Preparation of bio-charcoal from sewage sludge and its performance on removal of Cr (VI) from aqueous solutions

Sludge-derived bio-charcoal (SDBC) was prepared from municipal sewage sludge by chemical activation with sulfuric acid followed by carbonization in this study. The important parameters for SDBC preparation process, which greatly affected the characteristics of SDBC were investigated. The optimized soak proportion, soak time and pyrolysis time were 1:1 (w/v), 8 h and 30 min, respectively. Adsorption experiments were conducted as function of pH, SDBC dosage, temperature, contact time and Cr (VI) initial concentration. The equilibrium adsorption data were fitted well to the Langmuir adsorption isotherm (r2 > 0.99). The calculated values of ΔS0, ΔH0, and ΔG0 indicated that the adsorption was endothermic and not spontaneous. After 10 h of adsorption at pH 1.0 and 25 °C with an adsorption dosage of 1.4 g L− 1, the maximum adsorption capacity of 61.3 mg g− 1 was reached at an initial Cr (VI) concentration of 240 mg L− 1. The maximum adsorption capacity (mg g− 1) for Cr (VI) provided strong evidence of the potential of SDBC for removing Cr (VI) from aqueous solutions.