Ozonation and Granular Activated Carbon Adsorption for the Removal of Refractory Organic Matter and Decolorization During Wastewater Tertiary Treatment

This study investigated two different hybrid processes for the treatment of municipal secondary-treated biological effluents to meet the reuse of recycled water requirements for organic matter and color. The two hybrid treatment approaches were an oxidation-based treatment process (coagulation–sedimentation–deep-bed filtration [CSDF]–ozone oxidation) and an adsorption-based treatment process (CSDF-granular activated carbon [GAC] adsorption). The efficiencies of ozonation and GAC adsorption in removing chemical organic demand (COD), dissolved organic carbon (DOC), and color intensity were evaluated. The effect of CSDF as the pretreatment was also studied. Ozonation showed a much higher color removal efficiency (88%, 4.7 mg/L ozone dose) than GAC adsorption (23%). Organic matter with an apparent molecular weight of 2–3 kDa, being humus-like, might be the colored fraction in the secondary and CSDF effluents. Ozonation had a stronger ability to remove these substances than GAC adsorption, resulting in a visibly higher color removal efficiency. In addition, higher COD and DOC removal were achieved by ozonation when the average ozone dose was increased to 9.1 mg/L. Although both hybrid processes were reliable for reducing organic matter and color, the results show that ozonation is more suitable for simultaneously removing refractory organic matter and color.