Direct observation of fouling formation and removal from membranes

Fouling presents a huge challenge for membrane bioreactor (MBR) processes; however its mechanism is still not fully understood and the conventional techniques are not sufficient to complete the whole image of the fouling behaviour. Direct Observation (DO), as a non-invasive, in situ technique, offers an opportunity to visualize particle deposition on the membrane surface and to better understand the fouling mechanism.

In this work the DO technique is adopted to compare the properties of fresh, aged and bioactive fouling cakes in to distinguish between bio-deposition and biofilm. Sludge with a low MLSS concentration is filtered through a submerged PVDF hollow fibre membrane (pore size of 0.04 µm) module with a cross-flow configuration to form a fresh fouling cake. The aged and bioactive fouling cakes are formed by filtering the freshly fouled membrane with Milli-Q water and nutrition solutions, respectively. The DO technique is applied throughout the filtration tests to visualize of the cake structure evolution in real time. The results derived from direct observation in conjunction with hydraulic resistance measurements will give a better insight into the fouling mechanisms and fouling cake properties.

Periodical backwash will also be supplied to investigate the cohesion between membrane surface and biomass deposition. Additional observation techniques such as confocal laser scanning microscopy combined with cell staining will also be used to characterise the amount of living and dead microorganism and thus provide additional information on the bioactivity of the fouling cake.