Phosphorus Fractionation in Soils and Wastewater Sorbent Materials as an Indicator of Material Specific and Storage‐Dependant Availability

Abstract

Wastewater treatment with reactive filters and recycling the phosphorus (P)‐saturated materials as fertilizers in plant production is a suitable concept for a sustainable society. The objective of the present study was to evaluate the ability of the Hedley P fractionation scheme to separate different P fractions, including inorganic and organic P, in soils and sorbent materials used to reduce the P content of waste water. An additional aim was to determine changes in P fractions after storage for 8 months under different humidity regimes. This was to evaluate whether extractability of P is dependent on storage conditions between sorption of P and the subsequent use of the sorbent materials as P fertilizers. This study is the first one showing that in sorbent materials used for treatment of wastewater, the Hedley fractionation scheme separated Ca phosphates in the HC1 extract from Al and Fe phosphates in the NaOH extract. The different fractions could also be used to characterize soils of different origins, to separate liming treatments, and to approximately document soil P fertility, but could not assess differences in soil P status caused by different P fertilization in a single year. No significant influence of moisture regimes during storage on resin‐exchangeable P was detected. This increases the suitability of the studied sorbent materials for recycling P from wastewater to agricultural crops, because it indicates that plant availability of sorbed P does not change drasticaIly during the studied storage conditions.

Keywords:

• NaHCO₃‐, NaOH‐, and HCl‐extractable P fractions
• resin‐exchangeable P
• wastewater treatment materials

Acknowledgments

The study is a contribution to a sustainable society by removing phosphorus from wastewater using reactive filter media and recycling it back to agriculture. The authors would like to thank the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) for research funds within Organic Production, and Kerstin Uisk for her patience with the fractionation work. Dr Gunno Renman, Royal Institute of Technology, Stockholm, supplied opoka and SSAB Merox AB, Oxelösund, Sweden, supplied the blast furnace slag.