Impact of food-to-microorganisms ratio on the stability of aerobic granular sludge treating high-strength organic wastewater

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

Research output: Contribution to journalArticlepeer-review

95 Citations (Scopus)

Abstract

This work investigated the long-term stability of aerobic granular sludge treating high-strength organic wastewater in a semi-pilot scale sequential batch reactor (SBR). The reactor was operated for 316 days under different operational conditions. It was found that the F/M ratio is an important parameter affecting granules formation and stability. Three selection mechanisms were investigated: (1) cultivation and maturation at moderately high influent COD concentration (2500 mg/L) followed by increase in influent COD concentration to 7500 mg/L; (2) stressed cultivation and operation at high influent COD concentration of 4500 mg/L; and (3) alternate feed loading strategy (variable influent COD concentration across the daily schedule of cycles at 50%, 75%, and 100% of the peak concentration of 5000 mg/L). It was found that adopting high OLR at the reactor start-up accelerated the formation of granules. However, the overgrowth of biomass under high organics concentration negatively affected the stability of granules and led to disintegration due to the presence of methanogens in the granule core. Cultivation at high organics concentration resulted in a rapid loss of microbial diversity and reactor failure. Under alternate feed loading, adequate selection of microbial community was maintained and resulted in stable reactor performance. Moreover, a strong correlation between F/M ratio and the granules settling ability was observed. When F/M ratio exceeded 1.5 gCOD/gSS.d, granules showed poor settleability and under very high sludge loading rates (above 2.5), sludge bulking occurred and led to washout of sludge due to the strong selection pressure of short settling time. Operating the reactor at F/M ratio of 0.5–1.4 gCOD/gSS.d appears to favor stable long-term granule stability.

Original languageEnglish
Pages (from-to)287-298
Number of pages12
JournalWater Research
Volume147
DOIs
Publication statusPublished - Dec 15 2018
Externally publishedYes

Keywords

  • Aerobic granular sludge
  • Food-to-microorganism ratio
  • High-strength organic wastewater
  • Microbial diversity
  • Wastewater treatment

ASJC Scopus subject areas

  • Environmental Engineering
  • Civil and Structural Engineering
  • Ecological Modelling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution

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