Effect of reverse solute diffusion on scaling in forward osmosis: A new control strategy by tailoring draw solution chemistry

Abstract

We explored the specific role of reverse solute diffusion (RSD) on the scaling in osmotically-driven membrane processes (particularly forward osmosis (FO)). Both scaling precursors (e.g., Ca2 + and phosphate) and anti-scaling precursors (e.g., H+ and a chelating agent ethylenediamine tetraacetic acid (EDTA)) were used to investigate the effect of RSD and draw solution chemistry on calcium phosphate scaling. While draw solutions containing Ca2 + tend to promote calcium phosphate scaling, this effect was noticeable only if the specific RSD of Ca2 + (i.e., the ratio of Ca2 + flux to water flux) was greater than the original Ca2 + concentration in the feed water. The RSD of H+ and EDTA effectively suppressed scaling. For the first time, we demonstrated a new scaling control strategy for FO by the inclusion of anti-scaling functions in the draw solution chemistry. Our work has important implications for the design and operation of FO processes.