How reverse osmosis plants will address acid mine drainage and water stress in Gauteng
The government plans to install reverse osmosis packaged units to treat toxic acid mine drainage (AMD) to optimise the use of water and to help alleviate water stress in Gauteng.
The department of water and sanitation has applied to the forestry, fisheries and the environment department to update its environmental management programme report for the Eastern and Central basins on the Witwatersrand.
The amendment entails the installation of a million-litre-a-day reverse osmosis plant at both basins as part of its immediate and short-term interventions to treat acid mine drainage. AMD is harmful to humans, plants and animals because it is acidic and it carries heavy metals, atoms that emit radiation and salts in hazardous concentrations.
The mining waste is the toxic legacy of more than a century of gold mining on the Witwatersrand. During underground operations, water was pumped to the surface to enable the mining to take place. As mining stopped, the pumping of underground water ceased and the mine voids started filling with water.
The sulphide minerals in the rocks were exposed to water and oxygen, which resulted in the formation of acid mine drainage. The voids were progressively filled with acidic water.
In April 2011, the department of water affairs instructed the state-owned Trans Caledon Tunnel Authority (TCTA) to act as the agent for the design and implementation of short-term measures to manage and control acid mine drainage in the Western, Central and Eastern basins of the Witwatersrand goldfields.
The department said in its application that the proposed changes were designed to enhance sustainability by improving water efficiency within the treatment process.
The proposed amendment promotes resource efficiency by enabling the reuse of water within the lime mixing process, thereby reducing dependency on external potable water supplies without producing additional solid or liquid waste. The sludge will be brine resulting from extraction from water that is high in salts.
“The implementation of this amendment is expected to have a neutral or positive environmental impact rather than contributing to additional emissions, waste, or ecological disturbances.”
It said if the proposed amendment is not granted, this might negatively affect water conservation and resource management.
“One of the primary concerns is the misuse of potable water, which should be reserved for human consumption and essential domestic purposes,” the department said.
“Given the ongoing water shortages in the Gauteng province, this continued use of drinking water for industrial processes exacerbates existing supply challenges, placing further strain on an already limited resource.”
It did not respond to the Mail & Guardian’s inquiries on the cost of the project.
The Federation for a Sustainable Environment (FSE) supports the installation of the plant because it is aligned with the department’s best practice guidelines for reuse or reclamation of contaminated water in cases where the elimination of pollution is not possible, chief executive Mariette Liefferink said.
She said the intervention was commendable but the federation was concerned about the relative salts loads — 362 tonnes of total dissolved solids a day — reporting to the Vaal Barrage from the two treatment plants.
According to the TCTA’s and the department’s discharge monitoring results for the Central Basin AMD plant, about 69 million litres of acid mine drainage are pumped a day, neutralised and discharged in the Vaal River system. The sulphate load is about 2 728 milligrams per litre while the resource quality objectives for sulphate are 200mg/l.
The volumes of mine-influenced water pumped, neutralised and discharged from the Eastern Basin AMD plant is about 101 million litres a day, Liefferink said. The discharge into the Vaal River system contains about 1122mg/l sulphate.
The manganese levels of the water discharged into the Vaal River System from both plants “also significantly exceed the resource quality objectives”, Liefferink noted.
“Although no releases from the Vaal Dam were necessary to dilute the high salinity since the implementation of the short-term solution for AMD, the elevated concentrations of salt, in and below the Vaal Barrage, remain a concern.”