The activated sludge process is composed of five systems: a reactor/tank, aeration system, clarifier, RAS system, and WAS system.  The reactor provides the physical space for reactions to occur.  The aeration system provides oxygen to the microorganism/biomass we use.  The clarifier separates the biomass from the treated wastewater.  The RAS system returns the separated biomass to the reactor. The WAS system removes a portion of the biomass from to maintain the biological health of the system.  All of these systems work together to produce treated wastewater.  If one system fails, the whole process will eventually fail.  We must monitor the performance of each system and maintain all associated equipment in order for it to work well.

Which component do you think is the most important?