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The persistent release of synthetic dyes from industrial effluents constitutes a substantial ecological and toxicological hazard owing to their persistent molecular structure and biological recalcitrance. This review presents a focused evaluation of biochar derived from dye-laden sewage sludge (DLSS-B), highlighting its potential as a low-cost, sustainable adsorbent for dye removal from wastewater. DLSS, a byproduct rich in organic matter, inorganic minerals, and residual dyes, is thermochemically converted into biochar through pyrolysis. A critical assessment is conducted on how variations in pyrolysis temperature, thermal ramping rate, and inert gas environment influence the resultant biochar’s specific surface area (reaching up to 405 m²/g), pore architecture, and surface functional chemistry. DLSS-B exhibits high adsorption capacities ranging from 200 to 405 mg/g for dyes such as malachite green and crystal violet, primarily through π–π stacking, electrostatic interactions, and hydrogen bonding. Chemical modifications, including acid/alkali activation and metal doping, further enhance its adsorptive performance. Regeneration studies show that DLSS-B can retain up to 92% efficiency over five cycles, indicating strong reusability. Beyond dye removal, secondary applications such as soil amendment (non-food use) and energy recovery (~20 MJ/kg) are discussed. This review emphasizes the integrated role of pyrolysis engineering, surface chemistry, and reuse strategies in developing DLSS-B as a viable material for industrial dye remediation. • Sewage sludge biochar achieves up to 98% dye adsorption efficiency. • Chemical activation and Fe₃O₄ enhance biochar’s adsorption and separation. • Dye-laden biochar doubles as a soil enhancer and renewable energy source. • Biochar exhibits sustained adsorption performance over multiple regeneration cycles. • Pyrolytic biochar offers a sustainable solution for wastewater and sludge management.
Gupta et al. (Mon,) studied this question.