Influence of retention time on reactor performance and bacterial trophic populations in anaerobic digestion processes

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The influence of retention time (RT) on reactor performance and bacterial trophic populations has been investigated by using a CSTR anaerobic digester fed with starch as the major organic carbon source. RT does not have much effect on the population levels of hydrolytic bacteria and H2-producing acetogens. The population of hydrolytic bacteria remained at 108-109 MPN/ml for RTs between 244.8 and 1.5 h, and the population of H2-producing acetogens was 108-1011 MPN/ml when RT was longer than 3.12 h. However, RT has a considerable effect on the population levels of methanogens, homoacetogens as well as sulfate-reducing bacteria and on the composition of fermentative products. The populations of H2-utilizing methanogens and homoacetogens increased when RT decreased from 244.8 to 6 h, and the maximum levels of these bacteria were 7.9 × 109 MPN/ml at a RT of 6 h and 3.5 × 1010 MPN/ml at a RT of 12 h, respectively. In contrast, acetate-utilizing methanogens and CH3OH-utilizing methanogens were washed out at RTs of 12 and 4.2 h, respectively. Even at a RT of 1.5 h, methane was produced by H2-utilizing methanogens in the acidogenic reactor. The best RT for phase separation is at a RT of approx. 12 h.

Original languageEnglish (US)
Pages (from-to)27-36
Number of pages10
JournalWater Research
Issue number1
StatePublished - Jan 1994



  • H-producing acetogens
  • MPN method
  • anaerobic digestion process
  • bacterial population levels
  • homoacetogens
  • hydrolytic bacteria
  • methanogens
  • retention time

ASJC Scopus subject areas

  • Ecological Modeling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution

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