An increase in the C/N ratio resulted in a significantly higher nitrogen removal efficiency for both SBRs (Table 2). The maximum concentrations in nitrite and nitrate nitrogen detectable at the end of the sampled cycles were 0.4 ± 0.9 mg L1 and 0.4 ± 0.2 mg L1 for the glycerol SBR whereas these were 1.3 ± 0.8 mg L1 and 0.5 ± 0.5 mg L1 for the acetate SBR. In additional batch tests, no autotrophic nitrification was observed (data not shown). Without the presence of carbon, the biomass of both the glycerol SBR and the acetate SBR did not significantly decrease TAN while no production
of nitrite or nitrate could be observed.