In-vitro antioxidant evaluation and production of biochar from distillation waste biomass of Mentha arvensis

Extraction of essential oils from aromatic plants generates a large amount of distillation waste, which needs to be managed properly. Conversion of this waste into valuable compounds with different applications will not only reduce environmental pollution but also provide a new avenue for complete utilization. The objective of the present study was to explore the distillation waste of Mentha arvensis for dual utilizations through the extraction of bioactive antioxidant/phenolic compounds and to re-use the exhaustive residues for the fabrication of func-tional materials like biochar. For the extraction of antioxidants and phenolics, several aqueous polar solvents (methanol, ethanol and acetone) mixture were tried and 75 % aqueous methanol was found to be the best solvent in terms of extraction yield, total phenolic content and flavonoid content. The same extract also showed the highest antioxidant activity for DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS [(2, 2 '-azino-bis (3-ethyl-benzothiazoline-6sulphonic acid)] assay. After extraction of antioxidant/phenolics, the remaining exhaustive residues was re-used for the production of biochar, which was subsequently used as a potential soil amendment. A short-term soil incubation study was conducted with mentha distillation waste (MDW) biochar. The study indicated that MDW biochar can be used as an effective amendment for degraded soil as evidenced by im-provements in soil pH, cation exchange capacity, available nutrients (N, P, and K) status, and soil biological properties in terms of microbial biomass carbon and dehydrogenase activity. Thus, this study helped to develop a strategy for complete recycling of MDW under circular economic model, which may also promote environmental sustainability.