Tratamiento de efluentes acuosos contaminados con compuestos organoclorados

[ES] Los compuestos organoclorados son un tipo de residuos que han adquirido especial relevancia en los últimos tiempos, debido a sus características tóxicas y peligrosas, tanto para el medio ambiente como para los seres humanos. Su especial peligrosidad ha potenciado la búsqueda de alternativas para su tratamiento en las distintas corrientes donde se presentan. En este artículo se describe la problemática real de este tipo de compuestos, se exponen los principales contaminantes y se muestra una visión general de las alternativas para la eliminación de estos organoclorados de corrientes acuosas, detallándose en profundidad una de las alternativas de eliminación consideradas: la hidrodecloración catalítica en fase acuosa.Padilla Vivas, B.; Díez Sanz, FV.; Ordóñez García, S. (2005). Tratamiento de efluentes acuosos contaminados con compuestos organoclorados. 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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

Dehalogenation of halogenated aliphatic organic compounds in the presence of the bimetallic system palladized iron

Saturated and unsaturated chlorinated aliphatic hydrocarbons containing one to three carbons are commonly used as industrial solvents. These solvents are often found as contaminants in groundwater through improper disposal and many of them are carcinogenic. Remediation of groundwater containing these chlorinated compounds is of obvious importance. Methods such as air stripping and carbon adsorption involve the physical transfer of these contaminants onto activated carbon, and that does not diminish their toxicity. Other methods such as U.V. irradiation in the presence of ozone, hydrogen peroxide, or TiO₂, are not cost effective for large volume contamination problems such as polluted lakes, rivers and streams. Elemental iron has been shown to dechlorinate low molecular weight chlorinated aliphatic compounds but the observed end products were still partially chlorinated. We have established that the bimetallic system palladized iron (0.05% Pd) is preferable to elemental iron for the rapid and complete hydrodechlorination of 1- and 2-carbon chlorinated compounds with minimal loss of palladium. The major product observed from the hydrodechlorination of the 2-carbon chlorinated compounds was ethane. Methane was the major product observed from the hydrodechlorination of the 1-carbon chlorinated compounds. The palladized iron bimetallic system is also capable of reducing CFC's, nitro-organic compounds and inorganic species such as nitrate ions

Byproduct Formation During the Reduction of TCE by Zero-Valence Iron and Palladized Iron

Trichlorothene (TCE) was reduced with zero-valence iron and palladized iron in zero-head-space extractors. Progress of the reaction in these batch studies was monitered with purge-and-trap gas chromatography and a flame ionization detector. When a 5 ppm initial concentration of TCE reacts with zero-valence iron, approximately 140 ppb of vinyl chloride persists for as long as 73 days. The concentration of vinyl chloride (approximately 10 ppb) remaining with palladized iron is approximately and order of magnitude less than when zero-valence iron is the reductant. These data suggest that volatile byproducts may be under-represented in other published data regarding reduction in zero-valence metals. These results also demonstrate that the reduction of TCE with palladized iron (0.05 percent palladium) is more than an order of magnitude faster than with zero-valence iron. With a 5:1 solution-to-solid ratio, the TCE half-life with zero-valence iron is 7.41 hours, but is only 0.59 hours with the palladized iron