Water treatment technologies for oil sands mining Adrian Manlagnit (Note: This article written on 16 May 2009 presents the salient points of technical journal articles and related publications on the issue of water usage and treatment technologies in oil sands mining. The technical articles written by Erik Allen are commonly cited in the text. Full citations and/or credits are due to the authors and originators of the papers; the details of their papers are at the end of this article).

Water usage To produce oil from the oil sands field in Alberta, huge amount of water is used. Specifically, water is used to separate bitumen from the sand at a high water to oil ratio – the National Energy Board (2006) estimates that around 2 to 4.5 barrels of fresh Athabasca River water are used to produce a barrel of synthetic crude oil. Currently, total bitumen production is around 1 million barrels per day and with C$125 billion (All Projects Case vs. C$94 billion for base case – see below) to be further spent on oil sands investments in the next five years, production could reach up to 4.5 million barrels per day (Mbd) by 2015 (NEB 2006). Note that the timeframe of production could change.

Source: NEB 2006

This projected production at around 4.4 Mbd of synthetic oil would mean a withdrawal of 529 million cubic meters (3.3 billion barrels) per year from the Athabasca River, compared with 370 million cubic meters (2.3 billion barrels) at the current rate (NEB 2006). The water used for all oil sands mining projects, including current and approved projects, will total about 2% of the natural flow of the Athabasca River (CAPP 2008). The water is used for in-situ recovery of bitumen i.e. water is converted to steam to heat up the bitumen underground and then pumping it to the surface through wells. Waste water is usually alkaline, slightly brackish, and toxic to aquatic biota due to high concentrations of organic acids (Allen, 2008; Mackinnon and Sethi 1993). Strong regulation, i.e. zero discharge policy, has lead to mostly water recycling as practiced by

the oil sand producers. The other alternative is to tap underground aquifer hosting nonpotable, saline water for bitumen recover. The following figures depict the usage of recycled water by the Canadian Natural Resource Limited on their Primrose/ Wolf Lake project as well as on the Cold Lake project of Imperial Oil. Aside from recycled water, CNRL also taps brackish water to decrease fresh water usage.

Source: CAPP 2008

The decline in freshwater use for the Cold Lake project of Imperial Oil as seen in the graph is due to its recycling effort – 95% of water from bitumen production is recycled and deficiencies are filled up with deep saline waters and freshwater.

Source: CAPP 2008

Recycling and water treatment options Despite the aggressive recycling of ‘waste’ water by oil sand producers for re-use in the recovery process, repeated extraction cycles have resulted in the deterioration of water quality which could upset the bitumen extraction process through scaling, fouling, increased corrosivity and interference with extraction chemistry (Allen 2008; Kasperski 2003; Rogers 2004). Furthermore, with zero discharge policy, oil sand producers have to treat and properly dispose million of cubic meters of toxic process water and tailings, which are currently held in large tailings ponds (Allen 2008). With reclamation to depend on natural detoxification of process waters in tailings ponds, the viability is uncertain (Allen 2008, Quagraine et al 2005). To meet the concerns on waste water management in general, and ensure supply of recycled water for bitumen processing in particular, oil producers could avail of various water treatment technologies. Allen (2008) in his paper “Process water treatment in Canada’s oil sands industry: II. A review of emerging technologies”, enumerated various treatment processes. These include 1) adsorption; 2) membranes - microfiltration and ultrafiltration; 3) nanofiltration and reverse osmosis; 4) biological treatment; 5) advanced oxidation and 6) constructed wetlands. Adsorbents are used to remove a wide variety array of pollutants associated with oilfield produced waters, specially organic carbon compounds, oil and grease, and heavy metals (Allen 2008). Adsorbents can be activated carbon, natural organic matter, zeolites, clays and synthetic polymers. Micro and ultrafiltration are pressure-driven membrane processes that reject particles as small as 0.1 micrometer and 0.01 micrometer respectively (Allen 2008). The paper said lab and pilot scale studies using membrane to treat produced waters have shown over 90% oil rejection with permeate concentrations of less than 20 ppm. But on wider scale, problems such as fouling and membrane durability could occur (Allen 2008). Nanofiltration has the potential for partial demineralization, softening, and removal of soluble organic compounds from produced water as it can reject divalent ions, dissolved organic matters, pesticides and other macromolecules (Allen 2008, et al). Reverse osmosis, on the other hand, requires the feedwater to be forced against a concentration gradient though a semi-permeable membrane (Allen 2008). Studies have showed that using reverse osmosis, rejection of hardness typically exceeds 98% (residual concentration of 95%) can be achieved (Allen 2008).

Advanced oxidation could be either photocatalytic oxidation or sonochemical oxidation. The paper said that lab-scale experiments have shown that photocatalytic oxidation can decompose organic and inorganic pollutants in oilfield produced water. The degradation rates are dependent on efficient adsorption of pollutants into the catalyst, which could then be affected by the feedwater pH (Allen 2008, et al). Sonochemical oxidation involves the formation and collapse of bubbles when ultrasound is applied to a liquid i.e. produced water. This collapse of the microbubbles produces cavities (cavitation) of high temperature and pressure that can break or destroy particles or molecules. Used with oxidant such as hydrogen peroxide, the cavitation process in some studies has been demonstrated to degrade phenols, organic acids, and polyaromatic hydrocarbon (Allen 2008, et al). Constructed wetlands, since their earlier use to treat municipal and storm water, are becoming popular in the oil sector. The processes of pollutant removal in wetlands include sedimentation, adsorption, denitrification, photo-oxidation, plant uptake and volatililization (Allen 2008, et al). The paper said that wetlands have proven to be effective in removing contaminants in produced water but treatment performance is variable as shown in various pilot and full-scale studies i.e. 55-85% of BOD5, 53-86% for COD, 54-94% for oil and grease, and 10-94% for phenols. Allen has summarized the different treatment processes and their potential applications to treat produced water from the oilsands mining. Water treatment processes – problems and potentials (Allen 2008) Processes

Adsorption

Problems associated with treatment of produced water Incomplete pollutant removal; fouling from oil; cleaning and regeneration costs; low adsorption capacity

Microfiltration and ultrafiltration

Fouling from oil and solids; membrane durability; disposal of retentate

Nanofiltration and reverse osmosis

Fouling from oil, dissolved organics, and algal growth; membrane replacement costs; brine disposal

Significant technological advances

Target chemicals in oil sands process water

Organic modifications to clay adsorbents; natural and synthetic polymers with improved adsorption and regeneration properties Surface chemistry modifications to reduce fouling and permeate flux decline; chemical additives, aeration and ultrasound to reduce fouling Membrane modifications to reduce fouling from organics; ultra low pressure membranes; lower energy

Napthenic acids, bitumen, aromatic hydrocarbons, trace metals

Bitumen, suspended solids

Napthtenic acids, hardness, TDS, aromatic hydrocarbons

Biological treatment

Feedwater toxicity; incomplete pollutant removal; sludge disposal

Advanced oxidation

Incomplete pollutant removal; high energy costs; radical scavengers; oxidation by-products

Constructed wetlands

Flow capacity; feedwater toxicity; removal of salinity; bioaccumulation of toxicants by wetland biota; cold water operation

consumption GAC-FBRs and membrane bioreactors facilitate oxidation of recalcitrant compounds and protect biofilm from influent toxicity Solar photocatalytic systems; photo electrocatalytic process to reduce the effect of radical scavengers Subsurface designs for operation in cold climates; implementation of large scale wetlands to treat oilcontaminated water; improved understanding of degradation pathways

Napthenic acids, ammonium, bitumen, aromatic hydrocarbons

Napthenic acids, ammonium, aromatic hydrocarbons Napthenic acids, ammonium, bitumen, aromatic hydrocarbons

Conclusion The paper (Allen 2008) said that most of the water treatment technologies have shown the potentials to treat i.e. de-oil, soften, detoxify and demineralized, oilfield-produced water on a small-scale basis, but their effectiveness have yet to be proven at a bench or pilot levels. It suggested that further preliminary studies are needed on pretreatment requirements, performance on target pollutants, energy consumption and costs, among others to be able to compare these technologies to existing/ conventional technologies. There is a strong need to understand how the technologies would perform given the unique physical and chemical nature of produced water from oil sands mining in the larger scale. Sources and References Process water treatment in Canada’s oil sands industry: II. A review of emerging technologies. Allen, E. Journal of Environmental Science. pp. 499 – 524. 2008. Process water treatment in Canada’s oil sands industry: I. Target Pollutants and treatment objectives. Allen, E. Journal of Environmental Science. pp. 123– 138. 2008. Canada's Oil Sands – Opportunities and Challenges to 2015: An Update. National Energy Board (NEB). 85 pp. June 2006. Environmental Challenges and Progress in Canada’s Oil Sands. Canadian Association of Petroleum Producers (CAPP). 16 pp. 2008.