Abstract

The abiotic sorption efficiency of on-site wastewater treatment systems can be improved by using a strongly sorbing filter material that, if it retains phosphorus (P) in a plant available way, can be used as fertiliser when P saturation is achieved. Two materials, blast furnace slag and the siliceous sedimentary rock opoka, have shown a high P sorption capacity and were included in a set of experiments to investigate the P retention mechanisms from model P-solution. Experiments focusing on the P sorption, capacity and calcium (Ca) and PO4 determination were carried out. The pH was also measured. The P sorption experiment showed that some slags were efficient P retainers, while the opoka was the least efficient P retainer. The pH decreased in all samples as a function of P addition. In the slag samples, the Ca concentration also decreased as a function of P addition, suggesting Ca-P precipitation as the major P removal mechanism for the slag. The Ca and PO4 speciation data ruled out the formation of amorphous calcium phosphates and/or octacalcium phosphate as the major P removal mechanism. However, the calculated ion activity products displayed clear evidence that hydroxyapatite had precipitated above a certain critical supersaturation limit. This would explain the poor P retention efficiency of the opoka samples in this study as the ion activity products were too low. The finding that direct hydroxyapatite formation is the predominant P removal mechanism might have important implications for their possible use as fertiliser due to the poor solubility of hydroxyapatite. (C) 1999 Elsevier Science Ltd. All rights reserved.

Keywords

blast furnace slag; fertiliser; hydroxyapatite; opoka; P removal mechanisms

Published in

Water Research
2000, Volume: 34, number: 1, pages: 259-265
Publisher: PERGAMON-ELSEVIER SCIENCE LTD

UKÄ Subject classification

Water Treatment


Publication identifier

DOI: https://doi.org/10.1016/S0043-1354(99)00135-9

Permanent link to this page (URI)

https://res.slu.se/id/publ/69503