Water. desalination + reuse

August-September 2012

Water. Desalination + reuse

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_________ Professor Linda Zou, South Australian Water Centre for Water Management & Reuse, University of South Australia ___ RESEARCH CDI low-energy desalination can supply remote communities Editor's note: There has been a lot of media fuss recently about the work at the Massachusetts Institute of Technology on using graphene sheets in membrane desalination. Equally important work is going on in Australia on using graphene sheets as electrodes for capacitive deionisation (CDI). Supported by the National Centre for Excellence in Desalination, Professor Linda Zou has proved that CDI technology offers a viable alternative solution for brackish water treatment, especially in communities in remote areas where building a large and high-maintenance treatment plant is not practical. ACCESS TO adequate supplies of fresh water is a growing issue for Australia's inland regional and remote communities. Desalting saline, 'hard' brackish water has, until now, been a relatively energy-intensive and costly exercise in places where building a large reverseosmosis treatment plant is not practical. New research funded by the National Centre of Excellence in Desalination Australia (NCEDA) in two of its recent funding rounds has seen the development of capacitive deionisation (CDI) as a promising alternative technology to tackle these problems. the Australian Government will now help to finance more units and trials towards commercialisation of the technology. MEETING PUBLIC AND INDUSTRY DEMAND There is huge demand for small, decentralised desalination plants across regional and remote communities, and the mining, agricultural and health sectors. Most of these plants are membrane-based reverse-osmosis systems, which require high technical maintenance and suffer from severe scaling and fouling. For example, the high levels of reactive silica and ferric ions in the groundwater in the remote areas of the Northern Territory make the operation of highpressure desalination membrane systems difficult. In these conditions, CDI could be a useful alternative technology that achieves higher volumes of desalinated water without the current high use of energy and technical resources demand. Successful trials funded by NCEDA have positively evaluated the performance of a first portable commercial capacitive deionisation unit developed by the University of South Australia and its industry research partners in Wilora, a remote community in the Northern Territory 250 km from Alice Springs. Further funding allocated in June by NCEDA on behalf of HOW CDI TECHNOLOGY WORKS CDI can be described as an electrosorption process of salt ions onto electrodes used in desalination. By applying an external low electrical potential (1–2 V), salt ions from feed water are forced towards and then adsorbed by oppositely charged electrodes (see Figure 1). Deionization Saline water Pure water Fig 1. Capacitive deionisation process. Regeneration It targets the removal of salt ions, which are only a small percentage of the feed solution, compared with most other technologies that aim to shift water, which accounts for the majority of the feed solution. As a result, CDI requires less energy to operate. With the removal or reversal of the external electrical potential, the adsorbed ions are instantly released from the electrode. GRAPHENE NANOSHEETS AS ELECTRODE MATERIAL Porous carbon materials are the most important component in the CDI process, as they are used in the electrodes which play a significant role in determining August-September 2012 | Desalination & Water Reuse | 43 |

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