Circular Transition of Cooling Tower Blowdown Using Resin Wafer Electrodeionization (RW-EDI) Technology: Transforming Water–Energy System Hotspots

Cooling towers are vital in urban and industrial contexts but face challenges related to resource recovery, energy efficiency, and water scarcity within a circular economy. This study develops a mass balance model under a zero-liquid discharge (ZLD) framework, using experimental data to evaluate water–energy–carbon interactions enabled by the resin wafer electrodeionization (RW-EDI) process. We assessed the RW-EDI performance by examining limiting current density, hardness removal ratios, reclaimed water productivity, and energy consumption (EC) across different voltages and flow velocities. Our results indicate that determining the resulting reversible ion density is crucial for optimizing energy used in water splitting and ion separation. The RW-EDI stack’s EC ranged from 0.057 to 0.537 kW h/m3, with water productivity between 10.52 and 23.31 L/m2/h at voltages of 4.5–12 V. In a ZLD scenario of a cooling tower, as the blowdown cycles’ numbers increased from 5 to 35, the carbon intensity remained constant at 0.17 and 0.24 kg-CO2 equiv/m3 based on the U.S. and Taiwanese electrical emission factors, respectively. However, energy intensity savings ranged from 0.19 to 0.63 kW h/h for the U.S. benchmark and from 1.03 to 1.46 kW h/h for the Taiwanese benchmark. These findings contribute to enhancing urban water–energy–carbon resilience and support sustainable water circulation.