Emerging trends in municipal wastewater treatment, water reclamation and reuse, and resource recovery: Moving from linear to circular economy models

Municipal wastewater (MWW) is a complex and inherently heterogeneous matrix, rendering its release detrimental to human health and receiving environments, and making its treatment challenging. Yet, its complexity presents certain advantages and opportunities when viewed under the waste hierarchy and circular economy lenses. It grossly (∼99.9%) comprises water, which implies opportunities for water reclamation, while the remaining minor fractions contain valuable dissolved minerals and nutrients. Conventional treatment is effective at removing nutrients and biological content, typically employing treatment trains that combine physicochemical with biological processes. However, novel contaminants, such as emerging contaminants (ECs), largely escape intact, while water is not reclaimed and resources are not recovered. Here, MWW valorization avenues and challenges are distilled and critically reviewed, with emphasis underpinned and focused on minerals (nutrients such as fertilizers) recovery, energy (biofuel such as biogas) production, and water reclamation. To improve environmental sustainability, new technologies (e.g., artificial intelligence (AI), internet of things (IoT), digital twins, and data-driven predictive maintenance), along with renewable energy, should be used. Revenue from recovered products and reclaimed water can also support economic and social sustainability. Even though regional, particularly in the Global North, and international efforts (e.g., United Nations Sustainable Development Goal 6) have been undertaken, more effort is needed in the global policy arena. This review also provides a framework that can be adopted prior to selecting a technology for MWW treatment to ensure optimal efficiency and maximum water reclamation. Further research on the role of MWW in the global carbon budget and its importance for climate change intervention is needed.