Complete Removal of Organic Contaminants from Hypersaline Wastewater by the Integrated Process of Powdered Activated Carbon Adsorption and Thermal Fenton Oxidation

The feasibility of reusing hypersaline wastewater containing a high concentration of organic contaminants by a combined process of powdered activated carbon (PAC) adsorption and Fenton oxidation was investigated in this study. Operating conditions of the integrated process were optimized by jar tests. According to the results of molecular weight (MW) and full wavelength scanning analysis, most of the aromatic compounds with high MW (>1000 Da) were removed after adsorption pretreatment, but the effects of PAC adsorption on hydrophilic organic pollutants of low MW were rather limited. The adsorption followed a pseudo-second-order kinetic equation. Additionally, the strategy for maximizing the efficiency of both H2O2 and organic removal in saline wastewater was proposed. The Fenton efficiency was strongly dependent on both reaction conditions and feeding modes of reagents. Organic removal was significantly enhanced by slowing down the feeding rate of Fenton's reagents. Moreover, rapid acidification of the wastewater was observed after adding a small amount of Fenton's reagents, and the H2O2 dosage required for achieving a sufficient organic removal (effluent total organic carbon (TOC) < 200 mg/L) decreased by 22.2% with pH 3.0 maintained throughout oxidation process. Under the optimal oxidation conditions (reaction temperature = 80-90 degrees C, pH = 3, Fe2+/H2O2 molar ratio = 0.03), overall TOC removal efficiency of the integrated process was more than 95% of which 30% corresponds to the adsorption of PAC and 65% to the Fenton oxidation process. Furthermore, a pilot test indicated that the final effluent of the integrated process could conform to the standard for saline water recycle, confirming that this process provided a more economical and feasible alternative for reusing the hypersaline water contaminated with a high concentration of organic compounds.