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The initial degradation mechanisms of OH and 4-chloro-2-methylphenoxyacetic acid (MCPA) including molecular form and anionic form are studied at the MPWB1K/6-311+G(3df, 2p)//MPWB1K/6-31+G(d, p) level. Possible reaction pathways of H-atom abstraction and OH addition are considered in detail. By result comparison analysis, it is found that the reaction mechanisms for OH and two forms of MCPA are different, and most reactions for anionic MCPA are easier than those for molecular MCPA. For H-atom abstraction reactions, the calculated energies show that OH abstracting H-atom from -CH3 group of molecular MCPA is the most kinetically favorable process; the potential energy surface for anionic MCPA indicates that H-atom in -CH2 group is slightly easier to be abstracted than that in -CH3 group. For OH addition reactions, the addition of OH to the C1 site is the initial step for molecular MCPA and the predominant product is 4-chloro-2-methylphenol (denoted P3), while the C4 site is the most reactive site for anionic MCPA and the primary product results from the hydroxylation of the aromatic ring, which is in good agreement with the experimental observation. In additional, results from PCM calculations show that most reactions in water phase are more kinetically favorable than those in gas phase, though the mechanisms discussed above will not be changed. 相似文献
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Kyoung Jae Lim Bernard A. Engel Suresh Muthukrishnan Jon Harbor 《Journal of the American Water Resources Association》2006,42(3):629-643
ABSTRACT: Few studies have been conducted to explore the effects of initial abstraction on estimated direct runoff despite the widespread use of the curve number (CN) method in many hydrologic models to estimate direct runoff. In this study, use of a 5 percent ratio of initial abstraction (Ia) to storage (S) to estimate daily direct runoff with modified CN values for a 5 percent Ia/S value was investigated using the Long‐Term Hydrologic Impact Assessment (L‐THIA) geographic information system (GIS). In addition, the effects on estimated runoff of altering the hydrologic soil group due to urbanization were investigated. The L‐THIA model was applied to the Indiana Little Eagle Creek watershed with 5 percent and 20 percent Ia/S values, considering hydrologic soil group alteration due to urbanization. The results indicate that uses of a 5 percent la/S and modified CN values and Hydrologic Soil Group D for urbanized areas in model runs can improve long term direct runoff prediction. 相似文献
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甲苯硝化废水含有多种芳香族硝基酚类物质,毒性大、治理难。江苏淮河化工总厂根据络合萃取原理,选择QH溶剂作萃取剂、选用HL离心萃取器,对该种废水作四级逆相络合萃取法治理。土建、设备投资约40万元,处理每吨废水运行费为6.19元;甲苯类物质去除率达95%以上,2,6-二硝基甲酚去除率近90%,其他酚类物质基本去除;萃取剂经反萃取可循环使用。 相似文献
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Snoussi M Kitheka J Shaghude Y Kane A Arthurton R Le Tissier M Virji H 《Environmental management》2007,39(5):587-600
Anthropogenic factors associated with damming and water abstraction, and the resultant environmental pressures, are reviewed
in six African river catchments using records and forecasts of climatic, demographic, and land-use change. Changes in the
states of the flow regime through catchment drainage systems to the coastal sea are considered in conjunction with climate
change and other human-induced pressures. The impacts of these changes on downstream and coastal environments and their communities
are described in past, present, and future perspectives. Linkages between the issues and the pressures of damming and water
abstraction are appraised and scientific, policy, and management responses proposed aimed at remedying existing and perceived
future negative impacts. The study proposes that there is a need to integrate catchment and coastal management to account
for the whole water flow regime together with its human dimensions. Management priorities relating to the operation of existing
damming and abstraction schemes and planning of future schemes include the following: consideration of ways in which water
discharges could be adjusted to provide improvements in downstream and coastal environmental and socioeconomic conditions;
addressing the problem of sediment trapping impacting on the sustainability of dam reservoirs; and assessment of downstream
and coastal impacts of future schemes in the light of climate change forecasts. 相似文献
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