Multistage integrated systems for wastewater treatment and resource recovery: A systematic process design framework

The wastewater treatment paradigm is shifting from pollutant removal toward integrated systems that simultaneously achieve contaminant treatment and resource recovery. Despite extensive literature on individual technologies, systematic frameworks for designing multistage integrated wastewater treatment and resource recovery systems remain notably absent. This review addresses this gap by developing a comprehensive decision framework that guides designers from influent characterization through technology selection across pretreatment, main process, and post-treatment stages. The framework accommodates diverse integration strategies, ranging from fully unified treatment processes to stage-specific configurations where each treatment stage employs technologies tailored to its designated function. Rather than optimizing for a single criterion, the framework emphasizes holistic consideration of technical performance, economic viability, and environmental sustainability. To further clarify the practical application of the proposed framework, representative real-world examples have been incorporated throughout the review to illustrate how the conceptual decision-making approach can be translated into practical process design strategies under different treatment conditions and resource recovery objectives. It is worth noting that these examples are drawn predominantly from membrane bioreactor (MBR) and adsorbent-based systems, which serve as illustrative cases rather than defining the boundaries of the framework itself. The framework, much like a medical prescription, it is designed not for generic application but to be thoughtfully customized by practitioners according to site-specific feed characteristics and treatment and/or recovery objectives. This work contributes to the broader transformation of wastewater management from pollution control toward resource recovery, supporting the water sector transition to circular economy principles.