Graphite as catalyst for UV-A LED assisted catalytic wet peroxide oxidation of ibuprofen and diclofenac

Abstract

Ibuprofen (IBU) and Diclofenac (DCF) are two of the most common non-steroidal anti-inflammatory drugs used worldwide. Their occurrence in natural streams, as contaminants of emerging concern, evidences the inefficiency of conventional wastewater treatment plants for their removal. The photocatalytic methods developed so far usually demand either highly energetic light sources working in the UV-C range, or exclusive tailor-made catalysts, which compromise the economy of the process. In this work, IBU and DCF degradation are addressed in a UV-A LED (395 nm) assisted Catalytic Wet Peroxide Oxidation process using graphite as catalyst. Total IBU and DCF removal is achieved in t < 60 min working at [IBU or DCF]0: 20 µM, [H2O2]0: 800 µM, [Graphite]: 1 g · L−1 and pH0:3.0, with a 53% TOC removal and ECTOC: 31.0 kWh gTOC−1. Results show a high influence of the interaction between the graphite's surface and H2O2, which enables pollutant adsorption as first step in the oxidation reaction. Further redox reactions on the graphite surface lead to the cleavage of the reaction intermediates, making active sites available again. Nonetheless, in absence of an external energy source this process is very slow. UV-A radiation promotes these reactions as well as H2O2 decomposition into hydroxyl and hydroperoxyl radicals, enhancing the contaminant removal rate. The UV-A assisted CWPO process is also effective in surface water and WWTP effluent. Furthermore, graphite shows a great stability in IBU removal from WWTP effluent upon five consecutive cycles.