Treatment of Phenol in Water Using Microwave-assisted Advanced Oxidation Processes

Abstract

Phenol and its compounds are highly toxic even in low concentration, and have become the subject of intense research during the last two decades. Effluents from industries such as oil refining, paper milling, olive oil extraction, wood processing, coal gasification and textiles and resin manufacturing and agro-industrial wastes discharge phenols at levels much higher than the toxic levels set for this compound. Advanced Oxidation Processes (AOPs) such as UV, UV-TiO2, UV-H2O2, O3 and UV-O3 have become popular in recent years as efficient treatment methods for recalcitrant compounds like phenol. The effect of microwave (MW) and combined MW-UV treatment on degradation of phenol was studied in aqueous solution in the presence and absence of TiO2 under controlled temperature conditions. It was found that the efficiency of MW and MW-UV processes for the degradation of phenol was less than 10% after 120 minutes of treatment. However, the efficiencies of MW-TiO2 (hydrothermal) and MW-TiO2 (sol-gel) were slightly more than those of the above processes at 12 to 15% after 120 minutes, which might be due to adsorption of the phenol on the surface of TiO2 particles. It also was observed that MW-UV-TiO2 was superior to any other process studied for the degradation of phenol. At natural pH, the degradation efficiency of MW-UV-TiO2 (HT) on 1500 ppm of phenol in water was 23%, and for MW-UV-TiO2 (SG) it was 20%. Hence, it can be concluded that the catalyst (TiO2) prepared by the hydrothermal (HT) method had better catalytic activity than TiO2 prepared by the sol-gel (SG) method, which might be due to its structural and optical characteristics. Of the two developed reactors which are MW and a combined MW-UV reactor, MW-UV combined with TiO2 could be used for most successful degradation of phenol.