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- Bhattacharya, Prosun, et al.
(författare)
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Geogenic arsenic in groundwaters from Terai Alluvial Plain of Nepal
- 2003
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Ingår i: Journal de Physique IV. - : EDP Sciences. - 1155-4339 .- 1764-7177. ; 107, s. 173-176
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Tidskriftsartikel (refereegranskat)abstract
- The origin and mobility of arsenic (As) in the groundwater environment has received serious attention in recent years. Recent studies have reported naturally occurring As in groundwaters of the Terai Alluvial Plains (TAP) in southern Nepal, where groundwater exploitation has increased since the 1960s. The source of As in TAP is geogenic and leached primarily due to weathering of As bearing rocks and sediments in the Himalayas. In our present study, we have investigated the groundwater chemistry in the central part of the TAP in Nawalparasi district. TAP groundwaters are near-neutral to alkaline, with predominantly reducing character and high HCO3-, low SO4- and NO3- concentrations. Elevated HCO3 levels possibly result due to the oxidation of organic matter, low SO42- levels reflect sulfate reduction. Elevated NH4+ concentrations in these groundwaters suggest dissimilatory nitrate reduction in the aquifers. Total arsenic (As,.,) levels in groundwater varied from 1.7 mug/L to as high as 404 mug/L with dominance of As(III) species and elevated levels of dissolved Fe and Mn. Arsenic is mobilized in groundwaters as a result of desorption of As-oxyanions adsorbed onto Fe- and Mn-oxides as well as reductive dissolution of these surface reactive phases from the sediments along with release of As in anoxic groundwaters.
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| 2. |
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| 3. |
- Bhattacharya, Prosun, et al.
(författare)
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Metal contamination at a wood preservation site : characterisation and experimental studies on remediation
- 2002
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 290:03-jan, s. 165-180
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this investigation was to determine the occurrence of As, Cu, Cr and Zn in the soil at an abandoned wood preservation unit and to examine some possible extractants for the contaminants in the soil. The mean As content of the contaminated surface soils (0-10 cm) was 186 mg kg(-1), where as the mean concentrations of Cu, Cr and Zn in soils from the contaminated area were 26, 29 and 91 mg kg(-1), respectively. The elevated As content in the mineral soils is related to adsorption of inorganic As phases in the fine grained fractions, which are characterised by large surface area and high positive surface charge under the current acidic conditions. Cu and Cr were found to be rather mobile, which is reflected in their lower abundance in soils and significant accumulation in sediments in the drainage leaving the area. The fine fraction of the soil (<0.125 mm) has an average metal content increased by nearly 34% as compared to the <2-mm fraction conventionally used for the analysis and assessment of soil contamination. The <2-mm fraction constitutes approximately 65% of the total weight while the fine fraction (< 0.125 mm) constitutes approximately 10%. These facts, taken together, are essential for the choice of remediation measures. Oxalate solutions have been tested as extractants for soil remediation. Dark acid oxalate extraction dissolves the amorphous Al- and Fe-oxides and hydroxides and mobilises the adsorbed inorganic As species. Oxalate also acts as a ligand for the cationic heavy metals, releasing them from exchangeable sites. With a three-step sequential leaching, up to 98-99% of the metals could be removed. At lower concentrations and higher pH, the leaching decreased to approximately 70%.
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| 4. |
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| 5. |
- Mukherjee, A. B., et al.
(författare)
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Mercury in waste in the European Union : sources, disposal methods and risks
- 2004
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Ingår i: Resources, Conservation and Recycling. - : Elsevier BV. - 0921-3449 .- 1879-0658. ; 42, s. 155–182-
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Tidskriftsartikel (refereegranskat)abstract
- Over the recent decades, there has been widespread concern regarding the toxic impact of mercury (Hg) in the ecosystem due to its mobility, volatility and potential for bioaccumulation. Hg in fish and the aquatic environment is also a great problem in the Nordic region of the EU1 (European Union). Ho is classified as a dangerous chemical in the countries of the EU. Hg in the regulation of waste is regarded as a dangerous substance which, when contained in waste, is one of the properties, leading to a classification of waste as hazardous. Estimation of the quantity of Hg in waste within the EU countries is an important task although still incomplete. In this present study, Hg in waste in the EU has been estimated at around 990 metric tonnes (t) (including coal combustion products, landfills, chlor-alkali waste and incinerator slag) for the year 1995, and it is suggested that if complete information was available for the 15 member states, the amount would be 2-4 times larger. During the 1990s there were 45 Hg cell chlorine facilities in the EU and the amount of Hg in chlorine (Cl-2) was calculated at 95.2 t based on 14-17 g Hg t(-1) of Cl, capacity. The waste from coal-fired power plants in the EU member states contained about 16.5 t of Ha, which was transferred to products for road construction, and other industrial uses or stored in landfills. This Hg can then be exchanged between the atmospheric, aquatic and terrestrial compartments. Hg is occasionally recovered from waste, but this is often discouraged for economic reasons. Recovery units are found, for example, in Germany, France, Austria, and Sweden. The total amount of secondary Hg recovered from waste is not known. Metallic Hg and Hg-bearing waste are exported and imported from the EU member states, except for export from Sweden, which is banned by national legislation. The use of Hg in lamps and batteries is declining, and the Nordic countries, Germany and Austria have stringent regulations on the use of amalgam and Hg thermometers. It is found that 18% of municipal solid waste generated in the EU is burnt in incinerators, in order to decrease the volume. 88 t of Hg enter into the landfills of the EU through waste and residues from waste incineration. Prevention of the generation of hazardous waste containing Hg is one of the most challenging tasks for the EU, with regard to sustainable waste management.
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| 6. |
- Mukherjee, S.D., et al.
(författare)
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Critical parameters for parallel interconnects using VCSEL arrays and fiber image guides
- 2002
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 4942, s. 292-305
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Several thousand glass optical fibers fused together is routinely used as fiber image guides for medical and other image remoting applications. Fiber image guides also offer possibility for flexible optical interconnect links with potentially thousands of bi-directional parallel channels with data rates as high as 10 Gbps per channel, leading to more than Tera bits per second aggregate data transfer rates. A fair number of fiber image guide based link demonstrations using vertical cavity surface emitting lasers have been reported. However, little is known about designable parameters and optimization paradigms for applications to massively parallel optical interconnects. This paper discusses critical optical parameters that characterize a massively parallel link. Experimental characterizations were carried out to explore some of the fundamental interactions between single-mode 850 nm VCSELs and fiber image guides having different numerical apertures, 0.25, 0.55 and 1.00. Preliminary optical simulation results are given. Finally, potential directions for further experimental and analytical explorations, and for applicability into designable link systems are suggested.
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