Integrated Constructed Wetlands assessment and design for phosphate removal

Farmyard runoff is a major contributor to diffuse pollution according to the European Water Framework Directive. Free surface flow Integrated Constructed Wetlands (ICW) are a multi-disciplinary and holistic approach to farmyard runoff management by explicitly combining 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 study proposes novel ICW design guidelines and outlines findings of a case study of 13 ICW. The principal design criteria leading to adequate effluent water quality (i.e. molybdate reactive phosphate (MRP) 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 (approximately four cells) needs to be less than 1:2.2 (width to length). After ICW commissioning, improvement in terms of phosphorus reduction to usually less than 0.03 mg/l MRP in the receiving surface waters of the catchment can be observed. Findings show that phosphorus exported from ICW systems is associated with concentrations that are similar to typical background concentrations of phosphorus export rates from land to water.