Waste-to-value: Two-Step bioconversion of palm oil mill effluent into biodiesel and polyhydroxybutyrate

Converting waste from palm oil mill effluent (POME) into biodiesel and polyhydroxybutyrate (PHB) is a sustainable method for reducing pollution and lowering the cost of these eco-friendly products. This study employed an enzymatic process to convert the oil extracted from POME into biodiesel. The wastewater was then used for PHB synthesis. First, oil was extracted from POME and used as a substrate for biodiesel production. A mixture of immobilized Candida rugosa and Rhizomucor miehei lipases (1:1, w/w) on PHB was used as a catalyst. Under optimized conditions, the highest biodiesel yield (97.7 ± 0.6%) was achieved within 24 h. The biodiesel produced was characterized and compared with EN 14214 and ASTM D6751 fuel standards. The immobilized lipase maintained its activity over three reuse cycles, indicating its potential for cost-effective application. For PHB production, Caldibacillus thermoamylovorans strain PHA005 was used to synthesize PHB from wastewater remaining after oil extraction (WR-POME). Supplementing the effluent with 20 g/L molasses resulted in a maximum PHB production of 59.9 ± 0.5% cell dry mass (CDM) after 96 h, a 1.8-fold increase compared to the non-supplemented effluent. The extracted PHB was confirmed through GC and FTIR analysis. This research presents a sustainable and integrated strategy for POME valorization, producing high-value biodiesel and PHB.