Most activated sludge treatment facilities are designed for future maximum loading, with inflexible fixed process volume environments. However, many facilities operate at a fraction of their design loading, creating operational limitations. The FlexZone solves these limitations by modifying a conventional aerobic volume to include individually controlled subzones upstream of the fixed aerobic zone, utilizing both BioMix and aeration. Independent operation of BioMix and aeration with instrumentation feedback provides precise control of the environment to meet treatment objectives in real time.