Production of polyhydroxyalkanoates (PHAs) from waste: product recovery, techno-economic and ex-ante environmental assessment

Polyhydroxyalkanoates (PHAs) have received much attention as bio-based plastics that may contribute to future replacement of petroleum based plastics. Although research on microbial PHA production has been active for a couple of decades, their commercialization is still constraint by the high production costs. The main cost drivers of the process are: (a) raw materials (fermentation feedstock), (b) downstream processes for product recovery and purification, and (c) costs associated to maintaining a pure culture during the fermentation (e.g. fermenter costs and energy required for sterilization).

Several studies have integrated the PHA production process with wastewater treatment with a dynamic feast-famine enrichment system in order to reduce the cost from raw material and energy consumption aspects. This cultivation strategy has resulted in intracellular PHA content and biomass specific PHA production rates comparable to current pure culture practices, and it has already been demonstrated at pilot scale in industrial wastewater. We have studied the technical feasibility of purifying PHAs from such mixed cultures, addressing crucial aspects for scale-up such as purity, recovery yield, product degradation during processing and material properties. Several downstream processing routes are compared by means of techno-economic performance and Life Cycle Assessment. It is shown that PHA production from wastewater leads to reduced costs and environmental impact compared to sugar-based, pure culture fermentation processes. Furthermore, the choice of downstream processing route showed to have a large impact on the costs and environmental impact of the process, mostly through utility consumption, but also on the potential product applications (i.e. material properties).