2025 Articles

Enhancing water recovery in reverse osmosis by mitigating membrane scaling using thermomorphic hydrophilicity base-induced precipitation pretreatment

Fang, Yuren; Abu-Obaid, Sara; Galperin, Daniel; Yip, Ngai Yin

Membrane scaling remains one of the primary operating challenges in reverse osmosis (RO) desalination, especially for feedwaters with high scaling potential. The conventional mitigation approach of antiscalant dosing provides only temporary relief by delaying nucleation but adds cost and complexity, introduces other fouling risks, and leaves the underlying supersaturation of hardness ions, i.e., Ca2+ and Mg2+, unaddressed. This study investigates thermomorphic hydrophilicity base-induced precipitation (THBIP), a thermomorphic solvent-based emerging descaling technique, as an alternative pretreatment for scaling mitigation by selectively removing hardness cations from the feed. Bench-scale crossflow RO experiments using high-scaling propensity feed simulating irrigation drainage water demonstrated that THBIP pretreatment significantly reduced the rate of water flux decay by 14.7 % compared to untreated feed. THBIP-pretreatment extended the water recovery yield from 0.48 to 0.61 before severe scaling occurred, representing a 27 % productivity gain over the control. Whereas the untreated feed experienced catastrophic flux collapse shortly after the critical transition point, THBIP-pretreated membranes retained ≈61–66 % of their initial water permeability. Integrated thermodynamic, morphological, elemental, and crystallographic analyses revealed that initial scaling was driven by gypsum, whereas the critical transition was triggered by the subsequent onset of anhydrite precipitation. By suppressing anhydrite formation, which forms denser, less permeable deposits than gypsum, THBIP drastically reduced the flux decline rate by 71.7 % relative to the controls while preserving salt rejection. With the intrinsic advantages of chemical recyclability, feed pH rebalancing, and compatibility with low-grade heat utilization, THBIP offers a more effective and sustainable solution for managing high-scaling RO feeds.