Degradation of mono ethylene glycol wastewater by different treatment technologies for reduction of COD gas refinery effluent

Abstract

ABSTRACT Ozonation (O3) 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 H2O2 and S2O8 2- 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 O3, O3/H2O2, O3/Na2 S2O8, O3/GAC, O3/GAC/S2O8 2- and O3/GAC/H2O2 oxidation treatment systems were investigated. The optimal treatment conditions were obtained as O3 dosage of 0.81 g h−1, H2O2 (0.15 mol L−1), S2O8 2- (2 g L−1), GAC (7 g L−1), 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/m3 respectively for O3/GAC/S2O8 2- process and 91.0%, 82.5% and 0.877 kWh/m3 respectively for O3/GAC/H2O2 process. The MEG degradation rate constant by O3/GAC/H2O2 system about 6.2 times and O3/GAC/S2O8 2- system over 5.3 times were higher than O3. After calculation, the synergy factors in O3/GAC with H2O2/S2O8 2- systems are more than 4.7, demonstrating that both systems have a strong synergistic effect. The finding related to the OH° trapping agent illustrates that indirect oxidation by OH° 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 O3/GAC with H2O2 or S2O8 2- 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.