Influence of Agapanthus africanus on nitrification in a vertical subsurface flow constructed wetland

The aim of this study is to evaluate the influence of Agapanthus africanus (A. africanus) on nitrification in a vertical subsurface flow constructed wetlands (VSSFs) system. Two lab-scale VSSFs were operated: a) one was planted with A. africanus (vertical flow planted, VFP), and b) the other was unplanted (vertical flow control, VFC). The operation strategy was divided into three phases and consisted of increasing the ammoniacal nitrogen loading rate (ALR) (Phase I: 1.4; Phase II: 2.4; Phase III: 4.4 g NH₄⁺-N·m^-2·d^-1). Nitrification was evaluated in the system at two different depths in the VSSFs (30.5 cm and 60.3 cm, from the top of the system). The removal efficiencies of COD, BOD₅, TP, and PO₄^-3-P were above 40% in the VFP and VFC during all operation. The mean removal efficiencies of NH₄⁺-N were above 70%. Nitrification was the principal NH₄⁺-N removal mechanism in both systems and transformed more than 50% of the NH₄⁺-N to NO₃^--N. In terms of the effect of A. africanus on NH₄⁺-N removal during the three operational phases, nonsignificant differences between the two VSSFs were noted (p > 0.05). Thus, A. africanus did not influence nitrification. Finally, the analysis at different depths showed that nitrification occurred in the upper 30.5 cm.