Sustainability website / Case Studies 2005 / Xstrata coal / Using bioremediation to tackle acid mine drainage water

Using bioremediation to tackle acid mine drainage water

Acid mine drainage issues could be relegated to the history books if a research project aiming to reverse acid-generating processes at the Collinsville open cut coal mine in Queensland is successful.

Sulphuric acid is formed when sulphide-bearing minerals such as pyrite are exposed to air and water during mining. If not effectively managed, the acid can dissolve metals such as lead, zinc, copper, arsenic, selenium, mercury and cadmium into ground and surface water. Acid mine drainage is a significant issue at Collinsville because pyrite is spread across the mine's entire geological profile.

Existing management approaches include neutralising the water or removing the water through evaporation onsite during mine life and remediating the dams on closure.

The 18-month research project, funded by the Australian Coal Association Research Program (ACARP), is trialling a bioremediation technique that was initially developed by a team from Edith Cowan University for the Collie coalfields of Western Australia, which typically have lower sulphate levels. Organic material is added to mine water to support sulphate-reducing bacteria which convert sulphate back to sulphides, removing acidity and metals in the process. This approach also fosters a range of other biological processes which can increase alkalinity and pH levels.

Laboratory trials in 2005 determined the most effective ratios for adding organic matter during field dosing.

Joel May, Collinsville Environment and Community Advisor, said using the laboratory results, Collinsville would complete a large-scale passive biological remediation demonstration in 2006 with the findings expected to be published in early 2007.

"We're adopting what's called a BACI design – before, after, control and impact design – using four pit water storages. Three of the water storages will be used for control purposes while the fourth trial site will be monitored before, during and after the addition of organic material – in our case, treated sewage waste from the nearby municipal sewerage treatment plants combined with green waste such as lawn clippings," he said.

The objectives of the demonstration project are to determine:

• the quality of water that could be achieved using this technique;
• the long-term viability of the scheme;
• any potential health risks associated with the use of sewage; and
• opportunities created for beneficial pit lake and water end use.

"Through this project we are trying to find a sustainable approach to treating mine water. With the majority of water being contained at Collinsville coal mine being acidic, it would be fantastic if we could make use of that water, particularly in times of drought."

Joel said the project had the support of the Queensland Environmental Protection Agency and the local community.