A report released this week by the Goyder Institute for Water Research outlined findings from an investigation into small-scale desalination using capacitive de-ionisation (CDI) – an emerging technology – to improve water quality for growers in the Northern Adelaide Plains (NAP).
The Assessment of Small Scale Desalination by Capacitive Deionisation for Treatment of NAP Waters research project was led by Professor John Van Leeuwen (UniSA) and co-funded by the Department of Primary Industries and Regions, South Australia (PIRSA) and the Goyder Institute.
Around a third of South Australia’s horticulture produce comes from the NAP and it’s valued at over $340 million per year (2014-15, PIRSA). Production in the region has the potential to grow and help satisfy the increasing demand for food locally and internationally, but this is limited in part by water availability and quality.
The team’s field-based research showed that a single CDI unit was able to treat slightly brackish waters at flow rates of up to two kilolitres per day. Brackish groundwater (~<800 mg/L total dissolved solids [TDS]) and recycled water from the Bolivar wastewater treatment plant (~<1100 mg/L TDS) was processed to a quality that can potentially be used in soil-based horticulture, although this depends on a crop’s salt tolerance.
The capacitive de-ionisation (CDI) unit at the Bolivar treatment plant
Overall, the highest salt removal efficiencies of the CDI tested was around 50% for reclaimed water (average 30%) and 57% for groundwater (average 30%). Water recovery was 64% for reclaimed water and 72% for groundwater. Organic fouling was experienced with the recycled water and significantly reduced the efficiency of the CDI unit.
At its current stage of development the technology does not seem suited for the NAP advanced hydroponics industry, which needs water with very low TDS levels and have relied on reverse osmosis (RO) technologies. However, new generation, commercially sourced CDI technologies might have improved capabilities to the test unit used in this investigation. With further research and development, however, it could be a viable option in the future.
This Goyder Institute and PIRSA research project was also well supported by P’Petual Holdings, one of the largest greenhouse vegetable growers in Australia, and by Allwater, who operate the Bolivar treatment plant. The SA EPA, the Department of Water and Environment, and commercial irrigation equipment suppliers helped facilitate contact with representatives from the horticulture and hydroponic industries and provided key information on existing regulations, governance and needs of the future, including brine disposal.
CDI at P'petual Holdings
The project has reinforced how important fit-for-purpose and cost effective desalination processes are for horticulture in the NAP and industry expansion into the State’s northern corridor. The results will be of interest to businesses and to state government and local councils. Although the team’s findings have increased our understanding of CDI technology and its potential, many unanswered questions remain. The team will build on this research in future projects related to supporting the horticultural industry.
This project is a great example of the Goyder Institute’s collaborative model in action, with researchers, government and industry all working together. Contact Institute Director Kane Aldridge to find out more about the Institute and to get involved.