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51.
The Short Rotation Woody Crop (SRWC) concept has been applied in the establishment of experimental and commercial plantations in both the United States and Brazil. The SRWC concept involves the application of agricultural principles to the production of tree crops for fiber or fuel. Although extensive SRWC research has occurred in the United States during the past 10 to 16 years, commercial applications have been rather limited. On the other hand, Brazil has made considerable progress in producing SRWC on a large-scale commercial basis while simultaneously conducting research. It seems clear that both countries can gain from each other's experience in SRWC experimentation and commercialization. This paper discusses and compares SRWC system developments in both countries and suggests means of improving and expanding SRWC systems use.  相似文献   
52.
This article presents a numerical study on the effects of magnetic fields and internal radiation on the melt flow and solidification morphology during solidification processing of semitransparent oxide melts. The numerical solution of the integral differential equation characterizing the internal radiation and the magnetohydrodynamic equations describing the magnetic and transport phenomena is obtained by applying the combined discontinuous and continuous finite-element method. Deforming finite elements based on an arbitrary Eulerian-Lagrangian formulation are used to track the moving boundaries resulting from solidification. Computed results show that both internal radiation and external magnetic fields can have strong effects on the melt flow, temperature distribution, and solidification behavior during the melt processing of oxide materials.  相似文献   
53.
The Solvent Extraction Residual Biotreatment (SERB) technology was evaluated at a former dry cleaner site in Jacksonville, FL, where an area of tetrachloroethylene (PCE) contamination was identified. The SERB technology is a treatmenttrain approach for complete site restoration, which combines an active in situ dense nonaqueous-phase liquid (DNAPL) removal technology, cosolvent extraction, with a passive enhanced in situ bioremediation technology, reductive dechlorination. During the in situ cosolvent extraction test, approximately 34 kL of 95% ethanol/5% water (v:v) was flushed through the contaminated zone, which removed approximately 60% of the estimated PCE mass. Approximately 2.72 kL of ethanol was left in the subsurface, which provided electron donorfor enhancement of biological processes in the source zone and downgradient areas. Quarterly groundwater monitoring for over 3 yr showed decreasing concentrations of PCE in the source zone from initial values of 4-350 microM to less than 150 microM during the last sampling event. Initially there was little to no daughter product formation in the source zone, but after 3 yr, measured concentrations were 242 microM for cis-dichloroethylene (cis-DCE), 13 microM for vinyl chloride, and 0.43 microM for ethene. In conjunction with the production of dissolved methane and hydrogen and the removal of sulfate, these measurements indicate that in situ biotransformations were enhanced in areas exposed to the residual ethanol. First-order rate constants calculated from concentration data for individual wells ranged from -0.63 to -2.14 yr(-1) for PCE removal and from 0.88 to 2.39 yr(-1) for cis-DCE formation. First-order rate constants based on the change in total mass estimated from contour plots of the groundwater concentration data were 0.75 yr(-1) for cis-DCE, -0.50 yr(-1) for PCE, and -0.33 yr(-1) for ethanol. Although these attenuation rate constants include additional processes, such as sorption, dispersion, and advection, they provide an indication of the overall system dynamics. Evaluation of the groundwater data from the former dry cleaner site showed that cosolvent flushing systems can be designed and utilized to aid in the enhancement of biodegradation processes at DNAPL sites.  相似文献   
54.
55.
Steady-state monochloramine reduction in fixed-bed reactors (FBRs) was quantified on five types of granular activated carbon (GAC) using two background waters-one natural source water (LAW) containing 2.5-3.5 mg/L organic carbon and one synthetic organic-free water (NW). While more monochloramine was reduced at steady-state using NW compared to LAW for each GAC and empty-bed contact time studied, the differences in removal varied considerably among the GACs tested. Physical characterization of the GACs suggested that the degree of interference caused by natural organic matter (NOM) increased with increasing GAC surface area contained within pores greater than 2 nm in width. Acid/base and electrostatic properties of the GACs were not found to be significant in terms of NOM uptake, which indicated that size exclusion effects of the GAC pores overwhelmed the impact of the GAC surface chemistry. Therefore, selection of GAC to limit the impact of NOM on monochloramine reduction in FBRs should be based on pore size distribution alone, with the impact of NOM decreasing with decreasing mesoporosity and macroporosity.  相似文献   
56.
Bimetallic reductants are frequently more reactive toward organohalides than unamended iron and can also alter product distributions, yet a molecular-level explanation for these phenomena remains elusive. In this study, surface characterization of six iron-based bimetallic reductants (Au/Fe, Co/Fe, Cu/Fe, Ni/Fe, Pd/Fe, and Pt/Fe) revealed that displacement plating produced a non-uniform overlayer of metallic additive on iron. Batch studies demonstrated that not all additives enhanced rates of 1,1,1-trichloroethane (1,1,1-TCA) reduction nor was there any clear periodic trend in the observed reactivity (Ni/Fe approximately Pd/Fe > Cu/Fe > Co/ Fe > Au/Fe approximately Fe > Pt/Fe). Pseudo-first-order rate constants for 1,1,1-TCA reduction (kobs values) did, however, correlate closely with the solubility of atomic hydrogen within each additive. This suggests absorbed atomic hydrogen, rather than galvanic corrosion, is responsible for the enhanced reactivity of bimetallic reductants. In addition, all additives shifted product distributions to favor the combined yield of ethylene plus ethane over 1,1-dichloroethane. In rate-enhancing bimetallic systems, branching ratios between 1,1-dichloroethane and the combination of ethylene and ethane were uniquely dependent on kobs values, indicating an intimate link between rate-determining and product-determining steps. We propose that our results are best explained by an X-philic pathway involving atomic hydrogen with a hydride-like character.  相似文献   
57.
Capacity enhancement and volume reduction benefits of step-feeding fully aerobic bioreactors has been well documented. Application of step-feed technology to biological nutrient removal (BNR) systems, particularly those removing nitrogen alone or both nitrogen and phosphorus, is relatively new to the industry. In recent years, a number of full-scale step-feed facilities have been brought into service. This paper reviews nine full-scale step-feed biological nutrient removal systems--both nitrogen removal alone, and nitrogen and phosphorus removal. The objective is to compare the theoretical benefits of such systems with their actual operation. The predicted benefits of reduced bioreactor volume or increased process capacity, reduced energy usage, more robust nitrification performance, and the flexibility to tune (or de-tune) nitrification efficiency were verified in full-scale systems. Equations are also presented that may be used in the prediction of step-feed benefits. There are two primary drivers for considering a step-feed biological reactor system: 1. Reduced bioreactor volume for a defined capacity or performance or increased process capacity given a fixed bioreactor volume. 2. More robust nitrification performance. Full-scale operation of these step-feed nutrient removal systems provides a real world basis for the claimed benefits of step-feed operation. These systems have uniformly shown additional capacity. A number of them have also exhibited more robust performance, especially during storms. Where possible, side-by-side comparisons of full-scale step-feed systems with non-step-feed systems have exhibited greater process reliability and flexibility.  相似文献   
58.
This paper will deal with various methods of torque control for two-drum winders, some that have been more common in the past and others that have come into use in recent years. Before looking into specific methods of torque control, consideration will be given as to just what function the winder (any winder) performs, the type of operation required on two drum winders to accomplish this function, and how torque control can give this desired operation. Other factors influencing the quality of the rewound roll such as sheet quality, back-stand tension control, and rider roll pressure control will be discussed briefly. Areas (including grades and quality of web) where high back-stand tension or rider roll pressure cannot be utilized for roll density and therefore roll quality will be explained to emphasize the need for positive dependable torque control. Various methods of torque control will be considered along with advantages and disadvantages of each. Finally, results of automatic torque control for two specific installations will be discussed indicating the improved roll quality and ease of operation that has been obtained.  相似文献   
59.
During the past several years, and particularly since the Clean Air Mercury Rule (CAMR) was promulgated in June of 2005, the electric utility industry, product vendors, and the research community have been working diligently to develop and test Hg control strategies for a variety of coal types and plant configurations. Some of these strategies include sorbent injection and chemical additives designed to increase mercury capture efficiency in particulate control devices. These strategies have the potential to impact the fate of other inorganic hazardous air pollutants (HAPs), which typically include As, Be, Cd, Cr, Co, Mn, Ni, Pb, Se, and Sb. To evaluate this impact, flue gas samples using EPA Method 29, along with representative coal and ash samples, were collected during recent pilot-scale and field test projects that were evaluating Hg control technologies. These test programs included a range of fuel types with varying trace element concentrations, along with different combustion systems and particulate control devices. The results show that the majority of the trace element HAPs are associated with the particulate matter in the flue gas, except for Se. However, for five of the six projects, Se partitioning was shifted to the particulate phase and total emissions reduced when Hg control technologies were applied.  相似文献   
60.
Crisis management logic suggests that planning and preparing for crisis should be a vital part of institutional and policy toolkits. This paper explores the difficulties in translating this ideal into practice. It focuses on four key difficulties. First, crises and disasters are low probability events but they place large demands on resources and have to compete against front‐line service provision. Second, contingency planning requires ordering and coherence of possible threats, yet crisis is not amenable to being packaged in such a predictable way. Third, planning for crisis requires integration and synergy across institutional networks, yet the modern world is characterised by fragmentation across public, private and voluntary sectors. Fourth, robust planning requires active preparation through training and exercises, but such costly activities often produced a level of symbolic readiness which does not reflect operational realities. Finally the paper reflects on whether crisis preparedness is a ‘mission impossible’, even in the post‐9/11 period when contingency planning seems to be an issue of high political salience.  相似文献   
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