Valorization of Sewage Sludge with Pine Sawdust as Biochar: Optimization of the Torrefaction Conditions and Biochar Quality

Abstract

This work explores the effects of the temperature (250, 280, 310°C), time (20, 40, 60 min), sewage sludge mixing ratio (25, 50, 75%) on the solid fuel quality and yield of the biochar produced from sewage sludge blended with pine sawdust. The optimal conditions for the torrefaction of sewage sludge and pine sawdust were investigated by the response surface methodology. Mathematical models were developed on the weight yield, high heating value and ash content and experimental data were examined through analysis of variance. The results depicted that the effects of temperature and mixing ratio were more considerable than residence time for the three response variables. The optimum point for weight yield, HHV, ash were predicted to be 60.82%, 21.58 MJ kg-1 and 18.78% at 310°C, 20 min and sewage sludge mixing ratio of 25%, respectively. The experimental results show that the average values of the experiments were 56.4%, 22.9 MJ kg-1, and 21% for weight yield, HHV and ash content, respectively.