Integrated solid-state enzymatic hydrolysis and solid-state fermentation for producing sustainable polyhydroxyalkanoates from low-cost agro-industrial residues

Polyhydroxyalkanoates (PHA) are biodegradable bioplastics of interest as potential substitutes of petroleum-derived plastics that can be produced starting from lignocellulosic-derived residues. This study presents the combined solid-state enzymatic hydrolysis (SSEH) and solid-state fermentation (SSF) as a sustainable approach for obtaining PHA using the leftovers brewer's spent grain (BSG), grape pomace (GP) and olive-mill solid waste (OSW) as substrates. SSEH performance was influenced by the intrinsic characteristics of each residue, the temperature, and the type of enzymatic extract used. Thus, the maximum sugars release (0.16 g g(-1) of dry residue (gTS)) was obtained with GP. Furthermore, coupling SSEH and SSF promoted PHA yield increases of up to 54%, 41% and 31% for BSG, GP and OSW respectively, compared to SSF alone. The maximum PHA yield was achieved using hydrolyzed BSG with 12.5 mg g(-1) TS (0.33 g kg(-1) h(-1)). Results show the potential of this approach as an attractive alternative to obtain bioproducts such as PHA sustainably in residue-based systems. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.