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

• Hybrid constructed wetland system and final effluent quality monitored for 1 year.
• Vertical flow wetlands achieved high organic matter removal and nitrification.
• Horizontal and free water surface wetlands proved crucial for disinfection.
• Final effluents suitable for various reuse applications.
• A bypass from the imhoff tank to the horizontal wetland would help denitrificacion.

An experimental hybrid constructed wetland system consisting of 3 stages of different wetland configurations (i.e. two vertical flow beds (1.5 m2 each) alternating feed-rest cycles followed by a horizontal subsurface flow (2 m2) and a free water surface (2 m2) wetlands in series) and the quality of its final effluent 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 surface wetlands accomplished little denitrification, they enabled water disinfection to produce an effluent suitable for various reuse applications. Authors suggest partial bypass from the Imhoff tank to the horizontal subsurface flow wetland so as to provide a carbon source to promote denitrification. The treatment system performed equally well in terms of organic matter and ammonium removal both in warm and cold seasons. However, reduced nitrate retention took place in horizontal and free water surface wetlands in the cold season, presumably due to low denitrification activity at low water temperatures. In general, the three-stage hybrid constructed wetland system has proven to constitute an appropriate ecotechnology for wastewater treatment and reuse in small communities of warm climate areas.

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