Effects of sludge thermal-alkaline pretreatment on cationic red X-GRL adsorption onto pyrolysis biochar of sewage sludge

Thermal-alkaline pretreatment has traditionally been used to enhance anaerobic sludge digestion. In this study, after removing the supernatant, which could be used in anaerobic digestion, the Residual Solids of Thermal-Alkaline pretreated sewage Sludge (RSTAS) were used to prepare biochar via pyrolysis, which could then adsorb Cationic Red X-GRL(X-GRL). The experimental results showed that the RSTAS-biochar had a higher BET surface area and total pore volume than the biochar prepared from raw sludge (RS) (43.5% and 33.3%, respectively). The pretreatment enhanced the X-GRL adsorption capacity of the biochar by 1.5-49.2% at dosages between 12.5-100.0 g/g, and the highest adsorption capacity increased from 39.1 mg/g to 47.6 mg/g. The biochar from RSTAS had a wider application pH range for X-GRL adsorption. The kinetics and isotherms for X-GRL adsorption onto the two biochars were well fitted to the pseudo-second-order and Langmuir isotherm models, respectively, which suggested that thermal-alkaline pretreatment had little effect on the adsorption mechanisms of X-GRL onto biochar.