Degradation of mono ethylene glycol wastewater by different treatment technologies for reduction of COD gas refinery effluent
Creators: name: Rafieyan, Sayed Ghadir
name: Marahel, Farzaneh
name: Ghaedi, Mehrorang
name: Maleki, Afsaneh
Publisher: name: Taylor & Francis
Year: 2022
Subjects: subject: Space Science
subject: Environmental Sciences not elsewhere classified
subject: Chemical Sciences not elsewhere classified
subject: Ecology
subject: FOS: Biological sciences
subject: Biological Sciences not elsewhere classified

description: Ozonation (O<sub>3</sub>) is a widely used advanced oxidation process (AOP) for the treatment of wastewater, while its drawbacks include high energy consumption and poor solubility must be reduced or eliminated. Hence, a combined catalytic ozonation process with H<sub>2</sub>O<sub>2</sub> and S<sub>2</sub>O<sub>8</sub><sup>2-</sup> was employed to degrade mono ethylene glycol (MEG) and eliminate ecological risks during the treatment of gas refinery wastewater. In this study, the reduction of chemical oxygen demand (COD) and MEG from wastewater by O<sub>3</sub>, O<sub>3</sub>/H<sub>2</sub>O<sub>2</sub>, O<sub>3</sub>/Na<sub>2</sub> S<sub>2</sub>O<sub>8</sub>, O<sub>3</sub>/GAC, O<sub>3</sub>/GAC/S<sub>2</sub>O<sub>8</sub><sup>2-</sup> and O<sub>3</sub>/GAC/H<sub>2</sub>O<sub>2</sub> oxidation treatment systems were investigated. The optimal treatment conditions were obtained as O<sub>3</sub> dosage of 0.81 g h<sup>−1</sup>, H<sub>2</sub>O<sub>2</sub> (0.15 mol L<sup>−1</sup>), S<sub>2</sub>O<sub>8</sub><sup>2-</sup> (2 g L<sup>−1</sup>), GAC (7 g L<sup>−1</sup>), pH of 11 and 60 min reaction time. The results revealed that the highest rate of degradation of MEG, COD reduction and the minimum electrical energy per order from the wastewater were 87.6%, 78.1% and 1.01 kWh/m<sup>3</sup> respectively for O<sub>3</sub>/GAC/S<sub>2</sub>O<sub>8</sub><sup>2-</sup> process and 91.0%, 82.5% and 0.877 kWh/m<sup>3</sup> respectively for O<sub>3</sub>/GAC/H<sub>2</sub>O<sub>2</sub> process. The MEG degradation rate constant by O<sub>3</sub>/GAC/H<sub>2</sub>O<sub>2</sub> system about 6.2 times and O<sub>3</sub>/GAC/S<sub>2</sub>O<sub>8</sub><sup>2-</sup> system over 5.3 times were higher than O<sub>3</sub>. After calculation, the synergy factors in O<sub>3</sub>/GAC with H<sub>2</sub>O<sub>2</sub>/S<sub>2</sub>O<sub>8</sub><sup>2-</sup> systems are more than 4.7, demonstrating that both systems have a strong synergistic effect. The finding related to the OH<sup>°</sup> trapping agent illustrates that indirect oxidation by OH<sup>°</sup> plays a vital role in the degradation of MEG. The performance of GAC stability was checked and resulted in the GAC also showing good stable catalytic activity in five consecutive cycles of use. The degradation pathways of MEG in the O<sub>3</sub>/GAC with H<sub>2</sub>O<sub>2</sub> or S<sub>2</sub>O<sub>8</sub><sup>2-</sup> system were proposed based on intermediate analysis. The main intermediates found in MEG oxidation include glycolaldehyde, glycolic acid, glyoxal, glyoxylic acid, oxalic acid and formic acid. Finally, modification of wastewater treatment suggested that the burping phenomenon and the glycol foaming tendency were not observed.