Pilot-Scale Acidogenic Fermentation of Reground PastaByproduct for Polyhydroxyalkanoate Production with Mixed MicrobialCultures

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.