Biofilm is a dominant form of existence for bacteria in most natural and synthetic environments.Formation of biofilm within a porous matrix reduces the pore size and total empty space of the system, altering the porosity and permeability of the medium. This change in the pore size distribution can be quantified by expressing the porous structure utilizing a proper geometric network. Moreover, biofilm formation on the surface of adsorptive media such as granular activated carbon (GAC) has been extensively used to remove organic materials, nitrogen species, heavy metals and other contaminants in wastewater treatment. A phenomenological model for the biofilm resistance against antibiotic activity is analyzed as well. The next part of this book deals with proper modeling of the human eye response to thermal disturbances. A comprehensive thermal analysis has been performed on the eye to properly represent the physiological aspects of it. Finally, an analytical investigation of the thermal performance of cylindrical and flat shaped heat pipes utilizing nanofluids is developed.