Data underlying the research of Efficient Hydrothermal Pretreatment of Mixed PHA/PLA and Consequent Continuous Anaerobic Fermentation into VFA

Recycling biobased biodegradable plastics such as polyhydroxyalkanoates (PHA) and polylactic acid (PLA) is essential for developing a circular economy. This study presents an integrated strategy that combines batch hydrothermal processing at 150℃ with continuous open-culture fermentation to convert PHA and PLA into C₂-C₆ carboxylates. Co-hydrolysis in a carboxylic acid solution significantly enhanced PHA depolymerization compared to PHA hydrolysis alone. Among various catalytical supplements, PLA addition notably improved PHA hydrolysis, achieving up to 91% dissolution. Throughout fermentation, acetate and <em>n</em>-butyrate were the primary products. In Phase VI, co-fermentation of PHA hydrolysates (~10 g/L 3-hydroxybutyrate) and PLA hydrolysates (5 g/L lactate) yielded acetate (4.4 g/L), <em>n</em>-butyrate (8.0 g/L), and <em>n</em>-caproate (0.3 g/L), while also reducing the need for KOH for pH control. An overall conversion efficiency of 89% from bioplastics to carboxylates was achieved, with a high <em>n</em>-butyrate selectivity of 71%. Supplementing with ethanol (7 g/L) further enhanced chain elongation, increasing <em>n</em>-butyrate concentration to 10.1 g/L, although excess ethanol oxidation was observed. This study demonstrates, for the first time, the successful continuous open-culture fermentation of PHA and PLA hydrolysates into carboxylates. Microbial community analysis identified <em>Clostridium tyrobutyricum</em> as a key species likely responsible for dominant <em>n</em>-butyrate production.