Fuel cell/EDR hybrid powers its own wastewater treatment

A hybrid device using electrodialysis reversal (EDR) developed at Pennsylvania State University could be used to treat wastewater using the wastewater itself as fuel.

In a paper Energy Capture from Thermolytic Solutions in Microbial Reverse-Electrodialysis Cells, authors Roland D Cusick, Younggy Kim and Bruce E Logan, from the Department of Civil & Environmental Engineering, report in Science journal that the use of microbial power cells with EDR can clean water and use its own electrical power to be self-sustaining.

EDR allows for capture of energy from salinity gradients between salt and fresh waters, but potential applications are currently limited to coastal areas and by the need for a large number of membrane pairs. Using salt solutions that could be continuously regenerated using waste heat (≥40°C) with conventional technologies would allow much wider application of salinity-gradient power production.

“We used EDR ion-exchange membrane stacks in microbial EDR cells to efficiently capture salinity gradient energy from ammonium bicarbonate salt solutions,” the researchers explain. “The maximum power density using acetate reached 5.6 W/m²-cathode surface area, which was five times that produced without the dialysis stack, and 3.0 ±0.05 W/m² with domestic wastewater.”

IEEE Spectrum, reporting the paper, says that use of ammonium bicarbonate salt instead of saltwater was critical to the hybrid’s success. The salt can be separated from the solution by heating it to a little more than 40°C, allowing it to be recycled using waste heat from industrial processes.

This use was developed by Yale University professor Menachem Elimelech for use in forward-osmosis desalination and pressure-retarded osmosis. According to Elimelech, scaling up Penn State’s hybrid device will require overcoming technical issues associated with both ERD and microbial fuel cells.

“Scaling is always an issue,” Elimelech told IEEE Spectrum.