Unlocking Zero Liquid Discharge: A Parallel Water Supply Strategy to Realize Selective Salt Crystallization for Long-Term Interfacial Solar Evaporation

Abstract

Interfacial solar evaporation offers a green and sustainable solution to solve clean water shortages via solar-driven desalination. However, salt crystallization and accumulation on solar evaporators have become the primary hindrances to the long-term practical application of interfacial solar evaporation technology. To tackle this challenge, a photothermal evaporator with a novel parallel two-water paths strategy is developed in this study. Unlike the conventional one-way water path, which generally leads to salt accumulation at the water supply end on the evaporation surfaces, thereby limiting the lifespan of the evaporator and compromising solar evaporation performance, here, with the second parallel water supply path, the ion diffusion and distribution within the solar evaporator is reconfigured and optimized. No salt accumulation occurs on either the evaporation surfaces or the water paths, eliminating the impact of salt crystallization on evaporation performance and enabling convenient salt collection. A high and stable evaporation rate of 3.09–3.26 kg m⁻² h⁻¹ is recorded over 84 h continuous evaporation of NaCl solution (3.5 wt.%) without salt accumulation on the evaporator, making it an ideal strategy for zero liquid discharge solar evaporation.