The mathematical models of microbial activity in stratified and homogeneous biofilms are discussed. The model is based on a nonlinear equation with a nonlinear term related to the reaction's rate. The timeindependent nonlinear equation is solved using the hyperbolic function method. The analytical expression of nutrient concentration and the effectiveness factor in a stratified and homogeneous biofilm are obtained for all values of parameters. The effect of the Thiele modulus, the diffusivity ratio between the surface and the bottom of the biofilm and the effective diffusivity at the bottom of the biofilm on concentration are discussed. Numerical results ( Matlab) are used to validate the analytical results, and there is a reasonable level of agreement.