The protein content of the biomass increased in both reactors concomitantly with higher C/N ratios (Table 3). However, this increase was only significant for the shift in C/N ratio from 5 to 10 in case of the acetate SBR. Although average protein content values for the biomass in the glycerol SBR were higher than those for the acetate SBR, no significant differences between the two could be under fully aerobic conditions. Starting on day 20, the walls of the reactors were cleaned regularly (ca. every 2 days) to remove biofilm growth. The biomass detached from the interior was left in the reactor for wash out. In the glycerol SBR, this resulted in granules morphologically similar to these on day 2 but larger in size (up to 10 mm). At the same time in the acetate SBR, mainly smaller granules (