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The conventional chemical reduction-precipitation technique in the removal of Cr(VI) from contaminated groundwater involves a two-step process whereby Cr(VI) is first reduced to Cr(III) at an acidic pH by a reducing agent and in a subsequent step, Cr(III) is precipitated as insoluble hydroxide at an alkaline pH. In a variation of this method, Fe(II) is added electrochemically to the Cr(VI) containing water. From a pure iron electrode, Fe(2+) ions are released into the solution and bring forth the reduction of Cr(VI). At the cathode, H(2)O is reduced whereby the OH(-) ions entering the solution keep the pH of the solution in the alkaline range. This latter fact greatly facilitates simultaneous reduction of Cr(VI) to Cr(III) and co-precipitation of hydroxides of trivalent Cr and Fe. On the basis of a set of experimental data, it is shown that this process is both thermodynamically and kinetically efficient, meaning, with the electrochemical method, rapid and nearly complete removal of Cr(VI) from a groundwater source with both high and low levels of Cr-contamination can be achieved. These factors make the electrochemical process superior to the conventional chemical process in remediation of Cr-contaminated groundwater. 相似文献
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Managing Baltic Sea fisheries under contrasting production and predation regimes: ecosystem model analyses 总被引:1,自引:0,他引:1
Based on an earlier published ecosystem model, we have explored possible effects of different management scenarios for the Baltic Sea. The scenarios include an oligotrophication of the system, a drastic increase in the number of seals, and changes in the fishery management. From these simulations we conclude that fisheries, seals, and eutrophication all have strong and interacting impacts on the ecosystem. These interactions call for integrated management. The modeling highlights the potential for conflicts among management mandates such as flourishing fisheries, rebuilt seal populations, and substantially reduced eutrophication. The results also suggest that fisheries management reference points have to be adjusted in response to changes in the presence of natural predators or ecosystem productivity. 相似文献
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Annika Åberg Mats Tysklind Tohr Nilsson Matthew MacLeod Annika Hanberg Rolf Andersson Sture Bergek Richard Lindberg Karin Wiberg 《Environmental science and pollution research international》2010,17(1):26-39
Background, aim, and scope
The main pathway for human exposure to the highly toxic polychlorinated-p-dioxins and polychlorinated furans [polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)] is via dietary intake. Other exposure pathways may, however, be important in close proximity to point sources, such as wood preservation sites, where PCDD/F contaminated chlorophenols (CP) were previously used. In this study, a heavily PCDD/F contaminated CP saw mill site in Sweden was investigated. Human exposure through a broad spectrum of exposure pathways was assessed. Such studies are in demand since the question whether contaminated sites represent a current or future risk can only be answered by detailed site-specific risk assessments. 相似文献4.
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Wulff S Lindelöw Å Lundin L Hansson P Axelsson AL Barklund P Wijk S Ståhl G 《Environmental monitoring and assessment》2012,184(4):2453-2464
A revised Swedish forest health assessment system is presented. The assessment system is composed of several interacting components
which target information needs for strategic and operational decision making and accommodate a continuously expanding knowledge
base. The main motivation for separating information for strategic and operational decision making is that major damage outbreaks
are often scattered throughout the landscape. Generally, large-scale inventories (such as national forest inventories) cannot
provide adequate information for mitigation measures. In addition to broad monitoring programs that provide time-series information
on known damaging agents and their effects, there is also a need for local and regional inventories adapted to specific damage
events. While information for decision making is the major focus of the health assessment system, the system also contributes
to expanding the knowledge base of forest conditions. For example, the integrated monitoring programs provide a better understanding
of ecological processes linked to forest health. The new health assessment system should be able to respond to the need for
quick and reliable information and thus will be an important part of the future monitoring of Swedish forests. 相似文献
6.
Natalia Broqvist Sture Hogmark Anna Medvedeva Staffan Gunnarsson 《Journal of Manufacturing Processes》2012,14(3):195-198
Maintaining a reasonably low cutting tool wear when producing forming tools is a general challenge in the development of new forming tool materials. The tool life of a hot forming tool steel (H13) has been significantly improved by reducing its Si-content from 1.0 to 0.06 wt.%. However, this modified H13 (MH13) also displays a reduced cutting tool life due to higher cutting forces and a stronger tendency to form built up layers (BUE) on the cutting edge. This paper explains why.Gleeble tests of MH13 revealed a significantly higher flow stress in the 820–900 °C temperature interval in MH13 compared to H13. Thermo-Calc simulations showed that when reducing the Si-content from 1.0 to 0.06 wt.% the initial temperature for ferrite-to-austenite transformation (A1) was reduced from 900 °C to 820 °C. Knowing that austenite has totally different mechanical and thermal properties than ferrite, the difference in A1 between the two steels explains the higher cutting forces and higher tendency for BUE-formation. The conclusion is that the difference in machinability between H13 and MH13 is primarily related to their difference in A1.An attempt was also made to find a new tool material composition that can combine the wear resistance of MH13 and the good machinability of H13. Thermo-Calc simulations were performed with slightly modified alloying content without changing its properties as a good forming tool material, with the aim to increase A1. For instance, reducing the Mn content from 0.5 to 0.05 wt.% proved to increase A1 from 820 to 850 °C. 相似文献
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Displacement ventilation and well-organized ventilation flow structures are emphasized. Perhaps the biggest advantage of displacement ventilation is its increased effectiveness in removing pollutants from a ventilated space and the efficient use of ventilation air. Several questions on how the systems should be designed to achieve optimal efficiency are still unanswered. Small variations in room geometries and air supply arrangements can totally change the conditions. Results from this investigation show the importance of an even distribution of the incoming supply air, numerically calculated age-of-air values and the influence of residual tracer concentrations on rneasured mean values for the age of air. 相似文献
10.
Mikko Hupa Rainer Backman Sture Boström 《Journal of the Air & Waste Management Association (1995)》2013,63(11):1496-1501
This article discusses nitrogen oxide emissions from various types of boilers in Finland. The boilers have been classified into 61 classes according to their size, combustion technique, and main fuel. A specific emission coefficient (ng NO2/J = mg NO2/MJ) for each class has been determined, based on literature surveys and actual measurements. The total NOX emission has been calculated for each class, using the emission coefficient and energy statistics. The effect of various techniques for emission reduction has also been investigated. The development of NOX emissions has been estimated for both the case where no preventing actions have been taken and for four defined cases where alternative reduction measures are assumed The total NOX emission from energy production in Finland was 107,000 tons NO2 in 1987. Seventy-five percent of this amount originated in boilers larger than 1 MWfuel effect (input effect), and the rest in smaller boilers and industrial processes. The most important boiler classes from the NOX emission’s point of view were coal-fired boilers, with an emission of approximately 38,000 tons NO2, peat-fired boilers and boilers fired with a mixture of fuels, emitting approximately 12,000 tons NO2 each. By 2005, the total NOX emission from energy production would increase 50 percent to approximately 160,000 tons if left uncontrolled. The emission level would be 140,000 tons if primary reduction techniques are applied, and 110,000 tons NO2, if catalytic NOX reduction devices are installed in boilers larger than 300 MW. 相似文献