we'll find a way that is very cost-effective and to a certain extent it could even be an energy-positive solution."