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91.
92.
Incorporating layer- and local-scale heterogeneities in numerical simulation of unsaturated flow and tracer transport 总被引:1,自引:0,他引:1
Feng Pan Ming Ye Jianting Zhu Yu-Shu Wu Bill X. Hu Zhongbo Yu 《Journal of contaminant hydrology》2009,103(3-4):194-205
This study characterizes layer- and local-scale heterogeneities in hydraulic parameters (i.e., matrix permeability and porosity) and investigates the relative effect of layer- and local-scale heterogeneities on the uncertainty assessment of unsaturated flow and tracer transport in the unsaturated zone of Yucca Mountain, USA. The layer-scale heterogeneity is specific to hydrogeologic layers with layerwise properties, while the local-scale heterogeneity refers to the spatial variation of hydraulic properties within a layer. A Monte Carlo method is used to estimate mean, variance, and 5th, and 95th percentiles for the quantities of interest (e.g., matrix saturation and normalized cumulative mass arrival). Model simulations of unsaturated flow are evaluated by comparing the simulated and observed matrix saturations. Local-scale heterogeneity is examined by comparing the results of this study with those of the previous study that only considers layer-scale heterogeneity. We find that local-scale heterogeneity significantly increases predictive uncertainty in the percolation fluxes and tracer plumes, whereas the mean predictions are only slightly affected by the local-scale heterogeneity. The mean travel time of the conservative and reactive tracers to the water table in the early stage increases significantly due to the local-scale heterogeneity, while the influence of local-scale heterogeneity on travel time gradually decreases over time. Layer-scale heterogeneity is more important than local-scale heterogeneity for simulating overall tracer travel time, suggesting that it would be more cost-effective to reduce the layer-scale parameter uncertainty in order to reduce predictive uncertainty in tracer transport. 相似文献
93.
微生物絮凝剂改善城市污水厂浓缩污泥脱水性能的研究 总被引:7,自引:2,他引:5
采用酱油曲霉(Aspergillus sojae)产生的微生物絮凝剂(MBF)作为污泥絮凝脱水剂,对城市污水处理厂浓缩污泥进行调理,确定该絮凝剂对浓缩污泥脱水的处理工艺参数为:微生物絮凝液最佳投加体积为6%~8%(体积比),发挥絮凝作用的最适污泥温度为28~32℃,最适pH为6~7。经微生物絮凝剂调理的污泥在3 000 r/min离心9 min,污泥脱水率高达82.7%,滤饼含水率降低至77.3%,污泥脱水后体积减至原来的1/5左右。 相似文献
94.
竹林土壤中甲基对硫磷降解菌的降解效果及其与土壤物理特性的关系 总被引:1,自引:0,他引:1
采用实验室控制试验研究了甲基对硫磷降解菌在竹林土壤生态系统中的降解效果及其与土壤物理特性的关系。试验结果表明,邻单胞菌(DLL-1)具有高效性,甲基对硫磷初始浓度为15 mg/kg干土,第5 d竹林土壤上、中和下层的降解率分别为88.6%、85.9%和79.2%,相应的半衰期为2.5、2.84与3.79 d。甲基对硫磷在土壤中的不同粒径范围吸附情况是不同的,从而影响DLL-1菌的降解效果,表现为土壤中粘粒含量与降解率呈显著正相关。孔隙度也是影响降解效果的一个因素,上中下3层的降解率随着孔隙度的减小而降低。 相似文献
95.
针对城市化进程加快引发的一系列环境污染问题,指出了加快污染防治设施社会化运营的必要性,并从污染治理设施的种类、污染治理设施的社会化运营分析和运作模式三方面论述了如何进行污染治理设施的社会化运营,从经济发展、污染防治设施运行、引入竞争机制等方面概述了污染防治设施社会化运营对区域环境与经济协调发展的影响。 相似文献
96.
Problem
To simplify the computation of the variance in before-after studies, it is generally assumed that the observed crash data for each entity (or observation) are Poisson distributed. Given the characteristics of this distribution, the observed value (xi) for each entity is implicitly made equal to its variance. However, the variance should be estimated using the conditional properties of this observed value (defined as a random variable), that is, f(xi|μi), since the mean of the observed value is in fact unknown.Method
Parametric and non-parametric bootstrap methods were investigated to evaluate the conditional assumption using simulated and observed data.Results
The results of this study show that observed data should not be used as a substitute for the variance, even if the entities are assumed to be Poisson distributed. Consequently, the estimated variance for the parameters under study in traditional before-after studies is likely to be underestimated.Conclusions
The proposed methods offer more accurate approaches for estimating the variance in before-after studies. 相似文献97.
98.
99.
Effect of the ecological water conveyance project on environment in the Lower Tarim River, Xinjiang, China 总被引:1,自引:0,他引:1
The dynamic response of groundwater level is examined in traverse and lengthways directions. Take the Yinsu section for an example, we have simulated groundwater levels before and after water-conveyance every time and calculated the incidence of groundwater on the both sides of the river. It is noted that the effect keeps growing with the water-delivery times increasing, from 570 m after the first times to 3,334 m after the eighth times. In addition, this paper involves the temporal response of the natural vegetation to water conveyance, vegetation coverage, planted-species number, dominant position and species diversity from 2002 to 2006. The findings indicate that the positive influence of ecological water conveyance project (EWCP) on the ecosystem in the Lower Tarim River is a long-term process. In this paper, we try to calculate water required for recovery of damaged ecosystem by using data available. This project is likely the base of research on water demand and the reference of measures for research on ecological water conveyance effect. 相似文献
100.
Evaluation of nitrification inhibitor 3,4-dimethyl pyrazole phosphate on nitrogen leaching in undisturbed soil columns 总被引:3,自引:0,他引:3
The application of nitrogen fertilizers leads to various ecological problems such as nitrate leaching. The use of nitrification inhibitors (NI) as nitrate leaching retardants is a proposal that has been suggested for inclusion in regulations in many countries. In this study, the efficacy of the new NI, 3,4-dimethyl pyrazole phosphate (DMPP), was tested under simulated high-risk leaching situations in two types of undisturbed soil columns. The results showed that the accumulative leaching losses of soil nitrate under treatment of urea with 1.0% DMPP, from columns of silt loam soil and heavy clay soil, were 66.8% and 69.5% lower than those soil columns tested with regular urea application within the 60 days observation, respectively. However, the losses of ammonium leaching were reversely increased 9.7% and 6.7% under the former treatment than the latter one. Application of regular urea with 1.0% DMPP addition can reduce about 59.3%-63.1% of total losses of inorganic nitrogen via leaching. The application of DMPP to urea had stimulated the inhibition effects of DMPP on the ammonium nitrification process in the soil up to 60 days. It is proposed that the DMPP could be used as an effective NI to control inorganic N leaching losses, minimizing the risk of nitrate pollution in shallow groundwater. 相似文献