Laboratory visualization experiments in fine- to very fine-grained sands (grain diameter <0.21 mm) reveal a previously unrecognized
air-flow geometry. This air-flow geometry is termed "chamber flow" and is characterized by: (1) a significant horizontal component,
(2) pervasive air-flow coverage within a region demarcated by a distinct, irregular boundary, and (3) the presence of predominantly
vertical inlet and outlet channels. The attributes of chamber flow differ significantly from channelized flow and pervasive/bubbly
flow, which occur at larger grain sizes and have been described in the literature by several researchers. Previous research,
which indicates a dramatic increase in contaminant removal time in sediments <0.2 mm, indirectly corroborates the phenomena
observed in this study. The extent of sediment column affected by chamber flow of sparge air ranges from 4–54% on an area
basis, and is approximately 28% on a volume basis. These values indicate that chamber air flow has the potential to affect
a much larger percentage of the sediment column than either channelized or pervasive/bubbly flow. Because of the irregularity
of air-flow chambers, in terms of both form and frequency, a detailed knowledge of stratigraphy is important to maximize air-sparging
efficiency at sites where chamber flow is likely to occur.
Electronic Publication 相似文献
Extracting aqueous solutions with or without additives are employed to solubilize contaminants in soil. Since water solubility is the controlling removing mechanism, additives are used to enhance efficiencies. These additives can reduce the time to treat a site compared to the use of water alone. Additives must be of low toxicity and biodegradable. The research in this area has focussed mainly on halogenated volatile organic compounds (VOCs) and is still quite limited for metal removal. Additives include surfactants, organic and inorganic acids, sodium hydroxide, which can dissolve organic soil matter, water-soluble solvents such as methanol, displacement of cations with nontoxic ones, complexing agents such as EDTA, acids in combination with complexing agents or oxidizing/reducing agents. Cationic, anionic and nonionic surfactants are particularly used for soil washing or flushing. They contain both hydrophobic and hydrophilic portions, making them ideal for solubilization of hydrophobic compounds. Numerous studies have indicated that surfactants enhance recoveries of non-aqueous phase liquids (NAPLs). There have also been indications that pretreatment of soil with surfactant washing to solubilize hydrophobic compounds such as PAHs enhances biodegradation of these contaminants. A few in situ field studies have been performed with surfactants. Large-scale treatment has been done mostly for organic removal. Soil pH, soil type, cation exchange capacity (CEC), particle size, permeabilities and contaminants all affect removal efficiencies. High clay and organic matter contents are particularly detrimental. Understanding the chemistry of the binding of the contaminant and the hydrogeology of the site are very important. Once the water is pumped from the soil, it must be extracted and then treated to remove the hydrocarbons and metals. Several technologies exist such as sodium hydroxide or sodium sulfide precipitation, ion exchange, activated carbon adsorption, ultrafiltration, reverse osmosis, electrodialysis and biological processes. Recycling of the surfactants is desired to decrease treatment costs.
This paper will provide an overview of the laboratory research, field demonstration and full-scale application of surfactants for the remediation of contaminated soil. The majority of pilot scale in situ flushing tests, particularly in the United States, have involved the use of surfactants and co-solvents. There are only a few full-scale projects however. Recent laboratory scale efforts by the authors concerning the use of biosurfactants, biologically produced surfactants, to enhance the removal of copper, cadmium and zinc from contaminated soils and sediments are discussed. Three types of biosurfactants were evaluated for their effectiveness. They included a lipopeptide called surfactin from Bacillus subtilis, a rhamnolipid from Pseudomonas aeruginosa and a sophorolipid from Torulopsis bombicola. The results indicated the feasibility of removing the metals with the anionic biosurfactants even though the exchangeable fractions were not significant. 相似文献
The objectives of this study are to design an optimal electro-enhanced permeable reactive barrier (E2PRB) system for the remediation
of trichloroethylene (TCE)-contaminated water using zero valent iron (ZVI) and direct current (DC) and to investigate the
mechanisms responsible for TCE degradation in different ZVI-DC configurations. A series of column experiments was conducted
to evaluate the effect of different arrangements of electrodes and ZVI barriers in the column on the TCE removal capacity
(RC). In twelve different combinations of ZVI and/or DC application in the test columns, the rate of reductive dechlorination
of TCE was improved up to six times with simultaneous application of ZVI and DC compared to that using ZVI only. The most
effective arrangement of electrode and ZVI for TCE removal was the column set with ZVI and a cathode installed at the down
gradient. Based on the electrokinetic study for the column systems with only DC input, single acid front movement could explain
different RCs. An enhanced dechlorination rate of TCE using E2PRB systems, compared to a conventional PRB system, was observed,
and is considered to be attributed to more electron sources: (1) external DC, (2) electrolysis of water, (3) oxidation of
ZVI, (4) oxidation of dissolved Fe2+, (5) oxidation of molecular hydrogen at the cathode, and (6) oxidation of Fe2+ in mineral precipitates. Each of these electron sources was evaluated for their potential influencing the TCE RC through
the electron competition model and energy consumption. A strong correlation between the quantity of electrons generated, RC,
and the energy-effectiveness was found. 相似文献
The recent global scenario in the mineral sector may be characterized by rising competitiveness, increasing production costs and a slump in market price. This has pushed the mineral sector in general and that in the developing countries in particular to a situation where the industry has a limited capacity to sustain unproductive costs. This, more often than not, results in a situation where the industry fails to ensure environmental safeguards during and after mineral extraction. The situation is conspicuous in the Indian coal mining industry where more than 73% production comes from surface operations. India has an ambitious power augmentation projection for the coming 10 years. A phenomenal increase in coal production is proposed from the power grade coalfields in India. One of the most likely fall-outs of land degradation due to mining in these areas would be significant reduction of agricultural and other important land-uses. Currently, backfilling costs are perceived as prohibitive and abandonment of land is the easy way out. This study attempts to provide mine planners with a mathematical model that distributes generated overburden at defined disposal options while ensuring maximization of backfilled land area at minimum direct and economic costs. Optimization has been accomplished by linear programming (LP) for optimum distribution of each year’s generated overburden. Previous year’s disposal quantity outputs are processed as one set of the inputs to the LP model for generation of current year’s disposal output. From various geo-mining inputs, site constants of the LP constraints are calculated. Arrived value of economic vectors, which guide the programming statement, decides the optimal overburden distribution in defined options. The case example (with model test run) indicates that overburden distribution is significantly sensitive to coal seam gradient. The model has universal applicability to cyclic system (shovel–dumper combination) of opencast mining of stratified deposits. 相似文献
Centrifuge tests were carried out to determine the effect of different alcohols and one glycol on a thin consolidated disc
of clay. The evolution of changes in the clay hydraulic conductivity with time was investigated and other structural changes
due to chemical attack were monitored. The findings presented here demonstrate that the hydraulic conductivity of the clay
appear to be generally related to the polarity of the chemicals and the dielectric constant, with the exception of butanol.
In the case of butanol at low flow rate and low stress level, the action of the chemical caused the clay to crack, with a
consequent large increase in flow. This effect on the clay hydraulic conductivity could be used for improving pollution remediation
especially when alcohols are associated with gasoline. 相似文献
Abstract: Sediment transfers in a short reach of the Kiwitea Stream, near Fielding, lower North Island, New Zealand, are assessed using morphological budgeting based on repeat digital elevation model (DEM) differencing. Field data were acquired using high-precision GPS in October 2004, May and November 2005. Two interpolation methods to construct DEMs were compared. Universal kriging and Triangulation with Linear Interpolation produced consistent results and mean errors of between 4 and 14 mm. DEM error increases where relief changes rapidly. Sediment transfers are derived only from the low-relief active channel and indicate a rapidly changing environment. Remediation works following 2004 flood impacts have reduced bank erosion. A highly mobile bed renders the channel system sensitive to small and frequent flood events. 相似文献