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181.
182.
IntroductionAmmoniumisveryimportantasaNsourceforalgaeduetothecapacityofmanyspeciestotakeupammoniummorerapidlythannitrate (Jones,1996 ) .UptakeofNH+4isofinterestbecausemanyspeciestakeupNH+4atratesthatgreatlyexceedgrowthrates (Pedersen ,1994 ) ,andareabletogrowrapi… 相似文献
183.
Carta D Cao G D'Angeli C 《Environmental science and pollution research international》2003,10(6):390-394
In this paper we review an interesting method of PET recycling, i.e. chemical recycling; it is based on the concept of depolymerizing the condensation polymer through solvolytic chain cleavage into low molecular products which can be purified and reused as raw materials for the production of high-quality chemical products. In this work our attention is confined to the hydrolysis (neutral, acid and alkaline) and glycolysis processes of PET chemical recycling; operating conditions and mechanism of each method are reported and described. The neutral hydrolysis has an auto accelerating character; two kinetic models have been proposed: an half-order and a second order kinetic model. The acid hydrolysis could be explained by a modified shrinking core model under chemical reaction control and the alkaline hydrolysis by a first-order model with respect to hydroxide ion concentration. To describe glycolysis, two different kinetic models have been proposed where EG can act or not as internal catalyst. Further experimental and theoretical investigations are required to shed light on the promising processes of PET chemical recycling reviewed in this work. 相似文献
184.
采用UV/Fenton高级氧化技术对酸性红B模拟废水进行处理,当进水浓度为400mg/L时,确定了各影响因素的最佳投加量:H2O2投加量为2mL/L,Fe^2+投加量为0.08g/L,最佳pH值为4;并采用一级动力学公式对酸性红B降解速率进行拟合,研究了反应条件对速率常数的影响。最后通过对单独UV法、单独Fenton法和UV/Fenton法3种处理方法效果的比较,发现UV与Fenton试剂具有协同作用。 相似文献
185.
186.
Reddy CM Drenzek NJ Eglinton TI Heraty LJ Sturchio NC Shiner VJ 《Environmental science and pollution research international》2002,9(3):183-186
INTENTION, GOAL, SCOPE, BACKGROUND: Identifying different sources and following reaction pathways of chlorinated organic contaminants in the environment can be challenging, especially when only their concentrations are available. Compound-specific stable chlorine measurements of some contaminants have recently been shown to provide additional information and an increased understanding of their biogeochemistry. These studies, however, have been generally limited to volatile molecules. OBJECTIVE: Here, the stable chlorine isotope ratios of the semi-volatile pesticide, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) were investigated. Specifically, the intramolecular stable chlorine isotopic compositions of DDT and the kinetic isotope effect (KIE) for the abiotic dehydrochlorination of DDT to 2,2-bis(p-chlorophenyl)-1,1-dichloroethene (DDE) were determined. METHODS: Selective chemical oxidation of DDT to dichlorobenzophenone (DCBP) and analysis of each compound was used to calculate the stable chlorine isotope ratios of the alkyl and aromatic chlorines in DDT. To determine the KIE for dehydrochlorination, DDT was reacted in a basic solution to yield DDE at 52 degrees C, 60 degrees C, and 72 degrees C for 3, 5, and 5 days, respectively. RESULTS AND DISCUSSION: Significant intramolecular stable chlorine isotopic differences were observed in one sample of DDT where the alkyl and aromatic delta 37Cl values were -5.76 +/- 0.45 and -2.21 +/- 0.24%@1000, respectively. Dehydrochlorination of DDT to DDE in basic solutions at 52, 60, and 70 degrees C resulted in a substantial intramolecular KIE where the alkyl chlorines of DDE shifted by approximately 3%@1000 relative to the alkyl chlorines in DDT. However, no temperature dependence was observed. The KIE, calculated by an iterative program, was 1.009. CONCLUSIONS: Intramolecular differences in the stable chlorine isotope ratios were observed in DDT and this is the first such finding. Dehydrochlorination of DDT yields a measurable and distinct intramolecular stable chlorine KIE. RECOMMENDATION AND OUTLOOK: The results of this study demonstrate the existence of significant intramolecular differences in chlorinated organic compounds. Many other chlorinated semi-volatile and volatile organic contaminants are synthesized from multiple sources of chlorine, and we recommend that similar studies be performed on many such molecules in order to attain a clear understanding of their intramolecular chlorine isotopic differences. The existence of a measurable KIE for the dehydrochlorination of DDT to DDE shows the potential strength of using isotopic measurements to investigate the biogeochemistry of these important compounds. For example, the isotopically depleted aqueous chloride produced by dehydrochlorination of DDT to DDE may be a useful tracer of these reactions in freshwater environments. 相似文献
187.
The statistical analysis of dynamic processes is a useful tool to learn how environmental and ecological systems work and how they respond to disturbances. In the context of human risk assessment of potentially harmful chemicals, many complex dynamic processes in terms of kinetics have to be taken into account. Thorough research of direct influence of chemicals to humans depends on investigations with animalsin vivo andin vitro. However, when animals serve as models of human systems, one critical step is the extrapolation from the risk observed in the experimental animals to the risk associated with the human organism. To extrapolate the observed risk in this case, the detailed knowledge of the relevant kinetic processes as well as their differences between species is fundamental. On the other hand experimental tools for these processes are quite restrictive. Based on simple experimental designs a statistical method is proposed for characterizing such kinetic processes using the well-known compartmental analysis tool and non-linear regression. The methodology is then exemplified by non-invasive toxicokinetic inhalation experiments with rats. 相似文献
188.
Yiliang HE Bin ZHAO Joseph B.HUGHES Sunh Soo HAN 《Frontiers of Environmental Science & Engineering in China》2008,2(3):326-332
The performances and kinetic parameters of Fenton oxidation of 2,4- and 2,6-dinitrotoluene (DNT) in water-acetone mixtures
and explosive contaminated soil washing-out solutions were investigated at a laboratory scale. The experimental results show
that acetone can be a significant hydroxyl radical scavenger and result in serious inhibition of Fenton oxidation of 2,4-
and 2,6-DNT. Although no serious inhibition was found in contaminated soil washing-out solutions, longer reaction time was
needed to remove 2,4- and 2,6-DNT completely, mainly due to the competition of hydroxyl radicals. Fenton oxidation of 2,4-
and 2,6-DNT fit well with the first-order kinetics and the presence of acetone also reduced DNT’s degradation kinetics. Based
on the comparison and matching of retention time and ultraviolet (UV) spectra between high performance liquid chromatography
(HPLC) and standards, the following reaction pathway for 2,4-DNT primary degradation was proposed: 2,4-DNT → 2,4-dinitro-benzaldehyde
→ 2,4-dinitrobenzoic acid → 1,3-dinitrobenzene → 3-nitrophenol. 相似文献
189.
潜流人工湿地氮循环生态动力学模型研究 总被引:1,自引:0,他引:1
人工湿地作为一种新型的处理技术,在水环境保护中具有重要的意义和广阔的应用前景。然而目前人工湿地的设计和运行主要是建立在统计数据和经验公式的基础上,对人工湿地去除污染物的内在机制尚缺乏定量化的认识。通过对潜流人工湿地氮循环生态动力学模型的研究,系统地分析了潜流人工湿地中氮素的去除机制,对将来完善人工湿地处理技术的设计、运行和预测方法具有一定的借鉴意义。 相似文献
190.
The existence of electrolytes in aquatic environment on the photocatalytic performance and coagulation of nanodispersed TiO2 hydrosol and the corresponding photocatalytic alteration were investigated by studying cations (Na+, K+, Ca 2+, Mg2+, and Al3+). The photocatalysis reactions of nano TiO2 with different dosages of electrolytes were measured by monitoring the degradation of Rhodamine B (RhB) under ultraviolet A (UV-A) irradiation over time. The results showed that the photocatalytic performance of TiO2 was improved by the presence of Al3+, while the performance was impaired by the other tested cations. The negative influences of divalent ions on the photocatalytic performance of TiO2 were more significant than monovalent ions. The TiO2 sol dispersed stable at nano scale at low concentration of electrolyte (< 0.01?mol/L) with slight change of pH, and coagulated into micro sizes at high concentration of electrolytes (> 0.1?mol/L) with larger increase or decrease of pH. The positive effects of Al3+ on the photodegradation rate of RhB might relate to the strong hydrolytic action of Al3+ in aquatic solutions. The photocatalytic processes of TiO2 in the presence of all ions followed the Langmuir-Hinshelwood model, and the reaction kinetic constant was increased with the decrease of pH caused by different cations. These work suggested a new perspective about the relationship between coagulation and photocatalytic performance of TiO2 hydrosols in electrolyte with hydrolysable cations, which demonstrated that TiO2 hydrosols may be suitable as photocatalysts in aquatic environments. 相似文献