Community analysis and physiological characterisation of bacterial isolates from a nitrifying membrane bioreactor

This thesis focuses on the identification of early colonisers on membrane surfaces used in wastewater treatment, as well as the physiological characterisation of bacterial cultures isolated from different micro-environments of a membrane bioreactor (MBR). The bacterial community composition of early biofilms on membrane surfaces under different hydrodynamic conditions (pressurised and non-pressurised) and of the activated sludge in an MBR were examined by culture-independent, molecular-based methods of PeR-denaturing gradient gel electrophoresis (PCR-DGGE) and peR cloning of 16S rRNA genes. A bench-scale, nitrifying MBR treating artificial waste was employed. The hollow fibre ultrafiltration membrane was made of polypropylene with an average pore diameter of 0.04 µm. Analysis of DGGE profiles of the sessile communities on membrane surfaces revealed that Tetrasphaera elongata species were important colonisers due to their ability to bind to membrane surfaces irrespective of the hydrodynamic context and exposure time. Interactions between isolates from the bioreactor and membrane surfaces were further investigated by characterising the physiological traits important in biofilm initiation and proliferation on membrane surfaces such as motility, auto-aggregation, co-aggregation, hydrophobicity and quorum sensing. Bacterial strains were isolated from floes and supemantant phases of the activated sludge as well as from pressurised membrane surfaces. Microbacterium sp. were prevalent in all culture collections. Physiological studies revealed Microbacterium sp. possessed high hydrophobicity and auto-aggregating activity that could contribute to their colonisation on membrane surfaces and persistence in floes