Water. desalination + reuse

DWR MayJune 2016

Water. Desalination + reuse

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| 26 | Desalination & Water Reuse | May-June 2016 RESEARCH Climate Change is ultimately the culprit not just for heating up the earth's atmosphere but also for injecting heat into research in desalination technology. With the growing incidence of record droughts the urgency to establish new sources of water has risen steadily for a number of years. Political and economic obstacles have intervened in some quarters but desalination and water reuse has nonetheless gathered momentum. The past 12 months have seen a shift not just in the intensity of the inquiry into "why" in respect of desalination, but also in the fervour behind the search for answers to the questions "what" and "how" do we desalinate. The dried up river beds around the world provide enough evidence for a response to the question why. But environmental considerations as well as issues around economic efficiency have fueled the desalination sector to reconsider "what" when looking for a source of raw water to purify. Seawater desalination and the concerns about danger to marine life with desalting seawater have made wastewater recycling the environmentally favoured proposition. As for how, researchers have explored beyond the chemical and physical stamping grounds for desalination and plundered the biological to come up with salt- removing technology. They have turned their sights onto the challenges in specific industries including mining and oil and gas production while others have looked to reduce radically the environmental and operational costs of desalination and water reuse. A recent report by market analyst, Frost & Sullivan, showed that growing global water scarcity had created opportunities for growth in the desalination market. Frost & Sullivan found that desalination revenues were poised to reach US$ 19.08 billion in 2019 from US$ 11.66 billion in 2015 with a doubling of desalination capacity by 2020. New possibilities have emerged throughout the past year. Some have little or no precedent while others have tackled old challenges. Irrespective of their approaches they are all chasing a quarry that is in open view. News of the shock A research team at Massachusetts Institute of Technology has developed a desalination system that deploys a strong electric field acting on a stream of flowing water. The field pushes ions in the salty water to one side of the flow and fresh water to the other so the two streams can readily be separated. This approach – called shock electrodialysis – is "a fundamentally new and different separation system," according to the leader of the research, professor of chemical engineering and mathematics, Martin Bazant. In the process, water flows through a porous column of glass particles sandwiched between electrodes that create "a very strong gradient," according to Bazant. The salt solution in the glass column divides into a high salt concentration flow and a low concentration flow. When the electric field reaches a certain intensity it creates a shock that splits the fresh and saline streams so they can be separated by a barrier placed at the dividing line between the two flows. With no membrane to effect separation, the process is not so susceptible to fouling as in reverse osmosis or even conventional electrodialysis says Bazant. The system removes contaminants as well as salt – and the electric field may also sterilize the stream according to the researchers. Bazant says the next step is to scale up the laboratory system for practical testing. He predicts initially at least, that shock electrodialysis would not compete with reverse osmosis for large-scale seawater desalination plant, but it could win in treating produced water such as effluent from fracking. Bazant says the system needs little infrastructure, so it could form the basis of portable systems for use in remote locations. crackiNg a ceramic problem A novel method for creating ceramic reverse osmosis membranes with sub-nonometre pores by using genetic material DNA as a template former overcomes the poor reproducibility encountered in conventional methods according to the developer of the technology, Cerahelix. In a paper presented at the AMTA and AWWA 2014 conference in Orlando, USA, Tyler J Kirkman, explained Cerahelix's process as "Manipulating DNA as a generic - not genetic - material to produce a pore structure that is unique in nanoflitration membranes." The process exploits DNA's property of aligning in a silica or titanium oxide sol gel to form columns. As the gel is fired to form a ceramic membrane on an alumina support the DNA is burnt off to leave pores with diameters of less than 1 nm. Kirkman claimed the membrane had an "inherent resistance to fouling." _________ Trevor Loveday, outgoing editor, Desalination and Water Reuse ___ Breaking new ground Trevor Loveday looks at some of the more inventive research that produced findings over the past 12 months.

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