Abstract A pilot-scale, pre-anoxic-anaerobic oxidation ditch was used in this study to treat municipal wastewater
with limited carbon source. A novel return activated sludge (RAS) pre-concentration tank was adopted for improving
the phosphorus removal efficiency and the effects of RAS pre-concentration ratio were studied. Under the optimal
operational condition, the suspended total phosphorus (STP) and the total phosphorus (TP) removal efficiencies
were around 58.9% and 63.9% respectively and the effluent 3
PO4− -P was lower than 0.8 mg·L−1. The reason is that
with the optimal RAS pre-concentration ratio, nitrate is completely removed with endogenous carbon source and
the secondary phosphorus release is strictly restrained in the pre-anoxic tank. Therefore, the anaerobic phosphorus
release and the carbon source uptake by phosphorus accumulation organisms (PAOs) in the sludge, which are extremely
important to the phosphorus removal process, can be fully satisfied. Furthermore, the oxidation-reduction
potential is proved to be suitable for controlling the RAS pre-concentration ratio due to influent fluctuation and
varied conditions. The novel modified system is also beneficial for PAO accumulation.
Keywords denitrifying phosphorus removal, nitrate, oxidation ditch, phosphorus, return activated sludge
pre-concentration, secondary phosphorus release
Abstract A pilot-scale, pre-anoxic-anaerobic oxidation ditch was used in this study to treat municipal wastewater
with limited carbon source. A novel return activated sludge (RAS) pre-concentration tank was adopted for improving
the phosphorus removal efficiency and the effects of RAS pre-concentration ratio were studied. Under the optimal
operational condition, the suspended total phosphorus (STP) and the total phosphorus (TP) removal efficiencies
were around 58.9% and 63.9% respectively and the effluent 3
PO4− -P was lower than 0.8 mg·L−1. The reason is that
with the optimal RAS pre-concentration ratio, nitrate is completely removed with endogenous carbon source and
the secondary phosphorus release is strictly restrained in the pre-anoxic tank. Therefore, the anaerobic phosphorus
release and the carbon source uptake by phosphorus accumulation organisms (PAOs) in the sludge, which are extremely
important to the phosphorus removal process, can be fully satisfied. Furthermore, the oxidation-reduction
potential is proved to be suitable for controlling the RAS pre-concentration ratio due to influent fluctuation and
varied conditions. The novel modified system is also beneficial for PAO accumulation.
Keywords denitrifying phosphorus removal, nitrate, oxidation ditch, phosphorus, return activated sludge
pre-concentration, secondary phosphorus release
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