Sustainable conversion of cassava peel waste into fermentable sugars and polyhydroxyalkanoate biopolymer

Cassava peel (CP), an abundant agro-industrial residue from cassava processing, was valorised as a renewable feedstock for fermentable sugar production via enzymatic hydrolysis and its subsequent use in polyhydroxyalkanoate (PHA) biosynthesis. Key variables influencing enzymatic hydrolysis were initially screened using a two-level Plackett–Burman Design, followed by process optimisation through Response Surface Methodology. A fully enzymatic, sequential one-pot hydrolysis strategy was developed and operated at a 30 mL working volume using water as the sole reaction medium, eliminating the need for buffering agents. High total reducing sugar (TRS) yields of 97.0–89.7% were achieved within 13–16 h across solid loadings of 5–20% (w/v). At 5% solids, 42.7 g/L TRS and 33.1 g/L glucose were obtained in 13 h, while increasing the solid loading to 20% produced 159.5 g/L TRS and 121.2 g/L glucose with only a modest reduction in yield. The use of water instead of buffered systems limited salt accumulation (∼0.5 g/L NaCl), thereby enhancing hydrolysate biocompatibility for downstream fermentation without requiring desalination. Structural, chemical, and thermogravimetric analyses confirmed extensive degradation of starch, cellulose, and hemicellulose, accompanied by lignin enrichment and increased substrate porosity, indicating effective biomass deconstruction. The resulting hydrolysates were directly utilised as carbon sources for Cupriavidus necator H16 cultivation without chemical supplementation. Intracellular PHA accumulation reached up to 84% (gPHA/gDCW), with a maximum volumetric titre of 1.37 g/L at a microplate screening scale (4 mL). Overall, this study demonstrates a simplified and resource-efficient enzymatic hydrolysis for converting CP into fermentation-ready hydrolysates at high sugar yields. The use of water as the sole reaction medium reduces salt accumulation and supports its potential integration into scalable biorefinery schemes for bioplastic production.