French vertical-flow constructed wetland design: adaptations for tropical climates

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Tropical Climate Adaptation

Background:

• French Outermost Regions face unique wastewater treatment challenges due to tropical climates and dual regulatory compliance (French and EU).
• Existing French vertical-flow constructed wetland (VFCW) systems require adapted design guidelines for tropical conditions, including area, filter number, plant selection, and materials.

Purpose of the Study:

• To assess the impact of tropical climate context on the design and performance of French VFCW systems.
• To establish new design guidelines for VFCWs in tropical regions based on experimental data.

Main Methods:

• Monitoring of three full-scale VFCWs treating raw wastewater in Mayotte and French Guiana over 1-6 years.
• Analysis of 28 daily composite flow samples per season (dry and rainy) at filter inlets and outlets.
• Benchmarking of performance against French mainland standards using Irstea's database.

Main Results:

• Warmer temperatures significantly improved removal efficiencies for Chemical Oxygen Demand (COD), Suspended Solids (SS), and Total Kjeldahl Nitrogen (TKN).
• A single stage of two parallel filters achieved over 90% removal for COD, SS, and TKN.
• Treatment plant footprint was reduced due to optimized performance in warm climates, requiring only 0.8 m²/p.e.

Conclusions:

• French VFCW systems are effective in tropical climates, with performance enhanced by higher temperatures.
• Optimized design, including a single twin-filter stage, can meet national quality objectives and reduce land requirements.
• The study provides crucial data for adapting VFCW technology to tropical environments, ensuring regulatory compliance and efficient wastewater management.