Effect of Hydraulic and organic loads in sequencing batch reactor on microbial ecology of activated sludge and storage of polyhydroxyalkanoates

In this research the production of polyhydroxyalkanoates (PHA) by activated sludge enriched in a sequencing batch reactor (SBR) at high organic load, has been investigated. The SBR was operated at four different organic load rates (OLR), in the range 8.5 - 40.8 gCOD/L/day, and hydraulic retention times (HRT) in the range 1 - 0.21 day, both being simultaneously varied by changing the cycle length from 2 h to 0.42 h. Both parameters affected the establishment of the feast and famine conditions needed for the selection of PHA-producing microorganisms. The highest observed values of polymer production rates and yields (∼ 400 mgCOD/gCOD/h and 0.53 COD/COD, respectively) were obtained at the lowest OLR investigated (8.5 gCOD/L/day), with a corresponding HRT of 1 day. Microbial community analysis, based on denaturing gradient gel electrophoresis (DGGE), revealed that hydraulic and organic loads also played a main role on the microbial speciation within the SBR.