Nitrate attenuation in degraded peat soil-based constructed wetlands

Abstract

Constructed wetlands (CWs) provide favorable conditions for removing nitrate from polluted agricultural runoffvia heterotrophic denitrification. Although the general operability of CWs has been shown in previous studies, the suitability of peat soils as a bed medium for a vertical flow through a system for nitrate attenuation has not been proven to date. In this study, a mesocosm experiment was conducted under continuous flow with conditions aiming to quantify nitrate (NO3-) removal efficiency in degraded peat soils. Input solution of NO3- was supplied at three different concentrations (65, 100, and 150 mg/L). Pore water samples were collected at different depths and analyzed for NO3-, pH, and dissolved N2O concentrations. The redox potential (Eh) was registered at different depths. The results showed that the median NO3-N removal rate was 1.20 g/(m2·day) and the median removal efficiency was calculated as 63.5%. The nitrate removal efficiency was affected by the NO3- supply load, flow rate, and environmental boundary conditions. A higher NO3- removal efficiency was observed at an input NO3- concentration of 100 mg/L, a lower flow rate, and higher temperature. The results of pore water pH and NO3- and N2O levels from the bottom of the mesocosm suggest that N2 is the dominant denitrification product. Thus, degraded peat soils showed the potential to serve as a substrate for the clean-up of nitrate-laden agricultural runoff.