Scaling Resistance in Nanophotonics-Enabled Solar Membrane Distillation.

This study compares the scaling behavior of membrane distillation (MD) with that of nanophotonics-enabled solar membrane distillation (NESMD). Previous research has shown that NESMD, due to its localized surface heating driven by photothermal membrane coatings, is an energy-efficient system for off-grid desalination; however, concerns remained regarding the scaling behavior of self-heating surfaces. In this work, bench-scale experiments were performed, using model brackish water, to compare the scaling propensity of NESMD with MD. The results showed NESMD to be highly resistant to scaling; a three times higher salt concentration factor (c/c0) was achieved in NESMD compared to MD without any decline in flux. Analyses of the scaling layer on NESMD membranes revealed that salt deposition was 1/4 of that observed for MD. Scaling resistance in NESMD is attributed to its lower operating temperature, which increases the solubility of common scalants and decreases salt precipitation rates. Precipitation kinetics measurements revealed an order of magnitude faster precipitation under heated conditions (62 °C, k = 8.7 × 10-2 s-1) compared to ambient temperature (22 °C, k = 7.1 × 10-3 s-1). These results demonstrate a distinct advantage of NESMD over MD for the treatment of high scaling potential water, where scaling is a barrier to high water recovery.