Scientists at Pennsylvania State University have developed an innovative process of obtaining energy from sewage.

The process involves combining microbial fuel cell technology with reverse-electrodialysis, which has produced 0.9 kilowatt/hours of electricity per kilogram of organic waste. The energy produced could potentially provide the power for water grids and turn waste water treatment plants into power stations.

Professor Bruce Logan, one of the scientists involved in developing the technology, has said that it could “take care” of the whole water system - the treating and pumping of water as well as treating the organic matter much faster.

In a report published in the Science Journal on 1 March, the scientists describe how they used reverse electrodialysis ion-exchange membrane stacks in microbial reverse-electrodialysis cells to efficiently capture salinity gradient energy from ammonium bicarbonate salt solutions.

The combination of both technologies has significantly improved efficiency in generating energy. Each individual technology currently has its limitations in creating electricity - the microbial fuel cell, which creates energy through wastewater hungry bacteria, has existed for decades but is inefficient, while reverse-electrodialysis, which needs many specialised membranes, is expensive.

"By combining the two technologies, we overcame the limitations of the fuel cell and synergistically generated energy for the reverse electrodialysis system," said Logan.

Though the figure of 0.9 kilowatt/hours of electricity per kilogram of organic waste is promising, sewage treatment usually consumes 1.2 kilowatt/hours per kilogram, indicating that power will still need to be generated from other sources for the time being.

There is great potential for the use of this technology in developing countries as sewage treatment plants would be better maintained given their new function of generating electricity for the local population.

Logan comments:

“"If you go into a country and give them a waste treatment system - the World Bank and others have done this - they do not keep it going, as it needs power and maintenance. It is a drain on the community. But if you can also provide electricity for lighting, or charging mobile phones, that's a game-changer."