Enhanced phosphorus removal from biological secondary effluent using denitrifying phosphorus-removal granular sludge

Abstract

With the phosphorus discharge standard getting more stringent, it is imperative to enhance phosphorus removal from biological secondary effluent (BSE) of wastewater treatment plants (WWTPs). This study proposed a semi-continuous process for enhanced phosphorus removal from BSE using denitrifying phosphorus-removal granular sludge (DPGS) in a fluidized reactor operating under the alternative anaerobic/anoxic mode. This study investigated the effects of hydraulic retention time (HRT) and treating volume of BSE on the enhanced phosphorus removal performance of this process. At the appropriate HRT and treating volume of BSE, this process reduced the total phosphorus of practical BSE from 0.54 to 0.14 mg/L with an average removal efficiency of 74.5 % and removed 2.1 mg/L nitrate in 95 days. Removed phosphorus from practical BSE was concentrated into a small volume of water via the anaerobic phosphorus release and anoxic phosphorus uptake of denitrifying phosphorus-accumulating organisms (DPAOs) in DPGS, which was conducive for phosphorus recovery via chemical precipitation. The metagenomic analysis reveals that the relative abundance of DPAOs in DPGS increased while that of denitrifying glycogen-accumulating organisms decreased during 95 days of operation. This study provides a more cost-efficient and eco-friendly process for WWTPs to enhance phosphorus removal from BSE and phosphorus recycling.