A study of the long-term operation of capacitive deionisation in inland brackish water desalination

• Calcium and magnesium scaling have limited effects on CDI long-term operation.
• Dissolved organic matter is the main cause of CDI electrode fouling.
• Energy consumption in term of Wh/g salt removed tends to increase with fouling.
• Current efficiency tends to decrease with the fouling of CDI electrodes.
• Mild alkaline and acid solutions were able to recover the CDI desalination capacity.

The long-term cleaning needs and response to different cleaning approaches of a portable capacitive deionisation (CDI) prototype unit were investigated at two Australian locations: Wilora, a remote community in the Northern Territory (NT), and Mawson Lakes, an urban area in South Australia (SA). The high levels of calcium, magnesium and silica at Wilora had a limited effect on long-term CDI operation; Wilora's groundwater had a low level of dissolved organics, causing no observed fouling. The current CDI technology proved suitable for direct application for brackish water desalination in this location. For comparison, ground water containing a higher level of dissolved organics was studied in Mawson Lakes, SA. A reduction in the salinity removal ability of the CDI cells was observed due to organic fouling. However, a relatively mild cleaning solution (0.01 M citric acid for calcium and magnesium scaling and 0.01 M sodium hydroxide for the organic fouling) restored the desalination capacity of the CDI unit to its initial level. This unit thus represents a viable alternative for brackish water treatment, especially in remote locations where building and operating reverse osmosis (RO) treatment plants is not practical. These findings can be used to guide on-site maintenance of CDI technology.