Israeli company, Emefcy, has developed a microbe-based technology that harvests energy while treating waste water.

The process starts with the same principle as most wastewater treatment – water is aerated so that bacteria in the liquid breaks down organic material. But instead of using electricity to push air into the water, Emefcy uses a permeable, polyethylene filter that allows air in but doesn’t let liquid out,

The polyethylene membrane surrounds a fuel cell chamber into which the waste water flows. Inside the fuel cell, anaerobic bacteria  release electrons. The electrons flow to an anode and then to cathodes in a separate chamber on the outside of the membrane, producing electric current.

(Image source: Emefcy via Wikimedia)
(Image source: Emefcy via Wikimedia)

Rather than the precious metals normally used in batteries and fuel cells, both the anode and cathode are made of a carbon cloth, which keeps the cost down to a level which is practical for use at a commercial scale.

One Emefcy fuel cell module, which is about a cubic meter in size, can treat about three cubic meters of waste water per day depending on the amount of organic material present. The bacteria consume about 80% of the sludge and produce approximately four watts of electricity for every kilogram of organic material that they consume.

The fuel cell is ideal for waste water that is high in organic material, such as that from agriculture and food processing rather than for processin municipal waste water.