The effect of temperature on the Fenton process has been studied within the range of 25−130 °C using phenol (100 mg/L) as target compound, 10 mg/L Fe2+, and a dose of H2O2 corresponding to the theoretical stoichiometric amount (500 mg/L) for mineralization. The TOC reduction was considerably improved as temperature increased. Whereas at 25 °C the TOC decreased less than 28%, a reduction of almost 80% was achieved at 90 °C. Beyond this temperature no significant improvement of mineralization was observed, although the rate of the process was considerably enhanced. Increasing the temperature leads to a more efficient consumption of H2O2 which indicates an enhanced iron-catalyzed H2O2 decomposition into radicals as temperature increases rather than the generally accepted thermal breakdown of H2O2 into O2 and H2O. Therefore, working at a temperature well above the ambient provides a way of intensifying the Fenton process since it allows a significant improvement of the oxidation rate and the mineralization percentage with reduced H2O2 and Fe2+ doses. Furthermore it would not represent a serious drawback in the case of many industrial wastewaters which may be already at that temperature. Besides, partial recovery of heat from the treated off-stream would always allow saving energy. The TOC time-evolution was well described by a kinetic model based on TOC lumps with apparent activation energy values in the range of 30−50 kJ/mol.

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A coupled coagulation−adsorption and high-temperature Fenton oxidation treatment has been applied for the treatment of three different industrial wastewaters bearing high concentrations of hazardous pollutants. High percentages of chemical oxygen demand (COD) removal (>85% for the pesticide and security inks effluents and 65% for the cosmetics ones) were achieved in a first step using FeCl 3 as coagulant and bentonite as adsorbent. This reduced dramatically the amount of H 2 O 2 required in the further high-temperature (120 °C) Fenton oxidation (HTF). Using the stoichiometric amount relative to COD around 70% of the remaining organic load was mineralized. The combined treatment allowed achieving the regional discharge limits of COD and ecotoxicity at a cost substantially lower than the solution used so far where the three wastewaters are managed as hazardous wastes. Working at high temperature would not represent an important drawback since around 90% of heat can be recovered from the treated off-stream.

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Fenton-like oxidation has proved to be highly efficient in the degradation of polychlorinated phenols (poly-CPs) at 50 °C provided that the H2O2 dose is adjusted appropriately. Using the theoretical stoichiometric H2O2/poly-CP molar ratio allowed a high mineralization of the starting poly-CPs, with negligible residual concentrations of chlorinated organic species and a dramatic reduction of ecotoxicity. Nevertheless, at substoichiometric H2O2 doses, a wide variety of chlorinated condensation byproducts (chlorinated diphenyl ethers, biphenyls, and dibenzofurans) were detected. A chlorinated aromatic iron-containing solid polymer was also formed. At these substoichiometric H2O2 doses, the ecotoxicity values even increased with respect to those of the starting poly-CPs. A reaction scheme is proposed to describe the Fenton-like oxidation of poly-CPs that includes all of the intermediates detected under substoichiometric conditions and used to develop a kinetic model based on TOC lumps. This kinetic model describes fairly well the time evolution of TOC upon the Fenton-like oxidation of poly-CPs.

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