Subsurface transport of phosphate (P) from fertilized agricultural fields to freshwaters may lead to eutrophication and reduced biodiversity in inland waters. Mitigation of eutrophic waters is difficult and costly. Reduction of P export to surface waters using filters installed in agricultural drains comprising P sorbing materials (PSM) may be a more efficient and cost-effective way to improve water quality. Several materials have been proposed as PSMs for use for cleaning agricultural drainage water.

The objective of the present study was to provide data on sorption behavior among a variety of PSMs in order to select a material that can quickly remove P from runoff water at both base and peak flow. This was done by screening 15 “local” PSMs’ for their ability to sorb and retain low orthophosphate concentrations (0-161 µM) at short equilibration time (<24 min) in both batch and flow-through cells. Further, in order to improve our understanding of phosphate sorption reactions and kinetics for different types of commercial available PSMs, three different types were studied by means of isothermal titration calorimetry, sorption isotherms, sequential extractions and SEM-EDS.

In conclusion, of the materials investigated the results from phosphate sorption and desorption studies clearly demonstrate that regarding phosphate sorption affinity, capacity and reactivity, iron oxide based PSM is superior as a filter material compared to the other tested materials.