My research addressed a novel type of environmental treatment technology known as the membrane biofilm reactor (MBfR), or the membrane-aerated biofilm reactor (MABR). These types of technologies provide new opportunities to improve current limitations of wastewater/water treatment systems. With the elevated use of energy per cubic meter of treated water, a critical need for alternative and more cost-efficient technologies exist. This research aims to contribute to a better understanding of the underlying processes that govern a MABR system and also to optimize the performance of these reactors. This improvement could shorten the gap between a novel technology and an industry competitive technology. I addressed four main topics:1.Economic Evaluation of the Air-Based, Hybrid Membrane Biofilm Reactor (HYBRID-MBFR2.Improving the Gas Transfer Rates of Closed-End Hollow-Fiber Membrane Contactors by Venting Lumen Ga3.Effect of Metabolic Activity on the Porosity of Counter-Diffusional Biofilm4.Modeling Biofilm Fluid-Structure Interactions Using a Viscoelastic Constitutive Model and a Phase-Field ApproachThe findings of this work highlighted the critical importance of investigating MBfRs using different approaches. Both scientific and economical evaluations need to be performed synergistically to advance not only in science, but also to develop competitive solutions to the water treatment area. Technologies that include biological and physical processes involve a very complex and linked set of processes. Understanding the individual effects of these processes in the overall performance is a difficult task and must be performed with an appropriate balance between the different scales. The presented results provided some details of critical factors that must be addressed in future studies and also opened new areas of biofilm research.