Bacterial competition in activated sludge: Theoretical analysis of varying solids retention times on diversity

P. E. Saikaly, D. B. Oerther*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Scopus citations


A mechanistic model for activated sludge sewage treatment was developed to predict exploitative competition of six aerobic heterotrophic bacterial species competing for three essential resources. The central hypothesis of the model is that in a multispecies/limiting resource system the number of coexisting bacterial species, N, exceeds the number of limiting resources, K, available for them. The explanation for this is that for certain species combinations, the dynamics of the competition process generate oscillations in the abundances of species, and these oscillations allow the coexistence of greater number of species than the number of limiting resources (N > K). This result is a direct contradiction of an existing activated sludge steady state competition theory, "the principle of competitive exclusion," which states that the competition process proceeds to equilibrium, allowing only N ≤ K species to coexist. The model was used to investigate the effect of varying solids retention times on the diversity of species using the conventional, completely mixed activated sludge configuration. The results of model simulations showed that for a certain range of solids retention times (2.28-5.66 days) the competition of six species for three essential resources produces oscillations within the structure of the bacterial community allowing for the sustained growth of more than three species on three resources.

Original languageEnglish (US)
Pages (from-to)274-284
Number of pages11
JournalMicrobial ecology
Issue number2
StatePublished - Oct 2004
Externally publishedYes

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology
  • Soil Science


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