July 2006 ISSUE
Recycling Water Has Never Been Cooler
By Francine Maxwell
Editorial Assistant
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The Dynamic Trio |
In a bid to find a way to recycle water using what Mother Nature provides naturally, Drs. Robert Donahue, P.Eng., Kevin Biggar, P.Eng., and Dave Sego, P.Eng., came up with something really cool. Literally.
The three lead a group of researchers whose main focus is freezing things and then separating them. Freeze separation technology is the art of allowing contaminated water to freeze in controlled conditions and then purify as it separates itself. That purified water can be re-used in a number of manners and industries such as farming, mining and even the oil sands.
While not a new idea, it is new in application to the northern regions of Canada.
Their research and subsequent testing have earned these three engineers the Environmental Excellence Summit Award. They’re efforts involve re-using something a lot of us take for granted: good old water.
“Water is our most precious commodity, more than gold, more than oil. The common thread in all our research is water and water quality. Once we’ve used up the water, that’s it, we die. Being able to recycle it helps us all survive,” said Dr. Donahue.
In general, here’s how the technology works. During freezing, ice crystals are formed and reject any contaminants. The more the water freezes, the more the contaminants are pushed into the non-frozen water, which becomes quite concentrated.
The freezing point of the remaining impure water deceases as this process continues, leaving the less contaminated water frozen. The purified water can then be thawed and re-used.
The application differs for each industry it would benefit. In mining, it is the mine tailings pond that the technology, called spray freezing, is used for.
The water used during ore extraction carries many waste solids, otherwise known as tailings. Those tailings are stored in a pond.
Because of the nature of the waste in the water, there are environmental concerns about contamination seeping into ground water. With freeze separation, those contaminants are isolated by pumping contaminated water through a nozzle and spraying a fine mist of it into cold air during winter months.
The result is a pile of ice pellets that, while thawing, will eliminate between 50 and 99 per cent of the waste products by only melting between 30 and 40 per cent of the ice spray.
In the oil sands, a similar process is used. Pulse trickle freeze separation provides an economical alternative treatment process to separate dissolved chemicals from the water used to separate bitumen from the oil sands.
Fresh water is imported to the site for use during bitumen separation. Recycling efforts of that water are hampered by the number and volume of naturally occurring chemicals in the oil sands, mostly salt. Current recycling programs for bitumen extraction water do not include desalination of the water, because it’s quite costly.
Using the pulse trickle freeze method, the chemicals are removed from the water, incluing the salt. By freezing the waste water in thin layers, saline flows on top-drains on the ice, unable to freeze.
By adding successive layers of water, the amount of saline flowing increases.
A slight incline of the ice makes collection of the saline water simple. What
isn’t run off is flushed out, again with thawing.
As much as 100 per cent of the salt was removed from the water in testing, during
which very little of the actual ice was melted.
Finally, agriculture will reap the benefits of yet another version of this technology, known as thin layer freeze separation. Currently, hog manure is stored in lagoons or in tanks until such time as it can be spread on fields. This treatment process can prove costly to the environment.
Lagoons can overflow with a hard rain and storage tanks can rupture. The odour is powerful enough to knock a person unconscious.
By using thin layer freeze separation to treat hog manure, something which is composed mostly of water, the amount of storage is reduced and the end product has much less odour. Water is allowed to freeze in thin layers in a lagoon, creating nitrogen-rich concentrated pools, which can be collected and spread on fields when convenient.
As the amount of end product is much less than what was frozen initially, it can be transported great distances easily. The remaining water, now free of most of its contaminants, can be re-used elsewhere.
Dr. Donahue, who when he was younger actually wanted to be an artist and not an engineer, says that the expanse of the north and its longer cold months add to the viability of this technology.
“That may be the pioneering spirit of an engineer in me, but I like to work outside and it’s Canada and it’s cold, so why fight it? It’s naturally cold here, we can freeze things naturally and the lack of energy driven processing in this technology is a real incentive.”
Dr. Biggar, who has been working with this technology for about 10 years, says that using mechanical refrigeration to reproduce the results of freeze separation technology is just not economically wise.
“It would be too costly to have to use refrigeration systems to make it work. The beauty of this process is that Mother Nature provides the energy for the process free of charge in the winter. The costs, then, are pumping and storage, which makes freeze separation a very inexpensive treatment option.”
There is some interest in taking this technology to another level and trying to freeze-separate the salt and sand used on the roads in winter. This would be done in cooperation with the City of Edmonton at its sand recycling facility.
In the meantime, work will continue to make the current prototypes of the technology more compact and user-friendly.
The Environmental Excellence Award recognizes excellence in the application of engineering, geological or geophysical methods towards preservation of the environment and the practice of sustainable development.