Preparation, Optimization, and Characterization of Biochar Using Zero Liquid Discharge (ZLD) Sludge of a Wastepaper Based Paper Mill

This paper reports the preparation of biochar from sludge generated in a wastepaper-based paper mill operating on the Zero liquid discharge principles. Biochar has been prepared from sludge, hereafter referred to as Zero liquid discharge sludge, in a laboratory muffle furnace using the slow pyrolysis method. The effect of pyrolysis temperature and pyrolysis time on biochar’ yield, surface area, and pore volume of biochar has been studied by applying response surface methodology. The pyrolysis temperature and pyrolysis time were maintained in the range 450-750oC and 100-200 min. respectively, under the central composite design. It was found that temperature and time significantly impacted the biochar’s yield, surface area, and pore volume of biochar showing strong linear, quadratic, and interaction effects. ANOVA of the empirical models developed in this study was found to be efficient with high R² predicted, (R² adjusted – R² predicted) 0.2, adequate precision ˃ 4, and non-significant lack of fit value.  The optimum pyrolysis temperature and pyrolysis time were determined to be 539.65°C and 176.67 min correspondingly having desirability value 0.651. The optimized values of biochar’s yield, surface area, and pore volume for Zero liquid discharge sludge biochar were found to be 63.95%, 40.23 m²/g, and 0.048 cm³/g respectively. The physicochemical (proximate and CHNS) and instrumental (XRD, TGA, DSC, FT-IR, and SEM) analyses along with their comparison with other biochar reported in the literature confirmed the use of this biochar as an adsorbent in wastewater treatment.