When a bench-scale digester fed thickened mixed sludge was operated over an SRT range of 4-20days, removal efficiencies for total chemical oxygen demand and volatile suspended solids declined with decreasing SRT (especially <10days), but methanogenesis was stable for SRT as low as 5days. Quantitative PCR analyses showed that methanogens declined steadily for SRT <10days, with the acetate-cleaving Methanosaetaceae becoming more dominant. Clone-library analyses indicated significant shifts in bacterial population from 20 to 4day SRT: declining Chloroflexi (28 to 4.5%) and Syntrophomonas (9 to 0%), but increasing Bacteroidetes (12.5 to 20%) and two acetogenic genera belonging to the phyla Firmicutes and Spirochaetales (6.3 to 12%). Thus, the decrease in the apparent hydrolysis constant (k hyd-app) with higher SRT and the process limiting size of Methanosaetaceae with the lower SRT are proactive signs for defining rate limitation in anaerobic digestion.

Original languageEnglish (US)
Pages (from-to)10266-10272
Number of pages7
JournalBioresource Technology
Issue number22
StatePublished - Nov 2011


  • Anaerobic digestion
  • Hydrolysis
  • Methanogenesis
  • Sludge retention time (SRT)
  • Thickened mixed sludge (TMS)

ASJC Scopus subject areas

  • Bioengineering
  • Environmental Engineering
  • Renewable Energy, Sustainability and the Environment
  • Waste Management and Disposal


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