A conventional system consists of (at least) two separate tanks, each dedicated to one of the process steps:

an aeration tank (accumulation + regeneration) (step 1 & 2)

a sedimentation tank. The settled sludge is partly discharged in a process called 'sludge wasting' and partly recycled to the aeration tank (step 3)

The conventional system allows continuous operation but requires sludge recycling equipment and more equipment (e.g. more reactors).

Advantages of the conventional system :

continuous influent and effluent flow rate

constant water level

Disadvantages of the conventional system

limited flexibility

requires devices for sludge raking

requires devices for sludge re-circulation

special configuration of sedimentation tanks

large footprint