Catalytic Ozonation of Phenolic Wastewater: Identification and Toxicity of Intermediates

A new strategy in catalytic ozonation removal method for degradation and detoxification of phenol from industrial wastewater was investigated. Magnetic carbon nanocomposite, as a novel catalyst, was synthesized and then used in the catalytic ozonation process (COP) and the effects of operational conditions such as initial pH, reaction time, and initial concentration of phenol on the degradation efficiency and the toxicity assay have been investigated. The results showed that the highest catalytic potential was achieved at optimal neutral pH and the removal efficiency of phenol and COD is 98.5% and 69.8%, respectively. First-order modeling demonstrated that the reactions were dependent on the initial concentration of phenol, with kinetic constants varying from 0.038？min？1？？([phenol]o = 1500？mg/L) to 1.273？min？1 ([phenol]o = 50？mg/L). Bioassay analysis showed that phenol was highly toxic to Daphnia magna (LC50 96？ ？mg/L). Comparison of toxicity units (TU) of row wastewater (36.01) and the treated effluent showed that TU value, after slightly increasing in the first steps of ozonation for construction of more toxic intermediates, severely reduced at the end of reaction (2.23). Thus, COP was able to effectively remove the toxicity of intermediates which were formed during the chemical oxidation of phenolic wastewaters. 1. Introduction phenol is a hazardous contaminant and classified as a toxic and priority hazardous contaminant in the list of USEPA [1], which can be found in aqueous effluents from various industries such as the petrochemical plants, petroleum refineries, manufacturing of resins and plastics, steel production, coal conversion, surface runoff from coal mines, dyestuff, tanning, paint stripping operations, pulp and paper, pesticides, pharmaceuticals, medications, and food processing industries [2, 3]; Environmental Protection Agency has limited this contaminant concentration in surface waters to less than 1 ppb [4]. Due to its toxicity and hazardous character and an increasing social concern on environment, it is required to be removed prior to discharging to the environment. Therefore, because the traditional methods of treatment of phenolic wastewaters such as physical and biological processes are not sufficient and have their own limitations, there is a need to use effective strategies of treatment. Many investigations are available regarding the use of advanced oxidation processes (AOPs) such as ultrasonic, photooxidation, photocatalytic oxidation plasma, Fenton, photo-Fenton, wet oxidation, and ozone/ultraviolet (UV) for the degradation