Intracellular polymers in aerobic sludge of sequencing batch reactors

The formation and characteristics of intracellular polymers in aerobic sludge of sequencing batch reactors were investigated at ambient temperature under balanced nutrient conditions. Three substrates of different chemical natures, including fatty acid (acetate), carbohydrate (glucose), and aromatic (benzoate), were fed to individual reactors. When substrates were initially in excess, the sludge in all reactors was capable of converting soluble substrates into intracellular polymers under aerobic conditions. Acetate (up to 27%) and benzoate (up to 51%) were converted to poly-beta-hydroxybutyrate, whereas glucose (up to 33%) was converted to intracellular carbohydrates. The initial substrate depletion rates were 208-243 mg-C/g-VSS/h for acetate, 491-590 mg-C/g-VSS/h for benzoate, and 405-558 mg-C/g-VSS/h for glucose. When external substrates were absent in the mixed liquor, the intracellular polymers could be consumed by the sludge for endogenous respiration under aerobic conditions or as a carbon source for denitrification under anoxic conditions. These results suggest a dynamic metabolic mechanism in the sequencing batch reactors.