In the literature on treatment wetlands, a technology that is fast gaining popularity in Tanzania as well as elsewhere
in the world, there are misconceptions and missing background links which do not auger well for the development
and dissemination of the technology. The misconceptions and missing links pertain to the background, types and classification,
treatment mechanisms, and applicability of the technology. These deficiencies constitute the premise of this paper.
The paper outlines the background of engineered wetland systems (EWSs) starting with natural treatment systems as a
whole, expounding on the reversible transformations between wetlands and aquatic as well as land treatment systems. It
particularly dwells on the background, classification, components, functions, treatment mechanisms, and performance as
well as applicability of EWSs. Notably, the paper encompasses a discussion on mechanisms that affect pollutants removal
in non – conventional EWSs like those employed in environmental remediation of contaminated sites. The paper also profiles
treatment performance efficiency data for some existing EWSs. Furthermore, it discusses the applicability of the
technology in Tanzania.