Cyclooctane tropospheric degradation initiated by reaction with Cl atoms

Goal, Scope and Background Within the non-methane hydrocarbons, alkanes constitute the largest fraction of the anthropogenic emissions of volatile organic compounds. For the case of cyclic alkanes, tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase. Nevertheless, Cl atom reaction rate constants are generally one order of magnitude larger than those of OH. In the present work, the reaction of cyclooctane with Cl atoms has been studied within the temperature range of 279–333 K. Methods The kinetic study has been carried out using the fast flow tube technique coupled to mass spectrometry detection. The reaction has been studied under low pressure conditions, p=1 Torr, with helium as the carrier gas. Results The measured room temperature rate constant is very high, k=(2.63±0.54)×10⁻¹⁰ cm³molecule⁻¹s⁻¹, around 20 times larger than that for the corresponding OH reaction. We also report the results of the rate coefficients obtained at different temperatures: k = (3.5±1.2)×10⁻¹⁰ exp[(−79±110)/T] cm³ molecule⁻¹ s⁻¹ within the range of 279–333 K. This reaction shows an activation energy value close to zero. Discussion Quantitative formation of HCl has been observed, confirming the mechanism through H-atom abstraction. The reactivity of cyclic alkanes towards Cl atoms is clearly dependent on the number of CH₂ groups in the molecule, as is shown by the increase in the rate constant when the length of the organic chain increases. This increase is very high for the small cyclic alkanes and it seems that the reactions are approaching the collision-controlled limit for cyclohexane and cyclooctane. Conclusions These results show that gas-phase reaction with Cl in marine or coastal areas is an efficient sink (competing with the gas phase, OH initiated degradation) for the Earth’s emissions of cyclooctane, with a Cl-based lifetime ranging from 11 to 2000 hours, depending on the location and time of day. Recommendations and Perspectives Cl and OH fast reactions with cyclooctane are expected to define the lifetime of cyclooctane emissions to the atmosphere. The degradation of cyclooctane occurs in a short period of time and consequently (under conditions of low atmospheric mass transport), close to the emission sources enabling a significant contribution to local effects, like the formation of photochemical smog. ESS-Submission Editor: Prof. Dr. Gerhard Lammel (lammel@recetox.muni.cz)     

Characterization of an urban landfill soil by using physicochemical analysis and solid phase microextraction (SPME)—GC/MS

We have aimed at characterizing top soil samples taken in-situ from five different locations of the unregulated dumping site in Eskişehir/Turkey for a period of six months. The study is the first attempt in the city and in Turkey, regarding particularly the SPME (Solid Phase Microextraction Technique) analysis method utilized. A comprehensive research has been conducted to produce critical soil data to be used for indicating current risks as well as the urgency of rehabilitating the site and establishing a sanitary landfill in the site. Conventional physicochemical analytical methods and SPME technique were used to analyze the samples. Physicochemical analyses were performed for determining the pH, total dried matter, volatile matter, total nitrogen, phosphorus, macro elements and heavy metals. Meteorological data were also recorded for the same period. SPSS.10.0 statistical program was used to determine the correlation between meteorological data and physicochemical analysis results. Mean values were used in the correlation analyses. These data indicated that the air temperature and precipitation have significant effects on soil characteristics. SPME, coupled with GC/MS, was used to identify eighty six volatile and semi-volatile organic compounds contained in soil samples. The samples were extracted by headspace SPME with heating (δHS-SPME). SPME analyses were conducted using a commercially available polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber having a film thickness of 65 μm (Supelco) as a capture medium. The experimentally optimized headspace sampling conditions were arranged (15 min. at 50^˚C) before a 30 min. sampling period.     

Oxidative transformation of polybrominated diphenyl ether congeners (PBDEs) and of hydroxylated PBDEs (OH-PBDEs)

BACKGROUND, AIM, AND SCOPE: The historical and widespread use of polybrominated diphenyl ethers (PBDEs) as flame retardants in consumer products worldwide has caused PBDEs to now be regarded as pervasive environmental contaminants. Most recently, hydroxylated PBDEs (OH-PBDEs) and methoxylated PBDEs (MeO-PBDEs) have emerged as environmentally relevant due to reports of their natural production and metabolism. An important parameter for assessing the environmental impact of a chemical substance is persistence. By formulating the concept that persistence is the result of the substance's physicochemical properties and chemical reactivity, Green and Bergman have proposed a new methodology to determine the inherent persistence of a chemical. If persistence could be predicted by straightforward methods, substances with this quality could be screened out before large-scale production/manufacturing begins. To provide data to implement this concept, we have developed new methodologies to study chemical transformations through photolysis; hydrolysis, substitution, and elimination; and via oxidation. This study has focused on adapting an oxidative reaction method to be applicable to non-water soluble organic pollutants. MATERIALS AND METHODS: PBDEs and one MeO-PBDE were dissolved in tetrahydrofuran/methanol and then diluted in alkaline water. The OH-PBDEs were dissolved in alkaline water prior to reaction. The oxidation degradation reaction was performed at 50 degrees C using potassium permanganate as described elsewhere. The pH was maintained at 7.6 with disodium hydrogen phosphate and barium hydrogen phosphate, the latter also serving as a trapping agent for manganate ions. The oxidation reactions were monitored by high-performance liquid chromatography and reaction rates were calculated. RESULTS: The OH-PBDEs have very fast oxidative transformation rates compared to the PBDEs. The reaction rates seem to be primarily dependent on substitution pattern of the pi-electron-donating bromine substituents and of bromine content. There are indications that further reactions of OH-PBDEs, e.g., methylation to the MeO-PBDEs, decrease the oxidation rates, and thereby generate more persistent substances. DISCUSSION: The resistance of PBDEs to oxidation, a major degradation pathway in air, should be further investigated, since these compounds do undergo long range transport. With slight modifications, the original method has been adapted to include a larger variety of chemical substances, and preliminary data are now available on the oxidative transformation rates for PBDEs and of OH-PBDEs. CONCLUSIONS: The original oxidation degradation method can now include non-water soluble compounds. This modification, using low concentrations of test chemicals, allows us to measure oxidative transformation rates, for some of the lower brominated DEs, data that can be used to assess their persistence in future model calculations. Oxidative transformation rates for PBDEs are slow compared to those for the OH-PBDEs. This suggests that OH-PBDEs, when released into the environment, undergo faster oxidative metabolism and excretion than the PBDEs. RECOMMENDATIONS AND PERSPECTIVES: To evaluate the modified method, more degradation reactions with non-water soluble compounds should be investigated. Recent studies show that OH-PBDEs are present in rats and in humans and, because of their activity as endocrine disruptors, determining their subsequent environmental fate is of importance. The resistance of PBDEs to oxidative degradation should be acknowledged as of possible future concern. Several other compound classes (such as polychlorinated biphenyls (PCBs), hydroxylated polychlorinated biphenyls (OH-PCBs), and pharmaceuticals) need to be subjected to this screening method to increase the database of transformation rates that can be used with this model.     

Atmospheric chemistry of HFE-7000 (CF(3)CF (2)CF (2)OCH (3)) and 2,2,3,3,4,4,4-heptafluoro-1-butanol (CF (3)CF (2)CF (2)CH (2)OH): kinetic rate coefficients and temperature dependence of reactions with chlorine atoms

Background, aim, and scope  The adverse environmental impacts of chlorinated hydrocarbons on the Earth’s ozone layer have focused attention on the effort to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number of C–F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase. Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF₃CF₂CF₂OCH₃) (1) and its isomer CF₃CF₂CF₂CH₂OH (2). Materials and methods  Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube–mass spectrometric technique at 1 Torr of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266–333 and 298–353 K for reactions of HFE-7000 and CF₃CF₂CF₂CH₂OH, respectively. Results  The measured room temperature rate constants were k(Cl+CF₃CF₂CF₂OCH₃) = (1.24 ± 0.28) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹and k(Cl+CF₃CF₂CF₂CH₂OH) = (8.35 ± 1.63) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ (errors are 2σ + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k ₁(266–333 K) = (6.1 ± 3.8) × 10⁻¹³exp[−(445 ± 186)/T] cm³ molecule⁻¹ s⁻¹ and k ₂(298–353 K) = (1.9 ± 0.7) × 10⁻¹²exp[−(244 ± 125)/T] cm³ molecule⁻¹ s⁻¹ (errors are 2σ). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl radical. At 298 K and 1 Torr, yields on HCl of 0.95 ± 0.38 and 0.97 ± 0.16 (errors are 2σ) were obtained for CF₃CF₂CF₂OCH₃ and CF₃CF₂CF₂CH₂OH, respectively. Discussion  The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into account the error limits. Comparing the obtained results at room temperature, k ₁ and k ₂, HFE-7000 is significantly less reactive than its isomer C₃F₇CH₂OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and alcohols, the kinetic rate constant may be considered as not dependent on the number of –CF₂– in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties for a given application by changing the number of –CF₂– without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C₃H₇CH₂OH, respectively. Conclusions  The studied CFCs’ substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the marine boundary layer, τ _Cl values as low as 2.5 and 0.4 years for HFE-7000 and C₃H₇CH₂OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes under such conditions may constitute a relevant sink. In the case of CF₃CF₂CF₂OCH₃, significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would result in underestimations of lifetimes and GWPs. Recommendations and perspectives  The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge of the atmospheric behavior and the structure–reactivity relationship discussed in this work may also contribute to the development of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution is still required.     

Assessment of the efficiency and economic viability of various methods of treatment of sanitary landfill leachate

This study assesses the efficiency of various physico-chemical, biological and other tertiary methods for treating leachate. An evaluation study on the treatability of the leachate from methane phase bed (MPB) reactor indicated that at an optimum hydraulic retention time of 6 days, the efficiency of the reactor in terms of biological oxygen demand (BOD) and chemical oxygen demand (COD) removal was 91.29 and 82.69%, respectively. Recycling of the treated leachate through the municipal solid waste layers in the leachate recycling unit (LRU) resulted in a significant increase in the biodegradation of organics present in the leachate. Optimum BOD and COD removal efficiencies were achieved at the third recycle; additional recycling of the leachate did not produce any significant improvement. Physico-chemical treatment of the leachate demonstrated that alum and lime (Option 2) were more economical than coagulants lime and MgCO₃. A cost analysis of the economics of the various treatments revealed that the alternative treatment consisting of a MPB bed followed by a LRU and aerated lagoon is the most cost-effective treatment. However, the alternative consisting of a MPB followed by the LRU and a soil column, which is slightly more costly, would be the most appropriate treatment when adequate land is readily available.     

糖蜜酒精废水两相UASB处理有机物去除特征

应用气相色谱研究了糖蜜酒精废水两相ＵＡＳＢ处理工艺段中有机物的去除情况,结果表明,酸化反应器内,易降解有机物的去除率上为１００％,产甲烷段反应器内,因易降解化合物在酸化反应器内大部分被去除,剩下的化合物的在该段反应器内去除率偏小,仅为８０％。质谱结果证实,进水中的酚类化合物经两级处理后,被有效去除。     

Performance and dilemmas of urban containment strategies in the transformation context of Beijing

The implementation of urban containment policies is increasingly attracting attention in environment management. Rapid urban growth and the coexistence of decentralisation and marketisation challenge containment strategies that are implemented to control urban sprawl. This challenge is likely to be greater in a transformation country than in developed countries. This paper evaluates the performance of containment strategies in Beijing. The analysis shows that, to a large extent, containment strategies perform well; however, the decreased compactness of the fringes of the inter-suburban areas, caused by dispersed and illegal development, suggest that municipal containment strategies are being challenged by new trends towards local autonomy. Two similar dilemmas to those faced by developed countries are confronting those involved in the implementation of containment strategies in the current transformation process in Beijing: first, the municipal environmental goal might not be achieved by all local jurisdictions when local economic motivations are involved; and second, macro-scale containment policies are unlikely to control an urban sprawl fuelled by the growing power of market forces.     

垂直潜流人工湿地有机物积累及去向初步分析

为防治湿地堵塞、改善湿地处理效果,初步探讨了湿地中有机物的积累规律,并估算湿地中有机物不同去除途径的贡献率。结果表明,垂直潜流人工湿地中基质间积累的有机物主要是不可溶有机物,且粒径主要集中在5.00μm以上,分析是不同粒径有机物凝聚积累的缘故;垂向沿程基质间有机物的积累量受进水水力负荷影响明显;进入垂直潜流人工湿地中的有机物绝大部分都被生物(植物和微生物)吸收和利用而得以去除,该途径贡献率可达99.9%以上。     

蒙自矿冶重金属冶炼废水处理工程改造与实践

蒙自矿冶重金属冶炼废水深度处理工程主要对含重金属污酸和酸性污水处理系统进行改造。针对原有中和处理法存在的诸多问题,本工程在石灰中和处理的基础上新增电絮凝处理系统、化学沉淀微滤处理系统和深度处理系统。工程实践表明,该深度处理工程运行稳定,自动化程度高,处理效果好,废水达到《地表水环境质量标准（GB3838．2002）》Ⅲ类标准,经过处理后的水可全部用于生产系统,实现零排放,同时为冶炼行业重金属废水治理和污染控制提供实践经验。     

Determination of haloacetic acids concentrations in hospital effluent after chlorination by ion chromatography

The ion chromatography combined solid phase extraction (SPE) method was developed for the analysis of low concentration haloacetic acids(HAAs),a calss of disinfection by-products formed as a result of chlorination of hospital wastewater. The monitored HAAs included monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, dibromoacetic acid and trichloroacetic acid. The method employed a sodium hydroxide eluent at a flow rate of 0.8 ml/min, electrolytically generated gradients, and suppressed conductivity detection. To analyze the HAAs in real hospital wastewater samples, C18 pretreatment cartridge was utilized to reduce samples' turbidity. Preconcentration with SPE and matrix elimination with treatment cartridges were investigated and were found to be able to obtain acceptable detection limits. Linearity, repeatability and detection limits of the above method were evaluated. The detection limits of monobromoacetic acid and dibromoacetic acid were 2.61 μg/L and 1.30 μg/L respectively, and the other three are ranging from 0.48 to 0.82 μg/L under 25-fold preconcentration. When the above optimization procedure was applied to three hospital wastewater samples with different treatment processes in Tianjin, it was found that the dichloroacetic acid is the major compound, and the growth ratios of the HAAs after disinfection by sodium hypochlorite were 91.28%, 63.61% and 79.50%, respectively.