REMEDIATION TECHNIQUE FOR CADMIUM CONTAMINATED GROUNDWATER: A SYSTEMATIC REVIEW

Heavy metal pollution in soil has seriously affected the living environment of human beings Among all heavy metal pollution, cadmium (Cd) is one of the most difficult to migrate pollutants in soil. Therefore, this systematic review includes the remediation techniques of Cd-contaminated groundwater that using. Different remediation techniques, including pump and treat, permeable reactive barrier, adsorption, biosorption, electrochemical, precipitation, ion exchange and bioremediation are reviewed. The advantages and disadvantages of some remediation technologies for cadmium from groundwater are outlined in order to assist the selection of a suitable technology for a groundwater remediation project. Bioremediation is a common remediation strategy used with low Cd concentrations due to the ability of the bacterial cells to bioremediate Cd

Predicting copper speciation in estuarine waters – Is dissolved organic carbon a good proxy for the presence of organic ligands?

A new generation of speciation-based aquatic environmental quality standards (EQS) for metals have been developed using models to predict the free metal ion concentration, the most ecologically relevant form, to set site-specific values. Some countries such as the U.K. have moved toward this approach by setting a new estuarine and marine water EQS for copper, based on an empirical relationship between copper toxicity to mussels (<i>Mytilus</i> sp.) and ambient dissolved organic carbon (DOC) concentrations. This assumes an inverse relationship between DOC and free copper ion concentration owing to complexation by predominantly organic ligands. At low DOC concentrations, the new EQS is more stringent, but above 162 μM DOC it is higher than the previous value. However, the relationship between DOC and copper speciation is poorly defined in estuarine waters. This research discusses the influence of DOC from different sources on copper speciation in estuaries and concludes that DOC is not necessarily an accurate predictor of copper speciation. Nevertheless, the determination of ligand strength and concentrations by Competitive Ligand Exchange Adsorptive Cathodic Stripping Voltammetry enabled the prediction of the free metal ion concentration within an order of magnitude for estuarine waters by using a readily available metal speciation model (Visual MINTEQ)

Temporal variability in dynamic and colloidal metal fractions determined by high resolution in situ measurements in a UK estuary

In recent environmental legislation, such as the Water Framework Directive in the European Union (WFD, 2000/60/EC), the importance of metal speciation and biological availability is acknowledged, although analytical challenges remain. In this study, the Voltammetric In situ Profiler (VIP) was used for high temporal resolution in situ metal speciation measurements in estuarine waters. This instrument simultaneously determines Cd, Cu and Pb species within a size range (ca<4. nm) that is highly relevant for uptake by organisms. The colloidal metal fraction can be quantified through a combination of VIP measurements and analyses of total dissolved metal concentrations.VIP systems were deployed over tidal cycles in a seasonal study of metal speciation in the Fal Estuary, southwest England. Total dissolved concentrations were 4.97-315. nM Cu, 0.13-8.53. nM Cd and 0.35-5.75. nM Pb. High proportions of Pb (77 ± 17) and Cu (60 ± 25) were present as colloids, which constituted a less important fraction for Cd (37 ± 30). The study elucidated variations in the potentially toxic metal fraction related to river flow, complexation by organic ligands and exchanges between dissolved and colloidal phases and the sediment. Based on published toxicity data, the bioavailable Cu concentrations (1.7-190. nM) in this estuary are likely to severely compromise the ecosystem structure and functioning with respect to species diversity and recruitment of juveniles. The study illustrates the importance of in situ speciation studies at high resolution in pursuit of a better understanding of metal (bio)geochemistry in dynamic coastal systems. © 2011 Elsevier Ltd

Cadmium resistant bacteria mediated cadmium removal: a systematic review on resistance, mechanism and bioremediation approaches

Cadmium-resistant bacteria that are used to remove cadmium (Cd) are becoming increasingly of the most important and hygienic method. Resistant mechanisms are involved in different ways, and some of them which can be used in cadmium removal techniques based on their molecular mechanisms and minimum inhibitory concentration (MIC). This review summarises recent improvements in understanding the mechanisms by which bacteria are either intrinsically resistant or acquire resistance to cadmium to be used as a way for cadmium removal

Trapped ion chain as a neural network

We demonstrate the possibility of realizing a neural network in a chain of trapped ions with induced long range interactions. Such models permit to store information distributed over the whole system. The storage capacity of such network, which depends on the phonon spectrum of the system, can be controlled by changing the external trapping potential and/or by applying longitudinal local magnetic fields. The system properties suggest the possibility of implementing robust distributed realizations of quantum logic.Comment: 4 pages, 3 figure

Determination and prediction of zinc speciation in estuaries

Lowering of the estuarine Environmental Quality Standard for zinc in the UK to 121 nM reflects rising concern regarding zinc in ecosystems and is driving the need to better understand its fate and behaviour and to develop and parameterise speciation models to predict the metal species present. For the first time, an extensive dataset has been gathered for the speciation of zinc within an estuarine system with supporting physico-chemical characterisation, in particular dissolved organic carbon. WHAM/Model VII and Visual MINTEQ speciation models were used to simulate zinc speciation, using a combination of measured complexation variables and available defaults. Data for the five estuarine transects from freshwater to seawater endmembers showed very variable patterns of zinc speciation depending on river flows, seasons, and potential variations in metal and ligand inputs from in situ and ex situ sources. There were no clear relationships between free zinc ion concentration [Zn2+] and measured variables such as DOC concentration, humic and biological indices. Simulations of [Zn2+] carried out with both models at high salinities or by inputting site specific complexation capacities were successful, but overestimated [Zn2+] in low salinity waters, probably owing to an underestimation of the complexation strength of the ligands present. Uncertainties in predicted [Zn2+] are consistently smaller than standard deviations of the measured values, suggesting that the accuracy of the measurements is more critical than model uncertainty in evaluating the predictions