Enhancement of nitrates removal in pilot-scale treatment wetland systems

The primary objective of the present study is to enhance the denitrification process in constructed wetlands (CWs), employed as an ecological and natural technology for wastewater treatment. Eco-friendly approaches have been tested to improve the nitrate removal efficiency in pilot-scale subsurface flow CWs. Initially, the system's performance was enhanced by using a natural substrate, namely cork, as a filter medium. Another approach is bio-inoculation into the rhizosphere of a bacterial strain with the potential capacity for nitrate removal, thereby reinforcing the synergy between the plant and microorganisms. Finally, the approaches were combined, and nitrate removal was assessed. The main results showed that the most effective nitrate removal from wastewater was achieved with cork (80%) compared to gravel (60%). Bio-inoculation into the rhizosphere of denitrifying bacteria significantly improved nitrate removal. Indeed, the nitrate removal rate by the inoculated CW filled with gravel, was higher than the non-inoculated system, with rates of 78% and 60%, respectively. Moreover, the highest removal rate of 99.77% was obtained with the inoculated system filled with cork.