Electricity-generating wastewater plants edge closer

Microbial fuel cells (MFCs), which use the electrons produced when bacteria ‘eat’ organic waste in water to induce a current, are a hot research topic as sources of clean energy and cost-free wastewater treatment at the same time.

Scientists have used MFCs to turn wastewater into renewable electricity and clean water for years, but only on small scales with currents not exceeding a few miliwatts due to cost and efficiency limitations.

The holy grail of combining wastewater purification with renewable energy production may be in sight, however, as researchers at Penn State University edge closer to a practical-scale solution.

“So far we have been waiting on the technology to scale this up to a larger size, and we’ve recently filed a patent disclosure on this – we believe that we now know how to do this,” Professor Bruce Logan, who heads the Penn State group, told edie.

“We still don’t know how to do it economically but the basic way that we do it should be economic in the near future,” he said, adding that the timescale for the results will depend on the level of funding the project receives.

While wastewater used to fuel the MFC comes at a zero, or even negative cost, the cell itself is made with expensive materials – corrosion-resistant conductors chosen for maximum efficiency.

The electricity-producing bacteria also come free of charge as researchers have learnt to make electricity with micro-organisms naturally occurring in human, animal or industrial wastewater.

“We don’t have to go out and find some magical bacteria but basically we can take a reactor we put wastewater into it … and if we pump it continuously we can continuously generate power,” Professor Logan explained.

“And we can actually treat the wastewater. The bacteria by degrading that organic matter can remove that organic matter but also in our case generate electricity.

“It’s like in [the film] Matrix – old people got hooked up to electrodes or to tubes or whatever and they were generating electricity for the aliens,” he said – except, in this case, “we’re the aliens.”

While they may seem somewhat Sci-Fi, MFCs are increasingly being used in practical applications. Wastewater treatment is most likely to emerge as the first practical use – domestic wastewater from a town of 100,000 people can produce around 2,3MW while providing cost-free water treatment.

Scientists now aim to maximise efficiency and bring down the costs of MFCs. Once built, an MFC used for wastewater treatment requires minimal maintenance and has zero running costs, making the technology ideal for use in the developing world where it could provide for some of the 2bn people currently lacking access to adequate sanitation.

The technology also cuts the costs of wastewater treatement, which in a developed country like the US eats up 5% of total electricity produced. MFCs could easily sustain all domestic, industrial and animal wastewater treatment in teh US, Prof Logan said. This may provide the competitive advantage the technology needs to break through to the open market:

“If I’m build a reactor like this just for electricity generation I’ve got to compete with oil. That’s pretty tough,” he explained.

But if it is used as a wastewater treatment device “all I have to do is save money. That’s why we think the first implementation is wastewater treatment.

“Then as we mass produce the reactors, learn how to make them better, and the cost of the materials improves, we might look to renewable electricity development.”

For more information see the Penn State MCF research site.

Goska Romanowicz