Structure of the fouling layer

Investigations have been carried out to assess the structure of the biofouling layer on the membrane and the influence of processing parameters on this structure.

For this characterization, different methods are being used. In the first place, confocal laser scanning microscopy (CLSM) has been used in combination with a range of staining methods and also using the reflective mode which is available on the Leica CLSM system.
The advantage of CLSM is that it provides 3-dimensional information on the layer structure with a high resolution and information on composition (e.g., EPS staining).

An example of the 3-Dimensional structure of a fouling layer, as generated by CLSM and Imaris image processing, is provided in the video below.

As generally known, flushing has a positive effect on membrane resistance and removes fouling layers. This is also true for the biofouling layer formed in GDM processes.This is illustrated in the pictures below, showing the membrane surface before (left) and after flushing (right).

The structure of the fouling layer could be assessed using CLSM, with staining of polysaccharides and cells, and using reflection to show solid matter (purple). Optical cross-sections of these membranes are shown below, before (left) and after flushing (right).

The pictures above were made after sacrificing the membrane (conservation and staining).
A totally new method of observing membrane fouling structures is now available using a flow cell which is suitable for visual analysis by CLSM as well as with Optical Coherence Tomography (OCT) (see picture below).

This part of the project aims to develop methods and systems that allow for on-line and in situ monitoring of the biofilm formation at different scales of characterization. In this way, a specific flow cell was developed. This flow cell can be operated with cross-flow and/or permeation and is suitable for both Confocal Laser Scanning Microscopy (CLSM) and Optical Coherence Tomography (OCT). CLSM and OCT are applied for the characterization of the micro- and meso-scale biofilm structures, respectively. Imaris® or ImagJ are used to rebuild z-stacks. A homemade Matlab® code is used to quantify Z-direction information from the OCT images: thicknesses, roughness coefficients, effective surface available for mass transfer, etc.