Intensification of the Fenton Process by Increasing the Temperature
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.
Available from: Inmaculada Ortiz
- ". Effect of temperature with H2O2 at 20% in: (a) 2-CP, H2O2 and TOC; (b) aromatic intermediates; (c) organic acids. Empty dots: 70 • C, filled dots: 20 • C. and attributed to the presence of unidentified oxidation intermediates , which may be aromatic condensation species . In addition, Cl − measurements were only balanced when the TOC was balanced . "
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ABSTRACT: This work assesses the influence of the operating conditions H2O2 dose (20 or 100% of the stoichiometric amount), temperature (20 or 70°C), and the presence of chloride in the oxidation medium in the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) during Fenton treatment of aqueous samples of 2-chlorophenol, 2-CP, one of the strongest precursor of PCDD/Fs. After 4h of oxidation in the experiments carried out with 20% H2O2 chlorinated phenoxyphenols and biphenyls, which are intermediates in PCDD/Fs formation, as well as PCDD/Fs were observed, resulting in concentrations 11 times higher than in the untreated sample. Additionally, when NaCl was also present in the reaction medium, PCDD/Fs were formed at higher extent, with a total concentration 74.4 times higher than in the untreated 2-CP solution. Results depicted a preferential formation of PCDFs over PCDDs, with dominance of lower chlorinated PCDD/Fs (tetra and penta-PCDD/Fs). Besides, the formation of the most toxic PCDD/Fs congeners (2,3,7,8-PCDD/Fs) was not favored under the operating conditions used in this work.
Available from: Juliana R. Steter
- "In this context, the in situ generation of H 2 O 2 has been employed in numerous electro-Fenton degradation reactions    carried out under diverse experimental conditions     , in which H 2 O 2 can to produce hydroxyl radicals ( "
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ABSTRACT: Electrodegradation of the azo dye amaranth using a modified gas diffusion electrode (MGDE), prepared with Printex 6L carbon black and 5.0% cobalt (II) phthalocyanine, has been investigated with the aim of developing an efficient method of treating contaminated effluent derived from the food and beverage processing industries. Hydrogen peroxide was electrogenerated at a potential of -0.7 V (vs. Ag/AgCl) under a constant flow of O2, and electrodegradations were performed in the absence or presence of Fe2+ or Fe3+ (electro-Fenton conditions). The removal of color and total organic carbon (TOC) from the dye solution was observed under all reaction conditions, although process efficiency was improved markedly by the addition of Fe ions. Following 90 min of electrolysis, maximal values for decolorization (79.3%) and mineralization (67.3%) were achieved in the presence of 0.15 mM Fe2+, and energy consumption (370.0 kWh kg-1 per kg of TOC removed) was minimal under these conditions. Concentrations of residual Fe in treated electrolytes were either below the permissible limit or could be rendered so by conventional treatment. It is concluded that the electro-Fenton reaction with Fe2+ and a MGDE represents a viable process for the degradation of amaranth in aqueous medium.
Available from: Ahmet Aygun
- "However, Hermosilla et al. (2009), claims that there was no significant increase in the COD removal when the temperature was increased from 298 to 318 K and COD removal results were constant at about 64%. Zazo et al. (2011) reported that increasing operating temperature had possitive effect on the TOC reduction. They found that TOC reduction of almost 80% was achieved at 363 K. Beyond this temperature no significant improvement was observed, although the rate of the process was considerably enhanced. "
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ABSTRACT: Treatment of young landfill leachate, collected from municipal solid waste site of city of Konya, was investigated by using the Fenton process. The leachate itself showed the characteristics of pH 7.25, COD 38.2 g L -1 and BOD 5 22 g L -1 . Ratio of BOD 5 to COD with 0.58 indicates that leachate can be defined young. Fenton oxidation of landfill leachate was expressed in two-stage process, where a fast initial reaction (H 2 O 2 /Fe 2+) was followed by a much slower one (H 2 O 2 /Fe 3+). Overall kinetics can be described by a second-order rate equation followed by zero-order one. The kinetic studies were undertaken at the different temperatures and reaction rates increcesed by increasing temperature. The apparent kinetic constants at 303 K are k = 3.16 x10 -3 L g -1 min -1 and k 0 = 0,171 g L -1 min -1 , respectively. Fenton reagents effectively degraded the leachate organics and most of the degradation was completed within 30 minutes for all temperatures. The performance of Fenton process was not only presented as a COD removal but also expressed as the amount of generated sludge and its properties. Sludge properties were revealed with Capillary Suction Time (CST) and Sludge Volume Index (SVI). The minimum CST value was obtained at the optimum molar ratio of 4.12 mol/mol and increasing temperature resulted in a positive effect on CST values. All SVI values were significantly low which indicates that sludge itself had good settling properties.
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