Waking up to potential of dirty water

Expansion of treatment can create additional revenue sources, writes Allan Seccombe

ANGLO Coal is expanding its water-treatment plant to handle 20-million more litres of polluted water a day from coal mines around Witbank. It is also seeking ways to bring down volumes and costs, including rehabilitation of minedout pits and dumps with bacteria.

The eMalahleni water treatment plant on the outskirts of Witbank is Anglo’s answer to treating water from large coal mines in the area. The water is loaded with salts and metals that have dissolved when the water, primarily from rainfall, percolates through tailings dumps and through the soil into old mine workings.

What started out as a project to clean the water to a high standard and release it into the nearby Nauwpoortspruit has developed into an important source of clean, cheap water for the municipality. Once the expansion of the plant is completed, up to 40-million litres would be available to the municipality, which needs about 140-million litres a day.

Bumping up the supply from the 16-million litres sent to it daily would cost about R100m. Anglo Coal needs 10-million litres a day for its operations.

The plant treats 30-million litres of water a day and an R832m expansion is under way to lift capacity to 50-million litres by March. The extra water is expected to be of poor quality, with higher levels of salts and acidity, which will bump up the treatment costs. The expansion will bring the cost of the plant, built in 2007, to R1.4bn.

The extra water will be pumped from mining areas where it had been treated on site in the past. Those processes were deemed to be no longer of an acceptable standard or as cost-effective as the eMalahleni plant, says Anglo Coal hydrology manager Thubendran Naidu.

The plant — built, operated and maintained by Aveng Water — was designed to return a better quality of water to the river than is currently flowing in it. The Department of Water Affairs set these high standards to dilute the pollution already in the river from mining, agriculture and sewage.

About 100-billion litres of water are stored in four mines in the Witbank region. That compares with 104-billion litres in the Witbank Dam, the main source of water for the community. The plant supplies below-cost water at R5.60 per cubic metre to the region compared with the municipality’s water tariff of R15.20 per cubic metre.

A similar plant was built by BHP Billiton near its Optimum colliery, which is now owned by Glencore, and the sole source of potable water for the town of Hendrina. BHP and Glencore are building another water reclamation plant near Middelburg and will treat 20-million litres a day based on Aveng technology. The R1.5bn plant, in which Glencore holds a 16% stake, will be built by September this year and commissioned by October 2015.

Unlike the eMalahleni plant, the Middelburg plant will pump clean water into a river upstream from the town, which can then draw the increased flows from the river to treat and supply to residents. The Middelburg plant will generate about 140 tonnes a day of sludge.

Water is a joint problem. It’s nearly impossible to find the source once it is below surface. A joint solution is good for everybody

“All the sludges will be disposed of in appropriate, licensed disposal facilities,” Glencore says.

It operates two other wholly owned water treatment plants, one of which, the 15-million-litre-a-day plant at its Optimum colliery, supplies more than 3-million litres a day to Hendrina, meeting all of the town’s drinking-water needs. It has started building a third plant to handle up to 18-million litres of water a day near Ogies.

Anglo Coal is “exploring its options” to participate in the Middelburg plant to treat water from its nearby Goedehoop colliery.

“Water is a joint problem. It’s nearly impossible to find the source once it is below surface. A joint solution is good for everybody,” Mr Naidu says, adding that BHP Billiton contributed towards the first phase of the eMalahleni plant, which treats 3.6-million litres of its water daily. It is not contributing to the expansion to 50-million litres.

The byproducts or waste could be useful revenue streams, which would offset the cost of cleaning the water, Mr Naidu says. Waste disposal costs can make up 25%-30% of life-cycle costs.

The sludge process extracts metals such as iron, magnesium and manganese as well as minerals such as sulphur, salts and highquality gypsum, which Anglo Coal sells to cement maker Lafarge.

The plant produces 200 tonnes a day of solid byproduct. The expanded plant will generate 600 tonnes of waste a day, an indication of the high pollution levels in the new water sources.

Anglo Coal is conducting tests on making bricks using the sludge, to make sure it is suitable and will not harm anyone’s health.

“We want to change our thinking about how we deal with this waste. We see use for it down the line,” Mr Naidu says. “This stuff, if you apply other technologies … you could recover materials that you could reuse in the plant, like lime, which we buy in. I could recover, using available technology, sulphuric acid, which we use.…

“The next phase of this journey is to find ways to minimise the amount of things we bring in and reuse as much as we can. It will

The intention is to reduce the volume of contaminated water coming into the plant by improving rehabilitation of mines in closure

hopefully make us more financially sustainable in the future,” he says.

The intention, ultimately, is to reduce the volume of contaminated water coming into the plant by improving the rehabilitation of mines in closure, says Henk Lodewijks, the Anglo Coal environmental manager overseeing the closure of nine operations. “There’s no money to be made in closures.”

Decreasing the amount of water to be treated by even 1-million or 2-million litres a day will result in critical cost reductions.

“The rehabilitation of our mines and what we do for mine closure will hopefully eliminate the need for us to treat water,” he says.

Part of this work is applying bacteria to break down certain types of weathered and discarded coal, which are no good for burning any more. This creates a rich, loamy soil in which plants thrive.

Anglo Coal has dubbed the project Fungcoal, which stems from research by Rhodes University.

“We are still in trials with Fungcoal. We still have to learn its potential; what it can do and what it can’t do,” says Mr Lodewijks.

A pilot project is about to start on a 10ha site at Landau colliery that is nearing the end of its life before the end of this decade. Anglo Coal wants the Department of Mineral Resources to monitor the project and give its approval, which will clear the way for a broader rollout of Fungcoal as an acceptable rehabilitation tool.

A small-scale test area shows thick growth of grass on portions with Fungcoal compared with ordinary topsoil. Companies collect topsoil in large dumps, ready to spread over filled-in pits, but problems arise if the soil has been left standing too long, with seeds and micro-organisms dying, making the process of rehabilitation longer and more costly, says Jaco Fick, the rehabilitation co-ordinator at Landau colliery.

While old mining areas and pits that have been filled are carefully landscaped to ensure water runs off, there is the need to clad dumps with scarce topsoil, and Fungcoal could reduce the amount needed.

By successfully covering dumps with vegetation, the problem of water percolating through the waste is reduced, ultimately minimising the amount of water needing treatment and cutting costs.