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461.
Virus retention and transport as influenced by different forms of soil organic matter 总被引:1,自引:0,他引:1
Organic materials are widespread in natural soil and aquatic environments. Their effect on virus transport is very important in assessing the risk for contamination of ground water by viruses. This study aimed to determine how different forms (mineral-associated and dissolved) of natural organic matter influence the retention and transport of two bacteriophages (MS-2 and phiX174) in two porous media (a sand and a soil). We found that mineral-associated organic matter significantly promoted the transport of one virus (MS-2) but not the other (phiX174) in a phosphate-buffered saline solution. Similarly, MS-2 was retained less in sand columns with increasing concentrations of dissolved humic acid, while little effect was observed for phiX174 under the same conditions. The two viruses have different surface properties and thus exhibited different reactivity to the metal oxides present on sand particles and were affected differently by organic matter. Because the organic matter used in the study was negatively charged and hydrophilic, blocking of virus sorption sites and increasing of virus-medium electrostatic repulsion arising from modification of the sand and virus surface by organic matter are probably responsible for the facilitated transport. For dissolved humic acid, its competition for sorption sites with viruses was an additional mechanism involved. This study suggests that the effect of organic matter varied depending on the organic material properties and the type of viruses involved. As a general trend, the effect of organic matter was dominated by electrostatic rather than hydrophobic interactions. 相似文献
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463.
在介绍工艺安全管理基本概念的基础上,以美国最大炼油商Valero McKee炼油厂的火灾爆炸事故为倒.分析T Valero McKee炼油厂所存在的工艺安全管理问题,进而阐述了做细做实工艺安全管理工作的要点. 相似文献
464.
石油行业的项目施工往往是作业面广,施工危险性大,交叉作业普遍,项目施工管理难度很大。在项目施工时应着重关注以下几方面。 相似文献
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466.
Evaluating Beijing’s human carrying capacity from the perspective of water resource constraints 总被引:2,自引:0,他引:2
As the demands on limited water resources intensify, concerns are being raised about the human carrying capacity of these resources. However, few researchers have studied the carrying capacity of regional water resources. Beijing, the second-largest city in China, faces a critical water shortage that will limit the city’s future development. We developed a method to quantify the carrying capacity of Beijing’s water resources by considering water-use structures based on the proportions of water used for agricultural, industrial, and domestic purposes. We defined a reference structure as 45:22:33 (% of total, respectively), an optimized structure as 40:20:40, and an ideal structure as 50:15:35. We also considered four domestic water quotas: 55, 75, 95, and 115 m 3 /(person·yr). The urban carrying capacity of 10–12 million was closest to Beijing’s actual 2003 population for all three water-use structures with urban domestic water use of 75 m 3 /(person·yr). However, after accounting for our underlying assumptions, the adjusted carrying capacity is closer to 5–6 million. Thus, Beijing’s population in 2003 was almost twice the adjusted carrying capacity. Based on this result, we discussed the ecological and environmental problems created by Beijing’s excessive population and propose measures to mitigate these problems. 相似文献
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468.
在制备聚硅酸盐类混凝剂的过程中,聚硅酸的粘度是影响聚硅酸盐类混凝剂混凝效能的重要因素。以水玻璃为原料,硫酸、盐酸为酸化剂,采用酸性条件下制备聚硅酸的方法,研究pH值、二氧化硅浓度、温度、不同酸化剂等因素对硅酸聚合过程中粘度变化的影响,结果表明:粘度达到0.006 Pa.S前变化缓慢,粘度达到0.009 Pa.S后变化迅速,0.020 Pa.S以后在极短的时间内粘度急剧增大而胶凝;通过混凝搅拌实验确定制备聚硅酸铝混凝剂时聚硅酸粘度的最佳值,以此最佳值作为控制聚硅酸最佳聚合程度的指标。 相似文献
469.
This study aimed to determine the effect of exposure to heavy metals in pregnant women in Beijing, China. We also evaluated the association of these heavy metals with birth weight and length of newborns. We measured the levels of 10 heavy metals,including lead(Pb), titanium(Ti), manganese(Mn), nickel(Ni), cadmium(Cd), chromium(Cr), antimony(Sb), stannum(Sn), vanadium(V), and arsenic(As), in 156 maternal and cord blood pairs. An inductively coupled plasma mass spectrometry method was used for measurement. Pb, As, Ti, Mn, and Sb showed high detection rates( 50%) in both maternal and cord blood. Fourteen(9%) mothers had blood Pb levels greater than the United States Center for Disease Control allowable threshold limit for children(50 μg/L).In prenatal exposure to these heavy metals, there was no significant association between any heavy metal and birth weight/length. Moreover, we estimated the placental transfer efficiency of each heavy metal, and the median placental transfer efficiency ranged from 49.6%(Ni) to 194%(Mn)(except for Cd and Sn). The level and detection rate of Cd in maternal blood were much higher than that in cord blood, which suggested that Cd had difficulty in passing the placental barrier. Prospective research should focus on the source and risk of heavy metals in non-occupationally exposed pregnant women in Beijing. 相似文献
470.
针对太湖水草压榨液高有机物浓度的特点,研究采用消化污泥与颗粒污泥的混合泥接种内循环厌氧反应器(IC)处理太湖水草压榨液。启动初期采取快速提升负荷至4 kg/(m3·d)并长期稳定在该负荷,这种启动方式有利于提高污泥的活性,加速污泥颗粒化。调试历时95 d,逐步提高进水负荷,研究发现IC的最大容积负荷可以达到18 kg/(m3·d),为了能够稳定运行IC反应器,降低容积负荷到15 kg/(m3·d),此时COD的去除率在85%以上。研究表明:运用压榨技术处理太湖水草为今后处理各类水草提供了更多的技术选择,使得处理太湖水草不用局限于固体废物领域,将水草进行压榨能够妥善处理打捞上来的太湖水草,实现水草的减量化。 相似文献