Magnetic heterogeneous catalytic ozonation: a new removal method for phenol in industrial wastewater

Yousef Dadban Shahamat,Amir Hossein Mahvi,Ali Esrafili,Mahdi Farzadkia,Mitra Gholami,Simin Nasseri

doi:10.1186/2052-336x-12-50

Abstract

In this study, a new strategy in catalytic ozonation removal method for degradation of phenol from industrial wastewater was investigated. Magnetic carbon nano composite as a novel catalyst was synthesized, characterized and then used in the catalytic ozonation process (COP) and compared with the single ozonation process (SOP). The influential parameters were all investigated. The results showed that the removal efficiency of phenol and COD (chemical oxygen demand) in COP (98.5%, 69.8%) was higher than those of SOP (78.7%, 50.5%) and the highest catalytic potential was achieved at optimal neutral pH. First order modeling demonstrated that the reactions were dependent on the concentration of catalyst, with kinetic constants varying from 0.023 1/min (catalyst = 0 g/L) to 0.071 1/min (catalyst = 4 g/L), whereby the optimum dosage of catalyst was found to be 2 g/L. Furthermore, the catalytic properties of the catalyst remained almost unchanged after 5-time reuse. The results regarding the biodegradability of the effluent showed that a 5-min reaction time in COP reduced the concentrations of phenol and COD to the acceptable levels for the efficient post-treatment in the SBR in a 4-h cycle period. Finally, this combined system is proven to be a technically effective method for treating phenolic contaminants.

Highlights

Ozonation is one of the oxidation processes widely used for industrial wastewater pretreatment in which ozone molecules break down recalcitrant and toxic organic compounds into smaller molecules
In this study, the preparation and the assessment of properties of activated carbon (AC)/nano-Fe3O4 composite used as a catalyst in the catalytic ozonation of phenol have been investigated. This super paramagnetic nano-composite exhibited a catalytic effect on the ozone decomposition and reactive radical generation which was effectively separated from solution by applying a magnetic field and reused for several times
The findings indicated that phenol was mainly decomposed through a series of oxidation reactions occurring on the surface of the catalyst, and the radical scavengers present in wastewater could not affect the catalytic reaction

Summary

Introduction

Ozonation is one of the oxidation processes widely used for industrial wastewater pretreatment in which ozone molecules (as a strong oxidant) break down recalcitrant and toxic organic compounds into smaller molecules. The ozonation reaction is accomplished through two pathways: direct ozone oxidation and indirect free hydroxyl radical oxidation. In indirect free hydroxyl radical oxidation ozone is decomposed to free reactive radicals, which can cause a significant rise in pollutant removal efficiency [2,3]. (1) high energy consumption for ozone generation which could be costly; (2) in some cases ozonation is selective; (3) incomplete oxidation and low efficiency due to low reaction kinetics and limited mass transfer; [4] and incomplete mineralization of recalcitrant organics [5]. Studies were focused on improving the ozonation efficiency and overcoming the weakness of the single ozonation process (SOP)

Methods

Results

Conclusion