Chapter 20 - Constructed Wetlands

Wetlands have been recognized as a natural resource throughout human history. Their importance in their natural state is appreciated by such people as the Marsh Arabs around the confluence of the Tigris and Euphrates rivers in southern Iraq, as well as in managed forms (e.g., rice paddies, particularly in Southeast Asia) (Mitsch and Gosselink, 2000). The water purification capability of wetlands is being recognized as an attractive option in wastewater treatment. For example, the UK Environment Agency spends significant amounts of money on reed bed schemes in England and Wales. Such systems are designed, for example, to clean up mine water from collieries on which the constructed wetlands and associated community parks are being built. Reed beds provide a useful complement to traditional sewage treatment systems. They are often a cheap alternative to expensive wastewater treatment technologies such as trickling filters and activated sludge processes (Cooper et al., 1996; Kadlec and Knight, 1996). Vertical-flow and horizontal-flow wetlands based on soil, sand, and/or gravel are used to treat domestic and industrial wastewater (Sun et al., 1999). They are also applied for passive treatment of diffuse pollution, includingmine drainage (Mungur et al., 1997), as well as urban and motorway runoff after storm events (McNeill and Olley, 1998). Furthermore, wetlands serve as a wildlife conservation resource and can also be seen as natural recreational areas for the local community (Hawke and José, 1996). The functions of macrophytes within constructed wetlands have been reviewed previously. Phragmites spp., Typha spp., and other macrophytes typical for swamps are widely used in Europe and North America (Brix, 1999).