Removal of oil and oil sheen from produced water by pressure-assisted ozonation and sand filtration

Ever increasing energy demand worldwide necessitates energy supply, inevitably leading to an increasing volume of process waters containing hydrocarbon contaminants. Among them, dispersed and dissolved oils in produced water need to be removed adequately in order to reuse or avoid surface sheen from coastal discharge. We have recently developed a new ozonation technique coupled with sand filtration to quickly remove oil from process water and prevent oil sheen. The technique incorporates rapid, successive cycles of compression and decompression during ozonation. Gas bubbles expanding from small to large sizes occur that provide ample reactive zones at the gas–liquid interface, resulting in heightened chemical conversions—notably the conversion of hydrophobic hydrocarbon molecules into hydrophilic ones. This study examined the removal of hydrocarbons and sheen according to treatment parameters and configurations, as assessed by changes in turbidity, COD, BOD, and sheen presence following treatment. When a synthetic produced water containing 120 ppm of oil (about 100 ppm of dispersed and 20 ppm of soluble oil at a total COD of 320 mg L−1) was subjected to 10 pressure cycles (reaching 1.0 MPa; 20 s each) of ozonation and sand filtration at 6 cm min−1 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 to 2 NTU, and complete sequestration of surface sheen. The new technique offers a treatment alternative for produced water and likely other tailings waters, promoting safe discharge to the environment and beneficial uses of the water.