Biosynthesis of medium-chain length polyhydroxyalkanoates from pre-treated food wastewater

The escalating global plastic waste crisis, coupled with the challenges of managing high-moisture food waste from industrial processing, has prompted nations worldwide to pursue sustainable alternatives and comprehensive waste-reduction strategies. This study addresses this dual challenge by optimizing medium-chain-length polyhydroxyalkanoate (mcl-PHA) production from food wastewater (FWW) using Pseudomonas putida through an iterative refinement process, offering a solution that converts waste into biodegradable plastics.

In synthetic substrate tests, the highest PHA yield was 0.70 ± 0.05 g PHA/g VSS, with poly(3-hydroxydecanoate) constituting the majority (77.5 ± 2.6%) of the PHA composition, followed by poly(3-hydroxyoctanoate) (15.6 ± 8.8%). These tests underscored the potential of ethanol as a significant contributor to mcl-PHA biosynthesis. In actual substrate tests using pre-treated soluble FWW (P-FWW), the optimal PHA yield was 0.33 ± 0.02 g PHA/g VSS at an F/M ratio of 5. Lower F/M levels (5–25) predominantly produced short-chain-length PHA (scl-PHA), mainly in the form of poly(3-hydroxybutyrate), while higher F/M levels (50–100) favored mcl-PHA, specifically poly(3-hydroxydecanoate).

This study demonstrates that FWW can be effectively valorized as a sustainable feedstock for PHA production, transforming an industrial waste stream into a valuable biopolymer resource. By establishing the critical relationship between feeding strategy (F/M ratio) and PHA composition, this research provides practical guidelines for optimizing microbial biosynthesis at scale. These findings contribute to circular economy principles by simultaneously addressing food-waste management and reducing dependence on petroleum-based plastics, positioning PHA production from FWW as a viable pathway toward sustainable biomanufacturing.