Fosfor från små avlopp - kan vi bedöma markretentionen?

Abstract

In Sweden, approximately 1 million people rely on individual sewage systems to treat wastewater. These are often soil treatment systems, typically consisting of a septic tank followed by sand infiltration. The ability of these systems to remove phosphorus has long been debated. We review existing knowledge on phosphorus retention in soil-based systems under conditions relevant to Sweden and provide new estimates of soil retention based on previously collected experimental data, analysed in new ways, for example by use of the CD-MUSIC surface complexation model. We show that the top metre of the impacted soil can accumulate between 200 and 800 g P m-3. Phosphorus can be removed through adsorption to Fe and Al compounds, formation of organic phosphorus, and precipitation of iron and aluminium phosphates. In the unsaturated zone below 1 metre, if such a zone exists, phosphate adsorption is the main process. For 14 soil samples, the phosphate adsorption capacity varied between 41 and 545 g P m-3. Adsorption was strongly linked to oxalate-extractable Fe and Al (r² = 0.78). When specific data for the soil in question are lacking, we propose a conservative estimate of 20 g P m-3 for phosphorus retention. For the groundwater zone, where phosphorus sorption is poorly understood, we suggest a conservative estimate of 8 g P m-3. If oxalate extraction data are available, higher estimates may be justified. Finally, we emphasize the need 
for improved knowledge on phosphorus retention in the groundwater zone.

Keywords

phosphorus; soil treatment systems; retention, phosphate adsorption; unsaturated zone; ground-water zone; XANES spectroscopy; CD-MUSIC model

Published in

Vatten
2024, number: 4, pages: 186-195

SLU Authors

• Gustafsson, Jon-Petter

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Soil Science

Permanent link to this page (URI)

https://res.slu.se/id/publ/140529