Enhanced treatment of pharmaceutical wastewater by combining three-dimensional electrochemical process with ozonation to in situ regenerate granular activated carbon particle electrodes

The treatment of a real pharmaceutical production wastewater by electrolysis using three-dimensional electrodes (3D electrolysis), ozonation, and their combined process (3D/O-3) was investigated in this study. The pharmaceutical wastewater was characterized by a high organic concentration (total organic carbon (TOC) of 13,475 mg/L) and high acute toxicity (100% inhibition of the luminescent bacterial Vibrio fischeri). After 6 h treatment, 23% and 43% of TOC could be removed from the pharmaceutical wastewater by individual ozonation and the 3D electrolysis process using granular activated carbon (GAC) as the particle electrodes, respectively. However, the acute toxicity of the wastewater was hardly reduced by the two individual processes. In comparison, by sparging the ozone generator effluent (oxygen and ozone gas mixture) in the three-dimensional electrode reactor, the 3D/O-3 process considerably enhanced TOC abatement to similar to 71% and reduced the inhibition of the luminescent bacterial to < 70% in Microtox bioassays. These improvements can be mainly attributed to the enhanced hydroxyl radical ((OH)-O-center dot) production in the 3D/O-3 process via several reaction mechanisms, e.g., the reaction of sparged O-3 with in situ generated H2O2, the electrochemical reduction of O-3, and GAC catalyzed O-3 decomposition, which in turn enhanced the oxidation of organics in the bulk and those adsorbed onto the GAC particle electrodes. The results of this study indicate that there exists a synergistic effect between 3D electrochemical process and ozonation for the degradation of toxic organics in the pharmaceutical wastewater. Compared with the two individual processes, the 3D/O-3 process can thus provide a more effective option for the treatment of high-strength pharmaceutical wastewater.