Improved biological phosphorus removal induced by an oxic/extended-idle process using glycerol and acetate at equal fractions

Abstract

The Oxic/Extended-Idle (O/EI) regime is a promising technology for biological phosphorus removal (BPR) from wastewater, but the BPR efficiency might be affected by an insufficient amount of carbon source in raw wastewater. In this study, a novel strategy i.e., using acetate and glycerol at equal fractions as the carbon source, to simultaneously significantly improve BPR efficiency and reduce biomass waste of glycerol was reported. Experimental results showed that BPR efficiency could be enhanced when glycerol was not a dominant substrate, and the best BPR efficiency was 96.6 ± 1.2% when acetate and glycerol were at equal fractions. However, deterioration of BPR was observed when glycerol was the dominant substrate, and the worst BPR efficiency was 58.1 ± 1.8% when glycerol served as the sole carbon source. Fluorescence in situ hybridization analysis demonstrated that more polyphosphate accumulating organisms but less glycogen accumulating organisms were cultured in the activated sludge using acetate and glycerol at equal fractions. Further mechanism investigations revealed that the transformations of polyhydroxyalkanoates and glycogen, and the activities of key enzymes responsible for P removal (such as exopolyphosphatase and polyphosphate kinase) were all affected by the ratio of acetate to glycerol. In addition, the BPR performances between O/EI reactors and the classical anaerobic/oxic (A/O) reactors employing acetate and glycerol at equal fractions and solely glycerol were compared, the results showed that the Gly-fed O/EI reactor could drive better BPR performances than the Gly-fed A/O reactor. These results suggested that glycerol at moderate levels improved BPR, and waste glycerol could be an economical sustainable alternative to avoid carbon source deficiency in raw wastewater.