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Geochemical and Isotope Study of Trichloroethene Degradation in a Zero-Valent Iron Permeable Reactive Barrier: A Twenty-Two-Year Performance Evaluation

“…31 The most negative ε values reported are from systems where TCE degraded in the presence of iron sulfide (−27.9‰). 30 Taken at face value, the results shown in Figure 4e indicate that multiple transformation pathways occurred in the PRB. About 70% of the estimated ε values were characteristic of abiotic TCE degradation (Fig.…”

“…28,30,56 Laboratory derived isotope trends are typically examined using the Rayleigh equation: δ 13 C -δ 13 C 0 ≈ εln(C/ C 0 ), where δ 13 C -δ 13 C 0 is the carbon isotope separation, for example, between TCE at time t and time zero, ε is the process-dependent bulk enrichment factor: (α−1)10 3 , and C/C 0 is the fraction of reactant remaining at time t. Thus, in batch studies bulk enrichment factors are determined by linear regression of δ 13 C -δ 13 C 0 versus ln(C/C 0 ) and this approach has shown promise for discriminating biotic and abiotic degradation pathways and for estimating the extent of TCE degradation. 27,28,30,31,56 Applying this method at PRB sites is challenging because multiple degradation processes are possible (so a unique value of ε cannot be assumed) and C 0 may vary widely in heterogeneous systems, e.g., in cases where influent TCE concentrations are not constant in time or space. We estimated C/C 0 by computing the molar ratio [TCE/(TCE+cis-DCE+VC +ethene+ethane)] in samples collected within and down-gradient of the PRB, assuming that measured daughter product concentrations correlate with the amount of degraded TCE and that concentrations of daughter products entering the PRB were negligible.…”

“…Using this approach to estimate C/C 0 , apparent bulk enrichment factors ranged from −2‰ to −26‰ with a median value of −14‰ (n = 20; Figure 4e); the median value is in close agreement with a laboratory derived enrichment factor determined for Peerless ZVI (ε = −13.9‰). 26 Bulk enrichment factors determined for biotic degradation of TCE fall in the range from about −2.5‰ to −15‰ 30,49 and values less than about −14‰ are typical for abiotic degradation. 31 The most negative ε values reported are from systems where TCE degraded in the presence of iron sulfide (−27.9‰).…”

“…14 Recent studies developed and applied compound specific stable carbon isotope analysis to differentiate biotic and abiotic dechlorination processes and to evaluate the overall efficiency of contaminant degradation in field applications. [21][22][23][24][25][26][27][28][29][30][31][32][33] The first field demonstration of ZVI technology showed effective chlorinated solvent treatment over an initial five-year period of performance. 34 Warner et al 35 reported on the hydraulic and chemical performance of the first commercial PRB constructed in the U.S. with granular iron metal after 10 years of operation.…”

A discussion on “zhenren” in Chu bamboo and silk manuscripts

“… 1. For the translation of the quotations in this article, see the following references: Knechtges, 1982; Legge, 1971; Liang, 2005; Waley, 1999; Watson, 1974, 2003; Xu, 2003; Yang and Yang, 2008; Zhai and Mou, 2010.…”