A new concept of membrane module, the submerged hollow fibre membrane module, has been widely accepted for the wastewater membrane bioreactor. This thesis aims to optimize the operation and design of submerged hollow fibre systems. The enhancement of performance by bubbling, the effect of operational conditions, and the effect of module configuration have been investigated. In addition, theoretical models have been developed for the submerged system and their applications to system operation and design are discussed.

Experiments with both crossflow and 'dead-end' submerged system demonstrated that bubbling is effective in enhancing filtration performance, but the effect of gas flow rate is constrained because of the limited effect of bubbling on turbulence in two-phase flow. The experimental results also indicated that module configuration exerts crucial effects on the performance of the system. A better filtration performance can be obtained with vertical axial fibre position, small fibre diameters, and loose fibre bundle.

A Model describing the filtration behavior of the submerged hollow fibre at steady state shows that when the maximum initial flux is lower than the critical flux, the flux distribution along the fibre can be estimated according to a dimensionless parameter ξ = 4LR_i^-3/2R_m^-1/2 which includes fibre length and radius and hydraulic resistance. When the average imposed flux is lower than the critical flux but the maximum local initial flux is higher than the critical flux, a steady state can be achieved after an initial deposition. The filtration resistance caused by the initial deposition becomes significant when the fibre radius is smaller than 0.2 mm, particularly with long fibre length and high ratios of average to critical flux. The simulation also suggested that the optimal combination of fibre radius and length goes to small radius and short length.

Finally, according to the experimental results, it can be concluded that the submerged system is a very promising membrane module not only for water/wastewater treatment but also for bioprocess uses.