Impact of hydrodynamic perturbations on physical structure and microbiological composition of biofilm

Abstract : In natural environments as well as in industrial processes, microorganisms form biofilms. Hydrodynamic conditions are one of the key parameters influencing the microbiological and physical structures of a biofilm. In the present work, a method has been developed to count and characterize grazing population of a biofilm. We used hydrodynamic conditions to obtain biofilms having different microbiological compositions and superficial structures. We monitored two continuous bubbles columns, inoculated with aerobic activated sludge. One reactor was operated under a stable low hydrodynamic constraint while the second one was exposed to frequent high hydrodynamic perturbations. Microscopic images showed a very dense population of eukaryotic organisms such as rotifers, nematodes and ciliates. We developed an innovative approach to quantify the number of rotifers. The method is based on the analysis of microscopic images. Hydrodynamic perturbations modified both the morphological and microbiological structures: perturbations decreased the quantity of moving organisms, such as rotifers, whereas some streamers appeared.