Exploring the links between population dynamics of total and active bacteria and the variables influencing a full-scale membrane bioreactor (MBR)

Long-term dynamics of total and active bacterial populations in a full-scale membrane bioreactor (MBR) treating urban wastewater were monitored during nine months by temperature-gradient gel electrophoresis (TGGE) of partial 16S-rRNA genes, amplified from community DNA and RNA templates. The bacterial community, dominated by Alphaproteobacteria, displayed the required characteristics for a successful and steady contaminant removal under real operating conditions. The evolution of population dynamics showed that a fully-stable microbial community was not developed even after technical stabilization and steady performance of the MBR were achieved. Non-metric multidimensional scaling and BIO-ENV demonstrated that the trends of the populations were often mostly explained by temperature, followed by the concentration of volatile suspended solids and C/N ratio of the influent. These variables were mainly responsible for triggering the shifts between functionally redundant populations. These conclusions contribute to the prediction of the complex profiles of adaptation and response of bacterial populations under changing conditions.