Recent advances in Donnan dialysis processes for water/wastewater treatment and resource recovery: A critical review

Abstract

Due to its low chemical and energy consumption, Donnan dialysis offers major opportunities to improve contaminant removal and resource recovery from water and wastewater. Conventional Donnan dialysis reactors involve (i) a feed solution that contains a target ion to be removed, (ii) a draw solution with a high concentration of acid, base, or salt, and (iii) an ion-exchange membrane that separates the two solutions. The electrochemical potential gradients of the target and draw ions across the membrane facilitate transport phenomena that can be exploited for contaminant removal or resource recovery. In this critical review, we highlight the need for a consistent framework for the design and interpretation of Donnan dialysis systems using the Rd/w concept, evaluate the impacts of solution properties (e.g., pH, draw ion, competing ions), membrane characteristics (e.g., thickness, ion-exchange capacity, hydration, surface modifications), and system configuration (e.g., membrane surface area, reactor volume, mixing speed, crossflow velocity, integrated processes), and discuss Donnan dialysis applications for treatment and recovery of metals, nutrients, and other inorganic and organic chemicals. In each section, we make recommendations for future studies to both fill knowledge gaps and promote new opportunities. This critical review will serve as an important resource for future Donnan dialysis efforts to address grand challenges related to clean water and circular economies of essential elements.