Downstream processing and characterization of polyhydroxyalkanoates (PHAs) produced by mixed microbial culture (MMC) and organic urban waste as substrate

The utilization of food waste and sewage sludge as organic substrate from urban context for the synthesis of microbial Wpolyhydroxyalkanoates (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 (M-w) of 370-424 kDa while PHA recovered from thermally stabilized dried biomass had a 3-fold lower M-w (on average). The PHA decomposition temperatures T-d(10%) and T-d(max) were in the range 260-268 degrees C and 269-303 degrees C, respectively, not dependent on the monomeric composition or molecular weight. Thermal properties such as melting temperature (T-m(1) 132-150 degrees C; T-m(2) 155-167 degrees 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.

Automated summary

The research investigated the utilization of food waste and sewage sludge as organic substrate for the synthesis of microbial PHAs at pilot scale. Two stabilization methods, thermal drying and wet acidification, were found for preserving the amount of intracellular PHA produced by open mixed microbial culture. The extracted PHA from wet-acidified biomass had higher average molecular weights compared to PHA extracted from thermally stabilized dried biomass.