Abstract
Polyhydroxyalkanoates (PHAs) production at pilot scale has been recently investigated and carried out exploiting different process configurations and organic wastes. More in detail, three pilot platforms, in Treviso (North-East of Italy), Carbonera (North-East of Italy) and Lisbon, produced PHAs by open mixed microbial cultures (MMCs) and different organic waste streams: organic fraction of municipal solid waste and sewage sludge (OFMSW-WAS), cellulosic primary sludge (CPS), and fruit waste (FW), respectively. In this context, two stabilization methods have been applied, and compared, for preserving the amount of PHA inside the cells: thermal drying and wet acidification of the biomass at the end of PHA accumulation process. Afterward, polymer has been extracted following an optimized method based on aqueous-phase inorganic reagents. Several PHA samples were then characterized to determine PHA purity, chemical composition, molecular weight, and thermal properties. The polymer contained two types of monomers, namely 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) at a relative percentage of 92.6–79.8 and 7.4–20.2 w/w, respectively, for Treviso and Lisbon plants. On the other hand, an opposite range was found for 3HB and 3HV monomers of PHA from Carbonera, which is 44.0–13.0 and 56.0–87.0 w/w, respectively. PHA extracted from wet-acidified biomass had generally higher viscosity average molecular weights (Mv) (on average 424.8 ± 20.6 and 224.9 ± 21.9 KDa, respectively, for Treviso and Lisbon) while PHA recovered from thermally stabilized dried biomass had a three-fold lower Mv.
Highlights
Among different kinds of biopolymers, polyhydroxyalkanoates (PHAs) are one of the most interesting and promising thanks to their mechanical properties and biodegradability
As an alternative to industrial scale production based on pure culture (Gholami et al, 2016), the application of low-cost substrates based on organic wastes and by-products is of an extreme interest, specially coupled with the use of mixed microbial cultures (MMCs) that do not require
Three grades PHA produced from three different organic wastes have been extracted and characterized
Summary
Among different kinds of biopolymers, polyhydroxyalkanoates (PHAs) are one of the most interesting and promising thanks to their mechanical properties and biodegradability. Downstream processing, including PHA-rich biomass stabilization and polymer extraction, are among the most important factors affecting the overall PHA production cost and need to be optimized for pilot scale. Two types of stabilization method have been applied at pilot scale on PHA obtained from organic wastes, in order to preserve the amount of PHA produced after the accumulation step and its properties (Lorini et al, 2020). The recovered polymer was extensively characterized and resulted in good thermal and chemical properties, while it showed variable molecular weight (between 100 and 450 kDa) dependent on the applied stabilization method. Monomeric composition, i.e., 3HV content, showed to have effects on different polymer properties (Arcos-Hernández et al, 2013; Lorini et al, 2020), such as crystallinity
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