More than 90% of bacteria in nature form structures called biofilms. In a biofilm, different species of bacteria secrete the extracellular polymeric substance (EPS) to protect the whole committee from all kinds of hazards. Quantitatively understanding biofilms' biochemical and physical behaviors helps promote our medical technology, water treatment industry, and public health policies. Numerical modeling in cooperation with experimental investigations provides a powerful tool for such purposes. Modeling the whole life cycle of a biofilm is challenging due to the different temporal, and spatial scales are involved in the process. Also, complex reactions together with multiple phases always play essential roles in the study. In this paper, we present recently developed numerical techniques for modeling the bio-physical processes at different time scales of the life cycle of biofilms. At a large time scale, biofilm growth dominates. A space-time finite element numerical model is developed for such processes by solving multi-dimensional non-linear coupled advection-reaction equations. When it comes to a smaller time scale, the fluid-structure interaction (FSI) process, which corresponds to the biofilm-water interaction, becomes essential. Significantly, the biofilm detachment may happen immediately.  The detachment processes are often interested in the wastewater treatment industry as it has a crucial impact on the efficiency of the reactors. We investigate the sloughing of a biofilm with a poroelastic smoothed particle hydrodynamics (SPH) FSI model. With this model, we can explicitly consider the fluid phase inside and outside of the porous media. The model can also handle large deformations of the structure and the failure of the material, straightforwardly benefiting from the Lagrangian mesh-free property of the SPH method.