Bacteria Desalinate Water, Generate Power

Aug. 25, 2009 -- Bacteria can be used to turn dirty salt water into electricity and drinkable water, according to new research from scientists at Penn State University and Tsinghua University.

The research presents a new spin on microbial fuel cells, which have been used in the past to produce electricity or store it as hydrogen or methane gas.

"The idea of a microbial fuel cell is based on taking organic waste and turning it into a source of energy," said Bruce Logan, a scientist at Penn State and co-author of a paper in the journal Environmental Science and Technology.

"In this newest discovery, we figured we would desalinate water by modifying the electricity generated by the bacteria."

The researchers start with a cup full of water from a pond or other natural source. Among the millions of microbes in the sample, some of the bacteria (scientists haven't identified the specific species) will naturally produce electrons and protons inside their cells and transport them outside themselves.

Other bacteria scavenge those free electrons and protons and use them as fuel to create hydrogen, methane or other chemicals, which can serve as energy sources.

Using only two thin pieces of plastic, the researchers have discovered the key to harnessing the power of these microbes. The membrane created by the Penn State scientists can draw away the electrons, ions or gases created by the microbes, towards an anode or a cathode, which are positively and negatively charged electrodes.

Anode, cathode and membranes are all encased within a clear plastic case about the size of a small tissue box. Add a cupful of pond water between the two membranes, and the bacteria start their jobs. The entire process leaves almost pure -- about 90 percent -- water behind.

The exact purity of the water can be changed depending on the needs of the scientists or the desalination industry, if the process is scaled up commercially. These microbial fuel cells can create pure, drinkable water. It may also remove most of the salt from water to make conventional purification methods cheaper by reducing the amount of electricity necessary.

Whatever the resulting salinity, "this is the first time that any one has used a microbial fuel cell for desalination," said Hong Liu, a scientist at Oregon State University also developing microbial fuel cells.

"(Using this approach) you basically need zero power input, and it could even produce energy if you use organic material as the input," said Liu.

For now, microbial fuel cells, whether they desalinate water, generate electricity or create hydrogen, methane or other gases, are limited to small-scale laboratory devices. That will change next month, however, when Logan and his colleagues install a larger microbial fuel cell to turn waste water from a Napa Valley winery into hydrogen gas.

"This project is just a demonstration for now," said Logan. "But ultimately (the winery) could use the power generated by the microbial fuel cell to power cars, forklifts or other vehicles."