To decontaminate water flowing out of old Yukon mines, all you need is beer.
Or molasses.
Or anything carbon-based, really: wood chips, peat or straw.
It almost sounds too easy. After all, how could beer help remove metals like lead, cadmium, zinc, copper or arsenic from the water?
The principle is simple: bacteria present almost everywhere, called sulfate reducing bacteria (SRB), will feed on the carbon to transform the metal dissolved in the water back into a solid state.
The bacteria’s work is akin to reconstituting a cube of sugar previously dissolved in a cup of coffee.
For the past two years, two researchers at the Yukon Research Centre have been testing a variety of carbon sources to clean up contaminated mine water across the territory.
“We know those bacteria are very efficient, they’re like an army of soldiers working for us,” said Amelie Janin, who is in charge of the pilot project.
“Our job is to understand what are the conditions in which they are performing well, what are the foods that they need.”
The research is based on existing technology that’s been used for the past 15 years in the mining industry.
But when Janin started her work with her PhD student Guillaume Nielsen two years ago, little research had looked at the feasibility of such a project in the Yukon.
The biggest question was how much the cold would slow down bacterial growth.
Turns out, feeding carbon to the bacteria is all they need, no matter what the temperature is.
Nielsen and Janin have successfully moved from the lab phase — working with triplicates of small batches — to the pilot phase, treating 200 litres of contaminated water at a time.
The results are promising, Janin said, but there’s still need for more work to be done.
“Before a mine actually uses a technology they want to make sure it really works,” she said.
The implications of SRB for the Yukon are huge.
Currently mining companies rely on lime to treat contaminated mine water.
But it comes at the cost of shipping chemicals and equipment up north, on top of the labour requirements.
It also creates a lot of toxic sludge that has to be kept behind a dam.
That requires monitoring to prevent accidents like the 2014 spill of toxic sludge at the Mount Polley mine in British Columbia.
Carbon, on the other hand, is widely available and creates a smaller amount of sludge.
It also requires very little effort.
Water contamination in historic mines is a naturally occuring phenomenon: the ore, when exposed to water and oxygen, creates what is known as acid mine drainage (AMD).
It’s a mix of sulfate, metal, and acidic water.
The SRB feeds on the carbon and uses the sulfate to precipitate the metal back into a solid state.
“Now mines handle AMD at the source: they flood ore in a lake or use a tarp to cover it,” Nielsen explained.
For mining companies liable for historic mines, it means they have to treat the water forever.
So when a technique like SRB shows promising results, with the potential to cut the decontamination costs in half, mining companies are interested.
Mining company Alexco Resource Corp. has been using the technology for some of its mines since 1999, senior vice president Jim Harrington said.
Alexco owns the Bellekeno mine in Keno City, which temporarily shut down in 2013.
Alexco has been working with Janin and Nielsen on a pilot project using a mix of molasses and ethanol to treat the water at the Silver King mine in the Keno District.
While it’s a pilot project, the scale is far greater than test tubes: water comes out of the mine at 10 to 20 litres per second.
Nielsen and Janin help the company refine the technique used at the mine.
“Keno has its unique challenges,” Harrington said. “Molasses and alcohol seem to be very effective for the Keno microbes that live there.”
The high sugar content is what makes it so effective at the mine, Nielsen said, because it excels at stimulating bacterial growth.
“Imagine if you put molasses on a piece of bread, a bit of water, and leave it outside when it’s hot,” he said. “A day or a few hours later you won’t eat it because there’s so many things growing on it.”
The pilot project started two years ago, but the company only stopped using lime treatment a year ago because of the transition period required for SRB to kick in.
There are about 40 historical mines in Keno that require decontamination.
Harrington said the company is looking at several of 10 mines the company is responsible for.
The SRB treatment has the added benefit in some cases of reducing the need for treatment over time.
In Alexco’s case, the molasses-ethanol mix consumes some of the oxygen present in the mine, which causes the contamination in the first place.
That means less acid mine drainage and less carbon needed to decontaminate the mine.
It also doesn’t require storing sludge outside the mine.
“The real benefit of this, we’re doing this at the source,” said Harrington. “The sludge is retained within the mine (and) it’s very little sludge compared to lime.”
From a scientific perspective, SRB treatments have proven to be effective, Harrington said.
The pilot project aims to convince the federal government, which is also liable for part of the upkeep, that the new process is worth the investment.
“The federal government is always cautious to say something is proven,” Harrington said.
Ultimately it will be up to the feds and the First Nation of Nacho Nyak Dun to decide whether it’s an acceptable solution, he said.
So far he’s seen a lot of support from the First Nation.
For both Janin and Nielsen, working with the local community has been a good experience as they’ve been able to exchange information with people.
“It’s not just us giving them the information, they participate in collecting the information,” Janin said.
“Science is good but it’s no good if it’s not shared or used.”
Contact Pierre Chauvin at
pierre.chauvin@yukon-news.com