On a tunable capacitive multi-osmosis (CMO) system: Hybrid-scale modeling and mechanistic insights

We propose a capacitive multi-osmosis (CMO) system that can operate both in Forward Osmosis (FO) and Reverse Osmosis (RO) modes, depending on the electric potential difference across the membrane. We employ a hybrid-scale modeling approach that integrates pore-scale and membrane-scale models to evaluate system performance. The two models have been unified and validated via numerical investigations and physical experiments on a generic FO system. Based on insights from our models, we identify three competing drivers of osmosis under an electric field—pressure gradient, electroosmosis, and an anomalous drag. In conventional electric-assisted FO systems, the electrodes participate in superfluous electrochemical reactions due to contact with the feed and draw solutions. In the CMO system, the electrodes are placed outside the system and exert their electric field without physical interaction with the solutions or any system components, thereby preventing any reactions. The non-contact electric fields generated when the system is subjected to controlled electric potential differences can significantly enhance the permeate recovery in an FO system, paving the way for FO scale-up.