Reducing nitrogen and phosphorus from agricultural drainage using constructed wetland systems and open drains

Conservation of quality of the available water resources is very important in arid and semi-arid regions. Using constructed wetlands system for treatment of municipal, industrial and agricultural wastewater has attracted many attentions worldwide. Thus the direct discharge of wastewater contamination into water resources via chemical nutrients is prevented. Given the aquatic plants grown naturally in agricultural open drains, the aim of this study was to investigate the role of the open drains as the natural wetland systems for reducing nitrogen and phosphorus from the agricultural return flows. In this study, first in a laboratory scale, removal efficiency of nitrogen and phosphorus (in three replicates with concentration levels of 30 and 10 mg/l for both N and P) and four retention times (0.75, 1.5, 3.5 and 7 days) in constructed wetland systems containing two aquatic plant species (Phragmites australis and latifolia Typha) were studied and compared to a control system. The results showed that the system containing Phragmites australis has highest N and P removal efficiency. In the second stage in a field surveying in the range of 1000 m length of open drainage path and 200 m intervals, both drainage N and P concentrations were measured. The results indicated that concentrations of these two pollutants were reduced along with the open drain.