- Modelling and simulation of the oxygen-sag model are used to demonstrate the potential benefits of the application of user friendly numerical software packages in environmental engineering education and practice. The simulation is used to obtain the profiles of oxygen concentration, oxygen deficit, as well as de-oxygenation and re-oxygenation rates as function of distance for a steady river velocity. Simulations are carried out for various organic loads and ambient temperatures. It is shown that the solution profiles obtained by numerical simulation demonstrate the processes involved more than the point values provided by analytical solution. The use of the user friendly software packages encourages the students to ask “what if” questions, to carry out parametric studies and to learn by “discovery”. Due to the many benefits of modelling and simulation we can envision rapid spread of the use of simulation in environmental, chemical and biotechnology engineering education and practice.