Utilization of Spent Coffee Waste Biomass as a Promising Feedstock in Bioplastics Production Using Cupriavidus necator

Abstract

The increasing demand for sustainable bioplastics is constrained by the high production costs associated with refined carbon sources, highlighting the need for low-cost, renewable feedstocks. This study evaluated the potential of spent coffee grounds (SCG), an abundant and sustainable feedstock for generating polyhydroxyalkanoates (PHA) using Cupriavidus necator. First, SCG was subjected to solvent extraction to remove coffee oil, followed by extraction of phenolic compounds, and the remaining biomass was referred to as SCGO. The originality of this work lies in the systematic comparison of acid, alkaline, and peracetic acid pretreatments and their subsequent evaluation for microbial PHA production. SCGO was subjected to various chemical pretreatments, including acid (H2SO4), alkaline (NaOH), and peracetic acid (PAA) pretreatment. The effects of the different pretreatments on SCGO delignification, hydrolysis yield, and enzymatic saccharification to release monomeric sugars were evaluated. Among the tested methods, alkaline pretreatment provided the highest delignification efficiency, enzymatic saccharification, and fermentable sugar recovery, resulting in superior bacterial growth and PHA production. Under optimized conditions, the alkaline-pretreated SCGO hydrolysate supplemented with corn steep liquor produced a maximum biomass concentration of 6.5 ± 0.26 g/L, 60.0 ± 1.45% PHA accumulation, and a PHA titer of 3.89 ± 0.14 g/L. Structural and thermal characterization confirmed that the produced polymer possessed properties comparable to those of conventional poly(3-hydroxybutyrate) (PHB). Overall, this study demonstrates that integrated valorization of spent coffee grounds can effectively generate fermentable substrates for microbial PHA production, providing a sustainable approach for converting agro-industrial residues into high-value bioplastics while supporting circular bioeconomy strategies.