Respirometric activity of activated sludge in sequencing batch reactor depending on substrate and dissolved oxygen concentration

The effect of the food/microorganisms (F/M) ratio and dissolved oxygen (DO) concentration in sequencing batch reactors (SBRs) on the microbial activity has been examined. One of the SBRs was fed with synthetic wastewater containing inorganic carbon compounds (COD/N ratio 0.7 g COD/g N). To the other SBR, both inorganic and organic carbon was supplied leading to 6.9 g COD/g N. The F/M ratios in the reactors were 0.02 and 0.065 g COD/g cell COD, respectively. Under the above feeding conditions, two experimental series were carried out at DO concentration of 0.5 and 1.5 mg O2/dm3. The activity of the biomass was determined through respirometric tests based on the determination of oxygen uptake rate (OUR). Independently on operational parameters, nitrification was the process consuming the highest amount of oxygen. Both at the FIM ratio of 0.02 and 0.065 g COD/g cell COD, higher DO concentration resulted in increased carbonaceous and endogenous respiration.