Polyhydroxyalkanoate production using waste vegetable oil and filtered digestate liquor of chicken manure

The production of polyhydroxyalkanoates (PHA) using digestate of chicken manure combined with waste sunflower oil as no-cost feedstocks in a multi-stage process was investigated. Using Cupriavidus necator H16 in combined culture media, a maximum PHA accumulation of 4.6 ± 0.2 g/L at 75.1 ± 1.4% of cell dry matter and a residual cell matter yield of 1.5 ± 0.1 g/L were obtained after 96 hr of cultivation (30 °C, 160 rpm, pH 7.0) in flask-based experiments. Manure was acidogenically fermented in a continuous stirring tank reactor in fed-batch mode. The bioreactor was operated at varying organic loading rates (OLR) and hydraulic retention times (HRT) ranging from 1-4 g volatile solids (VS)/L/d and 4-8 days, respectively. Optimal operation was observed at an OLR of 4 g VS/L/d and an HRT of 4 days. Analysis showed the presence of significant amounts of ammonia, potassium, magnesium, calcium, and trace elements, i.e. Fe, Cu, Ni, Mn, Co, Zn, Cr in the digestate. The micro-filtered digestate was utilized as a complex culture media base while waste oil served as an additional carbon source and supplemented for effective PHA production. The total volatile fatty acid content of digestate greatly affected the growth performance of the PHA-producing microorganism Cupriavidus necator H16.