Comparative Analysis of MCDI and Circulation-MCDI Performance Under Symmetric and Asymmetric Cycle Modes at Pilot Scale

This study compares the operational performance of membrane capacitive deionization (MCDI) and circulation-MCDI (C-MCDI) under symmetric (2/2, 3/3, 4/4 min) and asymmetric (5/2, 5/3, 5/4 min) adsorption/desorption cycles to identify efficient operating conditions at the pilot scale. A pilot system was tested with a NaCl solution of about 1000 mg/L, and 15 consecutive cycles were conducted to evaluate removal efficiency, specific energy consumption (SEC), and stability. MCDI consistently achieved over 90% removal efficiency with SEC below 0.6 kWh/m³ across all modes, maintaining stable performance over 15 cycles. The 2/2 condition provided the shortest cycle time and the highest treated water productivity, making it the most efficient condition for the pilot-scale MCDI tested. C-MCDI showed stronger dependence on operating conditions, with the number of stable cycles ranging from 3 to 7 depending on desorption duration. Nevertheless, the 5/2 condition achieved about 91% removal efficiency with 0.58 kWh/m³ SEC, and its extended adsorption period yielded about 2.5 times more treated water per cycle than the 2/2 case. Overall, this work provides a comparative pilot-scale evaluation of MCDI and C-MCDI, highlighting their advantages, limitations, and potential applications, and offering practical insights for energy-efficient and sustainable desalination strategies.