Table 1.

Recent proposals for alternative uses of spent coffee grounds.

Starting Material	Technology	Product/Application	Ref.
		Energy
wood sawdust and SCG	pellet pressing	solid fuel pellets	[14]
SCG and larch sawdust or spruce shavings	high-pressure hydraulic briquetting press	solid fuel briquettes	[15]
SCG	pyrolysis	biochar/carbon cloth electrode/electricity generation and storage	[16]
SCG and reduced graphene oxide	vacuum-assisted impregnation	composite phase change material/solar energy storage	[17]
SCG	drying + oil extraction + transesterification	biodiesel	[18]
SCG	carbonization + CO2 activation	energy storage	[19]
		Chemicals
SCG extract and Xanthophyllomyces dendrorhous	drying, sterilization and water extraction	astaxanthin/cosmetics, supplements and food	[20]
SCG extract and Millerozyma farinosa	drying, sterilization and water extraction	glutathione/medicine, food supplements and cosmetics	[21]
SCG	defatting + drying + hot water extraction + incubation with ammonium sulfate + centrifugation + ultra-filtration + vacuum drying	surfactants	[22]
SCG	solvent extraction (ultrasound, microwave or β-cyclodextrin-assisted)	phenolics	[23]
SCG	high-pressure temperature extraction	chlorogenic acids and caffein	[24]
SCG	subsequent extractions (hexane, water and ammonium sulfate) + centrifugation+ ultrafiltration + vacuum drying	foaming agent	[25]
		Adsorbents
SCG	mixture with KOH and carbonization	biochar/ammonia removal from water	[26]
SCG	torrefaction	biochar/removal of diesel mixed in water	[27]
SCG	activation with NaOH, CaCO3 and carbonization	activated carbon/removal of methylene blue and methyl orange from water	[28]
SCG	no treatment	biosorbent/heavy metal (Cd) removal from aqueous solution	[29]
SCG	H3PO4 pyrolysis	microporous AC/removal of explosives from water	[30]
SCG	pyrolysis at 500 °C	biochar/removal of Norfloxacin (antibiotic) from water	[31]
SCG	washing with NaOH following by drying	biosorbent/recovery of dissolved metals (Fe, Al, Ca, Co, Mn, Ni, and Zn) from acid sulfate soil drainage	[32]
		Materials
SCG and epoxy resin	mixing and curing	Flame retardant in polymer	[33]
SCG and Polylactide (PLA) powder	decolorization, micro- and nano-processing and extrusion	polylactic acid composite for 3D-printing	[34]
SCG and pectin	continuous casting	biocomposite pectin film	[35]
SCG and plaster	mixture with water and drying	thermal insulation material	[36]
SCG and hydrogels	near infra-red laser irradiation and incorporation into poly(N-isopropylacrylamide) hydrogels	photothermal materials	[37]
SCG	carbonization + composite mixture (cyanate ester, graphene nanoplates and epoxy resin) +hot pressing	composite with electromagnetic interference (EMI) shielding properties	[38]
		Food products and ingredients
SCG	acid extraction followed by precipitation	bioactive peptides with antihypertensive and antioxidant potentials	[39]
SCG	microwave-assisted extraction of antioxidants, fermentation (Saccharomyces cerevisiae) and distillation	fermented and distilled alcoholic beverages	[40]
SCG	hydrolysis followed by fermentation with wine yeasts	alcoholic beverages	[41]
SCG	ethanolic extraction followed by addition of caramel, water, glucose syrup and vanillin	coffee-flavored liquor	[42]
SCG	extraction with isopropanol	antimycotic and anti-ochratoxigenic material; potential food ingredient with moderate cytotoxic and antibacterial activities	[43]