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Iron-Mediated Reductive Transformations: Investigation of Reaction Mechanism
... As seen from Figure 3a, the oil removal significantly enhanced from 53.35% to within 60 min when the catalyst dosage increased from 0.5 g·L −1 to 1.5 g·L −1 . removal slightly increased with a further increase in catalyst loading to 2.0 g·L removal increased with an increase in the catalyst loading as shown in Figure 3b the MG ribbon dosage is 2.0 g·L −1 , the COD removal stabilized at around 72%. N the organic molecule decomposition takes place via direct surface reaction on act species [39]. Increasing the amount of catalyst provides more active sites, achieving faster production rate of ·OH radical species. ...
... COD removal increased with an increase in the catalyst loading as shown in Figure 3b. When the MG ribbon dosage is 2.0 g·L −1 , the COD removal stabilized at around 72%. Normally, the organic molecule decomposition takes place via direct surface reaction on active iron species [39]. Increasing the amount of catalyst provides more active sites, thereby achieving faster production rate of ·OH radical species. ...
... As seen from Figure 3a, the oil removal significantly enhanced from 53.35% t within 60 min when the catalyst dosage increased from 0.5 g·L −1 to 1.5 g·L −1 . removal slightly increased with a further increase in catalyst loading to 2.0 g·L removal increased with an increase in the catalyst loading as shown in Figure 3 the MG ribbon dosage is 2.0 g·L −1 , the COD removal stabilized at around 72%. N the organic molecule decomposition takes place via direct surface reaction on ac species [39]. Increasing the amount of catalyst provides more active sites, achieving faster production rate of ·OH radical species. ...
Metallic glasses (MGs) with a unique atomic structure have been widely used in the catalytic degradation of organic pollutants in the recent years. Fe78Si9B13 MGs exhibited excellent catalytic performance for the degradation of oily wastewater in a Fenton-like system for the first time. The oil removal and chemical oxygen demand (COD) removal from the oily wastewater were 72.67% and 70.18% within 60 min, respectively. Quenching experiments were performed to verify the production of active hydroxyl radicals (·OH) by activating hydrogen peroxide (H2O2). The formation of ·OH species can significantly contribute to the degradation reaction of oily wastewater. Fe78Si9B13 MG ribbons were highly efficient materials that exhibited superior reactivity towards H2O2 activation in oily wastewater treatment. The study revealed the catalytic capability of metallic glasses, presenting extensive prospects of their applications in oily wastewater treatment.
... In contrast, Matheson and Tratnyek [56] and Weber [57] presented Fe 0 as an electron donor for the reductive transformation of dissolved organics in natural groundwaters (pH > 5.0). These reports contradict not only the then recent works of Khudenko [52] but also the seminal work of Whitney [58.59] demonstrating that in aqueous solutions, at neutral pH values, protons (from water dissociation -Equation 2) are only reaction partners for the electrochemical dissolution of Fe 0 (Equation 3). ...
... These reports contradict not only the then recent works of Khudenko [52] but also the seminal work of Whitney [58.59] demonstrating that in aqueous solutions, at neutral pH values, protons (from water dissociation -Equation 2) are only reaction partners for the electrochemical dissolution of Fe 0 (Equation 3). Surprisingly, Matheson and Tratnyek [56] have not considered these seminal works in their discussion and Weber [57] has also not considered them in his confirmation. Moreover, Weber [57] has also not considered them in his subsequent study which is erroneously regarded as confirmation of earlier results by Matheson and Tratnyek [56]. ...
... Surprisingly, Matheson and Tratnyek [56] have not considered these seminal works in their discussion and Weber [57] has also not considered them in his confirmation. Moreover, Weber [57] has also not considered them in his subsequent study which is erroneously regarded as confirmation of earlier results by Matheson and Tratnyek [56]. Nevertheless, Weber [57] was favoured as the confirmation of the theory presented by Matheson and Tratnyek [56]. ...
Keeping up-to-date with the literature is a great challenge for all scientists because analyzing and sorting published data can be very laborious and time-consuming. With the use of metallic iron (Fe⁰) in environmental remediation, scientists are facing such a challenging situation. Without an appropriate background, it can be very difficult to discern which information is plausible and which one is not. This communication demonstrates how the chemistry of aqueous iron corrosion (Fe⁰/H2O system) facilitates a critical assessment of the literature on the decontamination of waters polluted with metals and metalloids. It is reiterated that the pH-dependent solubility of iron and the extent of the oxidation from FeII to FeIII species determine the extent of contaminant mitigation in Fe⁰/H2O systems. Future remediation Fe⁰/H2O systems should be designed based on the science of iron corrosion under aqueous conditions.
... The idea that Fe 0 reduces selected contaminants under operational conditions was introduced in the peer-reviewed literature in 1994 [5] and was controversially discussed for the following five (5) years [6][7][8][9][10][11]. For example, Warren et al. [7] used several elemental metals (Al 0 , Fe 0 , Sn 0 and Zn 0 ) to treat carbon tetrachloride (CT) and reported on "unresolved mechanistic complexities". ...
... CT was one of the organic 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 compounds used in the 1994 seminal work [5]. On the other hand, Weber [9] used 4-aminoazobenzene as a probe molecule to 'confirm' that 'reductive transformation by Fe 0 is a surface-mediated process'. According to Weber [9], electron transfer at the Fe 0 /H 2 O interface is facilitated by appropriate "electron mediators". ...
... On the other hand, Weber [9] used 4-aminoazobenzene as a probe molecule to 'confirm' that 'reductive transformation by Fe 0 is a surface-mediated process'. According to Weber [9], electron transfer at the Fe 0 /H 2 O interface is facilitated by appropriate "electron mediators". Similar controversies have been reported on the removal mechanism of several inorganic contaminants [6,10,11]. ...
A survey of the literature on using metallic iron (Fe 0) for environmental remediation suggests that the time is ripe to center research on the basic relationship between iron corrosion and contaminant removal. This communication points the main problem which is based on the consideration that contaminant reductive transformation is the cathodic reaction of iron oxidative dissolution. It is recalled that properly considering the inherent complexities of the Fe 0 /H 2 O system will favor an appropriate research design that will enable more efficient and sustainable remediation systems. Successful applications of Fe 0 /H 2 O systems require the collective consideration of progress achieved in system' understanding. More efforts should be made to decipher the long-term kinetics of iron corrosion, so as to provide better approaches to accurately predict the performance of the next generation Fe 0-based water treatment systems.
... In fact the intrinsic reactivity cannot be measured but just be accessed by appropriate tools [34,37]. Tools based on oxidizing probing agents [19,20] are problematic because they consider Fe 0 as a reducing agent and parent of electrons for reductive transformation of contaminants [12,13,22,38]. On the other hand, they overlook two key issues: (i) the solvent, H 2 O (E 0 = 0.00 V) is also an oxidizing agent for Fe 0 and (ii) the omnipresent dissolved oxygen (E 0 = 0.83 V) is a further relevant oxidizing agent for Fe 0 . ...
... During the past 15 years, the EDTA test was further developed by Noubactep and colleagues to address several aspects of the design of efficient Fe 0 /H 2 O systems for water remediation [14,16,42,43]. The rationale for the EDTA test is that the initial iron dissolution in a 2 mM EDTA solution is a linear function of the time [38]. The slope of the corresponding line is characteristic (intrinsic reactivity) for the used Fe 0 (Section 6.5). ...
... Given that iron dissolution (from Fe 0 and FeCPs) is initially a linear function of the time [38], for a certain time (t 1 > t 0 ) after the initiation of the experiment (t 0 ) the total iron concentration ([Fe] t ) as defined in Eq. 1 is a linear function (of time). ...
There is a burgeoning interest in reliably characterizing the intrinsic reactivity of metallic iron materials (Fe 0) used in the water treatment industry. The present work is a contribution to a science-based selection of Fe 0 for water treatment. A total of eight (8) granular Fe 0 materials (ZVI1 to ZVI8) were tested. Fe 0 dissolution in ethylenediaminetetraacetic acid (EDTA test) and 1,10-Phenanthroline (Phen test) is characterized in parallel experiments for up to 250 hours (10 days). 50 mL of each solution and 0.1 g of each Fe 0 material are equilibrated in quiescent batch experiments using 2 mM EDTA or Phen. Results indicated a far higher extent of iron dissolution in EDTA than in Phen under the experimental conditions. The tested materials could be grouped into three reactivity classes: (i) low (ZVI4, ZVI6, ZVI7 and ZVI8), (ii) moderate (ZVI1 and ZVI5) and (iii) high (ZVI2 and ZVI3). The order of reactivity was the same for both tests: ZVI2 ZVI3 > ZVI1 ZVI5 > ZVI4 ZVI6 ZVI7 ZVI8. Phen results revealed for the first time the time-dependent variation of the kinetics of iron corrosion (corrosion rate) in short-term batch experiments. Overall, the results demonstrated the superiority of the Phen test for evaluating the initial stage of Fe 0 dissolution. Long-term term column experiments are recommended to deepen the acquired knowledge.
... "In the past two decades, zero-valent iron (ZVI) has attracted significant attention as a promising reactant for removal of various environmental contaminants from wastewater and groundwater due to its high reductive capacity, the environmental friendliness of iron, and the production of nontoxic iron oxides after the removal of the contaminants. ZVI In sentence 1, Sun et al. [26] have repeated the fatal mistake of early researchers on the Fe 0 /H 2 O system regarding Fe 0 as a reducing agent for contaminants (Ox) according reactions similar to Eq. 1 [27][28][29]. 'Red' is the reduced form of 'Ox' which is hopefully less mobile/toxic. However, Fe 0 oxidation by water, the solvent (Eq. ...
... In 1994, Matheson and Tratnyek [27] published a peer-reviewed article favouring direct reduction (electrons from Fe 0 ) as main path of contaminant reductive transformation. Two years later, their suggestions were confirmed by Weber [28]. Since then the reductive transformation paradigm was born, although no convincing argument was given. ...
... Since then the reductive transformation paradigm was born, although no convincing argument was given. To confirm the electrochemical nature of the interactions between Fe 0 and contaminants, Weber [28] used 4-aminoazobenzene (4-AAB) as probe molecule. 4-AAB is an aromatic azo compound that is certainly susceptible to reduction by Fe 0 to form aniline. ...
The starting argument of using metallic iron (Fe0) as an environmental remediation agent considered Fe0 oxidative dissolution as the anodic half-reaction of contaminant reduction. However, it has been repeatedly observed that both reactions are not simultaneous. The present article challenges the adequacy of the peer-review system when the starting position is biased. First, it argues that the presumption of contaminant reductive transformation (e.g. the status quo) is preferred by most Fe0 experts, including journal editors. Second, it recalls that the status quo strongly distorts the facts. Third, most Fe0 researchers have backed the status quo without question. Fourth, the legitimacy that experts and researchers lend to the status quo limits innovation opportunities. Abandoning the comfortable status quo is suggested as the way to restore room for constructive innovation in Fe0 research.
... For example, Matheson and Tratnyek (1994) used slowly stirred batch experiments (≤ 15 rpm) to suggest that chlorinated carbons (RCl) are removed from aqueous solution mostly via reductive degradation mediated by electrons from Fe 0 . Weber (1996) reported to have confirmed that reductive transformation by Fe 0 is a surface-mediated process while using 4-aminoazobenzene as a probe contaminant and a completely different experimental design. Weber (1996) also reported that the requirement that the contaminant contacts the Fe 0 surface for electron transfer can be circumvented by the addition of soluble electron mediators. ...
... Weber (1996) reported to have confirmed that reductive transformation by Fe 0 is a surface-mediated process while using 4-aminoazobenzene as a probe contaminant and a completely different experimental design. Weber (1996) also reported that the requirement that the contaminant contacts the Fe 0 surface for electron transfer can be circumvented by the addition of soluble electron mediators. Roberts et al. (1996) and ...
Permeable reactive barriers (PRBs) containing metallic iron (Fe0) as reactive materials are currently considered as an established technology for groundwater remediation. Fe0 PRBs have been introduced by a field demonstration based on the fortuitous observation that aqueous trichloroethylenes are eliminated in Fe0-based sampling vessels. Since then, Fe0 has been tested and used for treating various biological (e.g., bacteria, viruses) and chemical (organic and inorganic) contaminants from polluted waters. There is a broad consensus on the view that "reactivity loss" and "permeability loss" are the two main problems hampering the design of sustainable systems. However, the view that Fe0 is a reducing agent (electron donor) under environmental conditions should be regarded as a distortion of Corrosion Science. This is because it has been long established that aqueous iron corrosion is a spontaneous process and results in the Fe0 surface being shielded by an oxide scale. The multi-layered oxide scale acts as a conduction barrier for electrons from Fe0. Accordingly, "reactivity loss", defined as reduced electron transfer to contaminants must be revisited. On the other hand, because "stoichiometric" ratios were considered while designing the first generation of Fe0 PRBs (Fe0 as reductant), "permeability loss" should also be revisited. The aim of this communication is to clarify this issue and reconcile a proven efficient technology with its scientific roots (i.e., corrosion science).
... This coincidence was misinterpreted as a scientific fact and still prevails , Thakur et al. 2020. Investigations by Matheson and Tratnyek (1994) and Weber (1996) have been reported to confirm these observations. Moreover, it was claimed that the observation that organic pollutants can be reduced in Fe 0 /H2O systems was novel (Matheson andTratnyek 1994, Gillham 2008). ...
... Cementation with Fe 0 and Cu 2+ resulted in 98.5 % color removal, while the process without copper resulted in just 10 % color removal (Table 2). Tratnyek (1994) was claimed to be experimentally validated (Roberts et al. 1996, Weber 1996 and is still favored by the majority of active researchers on the remediation Fe 0 /H2O system (Naseri et al. 2017, Xiao et al. 2020a, Xiao et al. 2020b, Hu et al. 2021. ...
The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of the concept that reductive processes observed in remediation Fe0/H2O systems are mediated by primary (e.g., FeII, H/H2) and secondary (e.g., Fe3O4, green rusts) products of aqueous iron corrosion. The critical evaluation of the electron efficiency concept suggests that it should be abandoned. Instead, research efforts should be directed towards tackling the real challenges for the design of sustainable Fe0-based water treatment systems based on fundamental mechanisms of iron corrosion.
... Clearly, contaminant reduction in an Fe 0 /H 2 O system is rarely (or even never) the cathodic reaction simultaneous to Fe 0 oxidation. This fundamental knowledge preceded the mechanistic discussion within the Fe 0 research community [69][70][71]. In fact, three years before Matheson and Tratnyek [69], Khudenko presented a concept for the cementation-induced oxidation-reduction of organics [72][73][74]. ...
... It is important to recall that As is removed by adsorption and coprecipitation [77,78]. Accordingly, rationalizing the efficiency of Fe 0 /H 2 O systems for water decontamination by any electrochemical process involving the pollutants has been a huge mistake [69][70][71]. The electrochemistry-based reasoning implies the electrode potential of the couple Fe II /Fe 0 (E 0 = -0.44 ...
Researchers and engineers using metallic iron (Fe0) for water treatment need a tutorial review on the operating mode of the Fe0/H2O system. There are few review articles attempting to present systematic information to guide proper material selection and application conditions. However, they are full of conflicting reports. This review seeks to: (i) summarize the state-of-the-art knowledge on the remediation Fe0/H2O system, (ii) discuss relevant contaminant removal mechanisms, and (iii) provide solutions for practical engineering application of Fe0-based systems for water treatment. Specifically, the following aspects are summarized and discussed in detail: (i) Fe0 intrinsic reactivity and material selection, (ii) main abiotic contaminant removal mechanisms, and (iii) relevance of biological and bio-chemical processes in the Fe0/H2O system. In addition, challenges for the design of the next generation Fe0/H2O systems are discussed. This paper serves as a handout to enable better practical engineering applications for environmental remediation using Fe0.
... In the early 1990s, metallic iron or elemental iron (Fe 0 ), then termed as zero-valent iron (ZVI), was presented as a new material for water treatment including environmental remediation (Reynolds et al. 1990, O'Hannesin 1993, Lipczynska-Kochany et al. 1994, Gillham and O'Hannesin 1994, Matheson and Tratnyek 1994, Schreier and Reinhard 1994, Cantrell et al. 1995, Powells et al. 1995, Warren et al. 1995. Moreover, Fe 0 was presented as an environmental reducing agent (Matheson and Tratnyek 1994, Roberts et al. 1996, Weber 1996. Since then hundreds of scientific articles have been written and some 200 Fe 0 -based reactive barriers implemented over the wolrd (Bigg and Judd 2000, Scherer et al. 2000, Tratnyek et al. 2003, Henderson and Demond 2007, Gillham 2008, Phillips 2009, Bartzas and Komnitsas 2010, Li and Benson 2010, Comba et al. 2011, Gheju 2011, Choi et al. 2014, Obiri-Nyarko et al. 2014, Guan et al. 2015, Warner 2015. ...
... The discussion on the mechanism of Fe 0 in removing contaminants was initiated by Matheson and Tratnyek (1994) and was actively conducted for some four years (Lipczynska-Kochany et al. 1994, Cantrell et al. 1995, Warren et al. 1995, Eitzer 1996, Roberts et al. 1996, Weber 1996, Gu et al. 1998, O'Hannesin and Gillham 1998. Although a 'broad concensus' was made on 'reducing Fe 0 ' around 1998 (O'Hannesin and Gillham 1998) the discussion has continued until the present day (Noubactep 2007, Noubactep 2008, Gheju and Balcu 2001, Giles et al. 2011, Ghauch 2015, Noubactep 2015. ...
Metallic iron (Fe 0) has been suggested as an affordable, applicable and efficient material for environmental remediation. Mixed to soil or filled in reactive walls, Fe 0 is a feasible pathway to control contamination in seepage waters. Available information in the literature however presents discrepant evidence on the efficiency of this (still innovative) technology. On basis of a profound literarture study over the past 160 years, it is outlined that these discrepancies are explained by the aqueous chemistry of iron (corrosion). Neglected aspects contributing to the apparent complexity of the Fe 0 /H2O system are outlined. It appears that designing an efficient and sustainable Fe 0 remediation system is a pure site-specific issue and that available data are not (really) comparable. In particular, it was made clear that Fe 0 barriers that have been successfully working for more than one decade were not designed according to any scientific basis. While the success or failure of implemented reactive walls can be rationalized, more systematic research is needed for a science-based design of efficient and sustainable Fe 0-based systems for environmental remediation.
Cited as:
Noubactep C. (2019): Metallic Iron for Environmental Remediation: Prospects and Limitations. Chap. 36, A Handbook of Environmental Toxicology: Human Disorders and Ecotoxicology. J.P.F. D’Mello (ed), CAB International, 531–544.
... When coupled with the chemical reduction (degradation) of an oxidized contaminant (Ox), the spontaneous reduction reaction yielding a more biodegradable and/or hopefully less toxic reduced form (Red) is given by equation 1: 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Fe 0 + Ox Fe 2+ + Red (1) Fe 0 permeable reactive barriers (Fe 0 walls) have become an established technology for in situ groundwater remediation [10,13,14,16,23]. There is an almost consistent agreement in the literature about direct reduction (electrons from Fe 0 ) (Eq. 1) as the main mechanism by which Fe 0 Fe 0 reduces aqueous contaminants [14,[24][25][26][27][28]. Accordingly, Eq. 1 alone is always given as a the reduction scheme [28][29][30][31][32] and is implemented in modelling codes [13,33]. ...
... Accordingly, properly designed Fe 0 /H 2 O systems will efficiently treat water as research drawn from the last two to three decades has demonstrated their suitability for all classes of chemical contamination [10,12,16]. [67] has been only referenced eight (8) times (Table 3) [ [162][163][164][165][166] and has not been considered in some literature discussing the removal mechanisms of organics in Fe 0 /H 2 O systems [10,24,25,167]. The concept of Khudenko [67] was based on a profound understanding of the Fe 0 /H 2 O system [168][169][170] and corresponds to Noubactep's concept [39,40] that has been difficult to accept [48,49]. It is hoped that this independent proof will end the mechanistic discussion and orient all energies to design the next generation efficient Fe 0 /H 2 O systems for water treatment, including Fe 0 filters. ...
Elemental iron (Fe0) has been widely used in groundwater/soil remediation, safe drinking water provision and wastewater treatment. It is still mostly reported that a surface-mediated reductive transformation (direct reduction) is a relevant decontamination mechanism. Thus, the expressions "contaminant removal" and "contaminant reduction" are interchangeably used in the literature for reducible species (contaminants). This contribution reviews the scientific literature leading to the advent of the Fe0 technology and shows clearly that reductive transformations in Fe0/H2O systems are mostly driven by secondary (FeII, H/H2) and tertiary/quaternary (e.g. Fe3O4, green rust) reducing agents. The incidence of this original mistake on the Fe0 technology and some consequences for its further development are discussed. It is shown in particular that characterizing the intrinsic reactivity of Fe0 materials should be the main focus of future research.
... This opportunity can be used to address systemic flaws that have certainly threatened its development, and that were difficult to address some 10 years ago [1][2][3]. A central flaw is the long-held assumption that Fe 0 is a direct reducing agent for the chemical transformation of contaminants [4][5][6][7][8][9]. As a result, the large majority of published works is still considering Fe 0 as an environmental reducing agent [7,8,[10][11][12]. ...
... The idea that electrons from Fe 0 mediate contaminant reductive transformations was adopted from a seminal work by Matheson and Tratnyek [4]. Although controversial views were published during 1994 and 1995 [13,71,72] Weber [6] validated and generalized the results of Matheson and Tratnyek [4]. Despite this pseudo-scientific demonstration supported by further reports [5,73,74], O'Hannessin and Gillham [75] acknowledged that the reductive transformation concept was a 'broad consensus'. ...
The well-accepted assumption of metallic iron (Fe0) acting as electron donor for environmental remediation has created an unstable domain of knowledge for the past 23 years. This assumption is discouraging some outstanding and prospective scientists from correctly interpreting their experimental results. Such a situation is a recipe for long-term decline. The critical situation cannot be solved with simplistic approaches. It is now imperative to develop an understanding to defend the difficulties of this assumption and re-orient Fe0 mediated remediation research as a whole.
... The differential use of Fe 0 as a reducing agent (Matheson and Tratnyek, 1994;Weber, 1996) for about 5 years. However, it is not certain that (i) various nail types will give comparable 432 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 results or (ii) the same iron nails at locations with very different water chemistry would work 433 well. ...
... This tangible observation (a fact) yielded to hypothesis that Fe 0 was the 610 reducing agent (an hypothesis)(Matheson and Tratnyek, 1994). Unfortunately, the hypothesis 611 byMatheson and Tratnyek (1994) was considered a fact byWeber (1996) and validated as 612 such (Ebelle et al. 2016; Noubactep, 2016d). 613 ...
Researchers on metallic iron (Fe0) for environmental remediation and water treatment are walking in a valley of confusion for 25 years. This valley is characterized by the propagation of different beliefs that have resulted from a partial analysis of the Fe0/H2O system as (i) a reductive chemical reaction was considered an electrochemical one and (ii) the mass balance of iron has not been really addressed. The partial analysis in turn has been undermining the scientific method while discouraging any real critical argumentation. This communication re-establishes the complex nature of the Fe0/H2O system while recalling that, finally, proper system analysis and chemical thermodynamics are the most confident ways to solve any conflicting situation in Fe0 environmental remediation.
... ZVI's efficacy depends greatly on the characteristics surface area of the particle on which the reduction reaction mainly happens (Wang et al., 2016;Weber, 1996). In contrast, mZVI, nZVI (less than 100 nm in diameter) has a larger surface area and higher surface reactivity. ...
During the last century, large scale production of halogenated organic compounds and heavy
metals, specifically by industrial processes, and the inappropriate management of those products caused
a wide spreading of a variety of hazardous contaminants into the environment including a massive
contamination of the groundwater. Their presence and persistence have significantly influenced human
health and the environment. Recently, many technologies have been employed in order to reduce their
impacts. However, the majority of those technologies did not achieve the target, because of their high cost
and low efficacy in the reduction of contaminants. Nevertheless, a new technology of synergetic
interactions of (nZVI) zero-valent iron nanoparticles with two types of anaerobic bacteria; the
organohalide respiring bacteria (OHRB) and sulfate-reducing bacteria (SRB), have been investigated as
a promising technology for in-situ groundwater remediation. This powerful technique was successfully
utilized for the reduction of pollutants and converted to environmentally benign forms. This article
reviews and emphasizes the coupling effect of (nZVI-OHRB) and (nZVI-SRB) on the remediation process
of contaminated sites, in addition to a detailed illustration of the mechanism of the integration of (nZVIOHRB) and (nZVI-SRBs), and discussion of the influencing factors on the integrated system. Actually,
the technology presented here, though proven successfully, needs more case studies to better
understanding of the interactions between microorganisms and nZVI, as well as with the surrounding
environment for a better efficacy and finding the best solutions.
... In addition, the beeswarm plot in Fig. 7B shows the relationship between the direction of each feature value (higher or lower, presence or absence) and the result for the SHAP value. The plot shows that a larger ZVI surface area generally has a positive influence on the model output, which confirms that a higher surface area results in more active sites for nitrate interactions and thus increases the reduction rate [28,82]. ...
... A new method for the transformation of Azo dyes into easier bio-decomposition compounds with Nanoscale Zero-Valent Iron NZVI has been developed in this study. NZVI is an effective reducing agent for azo dyes [Nam and Tratnyek, 2000;Cao et al., 1999; and it is less cost than chemical methods, effective and environmentally friendly Masciangioli and Zhang, 2003;Chang et al., 2006;Hou et al., 2007;Shu et al., 2007;Fan et al., 2009], NZVI reduction is widely used in treating and remedying and dechlorinate waste waters contaminated with chlorinated compounds [Cheng et al., 2006], nitro aromatic compounds , nitrates [Huang et al, 1998] and heavy metals [Fiedor et al, 1998], and even for the deoxidization of more complex anthropogenic chemicals including pesticides [Fiedor et al, 1998] and dyes [Eykholt and Davenport, 1998;Bigg and Judd, 2001;Weber, 1996;Pereira and Freire, 2006]. The azo bond is cleaved when azo dyes are degraded by NZVI treatment process and an aromatic amines and amino-naphthol compounds are formed along with hydrazo (-NHNH-) as an intermediate . ...
In this study Nanoscale Zero-Valent Iron Fe 0 (NZVI) and Nano Zero Valent-Iron supported on pillared clay(NZVI/PILC) have been prepared and characterizations by physical method such as Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The degradation of acidic aqueous solutions of the Acid red 315 (AR 315) azo dye has been studied by NZVI, pillared clay (PILC) and NZVI-B. The effect of different process parameters, such as solution pH, amount of dosage (NZVI, PILC and NZVI/PILC), time reaction effect and other experimental variable, such as (Azo dye concentration and inorganic salts effect) has been investigated to determined optimization method for removal. The concentration of azo dye measured before and after treatment by using UV-Vis Spectrophotometry method. The experimental results showed that AR 315 azo dye solution (100 mg/L, 1.6×10-4 M) was completely removed by NZVI at optimum conditions (amount of NZVI = 1.0 g, 120 min and pH = 3). While the removal efficiency with NZVI/PILC and PILC were 80% and 0% respectively.
... There are mainly two schools; the clear discrepancies between them are identified by Noubactep (2015). The first school supports that Fe 0 is a strong reducing agent for contaminant reductive transformation: degradation of organics and/or precipitation of inorganics (Matheson and Tratnyek 1994, Weber 1996, Blowes et al. 1997. The second school subscribes that contaminants are adsorbed onto the surface of in situ generated iron corrosion products and/or are enmeshed within their matrix (Noubactep 2007, Noubactep 2008, Jiao et al. 2009, Noubactep 2009e, Ghauch et al. 2010, Noubactep 2010a, Noubactep 2011a, Noubactep 2012, Gheju et al. 2016, Noubactep 2022. ...
The concept that metallic iron (Fe0) is a reducing agent under environmental conditions has urged the large-scale application of Fe0 filters for environmental remediation and water treatment. During the past two decades, some 3,000 scientific articles have widely discussed the importance of processes yielding water treatment in Fe0/H2O systems. The current state-of-the-art knowledge is that Fe0 is the generator of (i) contaminant scavengers (iron hydroxides/oxides), and (ii) reducing agents (e.g. H/H2, FeII, green rusts, Fe3O4). In other words, contaminant reductive transformation in the presence of Fe0 is not mediated by electrons from the metal body (direct reduction).
The realization that Fe0 is not the reducing agent in Fe0/H2O systems has redirected fundamental researches on the operating mode of Fe0 filters. In this effort, a cationic azo dye (methylene blue, MB) has been presented as reactivity indicator to characterize changes in Fe0/H2O systems. The present study investigates the impact of contact time on the efficiency of Fe0/H2O systems. The research questions are "is there any direct relationship between experimental duration and system's efficiency?" If yes, how is the efficiency modified in the presence of natural additives such as manganese oxides (MnO2) and sand? Both research questions are justified by the evidence that the Fe0 surface is constantly shielded by an oxide scale which has been reported to mediate a 'reactivity loss' of Fe0 materials.
The methodology consists of (i) varying the experimental duration, and (ii) modifying the Fe0/H2O system by amending it with various amounts of MnO2 and sand. The efficiency of Fe0/sand/MnO2 systems for water treatment is characterized using methylene blue (MB) as reactivity indicator. Batch experiments using various weight ratios of Fe0 and the two additives were performed for up to six weeks (47 days). The impact of the intrinsic reactivity of MnO2 was characterized by using different types of MnO2. The MB discoloration process was investigated both under shaking and non-disturbed conditions.
The results clearly demonstrate the impact of increased contact time on the extent of MB discoloration in all tested systems (Fe0, Fe0/sand, Fe0/MnO2 and Fe0/sand/MnO2). As a rule, MB discoloration was improved by increased experimental duration. It was noted that the extent of MB discoloration is influenced by the diffusive (or advective) transport of MB from the solution to the reactive materials at the bottom of the test tubes. Without shaking, more time is needed for the transport of MB to the particles of tested materials. For experiments lasting for longer times, sand addition prevented Fe0 particles from compaction (cementation) at the bottom of the test-tubes. This enabled the long-term generation of iron hydroxides (new iron corrosion products) for the discoloration of MB by adsorption and co-precipitation. The same observation was made for Fe0/MnO2 systems. In other words, the addition of non-expansive materials (e.g. MnO2, sand) is necessary to sustain the efficiency of Fe0 filters. Shaking the test tubes increased the extent of MB discoloration by two different mechanisms: (i) speeding up the mass transport of MB solution towards the adsorptive materials, and (ii) speeding up the kinetics of Fe0 corrosion, creating new corrosion products. Discoloration processes occur due to MB diffusion and advection which are accelerated during the shaking operation. The results clearly delineate the complexity of the Fe0/MnO2/sand system and suggest that varying the experimental conditions will give more opportunities to discuss the efficiency of Fe0/H2O systems.
... It can also act as a coagulant for various anionic species when exposed to water, and Fe 0 can also be specifically used to generate Fe(II)/Fe(III). The reaction pathways have already been extensively described in the literature (Yan et al. 2013;Zhang 2003;Weber 1996). Main reactions of relevant redox pairs for contaminant of Fe 0 /H 2 0 systems are given in Table 1. ...
Zero-valent iron has been used for more than 130 years for water treatment. It is based on redox reactions as well as on sorption to the corrosion products of iron. It is successfully applied for the removal of metals and organic pollutants from groundwater and wastewater. There are different variations how zero-valent iron can be used, especially (i) permeable reactive barriers, (ii) fluidized bed reactors and (iii) nanoscale zero-valent iron. Permeable reactive barriers are used for in situ treatment of groundwater in trench-like constructions or in a funnel and gate system. Their advantages are low maintenance cost, inexpensive construction and prevention of excavation wastes, and their disadvantages are surface passivation and clogging of pores by corrosion products. Zero-valent iron nanoparticles are injected directly in contaminated soil or groundwater. Their advantages are a higher reactivity than coarse-grained zero-valent iron and their mobility in the subsurface to reach the contaminated areas. However, they also have some major disadvantages like fast ageing in the system, phytotoxicity, agglomeration during migration and high costs. The latest development is a fluidized bed process (“ferrodecont process”) which avoids the passivation and clogging observed in permeable reactive barriers as well as the high costs and toxicity issues of nanoscale zero-valent iron. First results of this technology for Cr(VI) and organically contaminated groundwaters and metal removal from industrial wastewaters are highly promising.
... At pH ranges > 5.0, the reaction between 45 Fe 0 and water produces an oxide layer (oxide scale) close to the Fe 0 surface which is of 46 fundamental importance for the efficiency of Fe 0 PRBs. In other words, the oxide scale on 47 were reported to be confirmed two years later by Weber (1996). Since then, environmental 53 scientists are mostly considering Fe 0 as a reducing agent for relevant aqueous species, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 Fe 0 /H2O systems should strive to entertain the two theories given above as concurrent 129 hypotheses and find out which one enables a better explanation of their experimental results. ...
Metallic iron (Fe0) has been increasingly used to remove toxics from water over the past three decades. However, the idea that metallic iron (Fe0) is not an environmental reducing agent has been vigorously refuted. Researchers presenting their findings in a scientific journal have to accept the burden of proving that their argumentation has any validity. This 30-year-lasting discussion within the Fe0 remediation community is alien to electro-chemists, as it is a century-old-knowledge. Nevertheless, the peer reviewed literature on "remediation using Fe0" seems to be dominated by evaluators thinking that Fe0 is a reducing agent. This communication challenges the view that Fe0 donates any electron to any dissolved species. The sole goal is to reconcile a proven efficient technology with its scientific roots, and enable the design of better Fe0 remediation systems.
... Later on, it was proposed for PCBs that under an acid environment, the electrons can move directly from Fe 0 to the PCB molecules and the Fe 2+ will be generated as a product (Fig. 2) (Gomes et al. 2016). The proposed mechanism for hydrodehalogenation reaction involves adsorption of the contaminants at nZVI surface followed by the breakage of carbon-halogen bonds (Sarathy et al. 2008;Weber 1996). ...
Polychlorinated biphenyls (PCBs) are synthetic organic compounds ubiquitously distributed worldwide due to their persistence, long-range atmospheric transport, and bioaccumulation. Owing to teratogenic properties, PCBs are a global environmental problem. Different physical, biological, and chemical techniques are utilized for the remediation of PCBs. This review paper discusses the recent development in photocatalytic and chemical techniques for the remediation of PCBs in contaminated soils. In particular, the photocatalytic degradation of PCBs combined with soil washing, Fe-based reductive dichlorination, and advanced oxidation process (Fenton advance oxidation and persulfate oxidation) is discussed and reviewed in detail. The review suggested that advanced oxidation is an efficient remediation technique with 77–99% of removal efficiency of PCBs. Persulfate oxidation is the most suitable technique which could work at normal environmental conditions (such as pH, temperature, soil organic matter (SOM), etc.). Different environmental factors such as pH, temperature, and SOM affect the Fe-based reductive dechlorination and Fenton advance oxidation techniques. The surfactants and organic solvents used in soil washing combined with photocatalytic degradation affect the degradation capability of these techniques. This review will contribute to PCBs degradation by the detailed discussion of development in chemical technique future perspective and research needs.
... Decomposition of organic materials by catalysts normally occurs by direct surface contact, as dye molecule decomposition is based on a surface reaction. Therefore, as the crystallite size reduction provides a larger surface area, it provides more photocatalytic reaction centers to adsorb large numbers of dye molecules, resulting in effective degradation of the dye [21,54,55]. Figure 9 shows the typical mechanism of photocatalysis. ...
In this study, Fe80−xCoxZr10Si10 (x = 0, 40, and 80 at.%) alloys were produced in the form of ribbons by melt-spinning technique to investigate the photocatalytic degradation efficiency of methylene blue dye. The color removal performance of these ribbons has been studied in detail. The X-ray diffraction analysis of the fabricated melt-spun ribbons confirmed the nanocrystalline nature with varying the Co content. The scanning electron microscopy analysis depicts the surface roughness increased Co content and the energy dispersive spectroscopy reveals that the experimental nominal composition values are quite close to each other. The vibrating sample magnetometer was used to study the magnetic properties of all three samples and from the M–H curves, it was confirmed that the magnetic properties were strongly dependent upon the alloy ribbons composition during melt-spinning. The time-dependent photocatalytic degradation of the methylene blue sample was investigated under UV light using UV–Vis spectrometry at room temperature. It was observed that the amount of degradation increased due to the increase in the amount of cobalt in Fe80−xCoxZr10Si10 (x = 0, 40, and 80) alloys used as a catalyst in methylene blue using photocatalytic degradation.
... Khudenko demonstrated the feasibility of using Cu 2+ cementation as a novel tool to generate Fe 2+ and H + for the reductive transformation of organics (Khudenko 1991). Khudenko (1991) was not considered while discussing the mechanism of RCl reduction from the middle of the 1990s onwards (Matheson and Tratnyek 1994, Warren et al. 1995, Weber 1996, O'Hannesin and Gillham 1998). ...
The global effort to mitigate the impact of environmental pollution has led to the use of various types of metallic iron (Fe(0)) in the remediation of soil and groundwater as well as in the treatment of industrial and municipal effluents. During the past three decades, hundreds of scientific publications have controversially discussed the mechanism of contaminant removal in Fe(0)/H2O systems, with the large majority considering Fe(0) to be oxidized by contaminants of concern. This view assumes that contaminant reduction is the cathodic reaction occurring simultaneously with Fe 0 oxidative dissolution (anodic reaction). This view contradicts the century old theory of the electrochemical nature of aqueous iron corrosion and hinders progress in designing efficient and sustainable remediation Fe(0)/H2O systems. The aim of the present communication is to demonstrate the fallacy of the current prevailing view based on articles published before 1910. It is shown that properly reviewing the literature would have avoided the mistake. Going back to the roots is recommended as the way forward and should be considered first while designing laboratory experiments.
... In 1903, Willis Rodney Whitney established the science of the Fe 0 /H 2 O system which convincingly demonstrated that, at pH > 4.5 and under immersed conditions, only water can oxidize Fe 0 in an electrochemical mechanism according to Eq. 2 [11]: Fe 0 + 2 H + ⇒ Fe 2+ + H 2 (2) In particular, Whitney [11] demonstrated two important facts: (i) carbonic acid (H 2 CO 3 ) accelerates corrosion by supplementing protons (H + ) in Eq. 2 or intensifying water dissociation, and (ii) dissolved oxygen (O 2 ) accelerates corrosion by consuming Fe 2 + and favouring the forward reaction in Eq. 2 (i.e., Le Chatelier principle). In other words, all reports on aqueous iron corrosion by O 2 are faulty. ...
... In 1903, Willis Rodney Whitney established the science of the Fe 0 /H 2 O system which convincingly demonstrated that, at pH > 4.5 and under immersed conditions, only water can oxidize Fe 0 in an electrochemical mechanism according to Eq. 2 [11]: Fe 0 + 2 H + ⇒ Fe 2+ + H 2 (2) In particular, Whitney [11] demonstrated two important facts: (i) carbonic acid (H 2 CO 3 ) accelerates corrosion by supplementing protons (H + ) in Eq. 2 or intensifying water dissociation, and (ii) dissolved oxygen (O 2 ) accelerates corrosion by consuming Fe 2 + and favouring the forward reaction in Eq. 2 (i.e., Le Chatelier principle). In other words, all reports on aqueous iron corrosion by O 2 are faulty. ...
The evidence that metallic iron (Fe ⁰ ) is not an environmental reducing agent has been declared to be a claim. Researchers presenting their findings in a scientific journal have to accept the burden of proving that their argumentation has any validity. This 30-year-lasting discussion within the Fe ⁰ remediation community is alien to graduate chemists, as it is a century old electrochemistry knowledge. Nevertheless, the peer review literature on "remediation using Fe ⁰ " seems to be aggressively controlled by self-appointed experts (e.g., journal editors) who are not tolerating any alternative thinking. This communication demonstrates the fallacy of the view that Fe ⁰ donates any electron to a dissolved species. The sole goal is to reconcile a proven efficient technology with his scientific roots, and enable the design of better Fe ⁰ remediation systems.
... In addition to ionic species, natural organic matter (NOM) occurring in soils and groundwater is known to influence the chemical degradation by ZVI, in terms of enhancement of solubilization, sorption and electron transfer (Chiou et al. 1987;Weber 1996;Watanabe et al. 2009;Louie et al. 2016). Tratnyek et al. (2001) have shown that the reduction of TCE and carbon tetrachloride by ZVI was inhibited by NOM (Ogeechee HA, Coal Creek HA and OGI Soil HA at 5 mg L -1 each) due to competitive adsorption on iron surface, but the presence of quinone compounds (juglone and AQDS) increased the reduction rate due to mediated electron-transfer. ...
... In addition to ionic species, natural organic matter (NOM) occurring in soils and groundwater is known to influence the chemical degradation by ZVI, in terms of enhancement of solubilization, sorption and electron transfer (Chiou et al. 1987;Weber 1996;Watanabe et al. 2009;Louie et al. 2016). Tratnyek et al. (2001) have shown that the reduction of TCE and carbon tetrachloride by ZVI was inhibited by NOM (Ogeechee HA, Coal Creek HA and OGI Soil HA at 5 mg L -1 each) due to competitive adsorption on iron surface, but the presence of quinone compounds (juglone and AQDS) increased the reduction rate due to mediated electron-transfer. ...
Chlorinated organic compounds (COCs) are common anthropogenic
contaminants encountered in soil and groundwater. COCs were
industrially produced for different applications, such as dry cleaning,
degreasing, or as pesticides. The presence of COCs in the environment is a major concern because of their toxicity and persistence. The most widely used method for their removal is the conventional pump-and-treat approach. However, this technology can hardly achieve a complete remediation because of geological characteristics and the presence of pore space pollution/adsorbed pollution, leading to a residual saturation.
Hence, in addition to the improvement of pump-and-treat systems, In situ chemical processes have been largely developed. These chemical processes involve the injection of chemical reagents for the removal of residual pollution source and/or the treatment of contamination plume. Chemical degradation of COCs can be achieved by oxidative or reductive processes. If chemical oxidation has been first developed for in situ application, chemical reduction is one of the most important emerging remediation techniques for COCs treatment. Due to the electronegative character of chlorine substituents, COCs can effectively be transformed via reductive pathways. Moreover, reductive dechlorination has shown higher efficiency on highly chlorinated compounds.
This chapter focuses on the presentation of the chemical reduction of the most common COCs pollutants, followed by kinetic and mechanistic approaches related to the use of iron-based particles. Developments of in situ chemical reduction technologies aiming to enhance remediation rates are also exposed. Influence of environmental conditions for in situ applications is then developed. Finally, a case study is presented.
... It is of critical importance to state that well-documented contaminant reductive transformation of both contaminants in the pure FeS 2 system [76,83] were not observed by both research groups. One reason for this is certainly the slow kinetics of Fe II -mediated reduction processes [66,84]. Accordingly, both research groups could independently demonstrate that the presence of Fe-sulfides improve contaminant removal in Fe 0 /H 2 O systems. ...
The general suitability of water treatment systems involving metallic iron (Fe 0) is well-established. Various attempts have been made to improve the efficiency of conventional Fe 0 systems. One promising approach combines granular Fe 0 and an iron sulfide mineral to form Fe 0 /Fe-sulfide/H 2 O systems. An improved understanding of the fundamental principles by which such systems operate is still needed. Through a systematic analysis of possible reactions and the probability of their occurrence, this study establishes that sulfide minerals primarily sustain iron corrosion by lowering the pH of the system. Thus, chemical reduction mediated by Fe II species (indirect reduction) is a plausible explanation for the documented reductive transformations. Such a mechanism is consistent with the nature and distribution of reported reaction products. While considering the mass balance of iron, it appears that lowering the pH value increases Fe 0 dissolution, and thus subsequent precipitation of hydroxides. This precipitation reaction is coupled with the occlusion of contaminants (co-precipitation or irreversible adsorption). The extent to which individual sulfides impact the efficiency of the tested systems depends on their intrinsic reactivity and the operational conditions (e.g. sulfide dosage, particle size, experimental duration). Future research directions, including the extension of Fe 0 /Fe-sulfide/H 2 O systems to drinking water filters and (domestic) wastewater using the multi-soil-layering method are highlighted.
... The major mistake of the Fe 0 remediation literature has been to consider that relevant contaminants are reduced by an electrochemical reaction (electrons from the metal) [134][135][136]. This section summarizes the extent of the confusion using a paper by Kamolpornwijit and Liang [137]. ...
A critical survey of the abundant literature on environmental remediation and water treatment using metallic iron (Fe 0) as reactive agent raises two major concerns: (i) the peculiar properties of the used materials are not properly considered and characterized, and, (ii) the literature review in individual publications is very selective, thereby excluding some fundamental principles. Fe 0 specimens for water treatment are typically small in size. Before the advent of this technology and it application for environmental remediation, such small Fe 0 particles have never been allowed to freely corrode for the long-term spanning several years. As concerning the selective literature review, the root cause is that Fe 0 was considered as a (strong) reducing agent under environmental conditions. Subsequent interpretation of research results was mainly directed at supporting this mistaken view. The net result is that, within three decades, the Fe 0 research community has developed itself to a sort of modern knowledge system. This communication is a further attempt to bring Fe 0 research back to the highway of mainstream corrosion science, where the fundamentals of Fe 0 technology are rooted. The inherent errors of selected approaches, currently considered as countermeasures to address the inherent limitations of the Fe 0 technology are demonstrated. The misuse of the terms "reactivity", and "efficiency", and adsorption kinetics and isotherm models for Fe 0 systems is also elucidated. The immense importance of Fe 0 /H 2 O systems in
... In the early 1990s, Fe 0 was independently presented as an environmental reducing agent and mostly tested for chlorinated hydrocarbons and other redox sensitive species (Matheson and Tratnyek 1994, Schreier and Reinhard 1994, Weber 1996 in subsurface reactive walls (termed as permeable reactive barriers -PRBs) (Gillham 2008, Guan et al. 2015. A case-by-case approach, termed as treatability studies was used to access the suitability of Fe 0 for individual contaminants (Scherer et al. 2000, Noubactep 2013a, Noubactep 2013b. ...
... Zero-valent iron (ZVI) has been widely used to promote TCE degradation as it is a highly reduced material and amenable to hydrogen ion generation (Farrell et al. 2000;Wilkin et al. 2003;Phillips et al. 2010;Burris et al. 1995;Kouznetsova et al. 2007). While the uses and reaction mechanisms of ZVI shavings versus nano-particles differ, overall, research has shown that as ZVI ages and deposits form on the particle surfaces due to constant contact with groundwater and the surrounding environment, dechlorination rates and pore space decrease over time (Weber 1996;Farrell 1996;Wilkin et al. 2003;Liu et al. 2005;Kouznetsova et al. 2007). Therefore, the use of this material may require occasional reintroduction into the biowall structure in order to preserve high dechlorination rates. ...
Trichloroethylene (TCE) is a highly effective industrial degreasing agent and known carcinogen. It was frequently buried improperly in landfills and has subsequently become one of the most common groundwater and soil contaminants in the USA. A common strategy to remediate TCE-contaminated sites and to prevent movement of the TCE plumes into waterways is to construct biowalls which consist of biomaterials and amendments to enhance biodegradation. This approach was chosen to contain a TCE plume emanating from a closed landfill in Maryland. However, predicting the effectiveness of biowalls is often site specific. Therefore, we conducted an extensive series of batch reactor studies at 12 °C as opposed to the typical room temperature to examine biowall fill-material combinations including the effects of zero-valent iron (ZVI) and glycerol amendments. No detectable TCE was observed after several months in the laboratory study when using the unamended 4:3 mulch-to-compost combination. In the constructed biowall, this mixture reduced the upstream TCE concentration by approximately 90% and generated ethylene downstream, an indication of successful reductive dechlorination. However, the more toxic degradation product vinyl chloride (VC) was also detected downstream at levels approximately ten times greater than the maximum contaminant level. This indicates that incomplete degradation also occurred. In the laboratory, ZVI reduced VC formation. A hazard quotient was calculated for the landfill site with and without the biowall. The addition of the biowall decreased the hazard quotient by 88%.
... Zero-valent iron (ZVI), such as iron powders and iron-based amorphous alloys, which are inexpensive, resourceful and non-toxic, has been successfully utilized in wastewater treatment industry [1,2]. ZVI has been reported to be efficient in the reductive decomposition of chlorinated organic compound [3,4], heavy metals [5] and azo dye [6]. Rapid decay of the degradation efficiency of the iron powders occurs due to the ready rusting, which restricts the extensive utilization in degrading azo dyes. ...
Nanoporous structures were fabricated from Fe76Si₉B10P₅ amorphous alloy annealed at 773 K by dealloying in 0.05 M H₂SO₄ solution, as a result of preferential dissolution of α-Fe grains in form of the micro-coupling cells between α-Fe and cathodic residual phases. Nanoporous Fe-Si-B-P powders exhibit much better degradation performance to methyl orange and direct blue azo dyes compared with gas-atomized Fe76Si₉B10P₅ amorphous powders and commercial Fe powders. The degradation reaction rate constants of nanoporous powders are almost one order higher than those of the amorphous counterpart powders and Fe powders, accompanying with lower activation energies of 19.5 and 26.8 kJ mol(-1) for the degradation reactions of methyl orange and direct blue azo dyes, respectively. The large surface area of the nanoporous structure, and the existence of metalloids as well as residual amorphous phase with high catalytic activity are responsible for the enhanced azo-dyes degradation performance of the nanoporous Fe-Si-B-P powders.
... Nanoscale zero valent iron (NZVI), as a new nanoparticle, has been extensively investigated in the role of removal of various environmental pollutants (Burris et al. 1995;Matheson and Tratnyek 1994;Noubactep 2009;Reynolds et al. 1990;Weber 1996). Moreover, many contaminants, such as organic compounds, nitrate nitrogen, metal, metalloid, and radionuclides, were successfully removed or degraded from an aqueous solution in labs by using NZVI (Adeleye et al. 2013;Bilardi et al. 2013;Choe et al. 2001;Crane and Scott 2012;El-Temsah et al. 2012;Lavine et al. 2001;Liendo et al. 2013;Liu et al. 2012;Mantha et al. 2001;Mukherjee et al. 2016;Noubactep et al. 2003;O'Carroll et al. 2013;Yan et al. 2013;Yun et al. 2013). ...
Nanoscale zero valent iron (NZVI) was synthesized by the reduction of natural limonite under hydrogen conditions. The adsorption performance of the as-prepared NZVI on phosphate was evaluated through batch and column experiments. The removal of phosphate (PO43−) significantly decreased with an increase of pH from 2.0 to 11, whereas a remarkable increase of PO43− removal was observed in the presence of SO42− and S2O32−. In addition, Cl− and NO3− also improved phosphate removal at concentrations of more than 0.2 mmol/L. Kinetic studies indicated that the removal process of PO43− on NZVI can be easily followed with the pseudo-second-order kinetic model. The removal of phosphate from the oxic system was significantly higher than that of the anoxic system, which was attributed to the formation of the secondary phase by the further oxidization of Fe2+. The adsorption capacity of the as-prepared NZVI of the oxic system was 16 mg/g, and the pH was 6.3. The column experiments further demonstrated that the as-prepared NZVI presented a high removal capacity for PO43−-P. These findings indicated that the as-prepared NZVI displayed an excellent ability to remove phosphate from aqueous solutions.
The environmental and health hazards created by industrial chemicals and consumer products must be minimized. For safer products to be designed, the relationships between structure and toxicity must be understood at the molecular level. Green chemistry combined with free radical research has the potential to offer innovative solutions to such problems.
Some solutions are "greener then others", and many necessitate significant financial investment. New technology will only be adopted if real benefit can be shown and sometimes adaptation of existing methods is the best option. The efficiency of processes must be assessed, not only in terms of the final yield, but also cost, environmental impact and waste toxicity.
This practical and concise guide showcases the sustainable methods offered by green free radical chemistry and summarizes the fundamental science involved. It discusses the pros and cons of free radical chemistry in aqueous systems for synthetic applications. All transformation steps are covered including initiation, propagation, and termination. Useful background knowledge is combined with examples, including industrial scale processes for pharmaceuticals and fine chemicals.
The book helps chemists to choose appropriate methods for achieving maximum output using a modern, environmentally conscious approach. It shows that, armed with an elementary knowledge of kinetics, an understanding of the mechanistic and technical aspects, and some common sense, it is possible to harness free radicals for use in a broad range of applications.
Streamlining Green Free Radical Chemistry is aimed at chemists, engineers, materials scientists, biochemists and biomedical experts, as well as undergraduate and postgraduate students. It encourages readers to question conventional methods and move towards the "Benign-by-Design" approach of the future. References to further reading are provided at the end of each chapter.
Zero-valent iron (ZVI) is one of the most widely used engineered materials for the remediation of chlorinated ethenes in the subsurface environment. The material has been widely used in various in situ remediation technologies including Fe-permeable reactive barriers (Fe-PRB) and subsurface injection of nanoscale zero-valent iron (nZVI) for contaminant plume attenuation and source zone remediation. However, there are two serious drawbacks when ZVI is used for the remediation of chlorinated ethenes: (i) ZVI tends to undergo rapid passivation which undermines its longevity for remediation applications, and (ii) ZVI has low dechlorination reactivity in the absence of catalyst additives. Bimetallic nanoparticles (BNPs), prepared by doping a small amount of catalytic metals (e.g., Pd or Ni), can significantly enhance the particles’ dechlorination reactivity. However, BNPs suffer rapid deactivation when exposed to groundwater media, and the BNPs deactivation mechanisms are still poorly understood.
The first part of this dissertation aims to investigate Ni-Fe BNPs and Pd-Fe BNPs deactivation mechanisms when exposing them to common groundwater solutes. Aging experiments were conducted by pre-immersing fresh prepared BNPs in solutions containing different groundwater solutes for 24 h prior to reacting the particles with trichloroethene (TCE) to assess their dechlorination reactivity. Analyses of reaction kinetics and product distribution and stable carbon isotope fractionation measurements suggest that Pd-Fe BNPs were sensitive to solute-induced deactivation, particularly in solutions containing chloride, bicarbonate, nitrate or sulfite ions. Although Ni-Fe BNPs possess higher electrochemical stability than Pd-Fe BNPs in the aqueous media, strong deactivation was observed in sulfate, nitrate, and phosphate solutions. Multiple modes of BNP deactivation were proposed for the two types of BNPs.
To overcome the intrinsic limitations of conventional and bimetallic ZVI materials, the second part of this dissertation aims to develop a new form of ZVI with higher dechlorination reactivity without the use of catalyst additives and a greater resistance to environmental passivation. A surface sulfidation treatment was designed and optimized for laboratory-made nZVI and commercial ZVI. The sulfided nZVI demonstrates remarkable improvements in dechlorination rates for chlorinated ethenes. Aging experiments indicated that sulfided nZVI possesses greater stability and maintains its dechlorination reactivity over long-term aging processes. Applying sulfidation treatment to commercial iron results in more efficient tetrachloroethene (PCE) and TCE degradation. Sulfidation treatment therefore represents a simple yet promising approach to increase the reactivity of ZVI using earth-abundant reagents in place of precious catalyst metals.
Amorphous Co78Si8B14 alloy, as a new potential catalyst, has hardly been used in the degradation of organic pollutant activated by peroxymonosulfate (PMS). In the study, the degradation performance of Orange II aqueous solution by PMS activated by amorphous Co78Si8B14 alloy in a heterogeneous catalytic process was studied at ambient temperature. The effects of initial solution pH, amorphous Co78Si8B14 alloy dosage and PMS concentration on Orange II degradation were examined in batch experiments. The results show that decolorization was strongly influenced by initial solution pH, amorphous Co78Si8B14 alloy dosage, and PMS concentration. The decolorization rate increased with the increase in pH value from 3 to 6.45. In contrast, it decreased sharply when the pH value of the solution increased from 6.45 to 11. The decolorization rate increased as the amorphous Co78Si8B14 alloy dosage and PMS concentration increased. Finally, the potential mechanism of Orange II removal by amorphous Co78Si8B14 alloy/PMS system was proposed systematically by comparing with the Co2+/PMS system.
Diesel contamination of soil due to oil spills, disposal of refinery waste, oil exploration constitutes a major environmental problem. This paper reports the remediation of diesel contaminated clay soil using Zn/Fe⁰ bimetallic nanoparticle stabilized Rhamnolipid (RMLP) and Tween-80 (TW-80) surfactant foams. Fe⁰, and Zn (x wt%)/Fe⁰ (x = 0.2, 2.0, and 10.0) bimetallic nanoparticles are synthesized by using sodium borohydride reduction method. The average particle size (from FESEM) is calculated to be 62, 57, 42 and 35 nm for the Fe⁰, Zn (0.2)/Fe⁰, Zn (2)/Fe⁰ and Zn (10)/Fe⁰ nanopowders, respectively. The highest foamability and foam stability of 109.6 and 108.5 mL, respectively are observed for the RMLP (12 mg/l) surfactant foam stabilized with 6 mg/l Zn (10)/Fe⁰ nanoparticles. The surface tension values reduce to the lowest value of 28.1 and 31.4 mN/m with the addition of 6 mg/l of Zn (10)/Fe⁰ powder in RMLP and TW-80 solutions of 12 mg/l, respectively. The maximum diesel removal efficiency of 83.8 and 59%, is achieved by RMLP (12 mg/l) foam stabilized by Zn (10)/Fe⁰ nanoparticles (6 mg/l) for the clay soil contaminated with 100 and 500 μl/g of diesel, respectively. The physicochemical properties of the nanoparticles are studied to explain the foam properties and the remediation behavior. These findings regarding the nanoparticle stabilized foams can offer a cost-effective environment friendly commercial solution for soil remediation in the future.
Science denial relates to rejecting well-established views that are no longer questioned by scientists within a given community. This expression is frequently connected with climate change, and evolution. In such cases, prevailing views are built on historical facts and consensus. For water remediation using metallic iron (Fe0), the remediation Fe0/H2O system, a consensus on electrochemical contaminant reduction was established during the 1990s and is still prevailing. Arguments against the reductive transformation concept has been regarded for more than a decade as 'science denial'. However, is it the prevailing concept that had denied the science of aqueous iron corrosion? This communication retraces the path used by our research group to question the reductive transformation concept. It is shown that the validity of the following has been questioned: (i) analytical applications of arsenazo III method for the determination of uranium, (ii) molecular diffusion as sole relevant mass transport process in the vicinity of the Fe0 surface in filtration systems, and (iii) volumetric expansive nature of iron corrosion at pH > 4.5. Item (i) questions the capability of Fe0 to serve as electron donor for UVI reduction under environmental conditions. Items (ii) and (iii) are interrelated as the Fe0 surface is permanently shielded by an oxide scale acting as diffusion barrier to dissolved species and conductive barrier to electrons from Fe0. The net result is that no electron transfer from Fe0 to contaminants is possible under environmental conditions. This conclusion refutes the validity of the reductive transformation concept and call for alternatives.
Scientific collaboration among various geographically scattered research groups on the broad topic of "metallic iron (Fe0) for water remediation" has evolved greatly over the past three decades. This collaboration has involved different kinds of research partners including researchers from the same organization, domestic researchers also from non-academic organizations as well as international partners. The present analysis of recent publications of some few leading scientists shows that after a decade of frank collaboration in search of ways to improve the efficiency of Fe0/H2O systems, the research community has divided itself into two schools of thought since about 2007. Since then, progress in knowledge has stagnated. The first school maintains that Fe0 is a reducing agent for some relevant contaminants. The second school argues that Fe0 in-situ generates flocculants (iron hydroxides) for contaminant scavenging, and reducing species (e.g. FeII , H2 , Fe3O4) but reductive transformation is not a relevant contaminant removal mechanism. The problem encountered in assessing the validity of the views of both schools arises from the quantitative dominance of the supporters of the first school who mostly ignore the second school in their presentations. The net result is that the various derivations of the original Fe0 remediation technology may be collectively flawed by the same thinking mistake. While recognizing that the whole research community strives for the success of a very promising, but yet to established technology, annual review articles are suggested as an ingredient for successful collaboration.
Over the past three decades, groundwater remediation using permeable reactive barriers (PRBs) has proven to be effective. The majority of installed PRBs uses metallic iron (Fe(0)) as a reactive material. However, the success of implemented Fe(0) PRBs is yet to be rationalized as Fe(0) is a generator of iron oxides (contaminant scavengers) and secondary reducing agents (e.g. Fe(II), Fe3O4, H2, green rust), This communication demonstrates that Fe(0) is not an environmental reducing agent. Therefore, more science-based investigations are needed to optimize the operation of Fe(0) PRBs. In particular, Fe(0) PRBs and Fe(0)-based water filters should be regarded as particular cases of "metal corrosion in porous media". A key feature of such systems is that the extent of Fe 0 corrosion temporally depends on the residual porosity (capillarity). Thus, the functionality of any Fe 0 PRB should be monitored in a way that the time-dependent variation of the kinetic of iron corrosion is discussed.
Natural siderite was selected as a raw material for preparing nano zero-valent iron (nZVI). The efficiency of the as-synthesized nZVI for PO3-₄-P removal was investigated, and the effects of the annealing temperature, pH, initial PO3-₄-P concentration, adsorption temperature and oxygen were investigated. The results indicated that after annealing at 550 °C, nZVI exhibited an average crystal size of 56.3 nm and a surface area of 14.1 m²/g. A decrease in pH and an increase in oxygen availability enhanced the removal efficiency. The adsorption process, which was spontaneous and exothermic according to the thermodynamic analysis, agreed well with the pseudo-second-order kinetic model. Based on the Langmuir equilibrium isotherms, the capacity of nZVI to adsorb phosphorus was determined to be 33.18 mg/L. The optimized conditions for the experimental conditions were defined by an orthogonal experiment as follows: initial P concentration 2 mg/L, initial pH 4, iron dose 2 g/L, adsorption time 60 min. The experimental results suggested that the as-prepared nZVI was a promising adsorbent for the removal of phosphate.
Methane (CH4) production from cassava pulp can be increased when cellulose, hemicellulose, and lignin are optimally degraded. In this study, alkaline hydrolysis and heat combined with scrap iron at a concentration of 50 g Scrap iron/kg TVS were processed in Hydraulic Retention Time (HRT) of 20 days. Semi-continuous experiments were conducted in a completely stirred tank reactor in 3 conditions (Con.). In Con. 1, the pH of cassava waste was adjusted to 7. In Con. 2, pH 10 cassava waste was used in alkaline hydrolysis with heat at the controlled temperature of 100 degrees Celsius for 30 minutes. Con. 3 was like Con. 2 with additional scrap iron. CH4 content had a maximum value of 0.90 m3 CH4/kg TVS in Con. 3, increasing by 2.00 times from Con. 1 and 1.55 times from Con. 2. After experiments, scrap iron was found in the form of Fe2+ (15.90 %) and Fe3+ (84.10 %) (the highest in the form of Fe3C) because when the microbes used iron electrons (Fe2+), they reduced carbon dioxide (CO2) and hydrogen sulfide (H2S) and caused the increase of CH4. When considering the amount of CH4 in Con. 3, there were significant differences (α <0.05) at a 95% confidence level compared with Con. 1 and Con. 2 using One-Way ANOVA : Post-hoc Tukey. This result can be applied to the biogas industries in which heat transfer energy occurs when the biogas power generator works simultaneously with scrap iron, waste material from the machinery industry. In the absence of waste heat and scrap iron, it is not necessary to use Alkaline hydrolysis with heat because when comparing CH4 in Con. 1 and Con. 2, there was no significant difference in the Pair t-test at a 95% confidence level.
Fe78Si11B9P2 metallic glass (MG) ribbons are proved to exhibit excellent comprehensive ability in azo dye treatment. The Fe78Si11B9P2 MG ribbons can degrade the azo dye effectively, which derived from high mass and electron transfer ability due to the cotton-like structure formed during the reaction. The degradation efficiency and reaction rate raise with the decrease of the initial Orange Ⅱ concentration, the increase of ribbon dosage and the proper addition of H2O2. The Fe78Si11B9P2 MG ribbons are more applicable in acidic and neutral solutions. Compared to the other reported Fe-based metallic glasses for dye degradation, the Fe78Si11B9P2 MG has a lower reaction activation energy and relatively good reusability in treating with azo dye. In addition, the achieved high COD removal indicates that the complex organic structures in azo dye can be decomposed completely by Fe78Si11B9P2 MG ribbons. This work not only provides a new effective and low-cost materials for wastewater treatment, but also promotes the practical applications of Fe-based MGs as functional materials.
The wide application of zero-valent iron (ZVI) technology was limited by its slow electron transfer rate because of the dense iron oxide on ZVI surface. In this study, we reported a method to improve the performance of ZVI by ball-milling ZVI with ethylenediaminetetraacetic acid (ZVI-EDTA). The pretreatment of ZVI with EDTA provided acidic sites for ZVI surface corrosion, and thus increased the amount of surface Fe⁰ from 7.23% to 30.12%. Because of the promoted surface Fe⁰ amount, the corrosion potential of ZVI-EDTA shifted from −0.66 V to −0.75 V, and the concentration of dissolved ferrous ions and total ions increased, resulting in high efficiency in Cr(VI) removal. This study provides an effective method for enhancing the reactivity of commercial ZVI powder, which could contribute to the wide application of ZVI technology, especially in heavy metal remediation.
High air pollution concentrations lead to serious health problems in urbanized and industrialized areas. In Istanbul, Golden Horn is a creek valley that is identified by its
special terrain that makes air pollutants difficult to disperse. The goal of this study is to determine the ozone levels in this region, considering that reducing ozone precursor
emissions accomplishes surface ozone control. Ozone in surface boundary layer is formed by photochemical reactions involving nitrogen oxides and is affected by urbanization, traffic, and industry. In order to investigate the air quality levels in Golden Horn, the surface ozone concentrations and its precursors (NO and NO2) in Alibeykoy and Kagithane regions are temporally analyzed herein. Moreover, the relationship of ozone with precipitation is also determined.
Metallic glasses (MGs) have recently attracted great attention in degrading azo dyes and other organic pollutants as a kind of environmental-friendly materials for wastewater remediation. In this paper, decolorization properties of MGs based on different iron-group elements (IGEs) were reported, and adsorption or reductive degradation of aqueous azo dye solutions was observed on the surface of glassy ribbons due to their different main constituents. The primary factor determining the occurrence of adsorption or degradation was considered to be the electronic nature of the MGs instead of their crystalline structures or surface states. Besides, some electrochemical information of the glassy ribbons in the azo dye solutions was also provided for understanding the mechanism of the decolorization process. Our findings suggest that such MGs based on IGEs may be good candidates for preparing tailored materials to treat azo dye solutions or other similar organic solutions.
In this study, we reported on the nano-scale nickel/iron particles loaded in carboxymethyl/nanofibrillated cellulose (CMC/NFC) hydrogel for the dechlorination of o-dichlorobenzene (DCB) in aqueous solution. The biodegradable hydrogel may provide an ideal supporting material for fastening the bimetallic nano-scale particles, which was examined and characterized by TEM, SEM-EDX, FT-IR and BET. The performance of the selected bimetallic particles was evaluated by conducting the dechlorination of DCB in the solution under different reaction conditions (e.g., pH, dosage of nickel/iron nanoparticles and temperature). The results showed that about 70% of DCB could be dechlorinated at 20 °C in 8 h, which indicated that the immobilized reactive material had a high reduction activity when Ni/Fe loading dosage in the hydrogel (18 wt%) was considered. Moreover, the reduction behavior agreed to the pseudo-first order reaction, in which the dechlorination rate was irrelative to the pH aqueous solution. A kinetic model for predicting the concentration of DCB during the reduction reaction was established based on the experimental data.
Dechlorination of chlorinated aliphatic hydrocarbons (CAHs) by zero-valent iron (Fe⁰) was found to be influenced by the competitive effects exerted by other groundwater contaminants. Laboratory column study of the competitive effects on CAH dechlorination by Fe⁰ indicated that the presence of 1,1,1-trichloroethane (1,1,1-TCA) in the trichloroethylene (TCE)-contaminated groundwater could decrease the normalized dechlorination rate constant (kSA) of TCE from 3.04 × 10⁻² to 2.74 × 10⁻² mL m⁻² hr⁻¹. In a similar fashion, introduction of chloroform (TCM) into the synthetic groundwater containing TCE and 1,1,1-TCA led to a 40 to 54% drop in TCE and 1,1,1-TCA kSA, thus indicating competition among TCE, 1,1,1-TCA and TCM during dechlorination reactions induced by Fe⁰. Activation energy ranging from 34.3 to 53.7 kJ/mol for the simultaneous dechlorination of TCE, 1,1,1-TCA and TCM by Fe⁰ showed that the process of the electron transfer from Fe⁰ to the CAHs is the dominant step limiting the rate of the dechlorination reactions so that the electron released from Fe⁰ is most likely in competition with TCE, 1,1,1-TCA and TCM during the dechlorination reactions. In addition to CAHs, abiotic reduction of hexavalent chromium [Cr(VI)] by Fe⁰ also exerted effects on TCE dechlorination leading to a 31% drop in TCE kSA after the addition of Cr(VI) into the TCE-contaminated groundwater. Groundwater geochemical factors such as alkalinity and contaminant concentration could potentially influence competition among TCE, 1,1,1-TCA, TCM and Cr(VI) during the abiotic reduction of chemical substances by Fe⁰. © 2007 by the American Society of Civil Engineers. All Rights Reserved.
The effect of several sulphur compounds: sodium sulphate, sodium sulphide, ferrous sulphide,pyrite and an organosulphonic acid on the kinetics of the iron (Fe °) induced degradation of carbon tetrachloride was examined under aerobic conditions. It was observed that all of the sulphur compounds investigated significantly accelerated the reaction. The mechanisms of the processes studied as well as their possible influence on the efficiency of the iron-induced dehalogenation of pollutants, both in situ and in above-ground treatment are discussed.
Chemical reduction, using a catalytically-activated metal powder as the reductant, has been found to degrade many toxicants found in chemical plant waste streams to non-toxic forms. The toxicants are chemically changed to a form innocuous to the environment, rather than remaining in a concentrated solution or transmitted to the air. The chemistry of the process and the means for carrying out the reaction are described. Several applications of the process are described. The allegedly carcinogenic trihalomethanes (THM's) (chloroform, bromoform) and intermediates were degraded in a six-month pilot test from an average 242 mu g/l to well below the EPA control level, with 75% of the samples analyzing less than 5 mu g/l THM's. Reduction of trichloroethylene, tetrachloroethylene and trichloroethane from about 250 mu g/l to less than 5 mu g/l is also described. Chlorobenzene was shown to be effectively degraded, with identification of the principal products as the vastly less toxic cyclohexanol. Successful degradation of a PCB waste to detection limits was shown, as well as the pesticide chlordane.
Solubilities and vapor pressures from the literature are combined with calculated octanol/water partition coefficients, K (sub ow), to assess the expected environmental behavior of about 50 dyes. The solubility suggests the potential for a 30- to 150-fold concentration enhancement in sediments and bioconcentration of about 1,000 times in the absence of metabolism. The data also indicate that solubilities computed from K (sub ow) for disperse dyes is 10 to 100 times smaller than reported for most other compounds. Henry's Law constants calculated from solubility and vapor pressure show that the disperse and vat dyes will be entirely gas-phase-controlled in their rate of volatilization from water and that the process will be extremely slow. No definitive conclusions can be drawn about the behavior of more recently developed disperse dyes. The available physical constants are compiled along with structures, Color Index numbers, CAS numbers, and names for 80 compounds.
The kinetics of reductive transformations of a series of monosubstituted nitrobenzenes and nitrophenols have been investigated in aqueous solution containing reduced sulfur species and small concentrations of either a naphthoquinone or an iron porphyrin. Boith the two naphthoquinones and the iron porphyrin used in this study mediated the reduction of the nitro group. In all three cases, the rate of reduction of the nitrobenzenes and of the nitrophenols was strongly pH dependent. Dissociated nitrophenols were reduced ~ 3-4 times more slowly as compared to the nondissociated species. For the substituted nitrobenzenes, the effect of substitution on the reaction rate could be described by a linear free energy relationship (LFER) of the general form log k = aE(h)(1') + b, where k is the second-order rate constant for reaction with the hydroquinone monophenolate or the iron porphyrin, respectively, and E(h)(1') is the one-electron reduction potential of the nitroaromatic compound. Competition between different nitrobenzenes was observed in the case of the iron porphyrin, while no effects were found for the reaction with the hydroquinones. The results of this study form an important base for the evaluation and interpretation of reductive transformation processes of nitroaromatic compounds in the environment.
Natural organic matter (NOM) from a variety of sources has been shown to mediate the reduction of substituted nitrobenzenes in aqueous solution containing hydrogen sulfide. Pseudo-first-order rate constants were proportional to NOM concentrations and increased with increasing pH and decreasing reduction potential (E(h)) of the solution. At fixed pH and E(h), the carbon-normalized rate constants (k(NOM)) of a given compound varied less than 1 order of magnitude among NOMs derived from various natural waters. The effect of substituents on the reaction rate could be described by a linear free energy relationship (LFER) of the general form log k(NOM) = aE(h)1'(ArNO2) + b, where E(h)1'(ArNO2) is the one-electron reduction potential of the nitroaromatic compound. Such LFERs were applied successfully to predict the k(NOM) values of previously untested compounds. The results of this study suggest that hydroquinone moieties within the NOM may play a pivotal role in the mediation of electron-transfer reactions involving organic pollutants.
Solubilities and vapor pressures from the literature are combined with calculated octanol/water partition coefficients, Kow, to assess the expected environmental behavior of about 50 dyes. Most of the older disperse dyes (those that have been in use for decades) have solubilities on the order of 10−7 to 10−6 m. This solubility suggests the potential for a 30- to 150-fold concentration enhancement in sediments and bioconcentration of about 1,000 times in the absence of metabolism. The data also indicate that solubilities computed from Kow (estimated by the substituent method) may be significantly overestimated and that the product of subcooled liquid solubility and estimated Kow for disperse dyes is 10 to 100 times smaller than reported for most other compounds.
Henry's law constants calculated from solubility and vapor pressure show that the disperse and vat dyes will be entirely gas-phase-controlled in their rate of volatilization from water and that this process will be extremely slow. No definitive conclusions can be drawn about the behavior of more recently developed disperse dyes. The available physical constants are compiled along with structures, Color Index number, CAS number and names for 80 compounds.
Laboratory tests were conducted to examine zero-valent iron as an enhancing agent in the dehalogenation of 14 chlorinated methanes, ethanes, and ethenes. All compounds were tested by batch procedures in which 10 g of 100-mesh electrolytic iron was added to 40 ml hypovials. Aqueous solutions of the respective compounds were added to the hypovials, and the decline in concentration was monitored over time. Substantial rates of degradation were observed for all compounds tested with the exception of dichloromethane. The degradation process appeared to be pseudo first-order with respect to the organic compound, with the rate constant appearing to be directly proportional to the surface area to volume ratio and increasing with increasing degree of chlorination. Column tests showed the process to proceed under flow conditions with degradation rates indpendent of velocity and consistent with those measured in the batch tests. When normalized to 1 m2/ml, the t50 values ranged from 0.013 to 20 hr, and were about 5 to 15 orders of magnitude lower than values reported for natural rates of abiotic degradation. The results indicate abiotic reductive dechlorination, with iron serving as the source of electrons; the mechanism is, however, uncertain. Based on the rapid rates of degradation, both in situ and aboveground applications for remediation of contaminated ground water are proposed.
Tetrachloroethylene was transformed by iron powder (4.1g/L) in oxygen-free, HEPES-buffered (pH 7) water at 50°C with a half-life of 20 days. The only products observed were the reactive intermediate, trichloroethylene, and ethene and ethane. 1,1,1-Trichloroethane, 1,1-dichloroethylene, and tetrachloroethylene were transformed by iron at room temperature in both autoclaved buffered water and in two non-autoclaved landfill leachates. The pattern and degree of removal were similar in all cases. Dichloromethane, 1,1-dichloroethane, and 1,4-dichlorobenzene were also tested, but were not removed from any of the systems. If manganese rather than iron was used, the substrates transformed depended upon the aqueous phase. Some biological transformations were seen in Leachate 2, but the activity was reduced by manganese and completely suppressed by iron.
This paper describes the development of, and one year's experience with, a screening method based on the measurement of the respiration rate of activated sludge for assessing the possible inhibitory effect of dyestuffs on aerobic waste-water bacteria. Of the 202 dyestuffs tested, about 10% showed an inhibiting effect such that should significant quantities be likely to reach a sewage treatment plant a closer assessment of the likely effects would be indicated.
Disperse Blue 79, a large volume disperse azo dye, and 2-bromo-4,6-dinitroaniline (BDNA), an important intermediate in the preparation of Disperse Blue 79, were readily reduced chemically and in three anoxic sediment-water systems studied; half-lives were on the order of minutes to hours. No reduction of Disperse Blue 79 or BDNA was observed however in a sediment-water system containing sediment with low organic carbon. The reaction kinetics of Disperse Blue 79 in the reducing sediments are biphasic, that is, the initial rapid loss of dye is followed by a much slower rate of transformation. The reaction pathways for the chemical and sediment-mediated reduction of Disperse Blue 79 were quite similar, suggesting that the chemical reduction of such complex chemicals can provide valuable insight into their reaction pathways in environmental systems. For Disperse Blue 79, a number of reaction products resulting from the reduction of both the azo linkage and aromatic nitro groups were formed. The sediment-mediated reduction of BDNA was regioselective resulting in the formation of a 3-bromo-5-nitro-1,2-diaminobenzene, which was further reduced at a much slower rate to 6-bromo-1,2,4-triaminobenzene. These results suggest that Disperse Blue 79 and BDNA may undergo reduction in some natural anoxic sediments, resulting in the subsequent release of potentially hazardous aromatic amines to the water column.
Reduction of chlorinated solvents by fine-grained iron metal was studied in well-mixed anaerobic batch systems in order to help assess the utility of this reaction in remediation of contaminated groundwater. Iron sequentially dehalogenates carbon tetrachloride via chloroform to methylene chloride. The initial rate of each reaction step was pseudo-first-order in substrate and became substantially slower with each dehalogenation step. Thus, carbon tetrachloride degradation typically occurred in several hours, but no significant reduction of methylene chloride was observed over 1 month. Trichloroethene (TCE) was also dechlorinated by iron, although more slowly than carbon tetrachloride. Increasing the clean surface area of iron greatly increased the rate of carbon tetrachloride dehalogenation, whereas increasing pH decreased the reduction rate slightly. The reduction of chlorinated methanes in batch model systems appears to be coupled with oxidative dissolution (corrosion) of the iron through a largely diffusion-limited surface reaction.