The dynamics of continuous biological processes is addressed in this paper. Numerical simulation of a conventional activated sludge process shows that despite the large differences in the dynamics of the species investigated. the orthogonal collocation on finite element technique with three internal collocation and four elements (OCFE-34) gives excellent numerical results for bioreactor models up to a Peclet number of 50. It is shown that there is little improvement in numerical accuracy when a much larger internal collocation point is introduced. Over and above Peclet number of 50, considered to be large for this process. simulation with the global orthogonal collocation (GOC) technique is infeasible. Due to the banded nature of its structural matrix, the method of lines (MOL) technique requires the lowest computing time, typically four times less than that required by the OCFE-34. Validation of the hydraulics of an existing pilot-scale subsurface flow (SSF) constructed wetland process using the aforementioned numerical techniques suggested that the OCFE is superior to the MOL and GOC in terms of numerical stability,