Industrial dye removal from tannery wastewater by using biochar produced from tannery fleshing waste: a road to circular economy

In this study, the capacity of biochars, derived from the pyrolysis of tannery fleshing waste (TFW) at 400 ?; 500 ? and 600 ?, in removal of red dye Sella Fast Red (SFR) from aqueous solutions and tannery wastewater was investigated under various experimental conditions in batch mode. Results show that for all applied biochars, the removed kinetics data were well fitted by the pseudo-second-order model, and the equilibrium state was obtained after 240 min of contact time. For an aqueous pH of 6 and a red dye concentration of 75 mg.L-1, the removed amounts increased from 26 mg.g(-1) to 39.86 mg.g(-1) when the used pyrolysis temperature was increased from 400 ? to 600 ?. Moreover, SFR adsorption data at equilibrium were well fitted by Langmuir model suggesting a probable monolayer adsorption process with a maximal removal capacity of 62.7 mg.g(-1) for BTFW-600 ?. The thermodynamic study demonstrated that SFR adsorption was endothermic for the three tested biochars. Desorption experiments with distilled water proved that SFR was significantly desorbed from the tested biochars, which offers possible reusability. On the other hand, BTFW-600 ? has demonstrated an important ability in removing SFR from real wastewater since only one dosage of 15 g.L-1 was enough to ensure more than 97% of dye removal. According to pH(ZC) and FTIR analysis, the possible mechanism toward SFR dye removal was attributed to electrostatic interactions that occurred between biochar and functional groups of SFR. This work could provide guidance for the value-added utilization of tannery solid waste and a practical way to remove dyes from tannery wastewater.