Membrane bioreactor: TMP rise and characterization of bio-cake structure using CLSM-image analysis

Membrane biofouling in membrane bioreactor (MBR) was analyzed quantitatively using a quantitative image analysis technique combined with confocal laser scanning microscopy (CLSM). The CLSM-Image analysis technique was (i) used to quantify the structure of bio-cake relating to the spatial change in the architecture, (ii) then applied to calculate the contribution of bacterial cell and extra-cellular polymeric substances (EPSs) to bio-cake resistances (Rc). A variation in the structural parameters of the bio-cake was found for different fluxes. EPS was more prevalent for the system operated under the lowest flux of 13 L/(m2 h). At this “subcritical” flux, the amount of EPS in the final bio-cake was greater than the amount of bacterial cells. This flux also gave the greatest rate of resistance rise towards the end of the period of operation. The profiles of each component (cell and EPSs) within the bio-cake were used to estimate the cake resistance (Rc). A particle size of less than 1 μm was required to have correspondence between theory and measurement. It was deduced that the steep TMP rise (labeled by others as Stage 3) is due to a combination of two mechanisms: inhomogeneous pore loss and changes in percolation due to EPS accumulation.

► CLSM-image analysis was used to quantify the bio-cake structure on membrane.
► Different level of contribution of bacterial cell and EPSs to bio-cake resistances (Rc).
► Combined mechanisms for the steep TMP rise was found.