Constructed wetlands for water pollution control - processes, parameters and performance

Abstract

constructed wetlands are now recognised as an ecologically sustainable option for water pollution control. Natural wetlands are biologically diverse ecosystem. They provide an array of physical, biological and chemical processes to facilitate the removal, recycling, transformation or immobilisation of sediment and nutrients. Most of these processes are facilitated by the wetland vegetation, associated biofilms and micro-organisms. Wetland ecosystems are complex and the interactions between abiotic and biotic components are fundamental to an understanding of the treatment processes. Constructed wetlands must therefore be designed to have the attributes of natural wetland ecosystems. The treatment efficiency of a wetland system requires a balance between pollutant loading rate and hydraulic retention time, which is also affected by the water quality and quantity of wastewater effluent or stormwater runoff: The size of a wetland will depend upon the volume of runoff, pollutant characteristics, desired level of treatment and the extent to which the wetland is expected to function as a flood retention basin. Water depth and extent of inundation will determine the types and species of aquatic plants. A combination of emergent, submerged and floating species should be selected. Pretreatment and detention times are crucial parameters to maximise pollutant removal efficiency. Sedimentation ponds are important in stormwater wetlands to remove particulates, but dense vegetated macrophyte zones are essential to enhance the removal of suspended solids and nutrients. Ecologists and engineers need to work together to maximise the treatment efficiency of constructed wetlands. Planners and landscape architects' must become involved to ensure that stormwater wetlands have a multi-functional role in the urban setting. Constructed wetlands offer the ideal challenge to environmental engineers allowing for the integration of engineering and ecological principles to find the technical solution to fit both nature and society.