Assessment of long-term phosphorus retention in an integrated constructed wetland treating domestic wastewater

Due to the nature of the phosphorus (P) removal mechanisms associated with constructed wetlands, the sustainability of P treatment is usually of high interest. As a result, a 4-year dataset from a typical multi-celled integrated constructed wetland (ICW) located at Glaslough in Co. Monaghan, Ireland was evaluated to determine the effects of longterm P loadings and hydrological inputs on P treatment. The ICW was intensively monitored year-round from February 2008 through March 2012 for total P and molybdate reactive phosphate (MRP). Domestic wastewater was loaded at 16.4± 0.96 g m2 year−1 for total P and 11.2±0.74 g m² year^{− 1} for MRP. Average mass reductions over the monitoring period were 91.4 and 90.1%, respectively. The area-based kinetic coefficients (K_{( 20 )}) of 11.8 for total P and 15.6 m year−1 for MRP indicated a high area-specific retention rate. The ICW appeared to have a sustained capacity for P adsorption and retention, but the treatment was influenced mainly by external hydrological inputs and fluctuations in wastewater loadings. Linear regression analyses showed a reduction in mass retention of both total P and MRP with increased effluent flow volumes. Monthly mass reductions exceeded 90% when the effluent flow volumes were less than 200 m³day^{− 1}. When monthly effluent flow volumes exceeded 200 m3 day^{− 1}, nonetheless, mass reductions became highly variable. Designs and management of ICW systems should adopt measures to limit external hydrological loadings in order to maintain sufficient P treatment.