Start up of biological sequencing batch reactor (SBR) and short-term biomass acclimation for polyhydroxyalkanoates production

Background: The adaptation/selection of mixed microbial cultures under feast/famine conditions is an essential step for polyhydroxyalkanoates (PHA) production. This study investigated the short-term adaptation of a mixed microbial culture (activated sludge) during the start up of a sequencing batch reactor (SBR). Results: Four different SBR runs were performed starting from different inocula and operated at the same organic load rate (8.5 gCOD L-1 d-1) and hydraulic retention time (1 day). At 3-7 days from SBR start up, the selected biomass was able to store PHA at comparable rate and yield with those obtained after long-term acclimation. Independently from the time passed, a short feast phase was the key parameter to obtain PHA storage at high rate and yield in the following accumulation stage (244 mgCOD g-1CODnonPolym h-1 for specific storage rate and 48% COD COD-1 as PHA content in the biomass). The DGGE profiles showed that the good storage performance and the structure of the microbial community were not fully correlated. CONCLUSIONS: The results suggest a new strategy for operating the PHA accumulation stage directly in the SBR, after very short biomass adaptation, instead of using two separate reactors for biomass enrichment and PHA accumulation, respectively.