A mixture of water, bitumen, clay and solvents cover some 170 square kilometres of Alberta’s landscape. These are the tailings ponds created by the Athabasca oil sands mining industry, and everyone agrees their volume needs to be reduced. In fact, thanks to recent advances in water recycling technologies, something is already being done. Up to 95 per cent of water used by the Athabasca region’s oil sands companies is recycled from these ponds – and that means less and less fresh water is being used in the first place.
“Water use and treatment in the oil sands is an important issue, and one on which we’ve made much progress in the last several years,” says Travis Davies, spokesperson for the Canadian Association of Petroleum Producers. According to the 2010 Responsible Canadian Energy Report, fresh water withdrawal by mining operations decreased by six per cent between 2009 and 2010 while production increased by four per cent.
“In-situ oil sands projects averaged 0.4 barrels of fresh water per barrel of oil produced in 2009–2010, our lowest rate achieved to date, which is actually lower than the 0.6 barrels of water needed for each barrel of oil in conventional production over same period,” Davies says. “This is reflective of increasing recycle rates and greater efficiency at in-situ operations, which now account for approximately half of oil sands production.”
Despite these advancements, the search for improvements continues, not just to recycle more, but also to reduce the number of existing tailings ponds. “Right now some of the legacy operators, such as Suncor, have an excess amount of tailings water that we want to be able to recycle for such uses as cooling water, utility water and in-situ operations,” says Prit Kotecha, Suncor’s manager of water strategy and solutions.
The next big idea
In 2010, five members of the Oil Sands Leadership Initiative (OSLI) launched a pilot project at Suncor’s Pond 2/3 to test the performance of a number of water treatment technologies. These were to be tried out in different conditions and combinations in an effort to determine an optimal solution for treating tailings pond water. The research was carried out by Suncor on behalf of OSLI during winter 2010 and spring 2011.
The pilot project researchers’ first step was to choose a combination of water treatment technologies that have the potential of being developed commercially. “In water treatment, each technology is specifically chosen to attack one or two parameters,” says Kotecha, who was one of the project’s leaders. “You never use just one specific technology. It is always a train of technologies. We did a technology review, then an overall evaluation process to select the technologies. The first technology, the dissolved air flotation, was chosen to remove oil and grease. Then we tested a slew of other filtration technologies to remove total suspended solids and finally we had reverse osmosis, which was there to remove total dissolved ions.”
The size of the equipment was chosen for each technology in proportion with what would be needed to build a hypothetical full-scale system. “So each technology had a different flow rate depending on its ability to be scaled up,” says Kotecha. “For example, the dissolved air flotation was 40 gallons per minute and the ultrafiltration was around 20.”
When deciding how to configure the train of technologies, the team had to consider not just the desired quality of recycled water but also the requirements of each of the technologies. For example, because the high levels of suspended solids and other fouling contaminants in raw tailings water can clog up the membranes of a reverse osmosis system, the team chose to pre-treat the water with ultrafiltration.
Once the equipment was set up, the tests of the ultrafiltration and reverse osmosis’ performance began under a wide range of conditions. These included varying levels of water turbidity as well as adding chemicals upstream. The team wanted to identify not just how all of the variables could affect the performance of the equipment but also how they affected the need for cleaning and maintenance.