[2S04e] 18. Biorefinery and Bioproduction - Part 3

5:30 PM - 5:45 PM JST(8:30 AM - 8:45 AM UTC)

[2BRBP-16] Two-stage biorefinery for thermostable high-purity PHA from food waste via high-titer lactic acid

○Nirakar Pradhan¹, Lijun Luo¹ (1. Hong Kong Baptist University (Hong Kong))

Keywords:

Lactic acid bacteria,Polyhydroxyalkanoates,Biorefinery,Organic waste valorization

Polyhydroxyalkanoates (PHA) are biobased and biodegradable polymers that can be produced from food waste (FW), offering a circular solution to plastic pollution and organic waste management. Conventional FW-to-PHA routes typically generate mixed volatile fatty acids at low titers, which challenges downstream PHA production by over-diluting cultures and limiting carbon availability during fed-batch fermentation. This often leads to low process yields. Unlike other acids, lactic acid (LA) can be produced from FW at substantially higher concentrations and yields, presenting a more efficient pathway. In this study, we demonstrate a complete two-stage bioprocess that first converts FW to high-titer LA and then to PHA.In the first stage, we used an enriched lactic acid bacteria (LAB) culture from anaerobically digested sludge to ferment FW under non-sterile conditions, producing approximately 60 g/L of LA with a yield of over 0.5 g LA/g volatile solids (VS). The resulting LA-rich broth was then concentrated to nearly 130 g/L and used directly as a non-sterile feed for PHA production. In the second stage, we conducted a fed-batch fermentation using the concentrated LA, achieving a final PHA concentration of approximately 11 g/L at 60 hours, which corresponded to a PHA accumulation of over 60% of the cell dry weight. Crucially, the produced PHA biopolymer showed high purity (>98%) and excellent thermal properties, with a melting temperature (T_m) of around 176 °C and a degradation temperature (T_d) of over 294 °C.This work successfully demonstrates the feasibility of an integrated process producing high-titer LA from FW and valorizing it directly as a carbon source for PHA synthesis. Our approach bypasses the common issue of low-titer acid intermediates and avoids costly sterilization steps, ultimately enabling the production of a high-purity, thermostable biopolymer from a real-world waste stream.