Nanoscale Metallic Iron for Environmental Remediation: Prospects and Limitations

The amendment of the subsurface with nanoscale metallic iron particles (nano-Fe0) has been discussed in the literature as an efficient in situ technology for groundwater remediation. However, the introduction of this technology was controversial and its efficiency has never been univocally established. This unsatisfying situation has motivated this communication whose objective was a comprehensive discussion of the intrinsic reactivity of nano-Fe0 based on the contemporary knowledge on the mechanism of contaminant removal by Fe0 and a mathematical model. It is showed that due to limitations of the mass transfer of nano-Fe0 to contaminants, available concepts cannot explain the success of nano-Fe0 injection for in situ groundwater remediation. It is recommended to test the possibility of introducing nano-Fe0 to initiate the formation of roll-fronts which propagation would induce the reductive transformation of both dissolved and adsorbed contaminants. Within a roll-front, FeII from nano-Fe0 is the reducing agent for contaminants. FeII is recycled by biotic or abiotic FeIII reduction. While the roll-front concept could explain the success of already implemented reaction zones, more research is needed for a science-based recommendation of nano- Fe0 for subsurface treatment by roll-front

Destruction of EDTA using Fenton and photo-Fenton-like reactions under UV-A irradiation

Degradation experiments using 5 mmol/l ethylenediaminetetraacetic acid (EDTA) solutions at pH 3 were performed in the presence of H(2)O(2) and metals such as Fe(2+), Fe(3+), Cu(2+) and mixtures of Fe(2+)/Cu(2+) and Fe(3+)/Cu(2+) under UV-A irradiation (366 nm)-photo-Fenton and photo-Fenton-like reactions-at different metal/EDTA concentration ratios in order to determine the best conditions for EDTA photochemical removal. Analogous dark reactions were performed for comparison. The reaction course was monitored by both EDTA and TOC determinations. Hydrogen peroxide demand was also evaluated in all cases. In terms of TOC removal, photo-Fenton-like reactions were remarkably more efficient than the analogous Fenton-like reactions. When EDTA was monitored, Fenton-like reactions showed variable performances, being more efficient with EDTA:Fe(2+) and EDTA:Fe(3+) ratios of 1:1. However, in these both cases, reaction rates were lower than the ones obtained under irradiation. Total mineralization ranged from 31% (Cu(2+) system) to 92% (Fe(2+), Fe(3+), Fe(3+) + Cu(2+) and Fe(2+) + Cu(2+) systems) after 4 h of irradiation. Percentage of TOC removal was higher in the presence of iron because some photoactive intermediates were probably formed during EDTA degradation. (C) 2004 Elsevier B.V. All rights reserved.1671596

EDTA destruction using the solar ferrioxalate advanced oxidation technology (AOT) - Comparison with solar photo-Fenton treatment

Degradation of ethylenediaminetetraacetic acid (EDTA; in the mmol/l range) at pH 3 was studied by the ferrioxalate/H(2)O(2) process under solar irradiation. A rapid total organic carbon (TOC) removal was attained in all cases, reaching almost 100% after 1 h solar exposure under the best conditions. In order to attain a high TOC removal yield, the pH must be rigorously controlled. The reaction rate increased with H(2)O(2) concentration; but its effect was not very marked. The final extent of degradation was found to decrease with higher ferrioxalate concentrations, probably by competition of oxalate with EDTA or its degradation products. In the absence of oxalate, EDTA could also be degraded to a reasonably good extent, with a TOC removal only slightly lower than when using ferrioxalate, which constitutes a good advantage from the economical point of view. The intensity of solar light was found to be a very important factor to improve the reaction. (C) 2002 Elsevier Science B.V. All rights reserved.1514169912112

Photocatalytic EDTA degradation on suspended and immobilized TiO2

The photocatalytic degradation of EDTA solutions (5 mM) has been studied under different conditions in the presence of TiO2 in suspension or immobilized on glass rings and in the absence and presence of Fe(111). Using the response surface methodology, the initial pH, amount of photocatalyst, and the Fe/EDTA molar ratio were optimized in order to obtain better degradation. Under optimized conditions, 90% EDTA degradation (at a 0.28 Fe/EDTA molar ratio) was reached after 60 min illumination at pH 3.0 and using 0.73 g L-1 TiO2. Increase of the acute toxicity (Microtox) was observed in the course of the reaction, and degradation intermediates were identified by GC/MS analysis. (c) 2005 Elsevier B.V. All rights reserved.1814170018819

Interactions between photodegradation components

<p>Abstract</p> <p>Background</p> <p>The interactions of <it>p</it>-cresol photocatalytic degradation components were studied by response surface methodology. The study was designed by central composite design using the irradiation time, pH, the amount of photocatalyst and the <it>p</it>-cresol concentration as variables. The design was performed to obtain photodegradation % as actual responses. The actual responses were fitted with linear, two factor interactions, cubic and quadratic model to select an appropriate model. The selected model was validated by analysis of variance which provided evidences such as high F-value (845.09), very low P-value (<.0.0001), non-significant lack of fit, the coefficient of R-squared (R² = 0.999), adjusted R-squared (R_adj² = 0.998), predicted R-squared (R_pred² = 0.994) and the adequate precision (95.94).</p> <p>Results</p> <p>From the validated model demonstrated that the component had interaction with irradiation time under 180 min of the time while the interaction with pH was above pH 9. Moreover, photocatalyst and <it>p</it>-cresol had interaction at minimal amount of photocatalyst (< 0.8 g/L) and 100 mg/L <it>p</it>-cresol.</p> <p>Conclusion</p> <p>These variables are interdependent and should be simultaneously considered during the photodegradation process, which is one of the advantages of the response surface methodology over the traditional laboratory method.</p