Since American society uses enormous amounts of energy, most which comes from fossil fuels like dirty coal or imported oil, how much energy are we flushing down the toilet? It may seem like I’m asking how much energy we waste as opposed to getting benefit from. That’s a good question, but it turns out there is ample energy in sewage that could be used to reduce our reliance on fossil fuels.
In 2004, an article appeared touting a new technology called a microbial fuel cell. It seemed a way to return to a century-old practice of collecting gas from rotting sewage to light street lamps. These cells generate electricity from waste water, taking advantage of chemical processes driven by bacteria as they feast on the sewage. In other words, these microbes, which purify water anyway, can give us electricity in the process using these fuel cells.
Before the development of the development of the microbial fuel cell, it was possible to extract methane in sewage or garbage using an anaerobic digester. That methane could be burned to operate a turbine like natural gas or any other fossil fuel.
The microbial fuel cell has at least one important advantage over anaerobic digestion: it makes electricity directly without having to extract or burn methane. Therefore, biological wastewater treatment can probably extract more energy from a particular amount of sewage and can certainly avoid the air pollution that burning methane produces.
At about the same time, scientists tested raw sewage from the Toronto wastewater treatment plant and calculated that the wastewater generated worldwide in 2004 contained a continuous supply of energy roughly equivalent to the annual output of 70 to 140 large nuclear plants. A more recent study concluded that the methods used in the 2004 study seriously underestimated the amount of energy available from wastewater. The newer study also investigated industrial wastewater and found that it has even more energy potential than municipal wastewater.
Currently, sewage treatment involves, among other things, allowing wastewater to stand in tanks and allow solids to settle to the bottom. The plant must deal with resulting sludge. They can compost it. They can burn it. They can spread it out on large tracts of land.
Whatever they do, it’s expensive and has some kind of environmental impact. Running wastewater through microbial fuel cells would produce energy while consuming matter that would otherwise become sludge.
We’ll never stop flushing sewage down the toilet, but I hope the potential of biological wastewater treatment and microbial fuel cells becomes more widely known. So far, no system large enough for an entire wastewater treatment plant has yet been developed. It will be interesting to see if the process and technology is indeed scalable.
If so, a costly municipal service can become a profit center for the local government. In the process, it will give the nation yet another way reduce its need for fossil fuels.