Slow pyrolysis of agro-food waste to produce biochar and activated carbon for adsorption of pollutants from model wastewater

Abstract

The increasing human population has induced more demand for food, and to cope with that demand agricultural production has been increased. The wastes generated from such activities resulted in environmental pollution and emanated the deterioration of the climate. Therefore, effective management and utilization of different kinds of wastes are crucial to mitigate greenhouse gas generation challenges upon natural decomposition and waste accumulation. Conversion of biogenic wastes to biofuels and bioproducts can address the energy crisis and play a role in environmental remediation. In this study, the first phase of work was focused on exploring the characteristics of food waste ( mixture of onion peel, carrot peel, bell pepper stalks, potato peel, celery head and leaves, watermelon shell, orange peel, pumpkin seeds and pistachio shells) and agricultural crop residues (e.g., canola hull and oar hull) to determine their candidacy for slow pyrolysis to produce biochar, bio-oil, and gaseous products. Process parameters of slow pyrolysis such as temperature, reaction time and heating rate were investigated for food waste to obtain maximum biochar yields. Furthermore, the obtained favourable conditions were utilized for the slow pyrolysis of individual food wastes and agricultural residues, and their detailed characterization was performed. Maximum biochar yields of 28.4, 28.8, and 29.1 wt. % were recorded for food waste, canola hull and oat hull, respectively, at favourable temperature, heating rate and reaction time of 600 °C, 5 °C/min and 60 min, respectively. In the second phase of this study, the biochar derived from food waste and agricultural residue at favorable conditions was used as the precursor for activation study to produce high-quality activated carbon. Steam-led physical activation and KOH-led chemical activation of biochar were conducted, and process parameters such as temperature (700-900 °C) and activation time (60-120 min) were investigated using Taguchi L18 (21 X 32) method. BET surface area and product yield were determined for each activated carbon product. The highest BET surface area of 1760 m2/g (food waste), 1718 m2/g (canola hull), 1334 m2/g (oat hull) with yields of 48.8, 48.6 and 51.3 wt.%, respectively, were obtained at favourable conditions for KOH led activation. Furthermore, the performance test for the biochar and activated carbon were substantiated through the dye adsorption study using model wastewater.