Mineral phosphate precipitates from septic-tank effluent, perth (Australia)

• Published in: Geoderma Vol. 39; no. 2; pp. 125 - 139
• Main Author: Whelan, B.R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.12.1986; Elsevier
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; Soil and rock geochemistry; Soils; Surficial geology; Phosphates; Western Australia; Electron probe data; Australasia; SEM data; Perth Basin; Oceania; Waste water; Soils; Precipitation; Podzols; Soil; Australia; Podzol
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/0016-7061(86)90071-6

The slime layer formed in soils at the base of four soak wells and leach drains discharging septic-tank effluent was removed and examined for discrete mineral phosphate precipitates using spot tests, a scanning electron microscope and an electron microprobe. Phosphate minerals were found only in the two septic systems over 10 years old that treated the waste water from the toilet alone. The pH of the slime layer of these systems was between 7 and 8. The precipitates were iron- and calcium-phosphates with compositions that did not correspond precisely to any well-known phosphate mineral. Although the composition differed among grains, any given phosphate grain was homogeneous. No discrete aluminium phosphates were found. Attempts to determine the identity of phosphate minerals from solubility product measurements were inconclusive. Precipitation of p phosphate from solution increases the capacity of soils with low adsorption characteristic to retain phosphate from waste-water.