Efficiency of Constructed Wetlands for Nutrient Removal

Currently, nutrients are not removed by standard wastewater treatment processes. Constructed wetlands placed after conventional wastewater treatment may be one way to remove nutrients before wastewater flows to receiving waters. To evaluate the effectiveness of constructed wetlands on nutrient removal, 5 constructed wetlands with varying amounts of sandy loam, compost, and shredded bark were tested. The same three plant species were planted in each wetland. Treated wastewater was placed in each planter and samples were taken after 2, 3, 4, 5, and 7 days. On average, total phosphorus increased by 289%, phosphate increased by 130%, total nitrogen decreased by 70%, nitrate increased by 23%, and ammonia decreased by 83%. The only nutrient impacted by residence time was ammonia where a peak residence time was achieved after 2–4 days. Soil mixture impacted total phosphorus, total nitrogen, and ammonia; the planters with 20% or less compost retained more nutrients than the planters with 30–40% compost. Leach test data suggests that the increase in total phosphorus and phosphate were caused by leaching of organic material present in the compost. Results show that constructed wetlands effectively remove nitrogen, but do not effectively remove phosphorus with the soil mixtures tested in this study.