A novel technique developed by University of Alberta civil engineering professors uses solar energy to accelerate the reclamation of tailings ponds.
These ponds are created as settling basin/storage containers for the mixture of water, sand, clay and residual oil left over after oil sands processing.
Instead of using UV lamps as a light source to treat oil sands process affected water (OSPW) retained in tailings ponds, professors Mohamed Gamal El-Din and James Bolton have found that sunlight treats the wastewater as efficiently and at a lower cost.
In a statement Gamal El-Din said: ‘We know it works, so now the challenge is to transfer it into the field. This alternative process not only addresses the need for managing these tailings ponds, but it may further be applied to treat municipal wastewater as well. Being a solar-driven process, the cost would be minimal compared to what’s being used in the field now.’
Oil sands tailings ponds contain a mixture of suspended solids, salts, and other dissolvable compounds including benzene, acids, and hydrocarbons.
According to the university, these tailings ponds can take over 20 years before they can be reclaimed. When applied to the tailings ponds, the solar UV/chlorine treatment process would reportedly make OSPW decontamination and detoxification immediate.
The sun’s energy will partially remove these organic contaminants due to the direct sunlight but when the sunlight reacts with the chlorine (or bleach) added to the wastewater, it produces hydroxyl radicals (powerful oxidative reagents) that remove the remaining toxic organic contaminants more efficiently. The chlorine leaves no residuals as the sunlight causes it to decompose.
It is claimed that in laboratory-scale tests the solar UV/chlorine treatment process removed 75 to 84 per cent of these toxins.
Gamal El-Din said: ‘With this solar process, right now, the wastewater on the top of the tailings ponds is being treated. But because we have nothing in place at the moment to circulate the water, the process isn’t being applied to the rest of the pond.
‘Because we are limited by the sunlight’s penetration of the water, we now must come up with an innovative design for a mixing system like rafts floating on the ponds that would circulate the water. Installing this would still be much more cost effective for companies. It is expected that the UV/chlorine process will treat the OSPW to the point that the effluent can be fed to a municipal wastewater treatment plant, which will then complete the purification process sufficiently so the water can be discharged safely into rivers.
‘This process has been gaining a lot of attention from the oil sands industry. We’re now seeking funds for a pilot-pant demonstration and are looking at commercialising the technology.’
Graduate students Zengquan Shu, Chao Li, post doctorate fellow Arvinder Singh and biological sciences professor Miodrag Belosevic also worked on the project.
Their findings were published in Environmental Science & Technology.
This research was funded by Trojan Technologies, NSERC Collaborative Research and Development (CRD) grant, Alberta Innovates-Energy and Environment Solutions, and Helmholtz-Alberta Initiative (HAI).