The enrichment and removal of arsenic (III) from water samples using HFSLM     

《Physics and Chemistry of the Earth》2012

At specific concentrations oxyanions such as arsenic pose a major threat to human beings and to the environment because of their ability to biomagnify. The World Health Organization has set the drinking water standard at 10 μg l⁻¹ for arsenic. It is in this regard that novel and cheaper methods to detect oxyanions and remove them from the environment are developed. In this work, we have developed sample preparation methods involving solid phase and liquid membrane for the extraction and enrichment of these oxyanions in aqueous environments. Various parameters which govern their optimal extraction and enrichment have been optimised. The manipulation of the liquid membrane extraction process was utilised to selectively extract arsenic (III) which is more toxic as compared to arsenic (V). The liquid membrane consisted of a combination of two organic solvents, and n-undecane and di-n-hexyl ether were used in a combination at various ratios of the two liquid membranes. The means of detection was by graphite furnace atomic absorption spectroscopy (GFAAS) as well as inductively coupled plasma optical emission spectroscopy (ICP-OES). The applicability of the method was tested in real wastewater samples where it was able to remove at least 50% of As (III) with enrichment factors of up to 20.  相似文献   

祁连山不同海拔氮磷循环细菌数量变化特征   总被引：2，自引：0，他引：2  

台喜生  杨秀丽  刘光琇  薛林贵  张勇  陈拓  张威  伍修锟  毛文梁 《冰川冻土》2014,36(1):214-221

祁连山植被的水源涵养作用对于维持黑河的流量至关重要,地下微生物参与生态系统的物质和能量循环,维持了地上植被的稳定,因而具有重要的生态作用. 研究分析了祁连山冰沟流域不同海拔梯度上硝化细菌、反硝化细菌、固氮细菌、解磷细菌和植酸矿化细菌的数量随土壤深度的变化规律. 结果表明：随土壤深度的增加,氮磷循环细菌的数量下降;随海拔升高,硝化细菌相对减少,而反硝化细菌和固氮细菌呈增多的趋势. 典范对应分析（CCA）显示,硝化细菌的数量变化主要受地下生物量和土壤pH值的影响,而反硝化细菌、固氮细菌、解磷细菌和植酸矿化细菌主要受植被盖度、地上生物量和土壤含水量的影响. 聚类分析表明,低海拔（E1-2 905 m和E2-3 128 m）浅层土壤（0~40 cm）聚类,而其深层土壤（60 cm）与高海拔（E3-4 130 m）土壤聚类,说明高海拔处土壤发育与低海拔处深层土壤的早期发育相类似. 研究表明,高山地区氮磷循环细菌数量的变化受到海拔主导下植被和土壤理化因子的共同作用.  相似文献   

Seasonal variation of fluxes and distributions of dissolved methane in the North Yellow Sea     

Jing Yang  Gui-Ling Zhang  Li-Xiao Zheng  Feng Zhang  Jing Zhao 《Continental Shelf Research》2010

The concentrations and sea-to-air fluxes of dissolved methane (CH₄) were investigated in the North Yellow Sea during August 2006, January, April and October 2007. Dissolved CH₄ concentrations showed obvious seasonal variation, with maximum values occurring in summer and lowest values occurring in winter. The saturations of dissolved CH₄ in surface waters ranged from 78.7% to 1679.7% with an average of 252.4%. The estimated atmospheric CH₄ fluxes using the Liss and Merlivat (LM86), and Wanninkhof formulae (W92) were (4.2±4.7), (11.6±10.3), (8.5±12.7) and (0.2±1.0), and (6.9±7.3), (14.6±22.3), (13.8±14.3) and (0.4±1.7) μmol·(m² d)⁻¹, respectively, for spring, summer, autumn and winter. Based on the average annual atmospheric CH₄ flux and the area of the North Yellow Sea, the annual CH₄ emission was estimated to be (2.4×10⁻²–4.2×10⁻²) Tg a⁻¹, which suggests that the North Yellow Sea was a net source of atmospheric CH₄.  相似文献   

Data assimilation for unsaturated flow models with restart adaptive probabilistic collocation based Kalman filter     

《Advances in water resources》2016

The ensemble Kalman filter (EnKF) has gained popularity in hydrological data assimilation problems. As a Monte Carlo based method, a sufficiently large ensemble size is usually required to guarantee the accuracy. As an alternative approach, the probabilistic collocation based Kalman filter (PCKF) employs the polynomial chaos expansion (PCE) to represent and propagate the uncertainties in parameters and states. However, PCKF suffers from the so-called “curse of dimensionality”. Its computational cost increases drastically with the increasing number of parameters and system nonlinearity. Furthermore, PCKF may fail to provide accurate estimations due to the joint updating scheme for strongly nonlinear models. Motivated by recent developments in uncertainty quantification and EnKF, we propose a restart adaptive probabilistic collocation based Kalman filter (RAPCKF) for data assimilation in unsaturated flow problems. During the implementation of RAPCKF, the important parameters are identified and active PCE basis functions are adaptively selected at each assimilation step; the “restart” scheme is utilized to eliminate the inconsistency between updated model parameters and states variables. The performance of RAPCKF is systematically tested with numerical cases of unsaturated flow models. It is shown that the adaptive approach and restart scheme can significantly improve the performance of PCKF. Moreover, RAPCKF has been demonstrated to be more efficient than EnKF with the same computational cost.  相似文献   

Micro-computed tomography pore-scale study of flow in porous media: Effect of voxel resolution     

《Advances in water resources》2016

A fundamental understanding of flow in porous media at the pore-scale is necessary to be able to upscale average displacement processes from core to reservoir scale. The study of fluid flow in porous media at the pore-scale consists of two key procedures: Imaging - reconstruction of three-dimensional (3D) pore space images; and modelling such as with single and two-phase flow simulations with Lattice-Boltzmann (LB) or Pore-Network (PN) Modelling. Here we analyse pore-scale results to predict petrophysical properties such as porosity, single-phase permeability and multi-phase properties at different length scales. The fundamental issue is to understand the image resolution dependency of transport properties, in order to up-scale the flow physics from pore to core scale. In this work, we use a high resolution micro-computed tomography (micro-CT) scanner to image and reconstruct three dimensional pore-scale images of five sandstones (Bentheimer, Berea, Clashach, Doddington and Stainton) and five complex carbonates (Ketton, Estaillades, Middle Eastern sample 3, Middle Eastern sample 5 and Indiana Limestone 1) at four different voxel resolutions (4.4 µm, 6.2 µm, 8.3 µm and 10.2 µm), scanning the same physical field of view. Implementing three phase segmentation (macro-pore phase, intermediate phase and grain phase) on pore-scale images helps to understand the importance of connected macro-porosity in the fluid flow for the samples studied. We then compute the petrophysical properties for all the samples using PN and LB simulations in order to study the influence of voxel resolution on petrophysical properties. We then introduce a numerical coarsening scheme which is used to coarsen a high voxel resolution image (4.4 µm) to lower resolutions (6.2 µm, 8.3 µm and 10.2 µm) and study the impact of coarsening data on macroscopic and multi-phase properties. Numerical coarsening of high resolution data is found to be superior to using a lower resolution scan because it avoids the problem of partial volume effects and reduces the scaling effect by preserving the pore-space properties influencing the transport properties. This is evidently compared in this study by predicting several pore network properties such as number of pores and throats, average pore and throat radius and coordination number for both scan based analysis and numerical coarsened data.  相似文献   

Oil refinery wastewater treatment using coupled electrocoagulation and fixed film biological processes     

《Physics and Chemistry of the Earth》2016

Oil refinery wastewater was treated using a coupled treatment process including electrocoagulation (EC) and a fixed film aerobic bioreactor. Different variables were tested to identify the best conditions using this procedure. After EC, the effluent was treated in an aerobic biofilter. EC was capable to remove over 88% of the overall chemical oxygen demand (COD) in the wastewater under the best working conditions (6.5 V, 0.1 M NaCl, 4 electrodes without initial pH adjustment) with total petroleum hydrocarbon (TPH) removal slightly higher than 80%. Aluminum release from the electrodes to the wastewater was found an important factor for the EC efficiency and closely related with several operational factors. Application of EC allowed to increase the biodegradability of the sample from 0.015, rated as non-biodegradable, up to 0.5 widely considered as biodegradable. The effluent was further treated using an aerobic biofilter inoculated with a bacterial consortium including gram positive and gram negative strains and tested for COD and TPH removal from the EC treated effluent during 30 days. Cell count showed the typical bacteria growth starting at day three and increasing up to a maximum after eight days. After day eight, cell growth showed a plateau which agreed with the highest decrease on contaminant concentration. Final TPHs concentration was found about 600 mgL⁻¹ after 30 days whereas COD concentration after biological treatment was as low as 933 mgL⁻¹. The coupled EC-aerobic biofilter was capable to remove up to 98% of the total TPH amount and over 95% of the COD load in the oil refinery wastewater.  相似文献   

Temporal and spatial variations in nutrient stoichiometry and regulation of phytoplankton biomass in Hong Kong waters: Influence of the Pearl River outflow and sewage inputs     

《Marine pollution bulletin》2009,58(6-12):335-348

In 2001, the Hong Kong government implemented the Harbor Area Treatment Scheme (HATS) under which 70% of the sewage that had been formerly discharged into Victoria Harbor is now collected and sent to Stonecutters Island Sewage Works where it receives chemically enhanced primary treatment (CEPT), and is then discharged into waters west of the Harbor. The relocation of the sewage discharge will possibly change the nutrient dynamics and phytoplankton biomass in this area. Therefore, there is a need to examine the factors that regulate phytoplankton growth in Hong Kong waters in order to understand future impacts. Based on a historic nutrient data set (1986–2001), a comparison of ambient nutrient ratios with the Redfield ratio (N:P:Si = 16:1:16) showed clear spatial variations in the factors that regulate phytoplankton biomass along a west (estuary) to east (coastal/oceanic) transect through Hong Kong waters. Algal biomass was constrained by a combination of low light conditions, a rapid change in salinity, and strong turbulent mixing in western waters throughout the year. Potential stoichiometric Si limitation (up to 94% of the cases in winter) occurred in Victoria Harbor due to the contribution of sewage effluent with high N and P enrichment all year, except for summer when the frequency of stoichiometric Si limitation (48%) was the same as P, owing to the influence of the high Si in the Pearl River discharge. In the eastern waters, potential N limitation and N and P co-limitation occurred in autumn and winter respectively, because of the dominance of coastal/oceanic water with low nutrients and low N:P ratios. In contrast, potential Si limitation occurred in spring and a switch to potential N, P and Si limitation occurred in eastern waters in summer. In southern waters, there was a shift from P limitation (80%) in summer due to the influence of the N-rich Pearl River discharge, to N limitation (68%) in autumn, and to N and P co-limitation in winter due to the dominance of N-poor oceanic water from the oligotrophic South China Sea. Our results show clear temporal and spatial variations in the nutrient stoichiometry which indicates potential regulation of phytoplankton biomass in HK waters due to the combination of the seasonal exchange of the Pearl River discharge and oceanic water, sewage effluent inputs, and strong hydrodynamic mixing from SW monsoon winds in summer and the NE monsoon winds in winter.  相似文献   

Implications of mycosporine-like amino acid and antioxidant defenses in UV-B radiation tolerance for the algae species Ptercladiella capillacea and Gelidium amansii     

Tse-Min Lee  Chia-Tai Shiu 《Marine environmental research》2009,67(1):8-16

Ultraviolet-B (UV-B) radiation (0.5, 1.0, 1.5, and 3.0 W m^?2) induced higher H₂O₂ production and lipid peroxidation in alga Gelidium amansii inhabiting in lower subtidal regions than upper subtidal alga Ptercladiella capillacea. Compared to G. amansii, mycosporine-like amino acid (MAA) concentration in P. capillacea was higher and can be increased by 0.5–1.0 W m^?2 UV-B, while carotenoid concentration was lower but also increased by 1.5–3.0 W m^?2 UV-B. UV-B increased ascorbate concentration, but to a higher degree in P. capillacea. UV-B decreased glutathione concentration, but to a higher degree in G. amansii. UV-B increased ascorbate peroxidase (APX) and glutathione reductase (GR) activities in P. capillacea but decreased them in G. amansii. UV-B increased superoxide dismutase and catalase activities, but to a higher degree in G. amansii. So, G. amansii suffered greater oxidative stress from UV-B radiation. P. capillacea can effectively reduce UV-B sensitivity by increasing sunscreen ability and antioxidant defense capacity.  相似文献   

Triaxial induction tool with electrode sleeve: FD modeling in 3D geometries     

Sofia Davydycheva  Dean Homan  Gerald Minerbo 《Journal of Applied Geophysics》2009,67(1):98-108

We have developed a finite-difference (FD) method to model the response of a multiple-spacing triaxial array induction tool with a multiple-electrode type sleeve. The FD software was verified versus two other independent modeling methods. The model response was checked for the FD grid refinement, while attempting to minimize run time. Many details of the electrode-sleeve geometry were studied using this method that led to the final electrode-sleeve design. The electrode sleeve reduces the response of the transverse couplings to eccentering in a conductive borehole. Quantitative agreement was found between the measurements and calculations. Using the FD software we study the tool response to various effects of 3D geometry.  相似文献   

Casualties and loss of life in bulk carriers from 1980 to 2010     

《Marine Policy》2013

Bulk carriers have been linked with high risks of structural failure and foundering, and with heavy loss of human life. This study used Lloyd's casualty records to investigate the extent to which dry bulk shipping has become safer over the last 30 years, and to identify shipping factors associated with the risks of bulk carriers' foundering and crew fatalities in recent years. Although there have been reductions over time in bulk carrier casualties and crew fatalities since the early 1980s, with an interim peak during the early and mid 1990s, there have been increases since 2005, linked partly to several bulk carriers that foundered when carrying nickel ore. Of 11 shipping factors considered, the strongest independent predictors of foundering and crew fatalities in recent years were the flag state, the cargo, the location of the casualty, weather conditions and the gross tonnage. Over the study period, elevated casualty and crew fatality rates were linked strongly with newly emerging or expanding flags.  相似文献