In this paper, the authors are proposing a systemic approach of a wastewater treatment plant. In this sense, a series of simplified constructive schematics are suggested, combined with a block diagram, of a loop control system for dissolved oxygen in the case of oxygenation via a surface aerator for active sludge processes and second, of bubble oxygenation in the case of biological aerobic process, schematics that are useful in the conceptual designing process of said type of station.