『Abstract
　Phosphorus (P) leaching from on-site wastewater treatment systems may contribute to eutrophication. In developed countries the most common on-site treatment technique is septic systems with soil infiltration. However, the current knowledge about long term P removal in soil treatment systems is not well developed and the data used for estimation of P losses from such systems are unreliable.
　In this study we sampled four filter beds from community-scale soil treatment systems with an age of between 14 and 22 years to determine the long-term P removal and to investigate the chemical mechanisms behind the observed removal. For one site the long-term P removal was calculated using a mass balance approach. After analysis of the accumulated P, it was estimated that on average 12％ of the long-term P load had been removed by the bed material. This indicates a low overall capacity of soil treatment systems to remove phosphorus. Batch experiments and chemical speciation modelling indicated that calcium phosphate precipitation was not an important long-term P removal mechanism, with the possible exception of one of the sites. More likely, the P removal was induced by AlPO4 precipitation and/or sorption to poorly ordered aluminium compounds, as evidenced by strong relationships between oxalate-extractable Al and P.

Keywords: On-site wastewater treatment; Soil treatment system; Phosphorus; Removal mechanisms; Chemical speciation modelling; Batch experiment』

1. Introduction
2. Material and methods
　2.1. Investigated sites
　2.2. Collection and basic characterization of samples
　2.3. Mass balance calculations
　2.4. Analysis of HNO3-digestible P
　2.5. Oxalate extraction
　2.6. Batch experiments
　2.7. Chemical speciation modeling
3. Results
　3.1. General properties
　3.2. Phosphorus accumulation and mass balance
　3.3. Accumulation of iron and aluminium
　3.4. pH-dependence experiment
　3.5. Sorption experiment
4. Discussion
5. Conclusions
Acknowledgements
Appendix A. Supplementary data
References