Simultaneous recovery of water and antiscalant from cooling tower blowdown water by electrodialysis: Mechanism and cost-effectiveness

Abstract

Considering that the resource utilization of cooling tower blowdown water has not yet involved antiscalant recovery, this study conducted batch experiments to investigate the mechanism and effectiveness of electrodialysis for synchronous desalination and retention of antiscalant Amino Trimethylene Phosphonic Acid (ATMP). The results indicated that the migration flux of ATMP was much lower than that of inorganic salts, which could be attributed to the huge concentration and mobility differences between inorganic salts and ATMP, according to the extended Nernst-Planck equation, resulting in the preferential transmembrane electromigration of inorganic salts during the electrodialysis process. Thus, most of the ATMP was retained in the desalinated water (as make-up water) and reused in the circulating cooling water system. Under a reasonable working voltage of 60 V, using electrodialysis to treat simulated cooling tower blowdown water could retain 60.5 % of ATMP while achieving a 73.2 % desalination ratio, with an energy consumption of only 0.69 kWh·m⁻³. These values were extended to investigate the cost-effectiveness of using electrodialysis to treat cooling tower blowdown water with a 75 m³ h⁻¹ flow. Compared to the widely used reverse osmosis process, the electrodialysis process could reduce investment and annual operating costs by 12.6 % and 10.8 %, respectively, while also improving resource utilization benefits by 18.5 %. Thus, this method demonstrated excellent applicability.