Comparison of Solar-Powered MCDI and RO Groundwater Desalination for Mediterranean Agriculture

In order to provide an innovative and robust solution for groundwater desalination, an all-in-one smart cube for irrigation was developed within the EU-PRIMA research Project SmaCuMed in the field of sustainable irrigation. The smart cube is fully operated on solar energy and consists of a membrane capacitive deionization (MCDI) unit, a low-pressure reverse osmosis (LPRO) plant (< 16 bar), photovoltaic panels, and a cloud-based IoT system integrated with soil and water sensors (humidity, salinity, conductivity, pH) as well as a weather station for monitoring and controlling. The smart cube was tested on a test field in the region of Essaouira, Morocco, for the irrigation of Argan trees with three different qualities of water. First trials allow a comparison of the performance of the two different desalination technologies, whilst removing 33% of salt with the MCDI unit and 67% with the LPRO, respectively. The two technologies’ specific energy consumption (SEC) results in SECMCDI = 1.62 kWh/m3 and SECLPRO = 2.71 kWh/m3. In further trial tests, the removal target of the two different desalination technologies will be swapped, so that SEC values can be compared directly. The focus on testing the novel MCDI technology is to find optimum operational parameters for the application in the agricultural sector. Hereby, for MCDI, most energy-efficient desalination was achieved with constant current charge and discharge cycles, with additional zero voltage discharge phases in between. Long-term tests show no decrease in permeability and performance for both desalination technologies after six months of operation. The pilot plant shows the feasibility of MCDI use to irrigate Argan trees in Moroccan semi-arid regions. Furthermore, the SEC values indicate competitiveness with conventional LPRO usage.