Penn State discovers new electricity-generating desal process

Researchers from Pennsylvania State University and China have discovered a new desalination process that has a triple cleantech benefit. The process cleans wastewater, generates electricity and can remove 90 percent of salt from brackish water or seawater.

The researchers are hoping to prove that desalination is possible without the large amounts of energy required by reverse osmosis or electrodialysis. The high energy and infrastructure cost of reverse osmosis has inhibited the adoption of desalination in the United States because municipalities have been able to easily and cheaply pump water in from surrounding rivers and regions (see Largest desalination plant in Western world gets go-ahead).

"It currently takes a lot of electricity to desalinate water,” said Penn State Professor Bruce Logan, in a news release. “Using the microbial desalination cells, we could actually desalinate water and produce electricity, while removing organic material from wastewater.”

The team modified a microbial fuel cell, which uses naturally-occurring bacteria to convert wastewater into clean water and electricity, to desalinate salty water.

Typical microbial fuel cells have two chambers, one containing wastewater or other nutrients and the other containing water, according to the news release. Bacteria in wastewater consume the organic material, producing electricity.

The researchers altered the cell, adding a third chamber between the two existing chambers and placing certain ion-specific membranes—membranes that allow positive or negative ions through, but not both—between the central chamber and the positive and negative electrodes.

The study intended to show that bacteria could produce sufficient current to do this, but it ended up taking 200 milliliters of an artificial wastewater to desalinate 3 milliliters of salty water. The process, while not yet optimized, serves as proof of concept, according to Logan.

In addition to Logan, researchers included Xiaoxin Cao, Xia Huang, Peng Lian, Kang Xiao, Yinjun Zhou and Xiaoyuan Zhang from Tsinghua University in Beijing. King Abdullah University of Science and Technology of Saudi Arabia and Ministry of Science and Technology in China also supported the work.

Earlier this year, researchers at Yale University spinout Oasys said they developed a low-cost, low-energy desalination and purification technology for seawater, wastewater and industrial waste streams. The process, called engineered osmosis, reduces the energy needed to purify water to one-tenth of what's required by current desalination systems, according to Oasys (see Oasys develops energy-efficient osmosis for desalination).

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