Degradation of ibuprofen and phenol with a Fenton-like process triggered by zero-valent iron (ZVI-Fenton)

Abstract

It is shown here that ZVI-Fenton is a suitable technique to achieve effective degradation of ibuprofen and phenol under several operational conditions. Degradation of ibuprofen was possible in the pH interval 3-6 in both synthetic laboratory systems and actual wastewater (secondary treatment effluent), but operation at the higher pH values required higher H₂O₂ concentration and/or higher ZVI loading. In the case of real wastewater we offset the lower degradation efficiency, caused by the occurrence of organic and inorganic interfering agents, by carrying out multiple H₂O₂ additions. The studied wastewater sample had a buffer-capacity minimum at pH 4-5, and optimal treatment for ibuprofen degradation might take place at either pH 4 or 6. With a reagents cost in the order of 0.06-0.10 $ m^-3, the technique appears as very competitive and promising for tertiary wastewater treatment. There is a clear trade-off between savings in pH-fixing reagents and higher consumption of ZVI-Fenton reagents at the different pH values. The final choice in real application scenarios could be based on cost considerations (which favour pH 4) and/or the eventual fate of wastewater. For instance, wastewater reuse might place requirements on the salinity that is increased by the acidification/neutralization steps: in this case, operation at pH 6 is preferred. Interestingly, the ZVI-Fenton degradation of ibuprofen led to very low generation of toxic 4-isobutylacetophenone (IBAP, which is the ibuprofen by-product raising the highest concern), because of the combination of low formation yields and limited IBAP stability in the optimal reaction conditions. In addition to ibuprofen, phenol could be degraded as well by ZVI-Fenton. Interestingly, the ability of ZVI-Fenton to degrade both ibuprofen and phenol under similar conditions might open up the way to apply this technique to additional pollutants as well as to pollutant mixtures.

Keywords: Advanced oxidation processes; Fenton reaction; Pharmaceuticals and personal care products; Tertiary water treatment; Zero-valent iron.