Long-term aerobic granular sludge stability through anaerobic slow feeding, fixed feast-famine period ratio, and fixed SRT

Oliver Terna Iorhemen, Mohamed Sherif Zaghloul, Rania Ahmed Hamza, Joo Hwa Tay

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)


The deterioration of the structural integrity of aerobic granular sludge (AGS) in long-term operation is a major limitation of the AGS biotechnology. The present study explored AGS long-term stability at semi-pilot-scale using the combined strategy of long anaerobic slow feeding, 1:3 fixed ratio of feast-famine period within each cycle, and selective discharge of mature granules. Biomass characteristics, extracellular polymeric substances (EPS), dissolved oxygen and removal profiles were monitored. Results indicate that the 1:3 ratio of feast-famine period controlled the EPS content at a suitable level to allow for granular sludge stability. The system exhibited high proteins (PN) content of EPS, resulting in high PN/polysaccharides (PS) ratios: 0.01–19 and 2.05–13.15 for loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS), respectively. Selective withdrawal of mature granules from the bottom of the reactor resulted in a good mix of new and old granules in the system. The strategy allowed for system stability as the reactor was operated for over 240 d without any granule disintegration. High removals of COD (98.3 ± 0.8 %), NH3-N (98.5 %), and TN (89±6 %) were achieved. Phosphate-P removal was in the range 50–100 %. EPS producers (Thauera, Flavobacterium and Meganema) and slow growing bacteria (Acinetobacter and Simplicispira) in the system contributed to the AG stability.

Original languageEnglish
Article number103681
JournalJournal of Environmental Chemical Engineering
Issue number2
Publication statusPublished - Apr 2020
Externally publishedYes


  • Aerobic granular sludge (AGS)
  • Extracellular polymeric substances (EPS)
  • Feast-famine regime
  • Granule stability
  • Selective discharge
  • Wastewater treatment

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • Waste Management and Disposal
  • Pollution
  • Process Chemistry and Technology


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