Nutrient release from integrated constructed wetland sediments receiving either farmyard runoff or domestic wastewater

There is a risk that contaminants within wetland sediment can either be remobilized or reach the groundwater due to infiltration if the wetland is unlined. This research study assesses laboratory-based integrated constructed wetland (ICW) mesocosms operated in a temperatureand pressure-controlled environment. The wetland columns were filled with contaminated sub-soil collected from the first cell of full-scale ICW systems treating either farmyard runoff or domestic wastewater. The aim was to examine nutrient removal within oxidized and reduced sediment layers throughout the soil profile. The mean removal efficiencies for the farmyard runoff mesocosms were mostly negative for all nutrients such as ammonia-nitrogen (-147.6%), nitratenitrogen (87.9%) and ortho-phosphate-phosphorus (-193.9%). Similar values were observed for domestic wastewater treatment mesocosms (system I planted with Phragmites australis and system II planted with Agrostis stolonifera): ammonia-nitrogen (I: -2.8%; II: -53.4%), nitratenitrogen (I: -61.1%; II: -41.7%) and ortho-phosphate-phosphorus (I: -180%; II: -198.3%). Findings indicate that nutrients trapped within sediments leach gradually out into the less contaminated inflow water. The capacity of nutrient retention decreases as the wetlands age. The sediments acted as nutrient sources instead of nutrient sinks. Moreover, the wetland cells planted with P. australis achieved better results than cells planted with A. stolonifera.