A team at Stanford University is working on new system that could eventually power wastewater treatment plants via the energy generated by microbes breaking down organics.
October 22, 2013—Researchers at Stanford University have developed a microbial battery system that harnesses the electrons created by microorganisms digesting organic material in wastewater to create electricity. The team is optimistic that this development will eventually lead to wastewater treatment plants that are energy self-sufficient.
Approximately three percent of all electricity consumed in developed countries goes to the treatment of wastewater. However, the organic material in the wastewater is sufficient to generate three to four times that amount of energy, according to the results of this research, which were published recently in theProceedings of the National Academy of Sciences.
The paper, “Microbial Battery for Efficient Energy Recovery,” was written by Yi Cui, Ph.D., an associate professor in the Department of Materials Science and Engineering at Stanford. The research was designed by Cui, Craig Criddle, Ph.D., a professor in the Department of Civil and Environmental Engineering, and Xing Xie, an interdisciplinary fellow.
Their work builds on the concept of microbial fuel cells, which have been under development for decades but are limited by the energy losses inherent in the biological and chemical processes that are used in such cells. Microbial fuel cells also tend to generate methane gas, a health hazard. But Cui says that the microbial battery has vastly superior efficiency. “Using this microbial battery to replace microbial fuel cells, we can increase energy efficiency by 5 to 10 times,” Cui says. “The efficiency can go up in the range of 30 percent.”
To make the battery, researchers introduced a microbial anode and a silver oxide/silver cathode into a container of wastewater, the two connected by an external circuit. Microbes attached to the anode oxidize the organic material in the wastewater, releasing electrons that pass through a circuit to the cathode. The cathode is then removed and oxidized to retrieve the energy and recharge the system.
“These microbes consume these organic carbon/hydrogen bonds and generate electrons,” Cui says. “They can use these electrons for synthesizing more organic molecules. So they can use this to grow or generate more microbes. Or—if you take out these electrons before they can use them—then you can let the electricity go out to do useful work.”
That work could include powering wastewater treatment plants, Cui says.
“In the wastewater treatment plant you need to consume the organics, anyway,” Cui says. “That’s a required step. Now this required step can turn into an energy-generation process to power the wastewater treatment plant. So that’s a good deal. It’s going to be self-sustained.”
But before the technology can be tested in the field, the research team needs to answer a challenge. Creating a large-scale version of the microbial battery they have tested would require a prohibitively expensive amount of silver oxide/silver.
“Using silver is expensive. For the large-scale deployment, that will be hard. In our labs, we are now developing a new electrode material to replace silver/silver oxide. We have some really promising candidates right now,” Cui says. Early indications are they have found a replacement that “costs virtually nothing.”
If further testing bears out the suitability of this replacement material, Cui says the next step is a pilot scale demonstration of the battery at a wastewater treatment plant. This could happen within two years if things go well.
“We would like to do our own field study and see what potential issues this might have,” Cui says. “After getting some of that understanding, we are going to move forward.”
Although their research has focused on wastewater because it is a plentiful source of organic fuel for a microbial battery, Cui says that deep-water environments—oceans and lakes—also have vast stores of organic material. Additionally, such solid wastes as the by-products from cheese and corn production could potentially be suspended in liquids as another source of energy for the microbial batteries.
