Phosphorus removal in constructed wetlands: can suitable alternative media be identified?
Removal of phosphorous in constructed wetlands is limited by the capacity of the media to adsorb, bind or precipitate the incoming P. To enhance P removal and the life span of constructed wetlands the approach might be to use natural sands rich in calcium or iron, to use an alternative 'artificial' medium with high P-binding capacity, or to establish external P-binding filters after the wetland. Our studies focused on the evaluation of calcium-rich materials potentially useful as P-binding media. The materials tested included calcite products, natural sands and seashells. Tests included assessment of physical and chemical properties of the materials, extractions in P-spiked water at different P concentrations to determine P-binding equilibrium isotherms, and column experiments. In addition, full-scale tests were performed with calcite in an external filter. The result showed that equilibrium isotherm is an indicator of the potential P-sorption capacity of the media, although the value is of limited application for the determination of the binding capacity in full-scale systems. The columns showed that the materials do bind phosphorus. However, the binding capacities are still insufficient for the establishment of external P-removal filter; the volumes of the filters would be too large to be of practical use.
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Department of Biological Sciences, University of Aarhus, Ole Worms Alle, Building 135, 8000 Aarhus C., Denmark. carlos.arias@biology.au.dk
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D000327:Adsorption; D001673:Biodegradation, Environmental; D002118:Calcium; D017753:Ecosystem; D005374:Filtration; D010758:Phosphorus / Q000737:chemistry / Q000302:isolation & purification*; D013696:Temperature; D014865:Waste Disposal, Fluid / Q000379:methods*
D010758:Phosphorus; D002118:Calcium