Vertical-horizontal subsurface flow hybrid constructed wetlands for municipal wastewater treatment in developing countries: A review

Abstract

The use of low-cost on-site wastewater treatment technologies, including constructed wetlands (CWs), is wide spread. Despite the purported high performance of vertical-horizontal subsurface flow (V-H SSF) hybrid CWs, data on implementation and performance in developing countries is scarce. Here, the design, operation and performance of V-H SSF hybrid CWs for treatment of municipal sewage in an effort to encourage and direct future research and assist technology choice were reviewed. Literature reveals that successful performance of V-H SSF hybrid CWs depends mainly on system design and is independent of mode of feeding. Moreover, performance and final effluent quality is high for biological oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solids (TSS) which are all reduced by over 80%. Despite high removal of ammonium-nitrogen (NH4 +-N), concentration in the final effluent remains above desired levels, which is attributed to the design of V-H SSF hybrid CWs based on BOD as a parameter of choice, rather than nitrogen. It was argued that further research on performance of V-H SSF hybrid CWs based on designs that consider both nitrogen in the form of NH4 +- N and BOD and assessment under different climatic conditions, is essential prior to mass implementation of this technology in developing countries.