Advances in capacitive deionization (CDI) systems for nutrient recovery from wastewater: Paving the path towards a circular economy

The escalating global population growth, the aspiration for improved living standards, environmental concerns, and the rising focus on circular economy frameworks have collectively emphasized the imperative to recover resources such as nutrients, water, and energy. Despite the notable advantages and technological capabilities of capacitive deionization (CDI) systems, their potential remains largely untapped. This comprehensive review aims to synthesize and analyze the progress made in CDI systems for nutrient recovery. It concentrates on two vital wastewater nutrients: nitrogen (N) and phosphorus (P). The study explores both conventional and advanced CDI systems, including CDI, membrane capacitive deionization (MCDI), flow electrode capacitive deionization (FCDI), and hybrid capacitive deionization (HCDI). In three key areas, a detailed framework for recovering nitrogen, phosphorus, and both is provided: (1) process optimization, (2) innovative cell design, and (3) process development for effectively integrating CDI with complementary techniques, enabling simultaneous ion recovery and the production of value-added products. Additionally, future perspectives on CDI development and expansion for nutrient recovery are discussed in this review with an emphasis on aligning these efforts with circular economy goals.