Fly ash as zero cost material for water treatment applications: A state of the art review

As the world's population grows, transportation across continents increases and rapid industrialization continues leading to surge in the energy consumption. Unfortunately, this has given rise to environmental concerns, with waste fly ash being discarded in alarming quantities − up to 1 billion tons annually. Fly ash (FA), a particulate byproduct of burning various waste materials, is a pressing issue due to its environmental impact on soil, water, and air. However, this waste can be repurposed for water treatment applications, offering a sustainable solution to waste management and water quality control. FA materials can be classified into different types based on the source of the feedstock. These include coal FA, sugarcane bagasse ash, rice husk ash, and wood FA. FA materials possess unique characteristics, such as high surface area, porous morphology, and contain various chemical functional groups, that make them ideal for use in various water treatment systems, including coagulation-flocculation, adsorption, Fenton, capacitive deionization, membrane processes, and catalysis. In this article, we critically review the utilization of FA materials in water purification applications with a specific focus on recent literature. By exploring the current trends and future prospects of using FA materials in water treatment applications, this review attempts to provide insights into sustainable waste management and water quality control.