Pilot-Scale Acidogenic Fermentation of Reground Pasta Byproduct for Polyhydroxyalkanoate Production with Mixed Microbial Cultures

The production of polyhydroxyalkanoates (PHAs) has been herein investigated by using an organic acid mixture originated from a pilot-scale acidogenic fermentation (AF) of reground pasta (RP) byproduct. The pilot-scale AF process was conducted either under no pH control or with the pH maintained at a value of 5.90, with the two obtained fermented mixtures termed RP-fermented 1 and RP-fermented 2, respectively. The fermented mixtures were fed to a lab-scale sequencing batch reactor (SBR), operated at short hydraulic retention time (HRT, 0.5 days) and sludge retention time (SRT, 1 day) and at two values of the applied organic loading rate (OLR) of 2.12 gCOD_ACIDS/Ld and 4.25 gCOD_ACIDS/Ld. During all of the SBR operating conditions, a high selective microbial pressure was established, as confirmed by both the microbiology analysis and the detected values of the storage yield (which reached a maximum value of 0.68 ± 0.04 COD_PHA/COD_ACIDS). A poly(hydroxybutyrate/hydroxyvalerate) copolymer and a poly(hydroxybutyrate/hydroxyvalerate/hydroxyhexanoate) terpolymer were produced with the RP-fermented 1 and RP-fermented 2 streams, respectively. When the OLR of 2.12 gCOD_ACIDS/Ld was applied to the SBR, the stored copolymer and terpolymer presented very similar molecular weights of 339 and 389 kDa, respectively.