Juan A. Zazo

Semicontinuous Fenton oxidation of phenol in aqueous solution. A kinetic study.

This work investigates the Fenton oxidation of phenol in a semicontinuous reactor where the overall amount of H(2)O(2) is distributed as a continuous feed upon the reaction time. The experiments were carried out at 25 degrees C and atmospheric pressure, with 100mg/L initial phenol concentration and iron dosages from 1 to 100 mg/L. H(2)O(2) aqueous solution was continuously fed during 4h reaction time up to an overall dose varying within the range of 500-5000 mg/L. The results in terms of evolution of phenol, H(2)O(2) and intermediates, as well as TOC abatement were compared with those obtained in conventional batch operation. It was found that the oxidation rates for phenol and intermediates were lower when adding the H(2)O(2) continuously. However, a higher abatement of TOC was reached at the end of the 4-h reaction time, in spite of a similar overall H(2)O(2) consumption. This is the result of a more efficient OH generation throughout the semicontinuous process, favouring the reaction with the organic species and reducing the occurrence of competitive scavenging reactions involving Fe(2+), H(2)O(2) and OH. Two kinetic models were proposed, one for describing the evolution of phenol, aromatics and H(2)O(2) and the other for TOC. The influence of the operating conditions on the kinetic constants was also studied, looking for the optimal conditions in terms of both, environmental and economic points of view.

Trends in the Intensification of the Fenton Process for Wastewater Treatment: An Overview

The implementation of increasingly stringent regulations for wastewater discharge has enforced research efforts toward either the implementation of novel treatments or the improvement of those presently available. The literature on the use of Fenton oxidation in wastewater treatment has established this method as one of the most effective and suitable process for the abatement of recalcitrant water pollutants. However, despite the many advantages of the conventional Fenton process, there are issues relative to pH modulation, the cost associated to H2O2 and catalyst consumption as well as to sludge disposal that limit a more extended full-scale application. In recent years, several solutions have been developed for the sake of improving Fenton (or Fenton-like) oxidation as a cost-effective technology. This paper presents a thorough review on the different ways of intensifying the Fenton by using radiation, electrochemistry, and/or heterogeneous catalysts, as well as by optimizing the main operating conditions in the conventional homogeneous system. The application of these enhanced technologies to synthetic and real industrial wastewaters is described and discussed.

Influence of plants on the reduction of hexavalent chromium in wetland sediments

This work addresses the effect that plants (Typha latifolia and Carex lurida) have on the reduction of Cr(VI) in wetland sediments. Experiments were carried out using tubular microcosms, where chemical species were monitored along the longitudinal flow axis. Cr(VI) removal was enhanced by the presence of plants. This is explained by a decrease in the redox potential promoted by organic root exudates released by plants. Under these conditions sulfate reduction is enhanced, increasing the concentration of sulfide species in the sediment pore water, which reduce Cr(VI). Evapotranspiration induced by plants also contributed to enhance the reduction of Cr(VI) by concentrating all chemical species in the sediment pore water. Both exudates release and evapotranspiration have a diurnal component that affects Cr(VI) reduction. Concentration profiles were fitted to a kinetic model linking sulfide and Cr(VI) concentrations corrected for evapotranspiration. This expression captures both the longitudinal as well as the diurnal Cr(VI) concentration profiles.

Case study of the application of Fenton process to highly polluted wastewater from power plant.

This work investigates the application of Fenton process to the treatment of a highly polluted industrial wastewater resulting from the pipeline cleaning in a power plant. This effluent is characterized by a high chemical oxygen demand (COD>40 g/L), low biodegradability and quite a high iron concentration (around 3g/L) this coming from pipeline corrosion. The effect of the initial reaction temperature (between 50 and 90 °C) and the way of feeding H2O2 on the mineralization percentage and the efficiency of H2O2 consumption has been analyzed. With the stoichiometric amount of H2O2 relative to initial COD, fed in continuous mode, more than 90% COD reduction was achieved at 90 °C. That was accompanied by a dramatic improvement of the biodegradability. Thus, a combined treatment based on semicontinuous high-temperature Fenton oxidation (SHTF) and conventional aerobic biological treatment would allow fulfilling the COD and ecotoxicity regional limits for industrial wastewaters into de municipal sewer system. For the sake of comparison, catalytic wet air oxidation was also tested with poor results (less than 30% COD removal at 140 °C and 8 atm oxygen pressure).

Oxidation of cosmetic wastewaters with H2O2 using a Fe/γ-Al2O3 catalyst

A catalyst based on Fe supported on gamma-Al(2)O(3) has been prepared and tested for catalytic wet peroxide oxidation (CWPO) of cosmetic wastewaters. The influence of the main operating conditions (space-time, temperature, and H(2)O(2) dose) have been investigated. Working with this self-made Fe/gamma-Al(2)O(3) catalyst at 85 degrees C, with a space-time of 9.4 kg(cat) h/kg(COD) and a dose of H(2)O(2), corresponding to 0.5 times the theoretical stoichiometric H(2)O(2)/COD ratio, a substantial COD reduction (around 80%) has been reached with a complete consumption of H(2)O(2). The locally allowable limit of COD for industrial wastewaters discharge to the municipal sewer system can be achieved at lower temperature and space-time. The catalyst showed a high stability in 100 h time on stream tests, where COD and TOC reductions around 82 and 60%, respectively, were maintained working at 85 degrees C and 9.4 kg(cat) h/kg(COD) space-time. Fe leaching from the catalyst upon that time on stream was lower than 3% of the initial load.

CWPO of 4-CP and industrial wastewater with Al-Fe pillared clays.

Catalysts based on pillared clays with Al-Fe have been synthesised from a commercial bentonite and tested for catalytic wet peroxide oxidation (CWPO) of aqueous 4-Chlorophenol (4-CP) solution and industrial wastewater from cosmetics manufacture. The effect of the synthesis procedure, the iron load and reaction temperature on the catalytic activity was studied using 4-CP as target compound. A lower temperature in the preparation of the pillaring solution, as well as a higher Fe load, gave rise to a higher catalytic activity, but also a higher leaching of the active phase. The best catalyst, in terms of catalytic activity, was also tested for treating cosmetic wastewater by CWPO. Experiments were carried out at 90 degrees C and atmospheric pressure and the influence of Fe load, catalyst concentration and H(2)O(2)/COD ratio (between 0.5 and 2 times the stoichiometric ratio) were analysed. Higher values of these parameters favour COD reduction. The Fe leaching in all cases was lower than 1.2 mg/L, indicating that these catalysts have a high stability under these experimental conditions.

Mineralization of naphtenic acids with thermally-activated persulfate: The important role of oxygen

This study reports on the mineralization of model naphtenic acids (NAs) in aqueous solution by catalyst-free thermally-activated persulfate (PS) oxidation. These species are found to be pollutants in oil sands process-affected waters. The NAs tested include saturated-ring (cyclohexanecarboxylic and cyclohexanebutyric acids) and aromatic (2-naphthoic and 1,2,3,4-tetrahydro-2-naphthoic acids) structures, at 50mgL(-1)starting concentration. The effect of PS dose within a wide range (10-100% of the theoretical stoichiometric) and working temperature (40-97°C) was investigated. At 80°C and intitial pH=8 complete mineralization of the four NAs was achieved with 40-60% of the stoichiometric PS dose. This is explained because of the important contribution of oxygen, which was experimentally verified and was found to be more effective toward the NAs with a single cyclohexane ring than for the bicyclic aromatic-ring-bearing ones. The effect of chloride and bicarbonate was also checked. The former showed negative effect on the degradation rate of NAs whereas it was negligible or even positive for bicarbonate. The rate of mineralization was well described by simple pseudo-first order kinetics with values of the rate constants normalized to the PS dose within the range of 0.062-0.099h(-1). Apparent activation energy values between 93.7-105.3kJmol(-1) were obtained.

Electro activation of persulfate using iron sheet as low-cost electrode: the role of the operating conditions

ABSTRACT This work assesses the role of the operational conditions upon the electro-activation of persulfate (PS) using sacrificed iron electrode as a continuous low-cost Fe2+ source. An aqueous phenol solution (100 mg L−1) was selected as model effluent. The studied variables include current density (1–10 mA cm−2), persulfate concentration (0.7–2.85 g L−1), temperature (30–90°C) and the solution conductivity (2.7–20.7 mS cm−1) using Na2SO4 and NaCl as supporting electrolyte. A mineralization degree of around 80% with Na2SO4 and 92% in presence of NaCl was achieved at 30°C using 2.15 g L−1 PS at the lowest current density tested (1 mA cm−2). Besides PS concentration, temperature was the main variable affecting the process. In the range of 30–70°C, it showed a positive effect, achieving TOC conversion above 95% (using Na2SO4 under the previous conditions) along with a significant increase in iron sludge, which adversely affects the economy of the process. A lumped and simplified kinetic model based on persulfate consumption and TOC mineralization is suggested. The activation energy obtained for the TOC decay was 29 kJ mol−1. An estimated operating cost of US

An overview on the application of advanced oxidation processes for the removal of naphthenic acids from water

3.00 per m3 was obtained, demonstrating the economic feasibility of this process.

Nanoscale Fe/Ag particles activated persulfate: optimization using response surface methodology

ABSTRACT Although the exploitation of new energy sources like oil sand or shale may efficiently relieve the urgency of energy shortage, it can also have significant and adverse environmental impacts since huge volumes of oil-containing wastewaters are produced yearly worldwide due to such activities. Naphthenic acids (NAs), which are reported to be bio-recalcitrant due to their structural complexity and toxicity, are the main harmful components of oil shale fracking processes and oil sand process-affected waters. Identification techniques are being continuously improved to deal with the growing analytical need for traditional NAs and emerging ones like oxy-, aromatic, and diamondoid NAs. Meanwhile, treatment approaches focused on technical solutions have been investigated in the past decades. Among these, advanced oxidation processes are the most studied. Different oxidizing agents, like ozone, hydrogen peroxide, and persulfate, among others, have been used, giving rise to a diversity of techniques. The current work presents an updated overview of these techniques with regard to their application for the removal of NAs from water.