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[en] There are currently over 1200 sites on the US Superfund's National Priorities List (NPL) of hazardous waste sites, and there are over 30, 000 sites listed by the Comprehensive Environmental Responsibility, Compensation and Liability Information System (CERCLIS). The traditional approach to remediating sites in the US has been to remove the material and place it in a secure landfill, or in the case of groundwater, pump and treat the effluent. These technologies have proven to be very expensive and don't really fix the problem. The waste is just moved from one place to another. In recent years, however, alternative and innovative technologies have been increasingly used in the US to replace the traditional approaches. This paper will focus on just such innovative remediation technologies in the US, looking at the regulatory drivers, the emerging technologies, some of the problems in deploying technologies, and a case study
[en] 2,6-Dinitro-1-iodobenzene and 2,4-dinitro-1-iodobenzene were deiodinated with tributylin hydride at different temperatures using various addition modes. The product ratios of 1,3-dinitrobenzene and the corresponding tributylstannyldinitrobenzene compounds were determined by NMR in order to evaluate the optimum conditions for impending tritiation experiments. (Author)
[en] Highlights: • TCBPA can be rapidly and completely dechlorinated by Pd/Fe bimetallic catalysts. • The observed rate constants are functions of dosages, initial concentration, Pd coverage and solution pH. • Pd dosage is the major factor in the observed rates of the reaction. • This is the first report investigating the dechlorination of TCBPA by Pd/Fe catalysts. -- Abstract: The Pd/Fe bimetallic catalysts of micron sizes were synthesized and the rates of tetrachlorobisphenol A (TCBPA) degradation were measured under various conditions using a batch reactor system. The results showed that TCBPA was rapidly dechlorinated to tri-, di- and mono-chlorobisphenol A and to bisphenol A (BPA). The observed rate constants (kobs) were found to increase as functions of the Pd coverage on the Fe particles and the dosages of the catalysts within the reactors. The kobs value decreased as the initial TCBPA concentration increased, suggesting that the TCBPA dechlorination may follow a surface-site limiting Langmuir–Hinshelwood rate model. The weakly acidic solution, especially at or near pH 6.0, also favored the dechlorination of TCBPA. At pH 6.0, Pd coverage of 0.044 wt% and catalyst dosage of 5 g L−1, TCBPA with an initial concentration of 20 μM was completely transformed within 60 min, and BPA was detected as the major product through the reaction time. Meanwhile, the kobs values measured at constant solution pH correlated linearly with the mass of particle-bound Pd introduced to the reactors, regardless of Pd/Fe catalyst dosage or Pd surface coverage. This study suggested that Pd/Fe catalysts could be potentially employed to rapidly degrade TCBPA in the contaminated environment
[en] The results of the ring opening reaction of N-protected-cis-2-vinyl-3-(benzyloxymethyl)aziridines as model compounds for cis-3-substituted-2-vinylaziridines with various heteroatom nucleophiles are summarized in Table 1. Methanol is a good nucleophile to provide the desired 1,2-amino-alcohol derivative as a single product in excellent yield. We analyzed briefly the effect of solvents with methanol. Although other solvents such as DMF and THF also gave the product, CH2Cl2 was employed as a preferred solvent because of the high yield and ease of handling. All the reactions were, therefore, examined in CH2Cl2 in the presence of BF3·OEt2 as a Lewis acid unless mentioned otherwise. All alcohols behaved as good nucleophiles to exclusively give the desired products (entry 1-7)
[en] Highlights: ► HCB contamination is still a serious environmental problem. ► Physiochemical technologies for HCB remediation and disposal are reviewed. ► Perspectives for most remediation technologies are proposed. ► Pilot and large scale remediation and disposal are presented. - Abstract: Hexachlorobenzene (HCB) is one of the 12 persistent organic pollutants (POPs) listed in “Stockholm Convention”. It is hydrophobic, toxic and persistent in the environment. Due to extensive use in the past, HCB contamination is still a serious environmental problem. Strong adsorption on solid particles makes the remediation difficult. This paper presents an overview of the physiochemical technologies for HCB remediation and disposal. The adsorption/desorption behavior of HCB is firstly described because it comprises the fundamental for most remediation technologies. Physiochemical technologies concerned mostly for HCB remediation and disposal, i.e., chemical enhanced washing, electrokinetic remediation, reductive dechlorination and thermal decomposition, are reviewed in terms of fundamentals, state of the art and perspectives. The other physiochemical technologies including chemical oxidation, radiation induced catalytic dechlorination, ultrasonic assisted treatment and mechanochemical dechlorination are also reviewed. The pilot and large scale tests on HCB remediation or disposal are summarized in the end. This review aims to provide useful information to researchers and practitioners regarding HCB remediation and disposal.
[en] The release of bound (nonextractable) 14C residues from soil previously treated with [14C]atrazine was investigated by incubation of the solvent-extracted soil with two species of Pseudomonas capable of metabolizing atrazine. The two species, 192 and 194, released bound 14C residues from the soil. Addition of glucose, known to increase microbiological activities, to the incubated soil appeared to enhance the release of soil-bound 14C residues, in particular in the presence of Pseudomonas species 192. The 14C bound residues in soil, mainly present as the parent compound and its hydroxy and monodealkylated analogues, were released into the incubation mixture and were subsequently metabolized by the two species involving dechlorination and dealkylation
[en] Enhanced reductive dehalogenation is an attractive treatment technology for in situ remediation of chlorinated solvent DNAPL source areas. Reductive dehalogenation is an acid-forming process with hydrochloric acid and also organic acids from fermentation of the electron donors typically building up in the source zone during remediation. This can lead to groundwater acidification thereby inhibiting the activity of dehalogenating microorganisms. Where the soils' natural buffering capacity is likely to be exceeded, the addition of an external source of alkalinity is needed to ensure sustained dehalogenation. To assist in the design of bioremediation systems, an abiotic geochemical model was developed to provide insight into the processes influencing the groundwater acidity as dehalogenation proceeds, and to predict the amount of bicarbonate required to maintain the pH at a suitable level for dehalogenating bacteria (i.e., > 6.5). The model accounts for the amount of chlorinated solvent degraded, site water chemistry, electron donor, alternative terminal electron-accepting processes, gas release and soil mineralogy. While calcite and iron oxides were shown to be the key minerals influencing the soil's buffering capacity, for the extensive dehalogenation likely to occur in a DNAPL source zone, significant bicarbonate addition may be necessary even in soils that are naturally well buffered. Results indicated that the bicarbonate requirement strongly depends on the electron donor used and availability of competing electron acceptors (e.g., sulfate, iron (III)). Based on understanding gained from this model, a simplified model was developed for calculating a preliminary design estimate of the bicarbonate addition required to control the pH for user-specified operating conditions.
[en] Competitor-supplied reactor vessel models are equipped with an in-core instrument (ICI) that measures the power distribution of the reactor core, which is inserted into the nuclear fuel assembly through the upper head of the reactor vessel. This is to exclude the risk of out-of-core release of the core melt through the lower ICI nozzle. Also, it is possible to effectively perform the cooling of the outer wall of the reactor or the cooling of the core melt with the core melting. The structure and shape of the reactor vessel is simple and does not require the installation of complex structures to guide and support the ICI. In this paper, IHA structure is changed as TM-ICI technology is applied. The ICI Cable from the RV Head will pass through the IHA. The reason for confirming the vibration characteristics of IHA was initial analysis for CEDM cooling fan and seismic design. In particular, the CEDM cooling fan should be designed to avoid the natural frequency of the IHA as a rotating device. The natural frequencies up to 100 Hz were analyzed. The peak value in Case 1 was 44 Hz in the horizontal direction and 37 Hz in the vertical direction. The peak value in Case 2 was calculated for two frequencies. Peak values at low frequencies are near 5 Hz in the horizontal and vertical directions. This is expected due to the isolation effect of the CEDM cooling fan. Peak values occurring at high frequency are issued at 43 Hz in the horizontal direction and 37 Hz in the vertical direction and are analyzed as natural frequencies of the IHA Air Plenum Assembly. As a result, the excitation frequency provided by the CEDM cooling fan is expected to have no influence on the IHA by isolation.