Urban Biorefinery Demonstration: Production of Polyhydroxyalkanoates from a Municipal Solid Waste

The production of short-chain-length polyhydroxyalkanoates (scl-PHAs) from municipal solid waste-derived volatile fatty acids (VFAs) has been demonstrated. The objective of the study was to evaluate the technical feasibility of the process under real operational conditions. Moreover, the process operation was conducted without pH and temperature control to reduce potential industrial implementation barriers, i.e., by simplifying the process control and minimizing the auxiliary services available for the process. A two-step bioprocess was developed, consisting of an enrichment phase in a 20 m3 fermenter operated for 214 days and an accumulation phase carried out in a 3 m3 batch fermenter across 39 accumulation cycles. In the enrichment phase, steady-state conditions were achieved once the feast/famine ratio was lower than 0.2 h/h. Thus, the impact of environmental conditions was analyzed. It was found that the system’s response was a destabilization of the culture under sharp variations at environmental temperature, followed by an adaptation period and final recovery of the system. During the accumulation phase, the impact of chemical oxygen demand (COD) feeding rates was assessed, with a maximum scl-PHA accumulation of 59 wt.% (2.87 g/L) recorded. The extraction process was also performed at demonstrative scale using dimethyl carbonate (DMC) as the solvent, yielding a scl-PHA recovery of 92% with a purity of 90%. These results confirm the technical feasibility of producing scl-PHAs from municipal organic waste at demonstrative scale, supporting the circular bioeconomy model.