Researchers review low and renewable energy desalination
A comprehensive review of some of the latest thinking in low and renewable energy desalination systems was provided on 25 February 2013 at a workshop staged prior to the AMTA/AWWA Membrane Conference in San Antonio, Texas.The workshop had assembled an international cast of speakers, including Samer Adham from Qatar's Global Water Sustainability Center, Linda Zhou from the University of South Australia and Gary Amy and Thomas Missimer from the King Abdullah University of Science & Technology in Saudi Arabia.
The audience of about 35 was updated on the state of play of techniques such as forward osmosis (FO), membrane distillation (MD), capacitive deionization (CDI), microbial desalination cells (MDC) and combined cycle solar and geothermal powered desalination.
As the workshop proceeded, it became clear that none of these techniques is ready yet to fully take on the commercial world, but many of them indicated that given time and the right application they will take their place alongside or even instead of existing popular technologies.
FO is the best publicised of the new generation and Amy Childers of the University of Nevada, Reno, focused on the pressure-retarded (PRO) version of FO, and its best-known implementation as a source of renewable energy. Talking about the Statkraft installation in Norway which uses the salinity differential between river and seawater to create energy, Childers said that today's systems only created a power density of around 2W/m², whereas what was required was nearer 8W/m².
She was looking forward to a pilot-scale PRO test which will take place soon at the Alamagordo test centre in New Mexico.
Samer Adham spoke about trials with membrane distillation using low-grade heat in Qatar. Five manufacturers had been invited to bid, with Scarab and Memsys eventually chosen to design pilot units at the Ras Abu Fontas desalination plant. Again, performance ratios for this technology are still only around half of what would be commercially required, said Adham.
Linda Zhou, whose work has recently been featured in D&WR, described the use of graphene electrodes for CDI, while Bruce Logan from Penn State University extrapolated from his better known work on microbial fuel cells into the use of the technique for desalination.