Long-term performance of a representative integrated constructed wetland treating farmyard runoff

Abstract

The integrated constructed wetland (ICW) system studied in this research paper was constructed as part of a series of 15 wetland systems to improve the water quality of an entire catchment area (Annestown Stream watershed, Ireland) dominated by farming activities. The studied ICW comprised four cells and was used for the treatment of farmyard dirty water from a dairy farm near Dunhill (Ireland). The performance of this system was evaluated through physical, chemical and microbiological parameters collected for 7 years. The removal efficiencies were relatively good if compared to the international literature: biochemical oxygen demand (97.6%), chemical oxygen demand (94.9%), suspended solids (93.7%), ammonia-nitrogen (99%), nitrate-nitrogen (74%) and molybdate reactive phosphorus (91.8%). A molecular microbiological analysis of sediment samples collected from the site indicated that the number of denitrifying bacteria detected in the ICW system was higher than the number of ammonia-oxidizing bacteria. The monitored nutrient concentrations in groundwater and surface waters indicated that this ICW system did not pollute the receiving waters. The results showed that ICW are likely to be efficient in removing nutrients from farmyard runoff rich in nitrogen and phosphorus.