Nitrogen removal in an integrated constructed wetland treating domestic wastewater

Abstract

The nitrogen (N) removal performance of a 3.25 ha Integrated Constructed Wetland (ICW) treating domestic wastewater from Glaslough village in County Monaghan, Ireland, was evaluated in this study. The ICW consists of two sludge ponds and five shallow vegetated wetland cells. Influent and effluent concentrations of two N species, namely, ammonia-nitrogen (NH₃-N) and nitrate-nitrogen (NO₃-N), which were measured weekly over 2 years, together with hydrology of the ICW provided the basis for this evaluation. The influent wastewater typically contained 40 mg L⁻¹ NH₃-N and 5 mg L⁻¹ NO₃-N. Concentrations of N in the ICW effluent were typically less than 1.0 mg L⁻¹ for both species. Overall, a total load of 2802 kg NH₃-N and 441 kg NO₃-N was received by the ICW and a removal rate of 98.0 % and 96.9 %, respectively, was recorded. Average areal N loading rate (245 mg m⁻² d⁻¹ NH₃-N and 38 mg m⁻² d⁻¹ NO₃-N) had a significant linear relationship with areal N removal rate (240 mg m⁻² d⁻¹ and 35 mg m⁻² d⁻¹, respectively) for both species. The areal first-order N removal rate constants in the ICW averaged 14 m yr⁻¹ for NH₃-N and 11 m yr⁻¹ for NO₃-N. Temperature coefficients (θ) for N reduction in the ICW were lower and less than unity for NO₃-N, suggesting that the variability in N removal by the ICW was marginally influenced by temperature.

Keywords:

• Domestic wastewater
• nitrogen
• integrated constructed wetland
• wetland hydrology

Acknowledgments

The authors thank Monaghan County Council for funding this research. Technical support and advice by Ms. Susan Cook (Waterford County Council, Ireland), Mr. Dan Doody, Mr. Mark Johnston and Mr. Eugene Farmer (Monaghan County Council, Ireland) are highly appreciated.