Enhancement of In Situ Bioremediation of BTEX-Contaminated Ground Water by Oxygen Diffusion from Silicone Tubing   总被引：1，自引：0，他引：1  

Thomas L. Gibson  Abdul S. Abdul  Paul D. Chalmer 《Ground Water Monitoring & Remediation》1998,18(1):93-104

A field study of oxygen-enhanced biodegradation was carried out in a sandy iron-rich ground water system contaminated with gasoline hydrocarbons. Prior to the oxygen study, intrinsic microbial biodegradation in the contaminant plume had depleted dissolved oxygen and created anaerobic conditions. An oxygen diffusion system made of silicone polymer tubing was installed in an injection well within an oxygen delivery zone containing coarse highly permeable sand. During the study, this system delivered high dissolved oxygen (DO) levels (39 mg/L) to the ground water within a part of the plume. The ground water was sampled at a series of monitors in the test zone downgradient of the delivery well to determine the effect of oxygen on dissolved BTEX, ground water geochemistry, and microbially mediated biodegradation processes. The DO levels and Eh increased markedly at distances up to 2.3 m (7.5 feet) downgradient. Potential biofouling and iron precipitation effects did not clog the well screens or porous medium. The increased dissolved oxygen enhanced the population of aerobes while the activity of anaerobic sulfate-reducing bacteria and methanogens decreased. Based on concentration changes, the estimated total rate of BTEX biodegradation rose from 872 mg/day before enhancement to 2530 mg/day after 60 days of oxygen delivery. Increased oxygen flux to the test area could account for aerobic biodegradation of 1835 mg/day of the BTEX. The estimated rates of anaerobic biodegradation processes decreased based on the flux of sulfate, iron (II), and methane. Two contaminants in the plume, benzene and ethylbenzene, are not biodegraded as readily as toluene or xylenes under anaerobic conditions. Following oxygen enhancement, however, the benzene and ethylbenzene concentrations decreased about 98%, as did toluene and total xylenes.  相似文献   

Titanomagnetites prepared at different oxidation conditions: Hysteresis properties     

A.A. Rahman  L.G. Parry 《Physics of the Earth and Planetary Interiors》1978,16(3):232-239

Atmospheres of different oxidation potentials were used to equilibriate samples at 1300°C starting with a stoichiometric composition xFe₂TiO₄·(1 ? x) Fe₃O₄ where x = 0.3 and 0.6. Samples were selected which appeared homogeneous in polished section and gave only spinel-type X-ray reflections. All specimens were found to have small amounts of included material of higher Curie point than the bulk material. Specimens were made by dispersing grains of known size in a non-magnetic matrix and the hysteresis properties were measured for these speciméns.  相似文献   

Self shielding of inclusions in titanomagnetite grains     

A.A. Rahman  L.G. Parry 《Physics of the Earth and Planetary Interiors》1975,11(2):139-146

Grains from a natural titanomagnetite are found to contain fine ex-solved regions with a higher Curie point than the host oxide. Experimental results are given, in which tests have been made of the influence of the magnetization of the ex-solution regions on the overall magnetization of specimens which contain a dispersion of the titanomagnetite grains in an inert matrix. The results are compared with those predicted by Stephenson for a model of similar properties.  相似文献   

Arsenic release from biotite into a Holocene groundwater aquifer in Bangladesh   总被引：1，自引：0，他引：1  

Ashraf Ali Seddique  Harue Masuda  Muneki Mitamura  Keiji Shinoda  Toshiro Yamanaka  Takaaki Itai  Teruyuki Maruoka  Kenji Uesugi  Kazi Matin Ahmed  Dipak Kumar Biswas 《Applied Geochemistry》2008,23(8):2236-2248

Continuous core sediments (to a depth of 90.1 m) taken at a transitional area of Holocene and Pleistocene deposits in Sonargaon, Bangladesh were characterized for their mineralogy and chemistry. Among the sediments of the lower part of the Holocene aquifer (depth: 18–29 m), where most domestic wells are installed, As is mostly fixed in biotite and organic phases. A positive correlation of As concentration with those of Al and Fe but not that of total organic C clearly suggests that biotite is a primary source of As. Although microbial reduction–dissolution of As-containing Fe oxyhydroxides is thought to cause As-enriched groundwater in the Ganges–Brahmaputra–Meghna delta plain, the authors conclude that chemical weathering of biotite is the primary formation mechanism and prevailing reducing conditions contribute to the expansion of As-enriched groundwater in the study area.  相似文献   

Holocene stratigraphy-of the Lower Ganges-Brahmaputra River delta in Bangladesh     

Sirajur Rahman KHAN  Md Badrul ISLAM 《Frontiers of Earth Science》2008,2(4):393-399

Major part of the Holocene Ganges-Brahmaputra delta occupies the southern and southwestern part of Bangladesh with a smaller part extending beyond the international boundary in the west. Five facies assemblages are documented in the lower deltaic plain in five different depositional environments: levee or levee complex, bil or depression, abandoned meander belt, interdistributary plain and estuarine plain. The thickness of the Holocene sediments ranges from 30 m to 70 m in the deltaic plain, usually floored by the Pleistocene stiff clays, with the exception of the abandoned meander belt deposit where Holocene channel sand deposited directly on the Pleistocene sand. Radiocarbon dates indicate that low-rate sedimentation has occurred in the northern part, where 4-6 m thick sediments were deposited since the mid-Holocene, whereas 10-30 mthick sediments were deposited in the southern part during the same span of time. In addition, significant coastal subsidence (3 mm/a on average), added by sea-level rise (1.5 mm/a, conservative rate) occurs in the study area, which serves as a negative factor in degrading the coastal plain of Bangladesh in the future, while taking into consideration the weaker sedimentation in the area.  相似文献   

Multicriteria decision analysis in water resources management: the malnichara channel improvement   总被引：2，自引：2，他引：0  

R. K. Chowdhury  R. Rahman 《International Journal of Environmental Science and Technology》2008,5(2):195-204

Multicriteria decision analysis tool is used in many water resources and environmental management projects. The Malnichara is one of the natural channels in Sylhet city (Bangladesh) responsible for storm runoff conveyance to the downstream Surma river. The channel is found to be encroached at many locations of the city and found to be very vulnerable. The authority has taken decision to improve natural channels by a traditional approach, e.g. constructing box culvert. In most cases, stakeholders’ participation is ignored in such type of decision making. Hence, efforts were made to evaluate three common alternatives viz. sodding natural channel, lined natural channel and box culvert for the channel improvement. The channel is hydrologically divided into two parts: the upper portion (Choukidekhi-Kanishail) and the lower portion (Kanishail-Topoban). Both parts were separately analyzed. Small groups of stakeholders were interviewed for the selection of criteria and for the assignment of weighed factor and scores. Experts’ opinions were also taken through consultation. Nine criteria from four categories such as technical, economic, environment and social aspects were selected. The relative performances of alternatives were evaluated using the weighed sum technique of multicriteria decision analysis. It was found that the sodding natural channel is the best alternative for both portions of the channel. However, the choice is very sensitive to the social criteria.  相似文献   

Kinetics and Thermodynamic Studies of Oxytetracycline Mineralization Using UV/H2O2          下载免费PDF全文

Anisa Ur Rahmah  Sabtanti Harimurti  Abdul Aziz Omar  Thanapalan Murugesan 《洁净——土壤、空气、水》2015,43(4):496-503

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Large-Scale Present-Day Plate Boundary Deformations in the Eastern Hemisphere Determined from VLBI Data: Implications for Plate Tectonics and Indian Ocean Growth     

A. Akilan  K. K. Abdul Azeez  H. Schuh  N. Yuvraaj 《Pure and Applied Geophysics》2015,172(10):2643-2655

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Analyses of the impact of climate change on water resources components,drought and wheat yield in semiarid regions: Karkheh River Basin in Iran   总被引：2，自引：0，他引：2       下载免费PDF全文

S. Ashraf Vaghefi  S. J. Mousavi  K. C. Abbaspour  R. Srinivasan  H. Yang 《水文研究》2014,28(4):2018-2032

Water resources availability in the semiarid regions of Iran has experienced severe reduction because of increasing water use and lengthening of dry periods. To better manage this resource, we investigated the impact of climate change on water resources and wheat yield in the Karkheh River Basin (KRB) in the semiarid region of Iran. Future climate scenarios for 2020–2040 were generated from the Canadian Global Coupled Model for scenarios A1B, B1 and A2. We constructed a hydrological model of KRB using the Soil and Water Assessment Tool to project water resources availability. Blue and green water components were modeled with uncertainty ranges for both historic and future data. The Sequential Uncertainty Fitting Version 2 was used with parallel processing option to calibrate the model based on river discharge and wheat yield. Furthermore, a newly developed program called critical continuous day calculator was used to determine the frequency and length of critical periods for precipitation, maximum temperature and soil moisture. We found that in the northern part of KRB, freshwater availability will increase from 1716 to 2670 m³/capita/year despite an increase of 28% in the population in 2025 in the B1 scenario. In the southern part, where much of the agricultural lands are located, the freshwater availability will on the average decrease by 44%. The long‐term average irrigated wheat yield, however, will increase in the south by 1.2%–21% in different subbasins; but for rain‐fed wheat, this variation is from ?4% to 38%. The results of critical continuous day calculator showed an increase of up to 25% in both frequency and length of dry periods in south Karkheh, whereas increasing flood events could be expected in the northern and western parts of the region. In general, there is variability in the impact of climate change in the region where some areas will experience net negative whereas other areas will experience a net positive impact. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Application of artificial neural networks in regional flood frequency analysis: a case study for Australia   总被引：4，自引：3，他引：1  

K. Aziz  A. Rahman  G. Fang  S. Shrestha 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(3):541-554

Regional flood frequency analysis (RFFA) is widely used in practice to estimate flood quantiles in ungauged catchments. Most commonly adopted RFFA methods such as quantile regression technique (QRT) assume a log-linear relationship between the dependent and a set of predictor variables. As non-linear models and universal approximators, artificial neural networks (ANN) have been widely adopted in rainfall runoff modeling and hydrologic forecasting, but there have been relatively few studies involving the application of ANN to RFFA for estimating flood quantiles in ungauged catchments. This paper thus focuses on the development and testing of an ANN-based RFFA model using an extensive Australian database consisting of 452 gauged catchments. Based on an independent testing, it has been found that ANN-based RFFA model with only two predictor variables can provide flood quantile estimates that are more accurate than the traditional QRT. Seven different regions have been compared with the ANN-based RFFA model and it has been shown that when the data from all the eastern Australian states are combined together to form a single region, the ANN presents the best performing RFFA model. This indicates that a relatively larger dataset is better suited for successful training and testing of the ANN-based RFFA models.  相似文献