Coupling adsorption and electrochemically mediated precipitation for enhanced water softening and antiscalant recovery

Electrochemical water softening, known for its chemical-free operation and modular design, offers a sustainable solution for cooling water management. However, the impact of antiscalants on the efficiency of electrochemical water softening remains poorly understood. Here we showed that even low concentrations (7.5 µM) of nitrilotris methylene phosphonic acid (NTMP), a representative antiscalant, significantly inhibit electrochemical softening efficiency while substantially increasing energy consumption. We propose a dual-benefit strategy integrating adsorption with electrochemically mediated precipitation to address this challenge in treating antiscalants-loaded cooling water. First, we probed the efficiency of iron-based adsorbents in mitigating NTMP under cooling water-relevant conditions. Our results show that bicarbonate hinders NTMP adsorption by altering the solution pH and the surface charge of the adsorbents. In contrast, hardness ions (Ca 2+ and Mg 2+ ) enhance NTMP adsorption by forming ternary complexes. Following adsorption, the subsequent electrochemical treatment achieves 83% calcium hardness removal at 20 A/m 2 with an energy consumption of 11.1 kWh/kg CaCO 3 in synthetic solutions. Notably, NTMP molecules desorbed from iron-based adsorbents retain their full anti-scaling capacity (100%), enabling recovery and reuse. This dual-function strategy mitigates antiscalant inhibition, enhances softening efficiency, and enables antiscalant recovery for reuse, advancing sustainable water treatment.