Valorisation of Residue of Mentha arvensis by Pyrolysis: Evaluation of Agronomic and Environmental Benefits

The elucidation of biochar properties across the various temperature ranges is necessary for the preparation of tailor made biochar from any feed stock. This paper reports selected physicochemical properties of biochar prepared from the residue of Mentha arvensis pyrolyzed at 450, 650 and 850 °C. Ultimate and proximate analyses, product distribution (bio-oil and biochar), TGA, Calorific values, FTIR, functional group analyses, cation exchange capacity and calcium carbonate equivalence of biochars revealed the variations and suitability of biochar for as a fuel feed stock and/or soil amendment. Bio-oil and biochars produced at 850 °C contained the highest carbon content (68 and 87%, respectively), and energy content (32 MJ/kg and 6837 kcal/mol, respectively) and could be a promising alternative for replacements of non-renewable-fuels. Biochar produced at 450 °C had the highest available nutrient contents (P: 47.3 mg/kg, NH 3 –N: 28 mg/kg, and NO 3 –N: 0.6 mg/kg), cation exchange capacity (161.8 meq/100 g) and calcium carbonate equivalence (83.5%) suitable and economical for soil fertility enhancement and liming of highly acidic soils (enhanced the pH up to 2.8 units at 6% application rate).