Altered Carbon Flow by Phosphorus Accumulating Organisms during Enhanced Biological Phosphorus Removal

The effect of carbon source availability on the enhanced biological phosphorus removal (EBPR) was evaluated. In order to assess the EBPR activity of polyphosphate-accumulating organisms (PAOs), the PAO-enriched sludge from a lab-scale sequencing batch reactor (SBR) and the activated sludge from a full-scale municipal wastewater treatment plant were tested and their EBRP performances were compared. With an excessive acetate spiking (1,000 mg COD/L) in the aerobic condition, EBPR activities of both sludges were disturbed. Meanwhile, when any carbon source was removed in the aerobic condition, both sludges showed good EBPR performances. However, PAO-enriched sludge showed 3∼5 times greater glycogen restoration per biomass than full-scale non-EBPR activated sludge. When a high acetate loading occurs under the anaerobic condition, PAOs are supposed to deplete internally stored polyphosphate, causing a ‘poly-phosphate (poly-P) limited condition’. Under such a condition, unlike the fullscale activated sludge, PAO-enriched sludge produced a higher fraction of poly-hydroxylvalerate (PHV). PAOs are thought to use the glyoxylate pathway as well as the methymalonyl-CoA pathway through a full or a part of tricarboxylic acid (TCA) cycle under the anaerobic condition.