Treatment of domestic sewage in a two-stage constructed wetland - Design principles

A two-stage constructed wetland capable of removing TSS, BOD and Total-N, and providing nitrification is described. The system consists of a horizontal subsurface flow constructed wetland followed by an intermittently loaded vertical flow constructed wetland. Recirculation is included as an option to enhance total-N removal. The design guidelines presented are based on experiences from various constructed wetland systems as well as traditional trickling filter technologies. The experiences from the first systems constructed according to this design in Poland show excellent removal of TSS and BOD as well as efficient nitrification and total-P removal throughout the year. It is possible that future refinements of the dimensioning principles will result in smaller and thus less costly systems.