Comparison of biochemical characteristics between PAO and DPAO sludges

A successful enhanced biological phosphorus removal （EBPR） was observed in both anaerobic- aerobic sequencing batch reactor （An-Ox SBR） to induce growth of phosphorus accumulating organism （PAO） and anaerobic-anoxic （An-Ax） SBR to induce growth of denitrifying PAO （DPAO）. Although the EBPR performance of An-Ox SBR was higher by 11.3% than that of An-Ax SBR, specific phosphorus release rates in the An-Ax SBR （22.8 ± 3.5 mg P/（g VSS.hr）） and the An-Ox SBR （22.4 ± 4.8 mg P/（g VSS.hr）） were similar. Specific phosphorus uptake rates under anoxic and aerobic conditions were 26.3 ± 4.8 mg P/（g VSS.hr） （An-Ax SBR） and 25.6 ± 2.8 mg P/（g VSS.hr） （An-Ox SBR）, respectively, which were also similar. In addition, an analysis of relationship of poly-β-hydroxyalkanoates （PHA） synthesized under anaerobic conditions with phosphorous release （Preleased/PHAsynthesized） and of PHA utilized under anoxic and aerobic conditions with phosphorous uptake （Puptaked/PHAutilized） verified that biological activities of EBPR per unit biomass between DPAO and PAO were similar. An analysis of the specific denitrification rate of DPAO showed that NO3-N can be denitrified at a rate that does not substantially differ from that of an ordinary denitrifier without additional consumption of organic carbon when the PHA stored inside the cell under anaerobic conditions is sufficiently secured.

Effect and mechanism of carbon sources on phosphorus uptake by microorganisms in sequencing batch reactors with the single-stage oxic process

To investigate the chief reason for phosphorus uptake by microorganisms affected by substrates in sequencing batch reactors with the single-stage oxic process,two typical substrates,glucose (R1) and acetate (R2) were used as the sole carbon source,and the performances of phosphorus removal and the changes of intracellular storage were compared. The experimental results showed that the phenomenon of excess phosphorus uptake was observed in two reactors,but bacteria's capability to take in phosphorus and its intracellular storage were obviously different under the same operational condition. After steady-state operation,total phosphorus (TP) removed per MLVSS in R1 and R2 was 6.7―7.4 and 2.7―3.2 mg/g,respectively. The energy storage of poly-β-hydroxyalkanoates (PHA) was nearly constant in R1 during the whole period,and another aerobic storage of glycogen was accumulated (the max accumulation of glycogen was 3.21 mmol-C/g) when external substrate was consumed,and then was decreased to the initial level. However in R2,PHA and glycogen were both accumulated (2.1 and 0.55 mmol-C/g,respectively) when external substrate was consumed,but they showed different changes after the period of external consumption. Compared to rapid decrease of PHA to the initial level,glycogen continued accumulating to the peak (0.88 mmol-C/g) in 2 h of aeration before decreasing. During the aeration,the accumulations/transformations of internal carbon sources in R1 were higher than those in R2. In addition,obvious TP releases were both observed in R1 and R2 other than PHA and glycogen during the long-term idle period; moreover,the release content of phosphorus in R1 was also higher than that in R2. The researches indicated that different aerobic metabolism of substrate occurred in R1 and R2 due to the different carbon sources in influent,resulting in different types and contents of aerobic storage accumulated/translated in bacteria of R1 and R2. As a result,ATP content provided for phosphorus uptake was different in R1 and R2,and the capability to take up phosphorus was also different from each other.