Lightweight materials in water and wastewater treatments: A systematic review

Lightweight materials, characterized by low density, high specific surface area, and porous structures, have gained prominence in water and wastewater treatment due to their advantages over traditional materials, including ease of transportation and installation, enhanced adsorption and catalytic efficiency, strong mechanical performance, reduced energy consumption, recyclability, and adaptability to various treatment systems. This review categorizes these materials into natural and synthetic types, detailing the characteristics of these lightweight materials. The significant advancements in preparation techniques, including foaming processes, phase separation, sol-gel methods, and 3D printing technology are comprehensively reviewed and discussed. Furthermore, the applications of these materials in adsorption, filtration, catalysis, and environmentally friendly water treatment facilities are overviewed. The study underscores the essential role of lightweight materials in enhancing water treatment efficiency and provides theoretical guidance for their selection. It also identifies future research directions, emphasizing the development of multifunctional composite materials, cost-effective preparations and regeneration methods, as well as the evaluation of sustainability and environmental impact throughout the materials' lifecycle analysis. These insights aim to promote the commercial use of lightweight materials in conventional operation of water industry (adsorption, filtration, catalytic processes) and green nature-based solutions for water/wastewater purification.