Australia's National Local Government Newspaper Online

Stirling Leads the Way in Acid Soil

Land developments around Spoonbill Shearwater Reserve, Stirling, have resulted in acidification of sulphidic soils, releasing various previously stable soil minerals, including iron and arsenic, into local groundwater flows. This has had implications environmentally as well as from the public health perspective.

In a jointly funded project with Edith Cowan University (ECU), a lake treatment system was designed and installed on one of the islands of the southern lake at Spoonbill Shearwater Reserve. The system uses a combination of lime neutralisation and biological remediation technologies developed by ECU. This is a pilot project and is the first of its kind in Australia and possibly the world.

Early results indicate the successful treatment of the lake water from an incoming pH 3.0 (highly acidic) to an outgoing pH of 7.9 (slightly alkaline). Additionally, sulphate concentrations have been reduced by 90 per cent, and nitrate concentrations by 73 per cent. Arsenic concentrations have been reduced by 40 per cent.

The treatment process follows three principal phases:

1. Neutralisation: The acidic water is neutralised as it passes through a vat where lime (sodium hydroxide) is added, followed by clarification in a settling tank.
2. Bioreactors: The neutralised water is then passed through a series of two organic bioreactors to lower the dissolved oxygen levels of the neutralised water and to convert heavy metals and arsenic into stable minerals. Essentially, the bio-reaction phase reverses the oxidation process that formed the acids in the first instance. Stimulation of the bioreactors has been with rotting potatoes and hardwood mulch sourced from municipal tree prunings.
3. Aerobic filtration: The treated water is re-aerated through bio-filtration amongst native reeds and rushes in the lake. Establishment of the bio-filter has involved the planting of 2,500 plants purchased by the City of Stirling and planted by students from ECU.