Techno-economic assessment of an hydrometallurgical process to simultaneously remove As, Cr, Cu, PCP and PCDD/F from contaminated soil

Industrial activities lead to the contamination of large amounts of soils polluted by both inorganic and organic compounds, which are difficult to treat due to different chemical properties. The efficiency of a decontamination process developed to simultaneously remove mixed contamination of industrial soils was evaluated at the pilot-scale, as well as operating costs associated to that process to define the best remediation approach. The results showed that the treatment of the coarse fractions (>0.250 mm) of 40 kg of soil by attrition in countercurrent mode allowed the removal of 17-42% of As, 3-31% of Cr, 20-38% of Cu, and 64-75% of polychlorinated dioxins and furans (PCDD/F). Removals of 60% for As, 2.2% for Cr, 23% for Cu, and 74% for PCDD/F were obtained during the treatment of attrition sludge (<0.250 mm) by alkaline leaching process. However, the results of the techno-economic evaluation, carried out on a fixed plant with an annual treatment capacity of 7560 tons of soil treated (tst), showed that the estimated overall costs for the attrition process alone [scenario 1] (CAD$ 451/tst) were lower than the costs of the process, which additionally includes an alkaline leaching step to treat attrition sludge [scenario 2] (CAD$ 579/tst). This techno-economic evaluation also showed that the process becomes competitive with current disposal options (thermal desorption and landfilling - CAD$ 600/tst) from a certain treatment capacity, which is around of 3465 tst/yr for the scenario 1 and 6930 tst/yr for the scenario 2. On the other hand, the techno-economic evaluations are crucial to selecting feasible decontamination process for a soil remediation project, with considerations of the type of contamination, site characteristics and cost effectiveness.

Optimizing removal of arsenic, chromium, copper, pentachlorophenol and polychlorodibenzo-dioxins/furans from the 1-4 mm fraction of polluted soil using an attrition process

The objective of this study was to evaluate, at a pilot scale, the performance of an attrition process for removing As, Cr, Cu, pentachlorophenol (PCP) and polychlorodibenzodioxins and furans (PCDDF) from a 1-4 mm soil fraction. A Box-Behnken experimental design was utilized to evaluate the influence of several parameters (temperature, surfactant concentration and pulp density) and to optimize the main operating parameters of this attrition process. According to the results, the concentration of surfactant (cocamidopropylbetaine-BW) was the main parameter influencing both PCP and PCDDF removal from the 1-4 mm soil fraction by attrition. The behavior of each 2,3,7,8-PCDD/F congener during the attrition process was studied. The results indicated that the concentration of surfactant had a significant and positive effect on the removal of almost all of the dioxin and furan. The removal of 56%, 55%, 50%, 67% and 62% of the contaminants were obtained for As, Cr, Cu, PCP and PCDDF, respectively, using the optimized conditions ([BW]= 2% (w.w-1), T = 25°C and PD = 40% (w.w-1)). These results showed that attrition in the presence of a surfactant can be efficiently used to remediate the coarse fractions of soil contaminated by As, Cr, Cu, PCP and PCDDF.

Degradation of polycyclic aromatic hydrocarbons in different synthetic solutions by Fenton's oxidation

The Fenton oxidation using phenanthrene (Phe), fluoranthene (Fle) and benzo[a]pyrene (BaP) as representative polycyclic aromatic hydrocarbon (PAH) contaminants was examined. The effect of the H₂O₂ concentration, the temperature and the competition between the PAHs in different solutions (methanol, surfactant and quartz) was investigated. The Fenton oxidation process was performed at pH = 2.5. The best conditions were recorded by adding 15 g H₂O₂ L^-1 with a molar H₂O₂/Fe²⁺ ratio of 10/1 at T = 60°C. Phe, Fle and BaP were efficiently degraded in aqueous solution (Phe = 99%, Fle = 99% and BaP = 90%). The present study demonstrated that Phe, Fle and BaP were degraded to intermediate compounds and also oxidized to carbon dioxide. Among the by-products obtained, phthalic acids and benzoic acid were recorded as the major products.

Monosodium glutamate and sweet taste: generalization of conditioned taste aversion between glutamate and sweet stimuli in rats

Even though monosodium glutamate (MSG) is a prototypical umami substance, previous studies reported that a conditioned taste aversion (CTA) to MSG, mixed with amiloride to block the taste of sodium, generalizes to sucrose. These findings suggest that the taste of glutamate mimics the taste of sucrose and raise the question of whether glutamate has a broadly tuned sweet taste component. To test this hypothesis, CTA experiments were conducted to test for generalization between MSG and several sweet stimuli: sucrose, glucose, maltose, saccharin and SC-45647. Strong bidirectional generalization was seen between MSG mixed with amiloride and sucrose, glucose, saccharin and SC-45647. Weak generalization was seen between MSG and maltose, and sucrose and maltose. None of the CTAs generalized to NMDA. These findings support the hypothesis that the taste of MSG has broadly tuned, sweet-like characteristics, possibly due to the convergence of afferent signals for MSG, natural sugars and artificial sweeteners.

Increase of junctional and background 16S (tailed, asymmetric) acetylcholinesterase during postnatal maturation of rat and mouse sternocleidomastoid muscle

Acetylcholinesterase (AChE) is found both in motor end-plate (MEP)-free and MEP-rich regions of rat or mouse muscle. We studied the developmental aspects of the localization of asymmetric 16S AChE in both regions of the sternocleidomastoid muscle, which has a well-defined zone of motor innervation. In the rat, the proportion of 16S AChE to total AChE increases in the MEP-rich region, and becomes significantly higher than in the MEP-free regions between the first and the second weeks after birth. In the mouse, at birth, the MEP-rich region already has a higher relative content in 16S AChE than the MEP-free regions. Total 16S AChE amounts increase during postnatal development, not only in the MEP-rich region but also in the MEP-free regions. Thus, 16S AChE is not eliminated from MEP-free regions during muscle maturation and growth. Two distinct pools of 16S AChE are distinguished in the muscles, both of which increase during postnatal development: junctional and background 16S AChE.

Polymorphism of acetylcholinesterase and identification of new molecular forms after sedimentation analysis

Acetylcholinesterase (AChE) is composed of several distinct molecular forms, which are identified and partly resolved by velocity sedimentation analysis on sucrose gradients. We made the assumption that each AChE form sediments as a peak of activity with a gaussian shape in the continuous sucrose gradient. We experimentally demonstrate that the complex AChE profiles can be decomposed in gaussian distributions of separate molecular entities. We performed a high salt-detergent extraction of AChE from mouse skeletal muscle and isolated fractions enriched in each particular from. These fractions were then submitted to a second sedimentation, to assess the stability and to further characterize each AChE form. Then, we calculated the statistical significance level of each AChE form and identified up to 9 separate molecular specifies in mouse adult muscle. These forms are the major "4 S", "6.5 S", "10 S", "12 S" and "16 S" and minor molecular active components of AChE. These results suggest complex structural interactions between catalytic and non catalytic subunits of AChE and do not simply fit the tailed asymmetric globular model of AChE with six molecular species.