Recycling of distillation by-products of Ocimum sp. as potential source of antioxidants as well as feedstock for biochar

Distillation by-products of two Ocimum sp. were recycled through extraction of phenolic compounds and development of functional material like biochar. For extraction, different solvents either sole or in aqueous combinations (25%, 50%, and 75%) were used. Fifty percent aqueous methanol provided highest extraction yield (11.37 and 14.81% for distillated materials of O. sanctum and O. basilicum, respectively) with total phenol content of 76.51 and 82.00 mg of gallic acid equivalent (GAE)/g of dry extract and total flavonoid content of 37.53 and 41.01 mg of quercetin equivalent (QE)/g of dry extract for distillated materials of O. sanctum and O. basilicum, respectively. This solvent extract exhibited highest antioxidant activity in terms of radical scavenging, reducing power and iron chelating ability with IC₅₀ of 94.02, 237.91, and 379.55 μg/mL for distilled O. sanctum and 89.48, 193.70, and 394.41 μg/mL for distilled O. basilicum, respectively. The exhausted biomasses were further utilized for development of biochar. Physicochemical properties (carbon content, porous surface morphology, and cation exchange capacity) of developed biochar indicated its agronomic as well as soil amendment potential. Thus, this study proposed a model biorefinery for distillation waste, which also support circular economy through effective recycling.