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Nutrient removal in subsurface flow constructed wetlands for application in sensitive regions
Summary
This study on a German wastewater treatment plant shows that iron-enriched sand effectively removes phosphorus. Reed bed filters achieved significant denitrification, though dilution impacted horizontal flow bed performance.
Area of Science:
- Environmental Engineering
- Water Treatment Technologies
- Wastewater Management
Background:
- Constructed wetlands (CWs) offer versatile wastewater treatment options.
- A research site in Wiedersberg, Germany, features a multi-stage CW system.
- The system includes primary settling, reed beds (vertical and horizontal flow), UV disinfection, and a phosphorus filter.
Purpose of the Study:
- To evaluate the efficiency of phosphorus (P) removal using different iron-containing sands.
- To assess denitrification rates in vertical flow (VF) and horizontal flow (HF) reed beds.
- To investigate long-term P-adsorption capacity using a novel filter medium.
Main Methods:
- Utilized four types of natural sands with varying iron content for P-elimination studies.
- Employed a gravelly sand filter, previously used for iron precipitation in drinking water, for long-term P-adsorption.
- Measured denitrification rates in VF and HF beds.
- Operated the system for over a year to gather performance data.
Main Results:
- Iron-enriched drinking water filter sand demonstrated high phosphorus adsorption capacity, with 250 g P/m³ adsorbed at a loading rate of 350 g P/m³.
- Median denitrification rates were 1.3 g N m⁻² d⁻¹ in VF beds and 0.25 g N m⁻² d⁻¹ in HF beds.
- High wastewater dilution (100–200%) likely reduced HF bed denitrification rates.
Conclusions:
- Iron-based filtration is a highly effective method for phosphorus removal in constructed wetlands.
- Vertical flow reed beds show promising denitrification performance.
- Further research is needed to optimize design and address challenges like high dilution rates in horizontal flow systems.