Transport at the microscopic interface

The growth of bacteria in water treatment membrane units is considered as one of the most prominent challenges this technology faces. Although biofouling is the most severe form of fouling for membrane based water purification processes, no generally accepted mechanism is present. There has been significant effort in elucidating the formation and growth of biofilms inside membrane purification units. In recent microfluidic experiments, it was hypothesized that the biofilm growth is associated with subtle secondary flow patterns that exist in square shaped channels. Furthermore, extensive fluid dynamics simulations (CFD) indicated that the local substrate and oxygen concentrations in biofilm covered flow channels govern the biofilm growth. Here, we seek to perform experimental investigations on the microscopic scale concerning convection and concentration profiling.

The group of Lammertink recently studied interesting fouling processes near microstructured membranes. Such membranes were developed to influence the flow profile as to reduce concentration polarization. New insight into the build-up of biofouling in these membranes was gained. We presented results where biofouling started at locations of frontal impact of fluid flow with obstacles (e.g. membrane spacers). Till then it was believed that biofouling would initiate at poorly refreshed sections of the module, i.e. downstream of obstructions. A detailed investigation of flow profiles in such modules and the corresponding biofouling formation are required for the development of biofouling reducing strategies.

In order to study the indicated processes at a high precision and magnification, I propose to use a microfluidic platform in which fluid flow (momentum transport) and concentration information (mass transport) will be obtained. The main arguments for using microfluidics include the well defined and controlled flow characteristics and the ease for microscopic observation. The required information on the fluid flow can be obtained via microPIV (Particel Imaging Velocimetry) measurements, while concentration information can be extracted from fluorescence intensity microscopy.