Kinetics and removal efficiency of nitrogen in constructed wetlands cultivated with different plant species for treating swine wastewater applied at different rates

Abstract

The present study sought to evaluate the efficiency and kinetics of nitrogen removal in Horizontal Subsurface Flow Constructed Wetlands (HSSF-CWs) cultivated with different plant species used in the treatment of swine wastewater (SWW), under different nitrogen loading rates (LRTKN). For this purpose, nine tanks measuring 2.0 × 0.5 × 0.6 m were used, one maintained without plants (CW1), while in the others two plant species were evaluated: CW3, CW5, CW7, and CW9 were planted with Tifton 85 grass (Cynodon spp.) and CW2, CW4, CW6, and CW8 were planted with cattail (Typha latifolia). The CWs received TKN application rates between 110 and 413 kg ha−1 day−1, and the removal efficiencies ranged from 27.6 to 44.9%. The average mass removal rates (MRR) for TKN and NH4+ ranged from 45.3 to 115.9 kg ha−1 day−1 and 28.9 to 66.5 kg ha−1 day−1, respectively. Tifton 85 grass and cattail contributed, respectively, to 2.22 to 8.7% and 0.03 to 1.67% of the TKN mass removed by the CWs (MRR), equivalent to extraction rates of 2.72 to 4.94 kg ha−1 day−1 and 0.04 to 1.11 kg ha−1 day−1. Coefficients estimated by conventional, modified, and residual first-order models ranged from 0.017 to 0.0187 day−1, 0.0691 to 0.1285 day−1, and 0.0298 to 0.0715 day−1, respectively. The modified first-order model and that with residual, due to their higher R2 values (R2 > 93%), indicated a good fit and considerable reliability of these equations to describe the processes of nitrogen removal from swine wastewater treated in HSSF-CW, and due to their mathematical simplicity and improvements in the representation of real behavior, they should be preferred for modeling of these systems.