Intracellular polymers in aerobic sludge of sequencing batch reactors

The formation and characteristics of intracellular polymers in aerobic slud ge of sequencing batch reactors were investigated at ambient temperature un der balanced nutrient conditions. Three substrates of different chemical na tures, including fatty acid (acetate), carbohydrate (glucose), and aromatic (benzoate), were fed to individual reactors. When substrates were initiall y in excess, the sludge in all reactors was capable of converting soluble s ubstrates into intracellular polymers under aerobic conditions. Acetate (up to 27%) and benzoate (up to 51%) were converted to poly-beta-hydroxybutyra te, whereas glucose (up to 33%) was converted to intracellular carbohydrate s. The initial substrate depletion rates were 208-243 mg-C/g-VSS/h for acet ate, 491-590 mg-C/g-VSS/h for benzoate, and 405-558 mg-C/g-VSS/h for glucos e. When external substrates were absent in the mixed liquor, the intracellu lar polymers could be consumed by the sludge for endogenous respiration und er aerobic conditions or as a carbon source for denitrification under anoxi c conditions. These results suggest a dynamic metabolic mechanism in the se quencing batch reactors.