ABSTRACT
In the activated sludge process, organic contaminants are oxidized by microorganisms under aerobic condition. It is called the activated sludge process because the sludge produced is an activated biomass. Since its invention in the early 20th century, many variations have been introduced to enhance its treatment efficiency while reducing capital and operating costs or to accommodate unconventional needs. The original activated sludge process based on the suspended culture with air bubbling is also called the conventional activated sludge (CAS) process to distinguish it from the variations such as those based on fixed or floating biofilm carriers, membranes, and unconventional biological reactor configurations. Membrane bioreactor (MBR) has been evolved from CAS by replacing the gravity-based clarifier (or the settling tank) with the membrane separation system.
