Wood waste, straw to clean oilsands tailing ponds
Activated carbon could act as biomass filter, say researchers, to cut GHG emissions.
CALGARY — A simple concept using straw or wood waste from the forestry and agricultural sectors might help cut greenhouse gas emissions and clean up water produced by Alberta’s oilsands.
Lead researcher David Layzell from the University of Calgary said studies have shown that straw and wood can be turned into a biocarbon tailored for absorbing acids found in tailings ponds.
“It’s actually a very simple idea. Many of us use charcoal filters or carbon filters on our tap water to take out odours that we don’t like or bad tastes or even chlorine,” he said.
“We took that idea and we thought instead of using charcoal or carbon that is made from coal, why don’t we make the activated carbon from biomass grown in agricultural and forestry regions?”
Layzell says filtration can remove 75 to 90 per cent of organic compounds from water produced by the oilsands. That includes naphthenic acids in tailings pond water, thereby preventing the formation and release of methane greenhouse gas.
Methane is a greenhouse gas that has about 25 times more warming potential in the atmosphere than carbon dioxide. Layzell said
“On the tailings water, we can remove up to 90 per cent of the organics and that should reduce significantly the amount of greenhouse gases that are produced when those organics in the tailings ponds get chewed up by the bacteria that live in those ponds and create methane gas,” he said.
“This is not going to be drinkable water because there are other challenges such as salt concentrations and other things … that have to be dealt with.”
Alberta’s oilsands mining industry currently uses about 123 million cubic metres of water annually that ends up in large tailings ponds.
Layzell said filtered tailings water could be reused in steam-assisted gravity drainage technology. Slagging or deposits that form within boilers would also be reduced significantly and lower the cost of maintenance.
He is working with Josephine Hill, a chemical and petroleum engineering professor at the Schulich School of Engineering in Calgary, and Andrei Veksha, a post-doctoral researcher with expertise in making activated carbons.
The researchers have successfully made small amounts of biocarbon from aspen residues using “slow pyrolysis,” a relatively low-temperature process that “burns” the biomass in the absence of oxygen.
“We’re looking for a cheaper process with lower energy input to make the activated biochar. This would minimize the cost per cubic metre of using it to treat oilsands water, while also maximizing the greenhouse gas benefit,” Hill said.
Layzell said the project is in its preliminary phase and its cost-effectiveness must be proven before it can be considered for the oilsands industry.
© 2013 The Canadian Press