Photochemical degradation and mineralization of phenol:: A comparative study

In this study, photochemical advanced oxidation processes (AOPs) utilizing the combinations of UV, UV/H2O2, and UV/H2O2/Fe2+ (Photo-Fenton process) were investigated in lab-scale experiments for the degradation and mineralization of phenol. The major parameters investigated were the initial phenol concentration, pH, hydrogen peroxide, and iron doses, and the effect of the presence of radical scavengers (PO43-, SO42-, and Cl- ions). It was observed that the phenol degradation efficiency decreased with increasing phenol concentration and pH in UV process. Maximum phenol oxidation efficiency for an initial concentration of 100 mg L-1 and at pH 3 was around 30% in direct photolysis. The efficiency increased to 97% with UV/H2O2 process, however, there was still negligible mineralization (9%) and the required irradiation time was still long (300 min). The results showed that the Photo-Fenton process was the most effective treatment process under acidic conditions. Complete disappearance of 100 mg L-1 phenol was achieved in 2.5 min and almost complete mineralization (97%) was also possible after 300 min of irradiation. The efficiency was negatively affected from H2O2 in UV/H2O2 process and Fe2+ in Photo-Fenton process over a certain concentration. The highest negative effect was observed with solution containing PO43- ions. Required reaction time for complete disappearance of 100 mg L-1 phenol increased from 2.5 min for an ion-free solution to 60 min for that containing PO43-. The photodegradation of phenol was found to follow the first-order law.