Valorization of spent coffee grounds through integrated bioprocess of fermentable sugars, volatile fatty acids, yeast-based single-cell protein and biofuels production.

[Display omitted] • Maximal VFAs and hydrogen yields reached 0.66 g/g-VS and 109 mL/g-VS, respectively. • SCG-derived VFAs offer a potential feedstock for microbial protein production. • Candida maltosa KKU-ARY2, a newly isolated yeast, accumulated protein of 43%. • Recycled solid residue after VFAs separation showed a promising methane production. Recovering nutrients from waste for biological processes aligns with sustainability principles. This study aimed to convert spent coffee grounds (SCG) into valuable products, including fermentable sugars, volatile fatty acids (VFAs), yeast-based single-cell protein and biofuels. Alkaline pretreatment was conducted before enzymatic hydrolysis, in which the pretreated SCG was hydrolyzed with varying enzyme loadings (20–60 filter paper units (FPU)/g-solid) and solid loadings (3–15 % w/v). The hydrolyzed slurry was utilized for VFAs and hydrogen production, yielding high values of 0.66 g/g-volatile solids (VS) and 109 mL/g-VS, respectively, using an enzyme loading of 50 FPU/g-solid and a solid loading of 3 % (w/v). The derived VFAs were used to cultivate a newly isolated yeast, Candida maltosa KKU-ARY2, resulting in an accumulated protein content of 43.7 % and a biomass concentration of 4.6 g/L. This study highlights the conversion of SCG into essential components, emphasizing the benefits of waste utilization through cascade bioprocesses. [ABSTRACT FROM AUTHOR]