Amino Acid-Assisted Dehalogenation of Carbon Tetrachloride by Green Rust: Inhibition of Chloroform Production

Abstract

Layered Fe-Fe hydroxides (green rusts, GRs) are promising reactants for reductive dechlorination of chlorinated solvents due to high reaction rates and the opportunity to inject reactive slurries of the compounds into contaminant plumes. However, it is necessary to develop strategies that reduce the formation of toxic byproducts such as chloroform (CF). In this study, carbon tetrachloride (CT) dehalogenation by the chloride form of GR (GR) was tested in the presence of glycine (GLY) and other selected amino acids. GLY, alanine (ALA), and serine (SER) all resulted in remarkable suppression of CF formation with only ∼10% of CF recovery while sarcosine (SAR) showed insignificant effects. For two nonamino acid buffers, TRIS had little effect while HEPES resulted in a 40 times lower rate constant compared to experiments in which no buffer was added. The Fe complexing properties of the amino acids and buffers caused variable extents of GR dissolution which was linearly correlated with CF suppression and dehalogenation rate. We hypothesize that the CF suppression seen for amino acids is caused by stabilization of carbene intermediates via the carbonyl group. Different effects on CF suppression and CT dehalogenation rate were expected because of the different structural and chemical properties of the amino acids.

Structure of single sheet iron oxides produced from surfactant interlayered green rusts

“…Synthesis of GR Cl followed the method described by Yin 24 comprising co-precipitation of Fe 2+ and Fe 3+ in the presence of glycine at a constant pH of 8.0 (±0.1). First, 400 ml of 70 mM glycine and 245 mM of NaCl solutions were added to a synthesis glass flask followed by capping the flask with a rubber septum and providing in-and outlets for flushing Ar gas (30 ml min -1 ) to avoid oxidation by air.…”

Effects of seepage velocity and concentration on chromium(VI) removal in abiotic and biotic iron columns

“…As shown in Figure 1d, the corrosion in the bio‐iron column was more serious than that in the abiotic iron column, where a ravine‐like morphology was generated and large hexagonal petals were observed. These hexagonal petals might be green rust (Yin, Li, et al., 2017), which has a higher specific surface area than Fe 0 and can also serve as an electron conductor to facilitate redox reactions or even serve as a reducing agent to reduce Cr(VI) directly (Skovbjerg, Stipp, Utsunomiya, & Ewing, 2006; Williams & Scherer, 2001).…”

“…Meanwhile, both iron corrosion and the Fe(II)–Fe(III) cycling process could be accelerated in the presence of microorganisms via the excretion of acidic extracellular polymer substances (Venzlaff et al., 2013) or the reduction of the sparingly soluble Fe(III) to soluble Fe(II), thus regenerating the reactive surface of the Fe 0 and improving the utilization of the Fe 0 (Videla & Herrera, 2005). In addition, large quantities of reactive corrosion products generated in the microbiologically influenced corrosion process also amended the overall elimination of Cr(VI) in the bio‐iron column (Yin, Li, et al., 2017). It can be seen that both abiotic and biotic iron columns showed smaller differences in breakthrough times between the seepage velocity of 569 and 1138 m yr −1 .…”

“…Elimination of Cr(VI) from aquatic environments has been widely studied by various methods, such as adsorption (Pradhan, Das, & Thakur, 1999), chemical reduction followed by precipitation (Daneshvar, Salari, & Aber, 2002; Yin, Li, et al., 2017), bio‐reduction and adsorption (Yin, Li, et al., 2017; Zhong et al., 2017), and membrane separation (Hafez, El‐Manharawy, & Khedr, 2002). Because Cr(III) is less soluble and can be easily adsorbed by soil colloids, reductive transformation of Cr(VI) to Cr(III) followed by precipitation using permeable reactive barriers (PRBs) filled with metallic iron has proved to be a promising technique to clean up Cr(VI) from groundwater (Melitas, Chuffe‐Moscoso, & Farrell, 2001; Wilkin, Su, Ford, & Paul, 2005).…”

“…In our previous studies, synergetic effects contributed by Fe 0 and mixed culture tested for the removal of organic pollutants via batch and column experiments (Yin, Li, et al., 2017; Zhong et al., 2017). Mass transport processes (e.g., seepage velocity) and pollutant concentration should be considered as essential factors affecting pollutant removal (Stroo & Ward, 2010).…”