The aim of the experiment was to analyze the particular processes (biomass synthesis, oxidation, denitrification and accumulation) during carbon removal from wastewater. The experiment was carried out in a sequencing batch reactor (SBR) in two series with different organic carbon compounds to nitrogen compounds ratio (COD/N). Organic carbon loading of activated sludge was 0.07 g COD/g·d. Organic carbon removal efficiency was higher at COD/N ratio 13 (98%), at COD/N ratio 3 (85%). Depending on COD/N ratio in waste, the processes of biomass synthesis, denitrification and intracellular accumulation changed. At low COD/N ratio biomass synthesis decreased; however, there was an increase in carbon used for denitrification and accumulation. It was observed that under fully aerobic conditions the activated sludge was able to store reserved materials expressed as poly(-â-hydroxybutyrate) PHB. When the lack of carbon source in waste was observed, the activated sludge used endogenous carbon resources as poly(-â-hydroxybutyrate) as electrons donor. Depending on activated sludge nitrogen loading, different times of endogenous denitrification were observed. In the first series the denitrification with endogenous carbon source was from the 8th hour in the second series during only 2 initial hours of the experiment. Biomass cellular respiration was on the level of 16% in both series.