Nitrogen elimination from landfill leachates using an extra carbon source in subsurface flow constructed wetlands

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Ecological Engineering

Background:

• Landfill leachate poses significant environmental risks due to high concentrations of ammonium-nitrogen (NH4-N) and chemical oxygen demand (COD).
• Effective nitrogen removal is crucial for mitigating eutrophication and water pollution from landfill sites.
• Constructed wetlands offer a sustainable approach to treating complex industrial wastewater.

Purpose of the Study:

• To evaluate the performance of a pilot-scale, three-stage constructed wetland for treating high-strength landfill leachate.
• To assess the nitrogen removal efficiency, focusing on nitrification and denitrification processes.
• To investigate the impact of system design and operational parameters on treatment efficacy.

Main Methods:

• A three-stage constructed wetland system comprising vertical flow (VF) and horizontal flow (HF) sand filters was implemented.
• Acetic acid was dosed into the HF system to facilitate denitrification.
• The system was monitored for ammonium-nitrogen (NH4-N) and COD concentrations, loading rates, and removal efficiencies.

Main Results:

• Stable nitrification rates of 94% were achieved in the VF stages at NH4-N loading rates up to 17 g m⁻²d⁻¹.
• Denitrification rates reached up to 98%, primarily dependent on acetic acid dosing.
• The system effectively eliminated nitrite produced in the HF stage via the subsequent VF stage.
• Combined with activated carbon, COD effluent concentrations were consistently controlled.

Conclusions:

• The three-stage constructed wetland design is highly effective for nitrogen removal from landfill leachate.
• The system demonstrates robust nitrification and efficient denitrification, with potential for further optimization.
• Constructed wetlands represent a viable and sustainable technology for managing challenging leachate streams.