Concentration installations are designed to transform low VOC concentrated gases with low flow rate into high VOC concentrated gases with low flow rate. Thus, for the concentrated waste gas flow rate is reduced, air treatment can be performed by a smaller installations. Roto concentrators allow the VOC in the exhaust gases to absorb by a rotary system with special padding (Zeolite or Activated Carbon). Then, via hot air passing in the reverse flow direction, it exposes these highly concentrated VOC gases and transfers them to air treatment plant. With this unit, the size and area of the end facility is reduced and investment and operation costs are reduced significantly.