Achieving enhanced biological phosphorus removal utilizing waste activated sludge as sole carbon source and simultaneous sludge reduction in sequencing batch reactor

Highlights: • Phosphorus removal and sludge reduction were simultaneously achieved in a reactor. • Tetrasphaera was enriched with the relative abundance of 91.9%. • Effluent P concentration was 0 using waste activated sludge as sole carbon source. • Cell death and lysis led to the sludge reduction in biological phosphorus removal. Achieving enhanced biological phosphorus removal dominated by Tetrasphaera utilizing waste activated sludge (WAS) as carbon source could solve the problems of insufficient carbon source and excessive discharge of WAS in biological phosphorus removal. Up to now, the sludge reduction ability of Tetrasphaera remained largely unknown. Furthermore, the difference between traditional sludge fermentation and sludge fermentation dominated by Tetrasphaera was still unclear. In this study, two different sequencing batch reactors (SBRs) were operated. WAS from SBR-parent was utilized as sole carbon source to enrich Tetrasphaera with the relative abundance of 91.9% in SBR-Tetrasphaera. PO₄³⁻-P removal and sludge reduction could simultaneously be achieved. The effluent concentration of PO₄³⁻-P was 0, and the sludge reduction efficiency reached about 44.14% without pretreatment of sludge. Cell integrity detected by flow cytometry, the increase of DNA concentration in the sludge supernatant and decrease of particle size of activated sludge indicated that cell death and lysis occurred in sludge reduction dominated by Tetrasphaera. Stable structure of activated sludge was also damaged in this process, which led to the sludge reduction. By analyzing the excitation-emission matrix spectra of extracellular polymeric substances and the changes of carbohydrate and protein concentration, this study proved that slowly biodegradable organics (e.g., soluble microbial byproduct, tyrosine and tryptophan aromatic protein) could be better hydrolyzed and acidized to volatile fatty acids (VFAs) in sludge fermentation dominated by Tetrasphaera than traditional sludge fermentation, which provided carbon source for biological nutrients removal and saved operation cost in wastewater treatment.