Abstract
The utilization of food waste and sewage sludge as organic substrate from urban context for the synthesis of microbial polyhydroxyalkanoates (PHAs) has been only recently investigated at pilot scale. Within this context, two stabilization methods have been found for preserving the amount of PHA intracellularly produced by open mixed microbial culture (MMC): thermal drying and wet acidification of the biomass at the end of PHA accumulation process. The extracted PHA from the two differently stabilized biomasses was then characterized with regard to 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 93.0–79.8 and 7.0–20.2 w/w, respectively. PHA extracted from wet-acidified biomass had higher average molecular weights (Mw) of 370–424 kDa while PHA recovered from thermally stabilized dried biomass had a 3-fold lower Mw (on average). The PHA decomposition temperatures Td10% and Tdmax were in the range 260–268 °C and 269–303 °C, respectively, not dependent on the monomeric composition or molecular weight. Thermal properties such as melting temperature (Tm1 132–150 °C; Tm2 155–167 °C) and melting enthalpy (26–70 J/g) were quantified in a relatively broad range according to the different stabilization-extraction method and obtained composition.
Highlights
Polyhydroxyalkanoates (PHAs) are one of the most interesting biopolymers due to their mechanical properties and biodegradability
The comparison of PHA content data collected for each inhibition test shows that there was not a significant decrease of the polymer for 48 h following the addiction of H2SO4 (97 wt% of initial content) (Fig. 2a), demonstrating that the agent is suitable for microbial activity quenching and PHA stabilization
Even though the present biomass was selected under fully aerobic environment, it maintained the capability of polymer degradation under anaerobic conditions
Summary
Polyhydroxyalkanoates (PHAs) are one of the most interesting biopolymers due to their mechanical properties and biodegradability. With particular attention for the MMC PHA-rich biomass, several non-chlorinated solvents have been firstly exploited [14] together with a biomass stabilization protocol, where a temperature range of 120–160 °C was adopted in order to preserve the polymer quality. The latter might be improved by optimization of time, temperature, and concentrations of reagents in the purification steps as a function of PHA composition [15]. The pulse feeding causes frequent variability in substrate concentrations that leads to a block formation depending on the substrate availability (e.g., 3hydroxyvalerate synthesis in the presence of propionate)
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