Effect of Long Sludge Retention Time on Biological Phosphorus Removal in A2/O Process

Abstract

Sludge retention time is an important parameter to the biological phosphorus removal system. This paper investigated the effect of long sludge retention time on biological phosphorus removal in Anaerobic/Anoxic/Aerobic process (A2/O). The results showed that prolonging sludge retention time (SRT) of the A 2 /O system had no significant impact on biological phosphorus removal efficiency, which slightly decreased from 92.9% (at an SRT of 12 d) to 92.1% (at an SRT of 30 d). Scanning Electron MicroscopeEnergy Dispersive Spectrometer (SEM-EDS) analysis demonstrated the relative content of phosphorus in dry activated sludge increased from 2.27% to 4.36%, which explained the excellent phosphorus removal performance at long SRT. At the same time, the average particle size increased from 201.57 μm to 256.99 μm, and the flocs at longer SRT had a more spherical and compact structure relative to that at shorter SRT. Our results demonstrated that long SRT was a sustainable way for biological phosphorus removal in A 2 /O process.