A three-step test of phosphate sorption efficiency of potential agricultural drainage filter materials

G. Lyngsie, O. K. Borggaard, H. C B Hansen

Research output: Contribution to journalArticlepeer-review

34 Citations (SciVal)


Phosphorus (P) eutrophication of lakes and streams, coming from drained farmlands, is a serious problem in areas with intensive agriculture. Installation of P sorbing filters at drain outlets may be a solution. Efficient sorbents to be used for such filters must possess high P bonding affinity to retain ortho-phosphate (Pi) at low concentrations. In addition high P sorption capacity, fast bonding and low desorption is necessary. In this study five potential filter materials (Filtralite-P®, limestone, calcinated diatomaceous earth, shell-sand and iron-oxide based CFH) in four particle size intervals were investigated under field relevant P concentrations (0-161μM) and retentions times of 0-24min. Of the five materials examined, the results from P sorption and desorption studies clearly demonstrate that the iron based CFH is superior as a filter material compared to calcium based materials when tested against criteria for sorption affinity, capacity and stability. The finest CFH and Filtralite-P® fractions (0.05-0.5mm) were best with P retention of ≥90% of Pi from an initial concentration of 161μM corresponding to 14.5mmol/kg sorbed within 24min. They were further capable to retain ≥90% of Pi from an initially 16μM solution within 11/2 min. However, only the finest CFH fraction was also able to retain ≥90% of Pi sorbed from the 16μM solution against 4 times desorption sequences with 6mM KNO3. Among the materials investigated, the finest CFH fraction is therefore the only suitable filter material, when very fast and strong bonding of high Pi concentrations is needed, e.g. in drains under P rich soils during extreme weather conditions.

Original languageEnglish
Pages (from-to)256-265
Number of pages10
JournalWater Research
Publication statusPublished - 2014 Mar 15
Externally publishedYes

Subject classification (UKÄ)

  • Environmental Engineering
  • Oceanography, Hydrology, Water Resources


  • Carbonates
  • Eutrophication
  • Farmland drainage
  • Iron oxides
  • Water quality


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