Three-stage hybrid constructed wetland system for wastewater treatment and reuse in warm climate regions

Abstract

tAn experimental hybrid constructed wetland system consisting of 3 stages of different wetland config-urations (i.e. two vertical flow beds (1.5 m2each) alternating feed-rest cycles followed by a horizontalsubsurface flow (2 m2) and a free water surface (2 m2) wetlands in series) and the quality of its finaleffluent were evaluated for about one year. Mean overall removal rates were as 97% TSS, 78% COD, 91%BOD5, 94% NH4-N, 46% TN and 4% PO4-P. Vertical flow beds achieved high organic matter retention (77%BOD5) and great nitrification capacity (74% NH4-N removal). Although horizontal and free water surfacewetlands accomplished little denitrification, they enabled water disinfection to produce an effluent suit-able for various reuse applications. Authors suggest partial bypass from the Imhoff tank to the horizontalsubsurface flow wetland so as to provide a carbon source to promote denitrification. The treatment sys-tem performed equally well in terms of organic matter and ammonium removal both in warm and coldseasons. However, reduced nitrate retention took place in horizontal and free water surface wetlands inthe cold season, presumably due to low denitrification activity at low water temperatures. In general, thethree-stage hybrid constructed wetland system has proven to constitute an appropriate ecotechnology for wastewater treatment and reuse in small communities of warm climate areas.