Vertical Loop Reactor (VLR)

Vertical loop reactor is an aerobic suspended growth activated sludge biological treatment process. It is an alternative for the conventional oxidation ditch. It is a series of reactors in rectangular tanks. It is associated with disc aerators mainly for mixing and coarse bubble diffusers for the supply of oxygen.

Working Principle
Vertical loop reactor is an oxidation ditch flipped over on its side. A horizontal baffle is used to divide the tank into upper and lower compartments. The difference between the conventional oxidation ditch and VLR is that the loop in the VLR is made in the vertical plane instead of the horizontal. The baffle separates the tank into two parts, upper and lower aeration compartments. Disc aerators are situated on top while coarse bubble diffusers are placed in the lower compartment for extra supply of oxygen. Diffusers are usually situated in the first third of the lower compartment. The channel flow guides the released bubbles.


VLR combines ORBAL and diffused aeration to get its proven high efficiency level. VLR tank can be much deeper and thus reduced footprint. Air diffusers are installed below the baffle plate and it travel the full length of the tank before being released after a minimum retention time and thus higher mass transfer efficiency.

Features and Benefits

• The common wall construction ensures lower construction costs.
• The small footprint requires less land area.
• The dual aerator design offers operating flexibility.
• The lengthy aeration retention time ensures low power costs.
• The coarse bubble design of diffusers makes it easy to meet peak oxygen demands.
• It is adaptable to DO stratification.