Acid assisted-hydrothermal carbonization of solid waste from essential oils industry: Optimization using I-optimal experimental design and removal dye application

Solid waste (SW) generated from extracting of essential oils from medicinal and aromatic plants (MAPs) is an abundant and renewable resource, but proper recycling is necessary to prevent negative environmental impacts from improper disposal. This study focused on converting SW from essential oil (EO) extraction industry by citric acid-catalyzed hydrothermal carbonization (c-HTC) coupled with chemical activation into a carbonaceous material to remove organic pollu-tants. For this purpose, an I -optimal design coupled with response surface methodology (RSM) was developed to investigate the relationship between the severity factor (SF) of the c-HTC process and citric acid dose (HTCcat) on carbon retention rate (CRR) and hydrochar mass yield (MY). Under optimal conditions (5.32 and 2 g for SF and HTCcat, respectively), an optimized hydrochar (HCop) was characterized by a CRR and MY of 71.02% and 56.14%, respectively. HCop was chem-ically activated by KOH solution (AHCop) and characterized by a specific surface area of 989.81 m2. g_1 , a pore volume of 0.583 cm3.g-1, a higher heating value (HHV) of 37.3 MJ/Kg, oxygenated sur-