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• The Potential of MFCs

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Every week, crews from the nearby Anheuser-Busch brewery bring buckets filled with wastewater to Lars Angenent, assistant professor of chemical engineering at Washington University in St. Louis (WUSTL), in St. Louis, MO.

Oddly enough, Angenent welcomes these shipments.

It’s all part of a program testing how efficiently a 6-liter microbial fuel cell can turn Anheuser-Busch’s wastewater into usable energy. And this project, which is still in the testing stages at Angenent’s university lab, is not the only example of a brewery testing the energy production of microbial fuel cells. Australian beer marker, Foster’s Beer, is currently teaming up with a group of scientists at the University of Queensland, in Australia, to test the energy-producing power of a recently installed microbial fuel cell at a brewery near Brisbane, Australia.

It’s little surprise that both breweries would explore the potential of the microbial fuel cells. By running their wastewater through the cells on a large-scale basis, the breweries would not only generate energy—they would also treat this waste, turning the streams into clean water. Ultimately, a system like Angenent’s allows the breweries to increase water efficiency while reducing water intake and wastewater disposal costs.

For Angenent, it’s a technology definitely worth exploring. The Angenent Lab at WUSTL focuses its research on bioenergy and bioaerosols. In the area of bioenergy, the lab and its researchers focus on boosting the performance and stability of anaerobic digesters, novel microbial fuel cell configurations, and mixed fermentation.

As part of this research, the Angenent Lab has developed a long working relationship with Anheuser-Busch. The brewery is always looking to develop more efficient ways of both dealing with its wastewater and generating energy.

Anheuser-Busch already uses anaerobic digestion to turn some of its brewery wastewater into methane gas. But the brewery recognizes that running wastewater through microbial fuel cells—better known as MFCs—would bring even more benefits to the bottom line.

“The combination of removing organic material and making electricity at the same time is a powerful one,” says Angenent. “You are now doing two things at once. Right now Anheuser-Busch doesn’t make energy from its anaerobic digesters. The brewery instead burns methane in boilers directly. In this case, they’d not only treat their wastewater—they’d make electricity, too.”

Angenent and other engineers who’ve studied MFCs, hope the projects being tackled for Anheuser-Busch and Foster’s will encourage other manufacturers to turn to the fuel cells. MFCs can have a significant impact on the way wastewater is treated, these experts say, once scientists overcome the challenges of expanding the fuel cells so that they can be used economically on a larger scale.

The Yatala Experience
Jurg Keller, director of the Advanced Water Management Centre at the University of Queensland, in Australia, and his engineers have had to overcome the normal technical challenges that come with such a major scale-up of a relatively new technology.

But one of the biggest challenges of the MFC pilot has come from an unexpected source: one of Foster’s other major environmental programs now taking place at the plant.

To increase water efficiency at the brewery and reduce water intake and wastewater disposal costs, the Yatala plant, also in Queensland, initiated a complete wastewater treatment and water recycling program. The plant now operates a system that includes anaerobic digestion with energy recovery, aerobic biological polishing, floatation/filtration, microfiltration, and reverse osmosis (RO). All the plant’s water goes through these processes before flowing back into the brewery as process water. This water is not used for the brewing process. Instead, the brewery relies on direct potable water that is taken into the plant for brewing.

Because of this intense treatment and recycling program, water consumption at the Yatala plant is now averaging about 2.2 liters of water per liter of beer produced. The downside of this for Keller’s team is that the wastewater from the brewery now contains very low salinity, or conductivity, because of the use of RO-treated recycled water. This makes the conductivity in the pilot program’s reactors quite low, which can lower the electric performance of the MFC.

The engineers overcame some of the issues associated with this problem by mixing some of the RO concentrate back into the MFC’s inlet stream, which brings back the salt that is being removed by the recycling system.

The larger-scale pilot program—a step up from testing MFCs in smaller, controlled lab conditions—has helped Keller and his team members learn more about this emerging technology. And that, Keller says, will only help speed the emergence of MFCs as a go-to mainstream technology.

The engineers are already working on optimizing the design of the MFC reactors, thanks to information they’ve gleaned from the pilot project at Foster’s, according to Keller.

“We’re learning by the day, almost, from this project,” he says. “We have particularly realized that there are a number of issues that only show up at this larger scale that are not encountered in the small-scale laboratory reactors.

“This is critically important if we want to make an impact with this technology eventually,” adds Keller. “This is why we would be happy to work with others on this, as well, and encourage others to also take that scale-up challenge.”

If enough engineers take up this challenge, that may be enough to convince private and public agencies to invest more funding into developing MFC technology, says Keller.

“There needs to be a clear dedication from regulators, industry, and the general population to foster and support energy-efficient processes and renewable energy sources such as this one,” he says. “While these technologies might still be more expensive now, the fact that energy costs in the near future will increase substantially, if not dramatically, means that we have to start looking for alternatives now, as we cannot expect to have ‘cheap solutions’ ready when we run out of nonrenewable energy sources.”

Experimenting in St. Louis
Angenent and his team’s 6-liter bench-scale MFC in the Angenent’s lab at WUSTL was made possible thanks to a grant from the National Science Foundation. Angenent and his fellow researchers feed their MFC with wastewater from Anheuser-Busch on a weekly basis. The researchers keep the excess wastewater in refrigerators, so that they always have enough on hand to maintain a constant waste stream through the MFC.

For more than half a year, they have been recording how much organic material the MFC removes from the wastewater, running Biochemical Oxygen Demand/Chemical Oxygen Demand tests to determine the unit’s effectiveness as a wastewater treatment system.

Because the project is still young and the research team’s findings aren’t yet ready for publication, Angenent does not want to go into detail on the bench-scale model’s results. He says, though, that he is pleased so far with the unit’s ability to remove organic material from waste streams.

The program will continue for several more years, says Angenent. The plan is for researchers to study the current MFC for about one-and-a-half years, and then create two more prototypes—second- and third-generation models—in the years that follow.

Anheuser-Busch has supported the project from its inception, he adds. The brewer has long worked with researchers at WUSTL on similar projects. Anheuser-Busch, for instance, already works with anaerobic digestion, taking brewery wastewater and turning it into methane gas. Angenent’s university department wrote a paper on these efforts.  “The people at Anheuser-Busch are definitely interested in looking at MFCs for long-term use,” says Angenent. “That is definitely our goal, too. At this point, this technology is still in the lab phase.

“Hopefully,” he adds, “in about two years we can get it to a pilot plan. And then, depending on the issues we find, we can see how long it takes to get to a full-scale program.”

In the not-too-distant future, he says he can see a time when breweries, like the ones operated by Anheuser-Busch and other manufacturing plants, will rely on MFCs as a matter of course.

The major challenge remains the issue of scale.

“The MFCs work very well in very small systems,” says Angenent. “But how can we scale it to a larger system without going into cost overruns? We have to make these practical.

“We are working toward that day,” he adds. “We’re not there at this point, but we have good ideas. We haven’t seen anything yet that we can’t one day overcome. There are problems, but we are making progress on solving them.”

And Angenent and Keller aren’t the only engineers excited about the possibilities of MFCs. A growing number of researchers are pointing to the fuel cells as a potentially powerful alternative source of energy.

The fact that MFCs not only generate energy, but clean water at the same time, makes them an ultra-efficient technology and makes them an easier sell to manufacturers. “The source for this energy is free; we will always have wastewater,” says Haluk Beyenal, assistant professor at the school of chemical engineering and bioengineering at Washington State University, in Pullman, WA. “We’re still working at developing MFCs that can power large-scale devices. We have proof of concept; we can design a MFC that produces electricity.

“But we’re not ready yet to use this energy in the mainstream,” continues Beyenal. “We’re still at the research stage.”

Beyenal has been studying MFC technology since 2001. All MFCs need to truly take off, he says, is more time, research, and, of course, funding. “We have many research groups with small amounts of funding looking at MFC technology right now,” he says. “We need a bigger group of people with large amounts of funding, so that we can do more research.

“MFC technology is a multi-disciplinary research area,” continues Beyenal. “Chemical engineers, electrical engineers, and mechanical engineers can all work together on this technology. We have to put all of them together. We then will have a better chance of success.”

Putting MFCs to the Test in Australia
Keller is hoping that the pilot program his team is tackling at Foster’s Yatala plant will help prove that MFCs can transform wastewater into energy efficiently and economically on a large-scale basis. He and his team of engineers installed a pilot-scale MFC at the brewery in September 2007. Since then, they’ve been charting the cell’s ability to transform the plant’s waste stream into usable energy, while removing the organic content of the stream and leaving behind clean water.

The MFC at Foster’s has a volume of about 1 cubic meter, and consists of 12 modules with carbon fiber anodes and cathodes. In a second phase of the project, the team will add 12 new modules of varying designs.

Keller explains that he and his team plan to monitor the pilot MFC until at least the end of 2008. His hope is that when the program ends, manufacturers will have tangible proof that MFCs are a viable option for treating and converting wastewater.

If this happens, Keller says it can help speed the acceptance and desire for MFCs by manufacturers. “The inspiration for this project came from our side, since we’ve had a number of lab-scale MFCs going for quite some time now, as have many others around the world,” says Keller. “But we really wanted to test what could be done on a semi-technical scale.”

Keller approached Foster’s with the idea, and the brewery reacted positively. This is little surprise: The experiment fits in with Foster’s corporate strategy of reducing the energy consumption at its plants and reducing its greenhouse gas emissions.

“This technology is at a very early stage of adoption in the industry, but it is highly encouraging to see forward-looking companies like Foster’s supporting such new initiatives both in direct cash and by other means of support,” he acknowledges.

For Foster’s, the possibility of using MFCs in at least some of their plant operations makes sound fiscal sense. The company already uses a highly efficient energy recovery system that incorporates both anaerobic digestion and biogas. Keller says that this recovery system already saves Foster’s about $600,000 Australian in yearly natural gas costs.

This dollar amount of savings means that the MFC system that Keller and his team are testing will more than likely never replace Foster’s existing anaerobic and biogas systems. It wouldn’t make economic sense for the company to scrap a recovery system that is already working so well. But the MFC system may have other applications in smaller operations of the company, Keller says, perhaps in wineries and small boutique breweries.