Polyhydroxyalkanoates production by mixed microbial cultures in sequencing batch reactors operated under different feeding conditions

The production of polyhydroxyalkanoates (PHA) by mixed microbial cultures (MMC) requires a multistage process, whereby the microbial selection of PHA-storing microorganisms plays a key role on the overall performance. A strategy to favor the microbial selection consists in the alternance of excess (feast phase) and absence (famine phase) of the external carbon source. In this work, three runs of a lab-scale Sequencing Batch Reactor (SBR) operated under different working conditions for the establishment of the feast and famine (F/F) regime were analyzed. A fixed organic loading rate of 4.25 gCOD (Chemical Oxygen Demand)/L d, and a fixed cycle length of 12 h were applied to the SBR. The F/F regime consisted of fully aerobic dynamic (ADF) or aerobic/anoxic (AE/ANOX) conditions. Results showed an intracellular PHA content as high as 40 ± 2 (%, w/w) when ADF conditions were applied with the organic feeding solution made of acetate (85 % on COD basis) and propionic (15%) acids. The hydroxyvalerate content in the stored polymer increased (from 25 ± 1 to 41 ± 3, % w/w) by increasing the propionic fraction (up to 35%) in the feeding solution. The AE/ANOX condition resulted in a lower PHA-storing ability which warrants further investigations.