Nutrient removal in tropical subsurface flow constructed wetlands under batch and continuous flow conditions

Area of Science:

• Environmental Engineering
• Wastewater Treatment Technologies
• Constructed Wetlands

Background:

• Subsurface flow constructed wetlands (SSF CW) are effective for wastewater treatment.
• Understanding operational modes (batch vs. continuous flow) is crucial for optimizing nutrient removal.
• The role of aquatic plants in different flow regimes requires further investigation.

Purpose of the Study:

• To compare the efficiency of batch versus continuous flow in tropical SSF CW for removing chemical oxygen demand (COD), nitrogen (N), and total phosphorus (TP).
• To quantify the contribution of higher aquatic plants to nutrient removal under both operational modes.

Main Methods:

• Experimental investigation of tropical SSF CW under batch and continuous flow conditions.
• Comparison of removal efficiencies for COD, ammonium, and TP in planted and unplanted systems.
• Analysis of the impact of hydraulic retention time (HRT) and plant presence on treatment performance.

Main Results:

• No significant difference in COD removal between batch and continuous flow.
• Batch flow demonstrated significantly higher ammonium removal (95.2%) compared to continuous flow (80.4%).
• Batch flow significantly enhanced TP removal (69.6% planted, 39.1% unplanted) over continuous flow (46.8% planted, 25.5% unplanted).
• Plants significantly improved ammonia oxidation and TP removal in both flow modes.
• Aeration from batch drain-and-fill operation contributed less oxygen than rhizosphere aeration by plants.

Conclusions:

• Batch flow operation is more effective than continuous flow for ammonium and TP removal in tropical SSF CW.
• Higher aquatic plants significantly enhance nutrient removal, particularly ammonia oxidation and TP removal.
• The drain-and-fill aeration in batch mode plays a role but is less significant than plant-mediated oxygen supply.