Sustainable wastewater treatment: Mechanistic, environmental, and economic insights into biochar for synthetic dye removal

Abstract

The contamination of aquatic environments by synthetic dyes poses significant environmental and health risks due to their structural complexity, toxicity, and resistance to biodegradation. Traditional treatment materials such as activated carbon, ion-exchange resins, and metal oxides are often limited by high cost, energy requirements, and post-use challenges. Biochar has emerged as a sustainable alternative, offering favourable physicochemical properties and characteristics, including large surface area, porosity, and functional groups, for effective dye adsorption. This review critically examines the production routes of biochar from diverse feedstocks, adsorption mechanisms involved in dye removal, and the influence of operational parameters such as pH, initial dye concentration, and modification techniques. Furthermore, we highlight recent modeling strategies, including machine learning approaches, for predicting dye adsorption performance. The potential for functionalization and activation of biochar to enhance dye removal efficiency is also explored. Beyond removal efficiency, this review evaluates the environmental implications and circular applications of dye-laden biochar, focusing on its stability, reusability, and integration into carbon management approaches. A bibliometric analysis is included to identify active research hubs, funding trends, and underexplored areas, providing a strategic perspective on the global development of this field. Overall, the review aims to support researchers, practitioners, and policymakers in advancing the design and application of biochar for cost-effective and environmentally sound treatment of dye-contaminated water.