The VSS content of the flocs increased and the ash content decreased as a function of time (Fig. 2). Starting at a C/N ratio of 5, the VSS content steadily increased until it remained constantly fluctuating around 90 ± 6.6% in case of the glycerol SBR and 60 ± 11% for the acetate SBR independent of the C/N ratio. The PHB content was assessed at the C/N ratios of 10 and 15 as an average value over these respective periods. In case of the glycerol SBR, the PHB content averaged 0.9 ± 0.4% at a C/N ratio of 10 which increased to 6.0 ± 2.9% at a C/N ratio of 15. For the SBR fed with acetate, values were higher averaging 13 ± 5.0% and 16 ± 4.7% at a C/N ratio of 10 and 15, respectively.