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排序方式: 共有1712条查询结果,搜索用时 343 毫秒
931.
932.
序批式人工湿地冬季低温脱氮的效能研究 总被引:6,自引:2,他引:4
针对目前连续流人工湿地脱氮效率低、易堵塞及冬季效能下降的问题,提出了采用新型间歇流序批式人工湿地处理小城镇污水的方案,研究探讨了两级序批式人工湿地在冬季低温条件下,停留时间及排空闲置时间对脱氮效能的影响.试验结果表明,在冬季低温5~10 ℃、每级序批式湿地运行工况为瞬时进水-反应24h-瞬时排水-排空闲置12h、氮负荷为1.92g·m-2·d-1、进水COD、NH 4-N和TN浓度分别为143mg·L-1、27.0mg·L-1和32.0mg·L-1时,出水COD、NH4 -N和TN浓度分别为27mg·L-1、3.9mg·L-1和16.5mg·L-1,COD、NH4 -N和TN的去除率分别为81.12%、85.56%和48.44%. 相似文献
933.
934.
粪大肠菌群快速测定——纸片法的应用 总被引:1,自引:0,他引:1
赵凌宇 《环境监测管理与技术》2007,19(4):18-20
采集苏州具有代表性的地表水水体22个点位的样品,进行粪大肠菌群的测定方法比较,结果表明,《粪大肠菌群快速测定--纸片法》适于测定受粪便污染程度较轻的湖泊水体.但是,该方法的培养时间对阳性管率有明显影响,认为16 h~18 h是比较理想的培养时间. 相似文献
935.
936.
Two species of butterflies, Euphydryas aurinia and Melitaea phoebe, coexist as two metapopulations in a 38-patch network in Hebei Province, China. A Markovian model, whose transition matrix is the product of two matrices which represent the local extinction and recolonization process respectively, is used to describe the metapopulation dynamics. The application of this model to the metapopulation, consisting of 12 local populations in the northern subregion, shows that the expected life times of E. aurinia and M. phoebe are 160 and 121 years respectively and usually nearly half of the patches are occupied by E. aurinia, while only 1–3 patches are occupied by M. phoebe. We claim that E. aurinia can persist for a long time while M. phoebe faces relatively big extinction risk. By comparing the population dynamics with and without migration, we find M. phoebe benefits much more from migration than E. aurinia. Most patches are occupied mainly by local populations for E. aurinia, while by immigrants from the 8th patch for M. phoebe, meaning that E. aurinia has a classical metapopulation structure while M. phoebe has a source–sink metapopulation structure. 相似文献
937.
Many environmental problems are linked to multiphase flows encompassing ecological issues, chemical processes and mixing or
diffusion, with applications in different engineering fields. The transition from a supercritical flow to a subcritical motion
constitutes a hydraulic jump. This flow regime is characterised by strong interactions between turbulence, free surface and
air–water mixing. Although a hydraulic jump contributes to some dissipation of the flow kinetic energy, it is also associated
with increases of turbulent shear stresses and the development of turbulent eddies with implications in terms of scour, erosion
and sediment transport. Despite a number of experimental, theoretical and numerical studies, there is a lack of knowledge
concerning the physical mechanisms involved in the diffusion and air–water mixing processes within hydraulic jumps, as well
as on the interaction between the free-surface and turbulence. New experimental investigations were undertaken in hydraulic
jumps with Froude numbers up to Fr = 8.3. Two-phase flow measurements were performed with phase-detection conductivity probes.
Basic results related to the distributions of void fraction, bubble frequency and mean bubble chord length are presented.
New developments are discussed for the interfacial bubble velocities and their fluctuations, characterizing the turbulence
level and integral time scales of turbulence representing a “lifetime” of the longitudinal bubbly flow structures. The analyses
show good agreement with previous studies in terms of the vertical profiles of void fraction, bubble frequency and mean bubble
chord length. The dimensionless distributions of interfacial velocities compared favourably with wall-jet equations. Measurements
showed high turbulence levels. Turbulence time scales were found to be dependent on the distance downstream of the toe as
well as on the distance to the bottom showing the importance of the lower (channel bed) and upper (free surface) boundary
conditions on the turbulence structure. 相似文献
938.
S. Rocky Durrans Steven J. Burian Stephan J. Nix Ahmed Hajji Robert E. Pitt Chi-Yuan Fan Richard Field 《Journal of the American Water Resources Association》1999,35(5):1213-1221
Hydrologic modeling of urban watersheds for designs and analyses of stormwater conveyance facilities can be performed in either an event-based or continuous fashion. Continuou simulation requires, among other things, the use of a time series of rainfall amounts. However, for urban drainage basins, which are typically small, the temporal resolution of the rainfall time series must be quite fine, and often on the order of 5 to 15 minutes. This poses a significant challenge because rainfall-gauging records are usually kept only for hourly or longer time steps. The time step sizes in stochastic rainfall generators are usually also too large for application to urban runoff modeling situations. Thus, there is a need for methods by which hourly rainfall amounts can be disaggregated to shorter time intervals. This paper presents and compares a number of approaches to this problem, which are based on the use of polynomial approximating functions. Results of these evaluations indicate that a desegregation method presented by Ormsbee (1989) is a relatively good performer when storm durations are short (2 hours), and that a quadratic spline-based approach is a good choice for longer-duration storms. Based on these results, the Ormsbee technique is recommended because it provides good performance, and can be applied easily to long time series of precipitation records. The quadratic spline-based approach is recommended as a close second choice because it performed the best most consistently, but remains more difficult to apply than the Ormsbee technique. Results of this study also indicate that, on average, all of the disaggregation methods evaluated introduce a severe negative bias into maximum rainfall intensities. This is cause for some well-justified concern, as the characteristics of runoff hydrographs are quite sensitive to maximum storm intensities. Thus, there is a need to continue the search for simple yet effective hourly rainfall disaggregation methods. 相似文献
939.
940.
Feng Zhao Xu Zhan Hai Xu Guangwei Zhu Wei Zou Mengyuan Zhu Lijuan Kang Yulong Guo Xingchen Zhao Zicong Wang Wei Tang 《环境科学学报(英文版)》2022,34(1):229-239
Eutrophication and harmful cyanobacterial blooms threaten water resources all over the world. There is a great controversy about controlling only phosphorus or controlling both nitrogen and phosphorus in the management of lake eutrophication. The primary argument against the dual nutrients control of eutrophication is that nitrogen fixation can compensate the nitrogen deficits. Thus, it is of great necessary to study the factors that can significantly affect the nitrogen fixation. Due to the dif... 相似文献