Organic matter evolution from oil sands to tailings sands used in land reclamation

 

Scope:
The Athabasca region of northern Alberta, Canada, is home to deposits of oil sands containing vast amounts (~ 173 billion barrels) of heavily biodegraded petroleum, known as bitumen.
Oil sands are recovered by surface mining or by in situ steam injection. The extraction of bitumen from oil sands by caustic hot water processing results in large volumes of fluid tailings, which are stored in on-site settling basins. There the tailings undergo a compaction and dewatering process, producing a slowly densifying suspension. The released water will be recycled for extraction. The fine tailings will be reclaimed as either dry or wet landscapes. (Leung et al., 2001)

Also after oil sands extraction anaerobic biodegradation will occur within the tailing ponds leading to a release of greenhouse gases into the atmosphere. Anaerobic biodegradation of hydrocarbons to end products like methane and carbon dioxide is possible by different groups of microorganisms: denitrifying bacteria, sulfate-reducing bacteria and methanogens. (Salloum et al., 2002)
 

Oil sand sample

Open pit mining and the extraction of the bitumen from the oil sands creates large and intense disturbances of varying landscapes. The area currently disturbed by mine operation covers about 530 km2 and the area of tailing ponds surpasses 130 km².
To produce 1 barrel of crude oil, 2 tons of oil sand and 2 – 3 tons of water (including recycled water) are required. (Kelly et al., 2009)

An issue of increasing importance is the land remediation and reclamation of oil sand areas in Canada and the reconstruction of these disturbed landscapes back to working ecosystems similar to those existing prior to mining operations. An important issue in this context is the identification of oil sand-derived organic compounds in the tailings, their environmental behaviour and the resulting chances and limitations with respect to land reclamation. Furthermore the biodegradation processes that occur in the tailings and that could lead to a decrease in hazardous organic compounds are important challenges, which need to be investigated.