Co-pyrolysis biochar derived from sewage sludge and lignin: Synergetic effect and adsorption properties

Abstract

Co-pyrolysis of sewage sludge (SS) and biomass is expected to improve the biochar quality. Lignin as a major component of biomass was selected for co-pyrolysis with SS. The characteristics and kinetics of co-pyrolysis were studied by thermogravimetric analyzer/differential scanning calorimetry (TGA/DSC) and Coats-Redfern method; the effects of pyrolysis temperature and mixing proportion on the biochar yield were investigated via muffle furnace experiment, and the porosity and methylene blue (MB) adsorption capacity of the obtained co-pyrolysis biochar were evaluated. The results showed that co-pyrolysis promoted the decomposition of mixture and reduced the reaction temperature. The reaction order model was the primary mechanism model for co-pyrolysis, and both promotion and inhibition effects were observed based on the obtained activation energy. At 400 ℃ and 600 ℃, the co-pyrolysis synergetic effect on biochar yield was weak, and synergy effect of inhibition on the porosity of biochar was caused by tar and ash adhesion. When temperature was elevated to 800 ℃, catalytic effect of alkali and alkaline earth metals (AAEMs) dominated the synergetic effect, promoted char decomposition, meanwhile, pores were dramatically developed. Co-pyrolysis of SS and lignin improved MB adsorption capacity of SS biochar from 14.04 mg g−1 to 180.36 mg g−1, indicating it to be a prospective method for waste to valuable biochar production.