Biochar from tannery liming sludge for dyeing wastewater treatment: Process optimization, performance evaluation, kinetics, and isotherm studies

The untreated tannery hair-burning liming sludge (THBLS) harms the ecosystem. The treatment and management of THBLS provide considerable complications. This study examined the removal of dye from real post-tanning wastewater of a tannery utilising biochar generated from THBLS. Biochar was characterized by proximate analysis, EDS, SEM, surface area measurement, XRD, FTIR, and pHpzc. The dye adsorption capability of biochar obtained from real post-tanning wastewater was examined under varying temperature, contact time, biochar quantity per batch, and relative solution pH. The biochar removed 87.487 % of the dye at a pH of 7.792, using 0.350 g of biochar in 40 mL of post-tanning wastewater for 25 min at 40ºC. The reductions of BOD 5 , COD, and salinity were 92.193 %, 87.429 %, and 53.198 %, respectively. The Freundlich isotherm model and pseudo-second-order kinetic model exhibited a strong fit to the experimental data, indicating dye adsorption was controlled in chemisorption. Thermodynamic analyses indicated that dye adsorption onto biochar was a feasible, exothermic, and spontaneous process. The adsorption properties of biochar were observed in the hydrogen bonds, electrostatic, π-π, and n-π interactions with dyes. The produced biochar can be reutilized following an alkaline wash with minimal functional degradation. Thus, the application of THBLS biochar can efficiently remove acid dyes from tannery post-tanning dyeing wastewater, thereby reducing environmental pollution. • Derived biochar from liming sludge characterized through FTIR, XRD, SEM, and EDS. • Dye, BOD 5 , and COD removal achieved at 87.487 %, 92.193 %, and 87.429 %, respectively. • Dye adsorption followed Freundlich isotherm and Pseudo-second order kinetics. • Interaction of dye adsorption on biochar was exothermic and chemisorption process.