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521.
Mark E. Hines 《Water, Air, & Soil Pollution: Focus》2006,6(5-6):523-536
Microorganisms are responsible for the bulk of transformations that occur in surficial sediments. They are most active at
redox boundaries where they can benefit from access to various oxidants and reductants generated during redox cycling events.
To illustrate the dynamics of microbially mediated processes, especially those involving sulfur and metal cycles, processes
were compared in habitats either bioturbated by a capitellid worm or inhabited by a salt marsh grass. The presence of macrofauna
and macroflora greatly altered the three-dimensional array of redox gradients in sediments, but the type and form of reductants
and oxidants provided varied greatly; clastic sedimentary infauna subducted solid phase organic material and iron oxides,
whereas plant roots released dissolved organic matter and oxygen. These differences resulted in a bioturbated system that
exhibited a rapid sulfur cycle (residence time of minutes), but a slower iron cycle (days), whereas vegetation caused a slow
sulfur cycle and rapid iron cycle. Alteration of sediments by higher life forms also greatly affected the composition and
relative abundances of sedimentary bacteria, even on short time scales. Although redox cycling at interfaces can be somewhat
predictable, variations in response to biological and physical perturbations demonstrated wide differences in the dynamics
of redox-mediated processes. 相似文献
522.
职业性有机溶剂中毒特点及防治对策探讨 总被引:3,自引:0,他引:3
随着有机溶剂应用的日益广泛,职业性有机溶剂中毒事件频繁发生。通过分析近年来的职业性有机溶剂中毒事故,探讨了职业性有机溶剂中毒的特点,并对如何有效预防职业性有机溶剂中毒提出了初步的建议,如可以通过改革工艺,加强通风排毒等措施来预防职业性有机溶剂中毒。 相似文献
523.
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525.
Electric power generating plants that use coal were among the key targets of Title IV of the 1990 Clean Air Act. Under the
first phase of the act, 110 coal-fired electric power plants were required to reduce their sulfur dioxide emissions by 1995
and nitrogen oxide emissions by 1996. Phase 2 of the act requires even greater reduction of sulfur dioxide emissions by 2000
and nitrogen oxide emissions by 2008. This study examines whether the 107 targeted plants (three plants went off-line) have
achieved the desired sulfur dioxide and nitrogen oxide emission levels.
The analysis of sulfur dioxide is based on data from 1990, 1995, and 1999. The findings show that although sulfur oxide increased
by 3% from 1995 to 1999, it decreased by 45% over the 1990–1999 period at the firm level for the targeted firms. The findings
also indicate that the overall reduction in sulfur dioxide was achieved by utilizing low sulfur coal and by purchasing emission
allowances. So far as nitrogen oxides are concerned, there has been a reduction of 14% over the 1990–1999 period, of which
7% was achieved during the 1995–1999 period. An evaluation of emissions at the plant level indicates that several plants do
not meet the emissions level for sulfur dioxide or nitrogen oxides.
These results provide a mixed scorecard for reduction in emissions both for sulfur dioxide and nitrogen oxides. Even though
there is reduction in the emissions on an overall basis at the firm level, several plants that have not been able to reduce
emissions deserve special attention to meet the goals of the act in reducing emissions. 相似文献
526.
527.
火电项目环境影响评价中污染控制水平分析 总被引:4,自引:0,他引:4
针对国家投资体制改革后我国火电迅猛发展的现象,以内蒙古地区作为研究对象,从2004年内蒙古地区拟建的36个火电项目的环境影响报告书中取得有关资料,分析了这些项目的环境影响控制情况,并对内蒙古地区火电发展的区域环境影响进行讨论.结果表明:即使内蒙古地区拟建项目全部建成投产,在火电装机容量增加33.68×106 kW的情况下,SO2排放量仅增加0.8×104 t/a;通过对城市中水、矿井疏干水的使用,节约新鲜水用量超过1×108 t/a,环境影响评价中对火电项目的SO2总量控制和节约用水控制效果较好.但是内蒙古地区拟建电厂区域累积用水总量很大,将加剧该地区水资源不足问题,而内蒙古地区作为我国能源输出地,需寻求可持续发展道路.建议加快开展规划环境影响评价,并考虑循环经济发展模式. 相似文献
528.
在Ru/Al2O3催化剂上用H2对SO2选择性催化还原的研究 总被引:2,自引:0,他引:2
本文对用H2来使SO2选择性催化还原为单质硫在Ru/Al2O3催化剂上的行为进行研究.当物料比经过优化确定为SO2/H2=12.8时,在500℃下,SO2的转化率为90%以上,单质硫的产率为70%左右.比较于其他的催化还原SO2的催化剂,本催化剂采用金属而不是金属硫化物,这样既省去了催化剂预硫化的过程,同时也使在有氧条件下的选择性催化还原成为可能.实验考察了O2及水蒸气存在对过程的影响.在实验过程中发现,H2S作为中间产物生成,可推论该过程在催化剂上分两步进行SO2首先在催化剂金属上被H2深度还原为H2S,然后在Al2O3载体的酸性中心上SO2与H2S发生Claus反应产生单质硫. 相似文献
529.
530.
Rattigan O. V. Dutkiewicz Vincent A. Das Mita Judd C. D. Husain Liaquat 《Water, Air, & Soil Pollution: Focus》2001,1(5-6):391-400
In-cloud oxidation of SO2 byH2O2 was investigated using a tracertechnique based on SO2–
4/Se ratios atWhiteface Mountain, New York during summer months from1990 to 1998. Cloud water samples collected at themountain's summit (1.5 km above mean sea level) andaerosols at a below cloud site (Lodge) located at 0.6km amsl and in cloud interstitial air at the summitwere analyzed for SO2–
4 and selectedtrace elements. Gaseous SO2 andH2O2were measured in realtime. Cloud water pH wasgenerally below 5.0 with a mean value of 3.6. Theresults show that significant in cloud oxidation occursin clouds during summer months varying from belowdetection to 62% with on average approximately 24% ofthe cloud water SO2–
4 produced from in-situ SO2 oxidation. During summer the clouds wereoxidant limited for approximately one third of thetime. 相似文献