Remediation of phenolic wastewaters by advanced oxidation processes (AOPs) at ambient conditions: Comparative studies

The efficiency of two AOPs operating at room conditions of pressure and temperature, ozonation (single and catalytic over the laboratorial Mn–Ce–O and the commercial N-150—Fe2O3/MnOx) and Fenton's process (homogeneous and over Fe–Ce–O), was simultaneously checked for the remediation of a phenolic mixture. Gathering up former individual results pointing out as most suitable treatments those involving solid catalysts, either for ozonation or Fenton's, a global conclusion elects this last process as the more interesting for industrial applications. In fact, the lower retention time required by H2O2+Fe–Ce–O 70/30 to attain an easily biodegradable effluent makes this technology truly attractive for in-situ remediation of this specific wastewater. These findings were mostly driven by the comparative ability to transform the non-biodegradable raw effluent into streams more amenable to further bio-processing. In this regard, biological parameters superposed chemical COD degradation within the ultimate selection reasons. Indeed, in all cases COD limits were not reached and a subsequent biological treatment is required. Despite COD removal for catalytic ozonation showed to be higher than for heterogeneous Fenton's (63% and 50%), BOD5/COD was contrarily favorable to Fenton's, which immediately conducted to a biodegradable mixture in the first minutes (0.78 in 10 min) while ozonation took more than 1 h to impart a biodegradable character.