Performance optimization and long-term evaluation of pilot-scale PV-powered membrane capacitive deionization (MCDI) in an arid oasis on the example of Morocco

Abstract

Across many oases in semi-arid and arid regions, water availability is steadily declining while soil salinity is increasing at an alarming rate. To address these challenges, the SuLaMo project proposed integrated sustainable land and water management concepts for agriculture, incorporating desalination as a viable source of irrigation water. This study experimentally evaluated a pilot-scale, photovoltaic-driven membrane capacitive deionization (MCDI) system for the desalination of brackish groundwater (TDS = 6.3 mS cm⁻¹). The investigation focused on finding practical steps to: (1) evaluate the effect of flow rate on adsorption capacity; (2) optimize the system configuration to maximize water recovery; (3) evaluate the long-term performance and the effect of scaling, electrode configuration and selective ion removal on system efficiency. Additionally, the effect of soil salinization was monitored during the trials. The results demonstrated the feasibility of MCDI for desalinating low-brackish water and mitigating long-term soil salinization. A trade-off between ion removal efficiency (RE), water recovery (WR), and energy consumption (SEC) was evaluated using a Pareto method. Steps for systematically optimizing the process are suggested. Pilot at low-cleaning operation resulted in optimized values of RE = 45%, WR = 69% and SEC = 2.75 kWh m⁻³ m⁻³. However, prolonged operation with infrequent cleaning resulted in significant scaling effects, a lower net flow rate and increased SEC. This indicates that frequent cleaning is essential, particularly when treating hard water. Further improvements in electrode adsorption capacity and anti-scaling operational strategies are necessary for the large-scale agricultural application of MCDI.