The Effects of Perturbations on Microbial Community Dynamics and Process Performance in Wastewater Bioreactors

Biological wastewater treatment is faced with increasing demand and more stringent regulations requiring improved performance. At the same time, the field is undergoing a revolution in how much we know about the microbial communities treating our wastewater using recent molecular and analytical techniques. Using bench-scale bioreactors, the microbial communities that treat wastewater and their functions were examined in response to sustained perturbations over the course of three experiments. Each experiment used molecular fingerprinting and sequencing techniques to determine microbial community composition and function to (1) predict wastewater treatment performance in membrane bioreactors using Support Vector Regression (SVR) modeling in response to sustained chemical perturbation, (2) determine the impact of an operational perturbation in the form of a change in reactor configuration from membrane to settling operation, and (3) investigate in detail the effect of sustained chemical perturbation on microbial community composition and function.;In the first experiment, we predicted process performance in membrane bioreactors using microbial community information as input. The reactors had been run in duplicate with stress input in the form of 3-chloroaniline (3-CA) and subsequent bioaugmentation which was targeted at 3-CA degradation. We found that broad-range parameters like Chemical Oxygen Demand (COD) and nitrogen removal were accurately predicted by the SVR, but specific contaminants like 3-CA were not as easy to predict using this technique with T-RFLP data.;In the second experiment we examined the changes in microbial community composition during the acclimation and change in configuration of four replicate bench-scale reactors using metagenomic sequencing. Here, we acclimated sludge from a wastewater treatment plant in four lab-scale reactors for three weeks using MBR operation, after which we changed two to run as conventional settling Sequencing Batch Reactors (SBR) for three additional weeks. We found that changes in microbial communities were not significant between these two configurations within the timelines we tested, but that community differences were beginning to take shape, while a core microbial community remained dominant in all four reactors.;In the third experiment, we used six replicate bench-scale SBRs to test the impact of sustained 3-CA input on the acclimated microbial community in a controlled experiment over a period of four months. Using a combination of T-RFLP and metagenomic sequencing, we found that the perturbed reactors exhibited decreased variation in community composition and performance compared to the control (unperturbed) reactors. We also found that the perturbed reactors were able to develop the ability to degrade 3-CA during the first month of the experiment, but this did not alleviate the reduced variation in community composition.;These experiments show that microbial communities change and adapt in response to varying perturbations. Using a suite of molecular and analytical approaches in our experiments, we found that while their compositional changes could not always be predicted, some of their functions were predictable, and the ecological findings regarding community diversity and assembly thereof may be applicable for understanding activated sludge dynamics toward future needs in wastewater treatment.