Reductive/oxidative treatment with superior performance relative to oxidative treatment during the degradation of 4-chlorophenol

This study obtained information on the effectiveness of the photo-assisted Fenton oxidation of 4-chlorophenol (4-CP) combined with zero-valent pretreatment. The kinetic rate parameters of the process as well as the operating conditions were determined. Homogeneous photo-assisted Fenton enhanced processes lead to ∼33% mineralization of 4-chlorophenol (1.25 mM) in solutions containing Fe-ions (2-10 mg/l) and H2O2 (10 mM) within 2 h under visible light irradiation. When this solution was pretreated with zero-valent Fe (14 g/70 ml) in Ar atmosphere, the mineralization attained levels of >80% after the second stage photo-assisted Fenton process. Intermediates that could be effectively degraded by photo-Fenton reactions were not attained in the absence of zero-valent Fe pretreatment. The pretreatment by zero-valent Fe under light lead to about 70% of the stoichiometric amount of chloride contained in 4-CP. Partial recovery of chloride ions indicated the formation of chloro-intermediates. These intermediates were experimentally detected by high-pressure liquid chromatograph (HPLC)-MS and the most important intermediates were identified. Fenton photo-assisted processes were effective employing very low concentrations of Fe2+(2-5 mg/l) after the pretreatment stage that do not need to be separated after the 4-CP degradation process. This is important for the practical application of the novel combined heterogeneous-homogeneous process. Evidence for the stable catalytic performance of the coupled process to degrade 4-CP is presented. The effect on the 4-CP degradation of Fe-ion, H2O2, 4-CP concentration and gas atmosphere was systematically investigated. The activation energy (Ea) of 2.66 kJ/mol was found for the abatement of 4-CP.