Abstract
Spent coffee grounds (SCG) are abundant, low-cost and versatile feedstocks for a wide range of high-valued end products. With a goal to achieve zero waste, this study aims to further broaden the diversity by using the residue for bioactive components, biodiesel production, as well as for the manufactures of activated carbon and fuel pellet. The analyzed SCG oil was rich in palmitic, oleic and linoleic acids. Polyunsaturated fatty acids accounted for more than 50 % of the oil composition. Among different extraction methods, microwave-assisted extraction (MAE) was found to be recommended for maximal yields of SCG’s oil (17.00 %) and total flavonoid content (TFC) (31.15 mg quercetin/g); while ultrasound-assisted extraction (UAE) was more efficient toward the recovery of lipid hydroperoxide (LP) (0.0191 mM) and total phenolic content (TPC) (13.500 mg AG/g). Optimal SCG-over-solvent ratio was another studied parameter. The research also confirmed the antioxidant capability of the coffee grounds. The production of SCG’s biodiesel followed the conventional esterification and transesterification processes. The assessment of the fuel complied with the American Standard for Testing Material (ASTM 6751); and most of the analyzed values satisfied the standards. The activated carbon (AC) generated from SCG demonstrated a comparable purification capacity. The BET surface area and total pore volume were 1,547 m2/g and 0.225 cm3/g. For optimal area’s value, a chemical activation by KOH, at 800 °C and 1:1-impregnation ratio was advisable. The solid waste after the oil extraction was used to produce fuel pellet with a high measured heating value (22 MJ/kg). The study underlined spent coffee grounds as a promising feedstock for biodiesel production. The residue offered not only a cut in raw material’s cost, but also an increase in net profit through the commercialization of other value-added by-products.
