Water. Desalination + reuse
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RESEARCH | 30 | Desalination & Water Reuse | May-June 2015 Engineers at the University of Colorado Boulder have invented a process that they claim simplifes the treatment of oil and gas wastewater by simultaneously removing salts and organic contaminants while producing energy. The Colarado researchers have published a technique that uses a microbe-powered battery. "The beauty of the technology is that it tackles two different problems in one single system," said University of Colorado Boulder associate professor of environmental and sustainability engineering and senior author of the paper Zhiyong Jason Ren. "The problems become mutually benefcial in our system and the process produces energy rather than just consumes it." The new technology – microbial capacitive desalination – exploits the energy-rich hydrocarbons in the wastewater by deploying microbes that consume them and release their energy. The energy is used to create a positively charged electrode on one side of a cell and a negatively charged electrode on the other, essentially setting up a battery. Engineers unveil oil and salt removal that produces energy Physicists warm to energy yield Lead author of the paper Casey Forrestal, who is working to commercialize the technology, said: "We use microbes to generate an electrical current that can then be used for desalination." Ren added: "Right now oil and gas companies have to spend energy to treat the wastewater. We are able to treat it without energy consumption; rather we extract energy out of it." Oil and gas operations in the US produce about 3.3 million Ml of wastewater a year. Its high salinity and organic contaminants make treatment diffcult and expensive using conventional techniques. Some oil and gas wastewater is currently being treated and reused, but that treatment process typically requires multiple steps and energy from diesel generators. Because of the diffculty and expense, wastewater is often disposed of by injecting it deep underground. The need to dispose of wastewater has grown in recent years with the production of shale gas and oil using hydraulic fracturing, or "fracking". Injection wells that handle wastewater from fracking operations can cause earthquakes in the region, according to research by University of Colorado Boulder scientists and others. The demand for water for fracking operations also has caused concern especially in arid regions of the US. Water for fracking operations in the West, for example, has become increasingly expensive for oil and gas companies. To try to turn the technology into a commercial reality, Ren and Forrestal have co-founded a startup company called BioElectric Inc. To determine if the technology offers a viable solution for oil and gas companies, they must frst show they can scale up the work they have been doing in the lab to a size that would be useful in the feld. The cost to scale up the technology also needs to be competitive with what oil and gas companies are paying now to buy water to use for fracking, Forrestal said. There also is some movement in state legislatures to require oil and gas companies to reuse wastewater, which could make BioElectric's product more appealing even at a higher price, the researchers said. Physicists at Utrecht University in The Netherlands have calculated that that energy producers theoretically can achieve a much higher yield when generating electricity by a version of so-called blue energy production – a means of harnessing the energy generated when saline and non- saline water mix. Conversely their fndings suggest a much more effcient means for desalinating brackish water. The researchers calculated that warming the non-saline water component to 50 0 C prior to mixing could double the yield. Heating it to 80 0 C could treble the output according to a report by René van Roij, Mathijs Janssen and Andreas Härtel published in December 2014 in Physical Review Letters. The gains at the lower temperature indicate promise in the use of industrial waste heat according to lead researcher Janssen: "By heating the water using waste heat, we kill two birds with one stone: blue- energy installations generate more clean, sustainable energy, and industrial waste heat is put to better use," he said. The Utrecht team's fndings hold implications for the reverse of blue energy – the desalination of brackish water for drinking water production. According to van Roij, the theory "predicts that the desalination of cold brackish water is considerably less expensive than that from warm brackish water." The researchers were investigating capacitative blue energy technology that harnesses the energy generated on charging a porous electrode alternately with saline and non-saline water. More established forms of blue energy include pressure retarded osmosis – so- called osmotic power – where energy is harvested from a salinity gradient across a semi-permeable membrane. A prototype reverse osmosis (RO) system developed by the US Navy has successfully completed testing for use in the service's newest class of warship – littoral combat ships – for use close to shore. The Naval Facilities Engineering and Expeditionary Warfare Centre (EXWC) that tested the 20,000 l/d system said it could boost drinking water production capacity and remove elevated levels of particles common in littoral waters. EXWC commanding offcer captain Mark K Edelson said: "The ability to convert seawater into freshwater, as these systems will provide, takes on even greater importance should our ships see actual combat or be deployed to the scene of a natural disaster." US Navy desalter is a shore thing