Last month, a Boston-based outfit called Cambrian Innovation began field testing a sewage treatment system that not only treats the wastewater, but produces modest amounts of electricity as well.
The system is based on what’s called a microbial fuel cell (MFC) and it’s a new take on an old idea.
Cambrian hopes that its system, called BioVolt, will be able, in one day, to convert 2,250 litres of sewage into enough clean water for a dozen or so people.
This opens the door for two things: small, distributed treatment systems and significant energy savings.
If it works, it will be a big deal.
Conventional treatment plants use a lot of energy, typically consuming 1.5 kilowatt-hours for every kilogram of pollutants removed. In the United States, treatment plants presently consume about three per cent of the country’s total energy demand.
But if MFCs can be made to work in field tests, it would open the way for people to recycle their own wastewater. That could become as commonplace, enthusiasts say, as putting a solar array on a roof.
The concept of MFCs has been around for a long time. They first show up in scientific literature in 1911 and again in 1931. But researchers appeared to lose interest because no one was able to scale the devices up successfully outside the laboratory.
As a result, by the late 1970s no one had a good understanding of how the cells worked. Some development work was done with the idea of using MFCs to generate electricity for developing countries. That was in the early 1980s, but nothing much came of it.
Then, early in 2007, the University of Queensland, in Australia, joined with Foster’s Brewing to develop and build a small prototype, which converted brewery wastewater into carbon dioxide, clean water and electricity.
What are these MFCs and what can they do? An MFC is a device that converts chemical energy to electrical energy through the action of micro-organisms working as bioanodes and/or biocathodes, usually separated by a membrane. The charge is created by ions moving through the membrane.
The key to all this is that the micro-organisms can be any number of bacteria.
Existing treatment plants use bacteria to metabolize the organic material in wastewater. At the end of the process, the bacteria can make up a third of the leftovers that must be disposed of. Before disposal, though — often in a landfill — this sludge, or "microbe cake," has to be sterilized by heating, then treated with chemicals. That process uses a lot of energy.
MFCs, however, use biochemistry to metabolize the contaminants.
BioVolt uses a couple of strains of microbes in a proprietary mix. As the bacteria in the mix respire, they liberate some electrons, which turns the set-up into a battery. There is an added benefit: the bacterial growth is slowed so that by the end of the process you have electricity but no sludge.
There’s a number of teams working on their own versions of MFCs. One is presently being tested by processing about 630 litres of hog waste per day. And a larger pilot system is soon to be commissioned in Tijuana, Mexico, just across the border from San Diego, Calif.
Orianna Bretschger, who heads that team, says she believes it’s on track for commercialization in the next three to five years.
Success for the MFCs seems to be just around the corner, so it’s not surprising that people are looking at them for uses other than wastewater treatment.
One of the more interesting projects in the pipeline is using MFCs in "smart" bricks that might be used for a lot more than just building walls.
I’ll return to this discussion in next week’s column.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@dailycommercialnews.com.
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