Aguilar-Lopez, R., M. L. Neria-Gonzalez, and G. Soto-Corte. “Tracking Substrate Trajectories in Continuous Aerobic Wastewater Reactors via Nonlinear PI Controllers”. Journal of Applied Research and Technology, vol. 4, no. 01, Apr. 2006, doi:10.22201/icat.16656423.2006.4.01.545.