Initial tests using a new technique show that it is possible to generate electricity from wastewater. In future, this could transform water-treatment plants into mini energy plants.
Researcher Annemiek ter Heijne is researching a new method of water treatment, whereby bacteria are allowed to grow on tiny granules, thereby purifying the water. Bacteria produce electrons as they grow. The granules serve as tiny rechargeable batteries that store the electrons. Draining the electrical charge into a special cell enables you to generate electricity from wastewater.
Ter Heijne recently published the first proof that this new method works: a trial reactor that supplies electricity. It does not generate much electricity at the moment, but measurements show that the new system will eventually generate substantial amounts of energy. Although the granules can store a considerable electrical charge, the actual generation process is not yet as efficient as it could be, says Ter Heijne. If the entire charge could be stored, the new technique would supply more energy than existing methods, such as anaerobic fermentation, in which bacteria are converted into biogas.
Ter Heijne uses activated carbon (Norit) granules in her reactor. The granules are full of microscopic cavities, and therefore provide a large surface area on which the bacteria can grow. Just one granule measuring approximately 2 mm provides a growth surface of approximately three square metres. Furthermore, the granules are cheap.
Over the next few years, Ter Heijne wants to find more efficient ways of draining the electrical charge. ‘Treating wastewater is currently an expensive business. If we can find an efficient way to harvest the electrical charge, water treatment might generate energy instead of costing money.’