The free surface flow Integrated Constructed Wetlands (ICW) concept explicitly combines the objectives of cleansing and managing water flow from farmyards with that of integrating the wetland infrastructure into the landscape and enhancing its biological diversity. This leads to system robustness and sustainability. Hydraulic dissipation, vegetation interception, and evapotranspiration create an additional freeboard at the outlet of each wetland segment and at the point of discharge, thus enhancing hydraulic residence time and cleansing capacity during hydraulic fluxes. The principal design criteria leading to adequate effluent water quality (i.e., molybdate reactive phosphorus less than 1 mg/l) from ICW are that the wetland area needs to be sized by a factor of at least 1.3 times the farmyard area and the aspect ratio for the individual wetland segments (i.e., approximately four cells) needs to be less than 1∶2.2 (width to length). Within a year of ICW commissioning, approximately 75% of farmyard runoff was intercepted, leading to improvements in the receiving surface waters of the catchment. Most of the recorded phosphate concentrations after ICW treatment agreed with the Irish Urban Wastewater Treatment Regulation 2001, which can be used as a benchmark to assess ICW treatment performance and which is usually applied unofficially to ICW even if it may appear to be too stringent. A case study of 13 ICW systems suggested that phosphorus exported from an ICW system was similar to the typical background concentrations of phosphorus export rates from land to water.
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Vol. 27 • No. 2