Pilot-scale evaluation of ozone-based treatment for organic contaminants in oilfield produced water

This study evaluates a pilot unit integrating a membrane contactor with an ozone gas injection system based on a self-priming gas–liquid pump for the degradation of a mixture of seven naphthenic acids (NAs) representing those typically found in oilfield-produced water (OPW) under alkaline saline conditions (pH ∼8, 100 g L −1 NaCl). First, the membrane contactor coupled with a self-priming gas–liquid pump was evaluated for a model organic compound, Venlafaxine (VLX), achieving >95% oxidation within 30 min, improving with increasing ozone gas (Q G ) and water solution (Q L ) flow rates, for a fixed applied ozone dose (AOD), and increasing transmembrane pressure (TMP) seems only to affect initial reaction kinetics. Ozonation of the NAs mixture showed strong structural dependence: 2-naphthoic acid (2-NA) degraded readily (97.5% in 10 min; k = 0.4 ± 0.1 min −1 ), whereas the remaining six NAs had limited removals (average = 46 ± 12%; k = 5–15 × 10 −3 min −1 ), even at 2.5 bar. To overcome these kinetic limitations, ozone (O 3 ) was combined with hydrogen peroxide (H 2 O 2 ) and/or persulfate (PS). The O 3 /H 2 O 2 process achieved the most extensive oxidation (>92% for all NAs), while O 3 /PS selectively benefited aliphatic species. The O 3 /H 2 O 2 /PS system provided broad-spectrum degradation (>87% for all acids; <5 min for 2-NA), confirming that complementary oxidation pathways are essential for efficient oxidation of both aromatic and aliphatic NAs. These insights offer a mechanistic foundation for optimizing O 3 -based oxidation systems for real-world OPW treatment.