Performance and bacterial community dynamics of aerobic granular sludge working at low temperature enhanced by melamine framework embedding

Abstract

Aerobic granular sludge (AGS) is becoming a well-established technology for wastewater treatment, which has shown outstanding performance in practical applications. However, the cultivation of AGS at low temperature is still a challenge. In this study, melamine framework (MF) was applied to promote sludge granulation at 10 ℃. Stable AGS with compact structure and excellent settle-ability was successfully cultured within 70 d. MF embedded inoculated sludge in the early stage to avoid sludge loss, and provided skeleton support for the granules in the later stage, which effectively accelerated the granulation process and improved the stability of AGS. Extracellular polysaccharides content increased significantly during granulation, with the decreased of protein to polysaccharides ratio. The system achieved high ammonium nitrogen, total nitrogen and total phosphorus removal efficiencies, reaching 96.6%, 70% and 99%, respectively, which were attributed to the enrichment of nitrifiers and denitrifying phosphorus accumulating organisms (DPAOs). The dominant DPAO changed from Dechlormonas to Flavobacterium during granulation, accompanied by the decrease of extracellular polymers (EPS) secreting genus Zoogloea and the increase of EPS degrading genus norank_f__Saprospiraceae. Even though, the AGS maintained structural stability, suggesting that MF pre-embedding and supporting might be an effective method for cultivation and stable operation of AGS at low temperature.