Impact of hydraulic loading rate and season on water contaminant reductions within integrated constructed wetlands

The impact of hydraulic loading rate (HLR) andseasonal temperature on contaminant removal efficiencieswithin an integrated constructed wetland (ICW) system of3.25 ha was assessed. The ICW system was designed totreat domestic wastewater from Glaslough (Ireland). Thecurrent loading rate is 800 population equivalents. Thesystem has shown good removal performances (2008 to2010). Mean concentration removal efficiencies were high:92% for chemical oxygen demand (COD), 98% for the5 days at 20°CN-allylthiourea biochemical oxygen demand(BOD), 94% for total suspended solids (TSS), 97% forammonia-nitrogen (NH3-N), 90% for nitrate-nitrogen(NO3-N), 96% for total nitrogen (TN), and 96% formolybdate reactive phosphate (MRP). The mean massremoval efficiencies were 92% for COD, 98% for BOD,96% for TSS, 92% for NH3-N, 83% for NO3-N, 90% forTN, and 91% for MRP. Loading rate fluctuations weremainly due to high variation in rainfall (0.4 to 400 m3 day-1)and in evapotranspiration rate (0 to 262 m3 day-1). Theinfluence on the removal efficiencies of the hydraulicloading rate (−0.7 to 15.3 cm day-1), which was based onoverall water balance, was negligible. This implies that thelarge footprint of the system provides a high hydraulicretention time (92 days)