Study On The Degradation Of Nonylphenol Ethoxylates In Aqueous Solution By Fenton Oxidation

Nonylphenol ethoxylates (NPEOs) are one of the most common nonionic surfactants in the markertplace. Many recent studies have reported that some metabolites of NPEOs, such as Nonylphenol (NP) and short-chain NPEOs (Nonylphenol mono-to diethoxylate, NP1-2EO) have the characters of difficult to further biodegrade, hydrophobic property and bioaccumulation. Moreover, these compounds have been proved to be weakly estrogenic to the organism, which belong to Endocrine Disrupting Chemicals (EDCs).At present, the research of the removal of NPEOs is primary on biodegradation, and the studies on the removal through Fenton oxidation are typically limited in their degradation comparison with various advanced oxidation or with different surfactants. Few researcher had systematically investigated the removal of NPEOs by Fenton oxidation process. In this study, the operating parameters of Fenton reaction were optimized through single-factor tests and orthogonal experiment. High-performance liquid chromatography (HPLC) analysis and gas chromatography-mass spectrometry (GC-MS) analysis were employed to monitor the degradation behaviors of NPEOs under Fenton reaction. Then we preliminarily explored the reaction kinetics and the degradation mechanism. The results were shown as follows:(1) The effects of initial pH value, hydrogen peroxide and ferrous ion dosages on the degradation of NPEOs in water samples were obvious, and increasing reaction temperature could enhance the removal rate. The orthogonal experiment indicated that the order of degree of influence on the NPEOs removal rate was dosage of H2O2, initial pH, molar ratio of H2O2/Fe2+and reaction time. And the determined optimal condition were H2O2dose of13.0mmol/L, molar ratio of H2O2/Fe2+of3, pH value of3.0and reaction time of15min. Under the optimum operation condition, the NPEOs concentration removal rate was94.93%.(2) The degradation of NPEOs in Fenton reaction primarily depended on the oxidation effect. A modified pseudo-first-order kinetic model was found to represent well the experiment results. The relations between the reaction rate constants with H2O2and Fe2+dosages and operating temperature were established based on the experimental data. Results indicated that the Fenton oxidation rate and removal efficiency were more dependent on dosage of H2O2than Fe2+, and the apparent activation energy (AE) in Arrhenius equation was determined to be17.5kJ·mol-1.(3) HPLC and GC-MS results shown that the relative percentage of shorter NPEOs kept increasing during the Fenton oxidation, while longer NPEOs kept decreasing. This result indicated that NPEOs with longer EO unit could be degraded easier than those with shorter EO unit. NP, short-chainNPEOs and NPECs were the dominant metabolites. The UV-vis spectral variation proved that benzene had been broken.(4) UV catalysis could enhanced the NPEOs removal rate of Fenton reaction, which could shorten the reaction time, but the UV irradiation intensity would not be helpful to NPEOs degradation.