USING ECOLOGY TO MITIGATE TOXIC SHOCK LOADS IN ACTIVATED SLUDGE

The objective of this study was to test the hypothesis that the selection of the solids retention time (SRT) for a suspended growth activated sludge wastewater treatment systems influences the level of biodiversity of the bacterial community. This hypothesis was tested using an ecologybased mechanistic model, laboratory-scale activated sludge bioreactors, and molecular biology tools. Simulation results demonstrated that bioreactors operated with an SRT of 2 days supported a more diverse bacterial community as compared to bioreactors operated with an SRT of 8 days. Six laboratory-scale bioreactors were operated in parallel at an SRT of 2 days or an SRT of 8 days, and samples of mixed liquor were removed to determine the level of biodiversity of the bacterial community using terminal-restriction fragment length polymorphism (T-RFLP) targeting 16S ribosomal RNA genes. Results from T-RFLP analyses confirmed simulation results suggesting that bioreactors operated at an SRT of 2 days have an increase in the number of different types of bacteria. This result is significant because ecology theory suggests that ecosystems with a greater number of different types of organisms have an increased capability to successfully withstand perturbation. Thus, we conclude that future work should test the hypothesis that operating conditions of bioreactors influence the level of biodiversity of the bacterial community resulting in systems with an enhanced capability to withstand toxic shock loads.