Yes Zafferullah, most of them are built after 2000...but the major part is still "old-fashioned". Many Contractors still provide ditch and extended aeration biological plants, though cheaper  and more advantageous Technologies are available ever since... The fact is that You are right. Regards

Published January 17, 2017 10:31 by Ing.Tiziano Zampollo, Employee at Water Engineers & Consultants - WEnCo