Treatment of produced water by pressure-assisted ozonation and sand filtration

Ever increasing energy demand worldwide necessitates energy production from heavy petroleum sources such as oil sands and oil shale. Extraction of bitumen from oil sands and in situ extraction of kerogen from oil shale result in large quantities of water containing hydrocarbon contaminants. The contents of dispersed and dissolved oils and other organic contaminants present problems for subsequent water uses and disposal. When discharged near shoreline, produced water with even trace oil results in sheen formation at the water surface. This research employs a new ozonation technique to treat water to remove oil and prevent oil sheen. Unlike ordinary ozonation practice, the new technique incorporates rapid, successive cycles of compression and decompression during ozonation. Nano/micro bubbles are created that provide reactive zones at the gas-liquid interface, resulting in heightened chemical conversions-most notably the conversion of hydrophobic hydrocarbon molecules into hydrophilic organic acids. This study examined the reduction of dissolved and dispersed hydrocarbons as well as prevention of oil sheen according to treatment extent and varied treatment parameters. Experimental results from a 2-stage treatment system suggest effective oil reduction and oil sheen prevention. Specifically, when a synthetic produced water containing 120 ppm of crude oil (100 ppm of dispersed and 20 ppm of soluble oil at a total COD of 320 mg/L) was subjected to 10 pressure cycles (reaching 100 psi; 20 s each) of ozonation and sand filtration at 6 cm/min as the first stage and then repeated by 20 cycles of ozonation and sand filtration, it resulted in removal of oil to 20 ppm as water-soluble organic acids, decrease of turbidity from 200 NTU to 2 NTU, and complete sequestration of surface sheen. Treatment results and removal mechanisms are discussed. The new technique has potential for treating produced and tailings waters, allowing safe discharge to the environment as well as making high-value reuses of the water possible.