An estimated 2% of our global power capacity is used to treat wastewater, at a cost of approximately $40 billion per year. But a new wastewater treatment process that uses microbial fuel-cell technology can produce enough energy to run the entire treatment process, cutting costs by 30 to 40%, as well as reducing the amount of leftover sludge by as much as 80%.
An Israeli company, Emefcy, developed the new process, which uses conventional microbial fuel-cell technology, combined with their own proprietary methods, and built an Electrogenic Bioreactor that can use wastewater as its fuel. In conventional wastewater treatment, air is forced through the water to aerate it and help bacteria break down organic matter, and with Emefcy's process, the same idea is used, but without having to power pumps for aeration. Their system pushes the wastewater through a "biogenic reactor", where air and water are flowing side-by-side, separated by membrane wall but both connected to an electrically-conductive surface where the bacteria grows.
The bacteria produces electrons that flow toward the oxygen in the air through their own naturally-occurring pili, or hair-like structures, which become electrically conductive and behave like a metallic wire in the reactor.
"The bacteria eat a lot to produce electricity and live a longer life because the environment is optimized for their survival, so sludge can be cut down by 80 percent. Roughly four watts of electricity are produced for every kilogram of organic material that the bacteria consume. The amount of electricity generated will not exactly power the entire town, or even the entire processing facility, but it can offset the energy used to clean the water." - Scientific American
The company is building a demo plant in Israel next year, using up to 16 of their modules, and they hope to be able to offer the scalable system commercially at some point in 2013, at an estimated cost of about $5,000 per module.
Some of the company's claims have been met with some skepticism, such as questioning whether the system would work at commercial scale:
"There is a tremendous difference between a demo system and upscaling to thousands of tons of wastewater, and a difference between artificially contaminated water used for laboratory testing and the real world, where you have different waste and different materials." - Itamar Willner, a professor at the Institute of Chemistry at the Hebrew University
Another researcher says that 80% of the energy generated by the microbes is lost during the process, as the electrons never reach the electrodes, but that perhaps a genetically engineered microbe may be able to improve the electron transfer efficiency.
Find out more about this microbial fuel cell technology at Emefcy.