Biomass-Derived Biochar for The Removal of Textile Dyes from Aqueous Solutions: A Review

The textile industry discharges massive volumes of coloured wastewater containing hazardous dyes. Traditional treatment methods such as coagulation, flocculation, membrane filtration and advanced oxidation often face high costs, high sludge production and low efficiency for recalcitrant dyes. Biomass-derived biochar has emerged as a low-cost adsorbent made by pyrolysing agricultural or industrial wastes. This review critically surveys recent literature on biochar for textile dye removal. It analyses sustainable feedstocks, structure-property relationships, comparative adsorption performance, adsorption mechanisms, practical constraints and research gaps. Data show that biochars activated with acids or metals can achieve removal capacities above 200 mg/g for certain cationic dyes, while even pristine biochars can remove anionic dyes at moderate capacities. However, reported adsorption capacities vary widely due to feedstock heterogeneity, pyrolysis conditions and experimental design. Regeneration efficiency often declines sharply after several cycles, and most studies use synthetic dye solutions rather than real textile effluents. The review identifies research gaps such as the lack of standardised testing, limited continuous-flow experiments and insufficient techno-economic analysis. Future work should integrate biochar adsorption with renewable energy and advanced oxidation, explore hybrid composites, and evaluate performance under realistic conditions.