Vertical flow constructed wetland as a green solution for low biodegradable and high nitrogen wastewater: A case...

The removal of nitrogen compounds from a pretreated explosives wastewater in vertical flow constructed wetland planted with Vetiveria zizanioides (0.24 m² × 0.70 m), filled with light expanded clay aggregates (Leca®NR 10/20), was studied. Experiments under constant hydraulic load, 50 ± 4 L m^-2 d^-1 and 83 ± 5 L m^-2 d^-1 without and with flooding level (25%), respectively, were made at different ammonium (3-48 mg NH₄⁺-N L^-1), nitrate (56-160 mg NO₃^--N L^-1) and nitrite (0.3-1.1 mg NO₂^--N L^-1) concentrations. Results indicate that without flooding level (unsaturated) the removal efficiencies obtained were 30 ± 9, 7 ± 1 and 96 ± 2%, respectively to NH₄⁺-N, NO₃^--N and NO₂^--N. When using flooding level and an external carbon source (C/N ratio from 1.3 ± 0.19 to 2.5 ± 0.20), the organic matter (COD) removal efficiencies were above 90%, 75% for NH₄⁺-N and 55% to NO₃^--N. Increasing the C/N ratio from 2.9 ± 0.21 to 4 ± 0.22 did not contributed to upgrade the efficiencies of COD, NH₄⁺-N and NO₃^--N removal. The denitrification process was occurred in aerobic conditions and nitrite production have ben occurred, probably due to the presence of aerobic conditions that inhibited partially denitrification.