Reduced efficiency remediation

Berthod, A., Causes and remediation of reduced efficiency in micellar liquid chromatography, /. Chromatogr. A, 780, 191, 1997. 

Faulkner, Hopkinson, and Cundy, 2005). Because of the adverse effect of OH on soil remediation, due to the immobilization of many metal ions by precipitation in alkalinized soils, and the reduced efficiency of electrokinetic remediation when sacrificial iron-rich electrodes are employed (e.g. Leinz, Hoover, and Meier, 1998), noncorrosive electrodes and techniques to minimize soil alkalinization are generally employed for electrokinetic remediation (e.g. Rohrs, Ludwig, and Rahner, 2002 Virkutyte, Sillanpaa, and Latostenmaa, 2002). However, low adsorption of Cr(VI) in soils occurs in alkaline conditions, whereas high adsorption of Cr(VI) is favored in acidic conditions (Reddy et al, 1997). Furthermore, the reduction of Cr(VI) to Cr(III) by the delivery of iron (Fe°, Fe " ) is fairly well documented (Rai, Sass, and Moore, 1987 Eary and Rai, 1991 Haran et aL, 1995 Powell et aL, 1995 Pamukcu, Weeks, and Wittle, 1997 Batchelor et al., 1998 Reddy et /., 2003). Accordingly,under an applied direct current (DC) electric field, stabilization of Cr(VI)-contaminated soils may potentially be achieved where oxidative dissolution of iron-rich anodic electrodes provides Fe(j,q) to react with the anode-bound migration of Cr(VI). Hence, the use of iron-rich sacrificial electrodes and soil alkalinization may find application in the electrokinetic stabilization of Cr(VI)-contaminated soils. This concept is explained in this chapter based on the results of laboratory stabilization experiments on three Cr(VI)-impacted soils taken from three sites within the UK. 

In this chapter, the possible causes of the reduced efficiency in MLC will be surveyed and a remediation path will be proposed and discussed. The chromatographic process is rapidly exposed pointing out the thermodynamics (retention time) and the kinetics (peak efficiency). The differences between a classical hydro-organic reversed mobile phase and a micellar phase are recalled. The kinetics of the chromatographic process can be modeled using the Knox equation that relates the reduced plate height to the... 

Antihistamines such as diphenhydramine are known for their sedating properties and are frequently used over-the-counter medications (usual doses 25-50 mg) for difficulty sleeping. Diphenhydramine is approved by the FDA for the treatment of insomnia and can be effective at reducing sleep latency and increasing sleep time.43 However, diphenhydramine produces undesirable anticholinergic effects and carryover sedation that limit its use. As with TCAs and BZDRAs, diphenhydramine should be used with caution in the elderly. Valerian root is an herbal sleep remedy that has inconsistent effects on sleep but may reduce sleep latency and efficiency at commonly used doses of 400 to 900 mg valerian extract. Ramelteon, a new melatonin receptor agonist, is indicated for insomnia characterized by difficulty with sleep onset. The recommended dose is 8 mg at bedtime. Ramelteon is not a controlled substance and thus may be a viable option for patients with a history of substance abuse. 

Biological activity can be used in two ways for the bioremediation of metal-contaminated soils to immobilize the contaminants in situ or to remove them permanently from the soil matrix, depending on the properties of the reduced elements. Chromium and uranium are typical candidates for in situ immobilization processes. The bioreduction of Cr(VI) and Ur(VI) transforms highly soluble ions such as CrO and UO + to insoluble solid compounds, such as Cr(OH)3 and U02. The selenate anions SeO are also reduced to insoluble elemental selenium Se°. Bioprecipitation of heavy metals, such as Pb, Cd, and Zn, in the form of sulfides, is another in situ immobilization option that exploits the metabolic activity of sulfate-reducing bacteria without altering the valence state of metals. The removal of contaminants from the soil matrix is the most appropriate remediation strategy when bioreduction results in species that are more soluble compared to the initial oxidized element. This is the case for As(V) and Pu(IV), which are transformed to the more soluble As(III) and Pu(III) forms. This treatment option presupposes an installation for the efficient recovery and treatment of the aqueous phase containing the solubilized contaminants. 

Treatment systems should be demonstrated to be effective, and expandable (or reducible), in a stepwise modular fashion to ensure efficient design and operation. At many sites, it is cost-effective to install several temporary treatment systems in parallel configuration, and remove them as the need is diminished until the stable rate is achieved where a single unit can handle the load. After careful analysis, it may be determined that the best procedure is to install and operate the system at the projected long-term rate from the onset. Although this plan may extend the longterm remediation time, cost savings on equipment purchase (or lease) or initial operation labor may be justified. 

According to vendor-supplied information, the INCA system can process aqueous solutions efficiently and greatly reduces costs for two major reasons (1) the technology costs much less than traditional treatment methods, and (2) the value of precious metals recovered during the process could offset the cost of remediation and may even result in a profit (D10759F, pp. 180-181). No specific cost information was available. 

One conclusion from the SITE evaluation was that the cost of the technology is small compared to the benefits of enhanced remediation and the reduced number of wells needed to complete the remediation (D10054P, p. iv). In addition, the DOE concluded that hydraulic fractioning decreased the time required to cleanup a site due to more efficient contaminant removal. As a result, the maintenance and operating costs over the life cycle of the project also decreased (D183771, section 5 p. 2). 

Heavy molecular weight hydrocarbons such as grease may require preprocessing to achieve remediation goals. The system is not designed to handle tars or asphalts. Sticky clays or fines fractions exceeding 40% may reduce operating efficiencies. 

Heterogeneities or anomalies in the soil will reduce removal efficiencies. Extreme pHs at the electrodes may inhibit the system s effectiveness. The electrokinetic remediation process is limited by the solubility of the contaminant, the desorption of the contaminants from the soil matrix, and reduction-oxidation changes induced by the electrode reactors. Electrokinetic remediation requires sufficient pore water to transmit the electrical charge. Contaminant and noncontaminant concentrations effect the efficiency of the process. 

ISEE is limited by the type of contaminant, pH, pore water chemistry, amount of pore water, contaminant and noncontaminant ion concentrations, precipitation reactions, and reduction-oxidation properties of the site. It may be difficult to estimate the time that will be required to remediate a site using this technology. Heterogeneities or anomahes in the soil will reduce removal efficiencies. ISEE is a developing technology. Further research is required to determine the technology s limitations and ramifications. 

Dechlorination occurred in parts of the soil column where reducing conditions (Eh-pH conditions) are dominant. The most significant reductive dechlorination of TCE occurred near the cathode, a source of electrons during electroosmosis. Results show the need to include a decay term in the transport equations. The results show that potential chemical transformation of chlorinated organic compounds could enhance the remediation efficiency during EO. 

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