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

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