Constructed Wetlands

Needs Address

Altered water use techniques

Adaptation effects

• Ecologically sustainable method of wastewater treatment to enhance water security in the face of restricted access usable water sources
• Constructed wetlands do not allow mosquitoes to breed and therefore limit the increase in waterborne diseases resulting from climate change

Overview and Features

Employs wetland vegetation to provide a controlled environment in which to treat wastewater. Constructed wetlands can be used to treat urban and industrial wastewater, though not sewage water. They include either Free Water Service systems, in which water flows above the ground with vegetation planted in the water bed, or Subsurface Flow systems, in which water flows through a porous material which has vegetation planted within it.

Figure 2: Free Water Flow System

Figure 2: Subsurface Flow System

Cost

• Relatively low costs for construction and operation
• Gravel and other resources for construction and site preparation processes can be very costly

Energy source

Human resources for construction

Ease of maintenance

• Low maintenance demands
• Maintenance tasks include removal of litter, replacing plants and removing weeds, controlling water flow etc.

Technology performance

• Inappropriate design processes in the past have hindered success in implementation and sustainability
• Constructed wetlands are able to manage changes in water levels and contamination densities
• Processing rates depend on environmental factors such as temperature, oxygen and pH, and water volume capacity

Considerations

• Comprehensive design processes require an interdisciplinary team of experts in chemistry, hydrology, soil science, plant biology, natural resources, environmental management, ecology, environmental engineering, surveying, and project management.
• The design and planning process must incorporate an understanding of the complex physical, biological and chemical aspects of the technology
• Requires the technical knowhow to plan, design and implement alongside knowledge of the most recent developments in the technology
• The design and operation of constructed wetlands must be adjusted according to the context of its implementation, accounting for differing climates and contextual priorities e.g. nutrient removal versus removal of pathogenic organisms
• Some wastewater may need to be pre-treated before applied to constructed wetlands in order to enable to appropriate functioning of the biological elements of the wetlands
• A lack of understanding of the complexity of ecological systems can hamper the effectiveness of constructed wetlands

Co-benefit, suitability for developing countries

• Provide green space, wildlife habitats and recreational and educational areas
• Constructed wetlands are a low-maintenance, ecologically sustainable, simple, robust, low cost and low energy technology thereby providing a feasible technology option in developing countries
• Land tenure issues can provide a barrier as the wetlands require large spaces in which to operate
• Operate at community level and are therefore located close to communities

Information Resources

Kayombo, S., Mbwette, T.S.A., Katima, J.H.Y., Ladegaard, N. and Jørgensen, S.E. n.d. Waste Stabilization Ponds and Constructed Wetlands Design Manual. UNEP-IETC and Danish International Development Agency (Danida). Available from: http://www.unep.org/ietc/Portals/136/Publications/Water&Sanitation/PondsAndWetlands_Design_Manual.pdf [18 January 2015]

Vymazal, J and Kröpfelová, L. 2008. Wastewater Treatment in Constructed Wetlands with Horizontal Sub-Surface Flow. Springer Science and Business Media B.V.