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Repairing Nature
Published in Daniel T. Rogers, Environmental Compliance Handbook, 2023
Chemical dehalogenation is a remedial method that removes halogens from contaminants. As covered in Chapter 3, halogens are contaminants with halogen atoms within their atomic structure. Halogens include fluorine, chlorine, bromine, and iodine. Common halogenated contaminants include several DNAPL VOCs, PCBs, and dioxins. The process of chemical dehalogenation generally involves the excavation of contaminated soil. The soil is typically sifted and crushed to remove larger objects and provide for better remedial treatment. The sifted soil is then mixed with chemical agents and heated in a reactor. During this process, a chemical reaction occurs that removes the halogen atom from the molecular structure of the contaminant, thereby destroying the contaminant or rendering it less harmful depending on the completeness of the reaction. There are two common types of chemical dehalogenation: (1) glycolate dehalogenation and (2) base-catalyzed dehalogenation (USEPA 2001g).
Nano-Catalysts and Colloidal Suspensions of Carbo-Iron for Environmental Application
Published in Matthew Laudon, Bart Romanowicz, 2007 Cleantech Conference and Trade Show Cleantech 2007, 2019
K. Mackenzie, H. Hildebrand, F.-D. Kopinke
ZVI in every form and particle size has its limitations concerning the pollutant spectrum which can be treated; e.g. iron completely fails for the dehalogenation of aromatic substances, such as PCBs, halogenated benzenes and phenols. However, the utilization of catalytic hydrodehalogenation with Pd catalysts can solve this problem. Palladium catalysts have proved to be well suited for promoting hydrodehalogenation reactions in the aqueous phase according to the equation ClHmXn + nH2 → ClHm+n + n HX [5]. The present paper aims at a treatment technique designed for special industrial wastewater contaminated with only small amounts of halogenated hydrocarbons – amounts which are nevertheless large enough to make a discharge into municipal sewage works impossible. The consequence is the necessity of expensive and energy-intensive incineration of aqueous waste. Therefore, especially for medium-sized enterprises, a decentralized selective wastewater dehalogenation treatment brings not only ecological credibility but also an important economic advantage.
Traditional and innovative methods for physical and chemical remediation of soil contaminated with organic contaminants
Published in Katalin Gruiz, Tamás Meggyes, Éva Fenyvesi, Engineering Tools for Environmental Risk Management – 4, 2019
É. Fenyvesi, K. Gruiz, E. Morillo, J. Villaverde
Dehalogenation is the process of removing covalently bound halogen from the contaminants. The main targets of the technologies are PCBs, polychlorinated-dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCFs), polychlorinated terphenyls (PCTs), and some halogenated pesticides. High organic content and water content in the soil decreases the efficiency. Two ex situ technologies are used; both apply base catalysis and enhanced temperature.
Dechlorination of 2,4-dichlorophenol by Fe/Ni nanoparticles: the pathway and the effect of pH and the Ni mass ratio
Published in Environmental Technology, 2022
Lujian Liu, Xia Ruan, Hong Liu, Xianyuan Fan, Jun Dong
2,4-DCP is considered a long-lived pollutant with high toxicity due to the presence of more chlorine atoms and its resistance to biodegradation. Reducing the toxicity and increasing the biodegradability through dehalogenation are the main methods for the treatment of chlorinated organic compounds. The byproducts 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and phenol (CA) are more biodegradable and have less toxicity [5, 6]. Zero-valent iron (ZVI) has attracted a considerable amount of attention as a powerful reducing agent since the 1980s [7–9]. The use of ZVI for the treatment of chlorinated phenols in wastewater and groundwater has been extensively explored in recent years [10, 11]. Nanoscale zero valent iron (n-ZVI) was found to be more reactive than microscale zero valent iron (m-ZVI) because of its higher specific surface area [12]. Iron acted as an electron donor in the reaction, while the chlorinated phenol received an electron and was thus reduced [13]. Researchers have assumed that chlorinated organic compounds react with iron via hydrogenolysis, involving stepwise replacement of the halogen by hydrogen [14, 15]. However, it has also been shown that it is not sufficient to remove chlorinated phenols even when n-ZVI particles are used [16]. Moreover, the formation of a hydroxide or oxide layer on the particle surface, during the reaction or upon the contact of the nanoparticles with air, significantly reduced its reactivity [17, 18].
Lindane degradation by root epiphytic bacterium Achromobacter sp. strain A3 from Acorus calamus and characterization of associated proteins
Published in International Journal of Phytoremediation, 2019
In our study, pH of the culture medium supplemented with lindane decreased significantly (p < 0.05) from 0 to 15th day in the presence of Achromobacter sp. strain A3 (Figure 1(b)). However, in uninoculated flask (control), no significant change (p > 0.05) in pH was observed. The removal of halogen atom from organic halogen compounds, known as dehalogenation, is the prime reaction in microbial degradation of these compounds. The halogen atoms are generally accountable for the toxicity of these xenobiotic compounds. During dehalogenation, the halogen atoms are replaced by hydrogen or hydroxyl group (Camacho-Pérez et al. 2012). To ascertain that decrease in pH of MSM is due to dehalogenation of lindane, i.e., dechlorination, dechlorination assay was performed. Result showed change in coloration of reaction mix from red (due to phenol red) to yellow in wells containing assay buffer, cell free extract of bacteria and substrate (lindane 10 mg l−1, 50 mg l−1, and 100 mg l−1) (C, D, E). No change of color was observed in wells containing assay buffer and cell-free extract of bacteria (but no substrate, B) (Figure S1).
Diffusion–advection process modeling of organochlorine pesticides in rivers
Published in Journal of Applied Water Engineering and Research, 2023
S. Cardenas, A. Márquez, E. Guevara
In the lowest PC1s (<20,000), the DDT’s metabolite, p.p’-DDD (Figure 4(c)) and Endrin (Figure 4(h)) shows a uniform tendency in the whole basin. The anaerobic conditions in the aqueous medium optimize the biodegradation of DDT by catalysis performed by the reductive dehalogenase enzyme to produce DDD (University of Minnesota 2003). The mechanism of reductive dehalogenation is hydrogenolysis, also known as hydrodehalogenation, which involves the replacement of a halogen atom by a hydrogen atom (Guevara 2016). DDD has been used as a pesticide, but its use was more limited compared to DDT (ATSDR 2002). Endrin can degrade when exposed to high temperatures or light, forming mainly ketone and Endrin aldehyde and has low water solubility (ATSDR 1996).