The effect of alkyl chain length on the degradation of alkylimidazolium- and pyridinium-type ionic liquids in a Fenton-like system

Background, aim, and scope  Ionic liquids are regarded as essentially “green” chemicals because of their insignificant vapor pressure and, hence, are a good alternative to the emissions of toxic conventional volatile solvents. Not only because of their attractive industrial applications, but also due to their very high stability, ionic liquids could soon become persistent contaminants of technological wastewaters and, moreover, break through into natural waters following classical treatment systems. The removal of harmful organic pollutants has forced the development of new methodologies known as advanced oxidation processes (AOPs). Among them, the Fenton and Fenton-like reactions are usually modified by the use of a higher hydrogen peroxide concentration and through different catalysts. The aim of this study was to assess the effect of hydrogen peroxide concentration on degradation rates in a Fenton-like system of alkylimidazolium ionic liquids with alkyl chains of varying length and 3-methyl-N-butylpyridinium chloride. Materials and methods  The ionic liquids were oxidized in dilute aqueous solution in the presence of two different concentrations of hydrogen peroxide. All reactions were performed in the dark to prevent photoreduction of Fe(III). The concentrations of ionic liquids during the process were monitored with high-performance liquid chromatography. Preliminary degradation pathways were studied with the aid of ¹H NMR. Results  Degradation of ionic liquids in this system was quite effective. Increasing the H₂O₂ concentration from 100 to 400 mM improved ionic liquid degradation from 57–84% to 87–100% after 60 min reaction time. Resistance to degradation was weaker, the shorter the alkyl chain. Discussion  The compound omimCl was more resistant to oxidation then other compounds, which suggests that the oxidation rates of imidazolium ionic liquids by OH· are structure-dependent and are correlated with the n-alkyl chain length substituted at the N-1-position. The level of degradation was dependent on the type of head group. Replacing the imidazolium head group with pyridinium increased resistance to degradation. Nonetheless, lengthening the alkyl chain from four to eight carbons lowered the rate of ionic liquid degradation to a greater extent than changing the head group from imidazolium to pyridinium. 1H-NMR spectra show, in the first stage of degradation, that it is likely that radical attack is nonspecific, with any one of the carbon atoms in the ring and the n-alkyl chain being susceptible to attack. Conclusions  The proposed method has proven to be an efficient and reliable method for the degradation of imidazolium ionic liquids by a Fenton-like reagent deteriorated with lengthening n-alkyl substituents and by replacing the imidazolium head group with pyridinium. The enhanced resistance of 1-butyl-3-methylpyridinium chloride when the resistance of imidazolium ionic liquids decreases with increasing H₂O₂ concentration is probably indicative of a change in the degradation mechanism in a vigorous Fenton-like system. H-NMR spectra showed, in the first stage of degradation, that radical attack is nonspecific, with any one of the carbon atoms in the ring and the n-alkyl chain being susceptible to attack. Recommendations and perspectives  Since ionic liquids are now one of the most promising alternative chemicals of the future, the degradation and waste management studies should be integrated into a general development research of these chemicals. In the case of imidazolium and pyridinium ionic liquids that are known to be resistant to bio- or thermal degradation, studies in the field of AOPs should assist the future structural design as well as tailor the technological process of these chemicals     

Profile of Methane Concentrations in Soil and Atmosphere in Alpine Steppe Ecosystem on Tibetan Plateau

The methane concentration profile from -1.5m depth in soil to 32m height in air was measured in alpine steppe located in the permafrost area. Methane concentrations showed widely variations both in air and in soil during the study period. The mean concentrations in atmosphere were all higher than those in soil, and the highest methane concentration was found in air at the height of 16m with the lowest concentration occurring at the depth of 1.5m in soil. The variations of atmospheric methane concentrations did not show any clear pattern both temporally and spatially, although they exhibited a more steadystable state than those in soil. During the seasonal variations, the methane concentrations at different depths in soil were significantly correlated （R^2〉0.6） with each other comparing to the weak correlations （R^2〈0.2） between the atmospheric concentra- tions at different heights. Mean methane concentrations in soil significantly decreased with depth. This was the compositive influence of the decreasing production rates and the increasing methane oxidation rates, which was caused by the descent soil moisture with depth. Although the methane concentrations at all depths varied widely during the growing season, they showed very distinct temporal variations in the non-growing season. It was indicated from the literatures that methane oxidation rates were positively correlated with soil temperature. The higher methane concentrations in soil during the winter were determined by the lower methane oxidation rates with decreasing soil temperatures, whereas methane production rates had no reaction to the lower temperature. Relations between methane contribution and other environmental factors were not discussed in this paper for lacking of data, which impulse us to carry out further and more detailed studies in this unique area.     

NaCl和KCl对厌氧污泥抑制的动力学研究

在厌氧颗粒污泥和厌氧絮状污泥系统中,进行盐质量浓度(NaCl或KCl质量浓度,下同)对厌氧污泥抑制动力学的研究,得到不同拟合的COD降解动力学方程及参数.实验结果表明:当盐质量浓度为10～30 g/L时,KCl对厌氧污泥的COD比降解速率的抑制程度大于NaCl;当盐质量浓度由0 g/L增至10 g/L时,半速率常数逐渐增加;当盐质量浓度由10 g/L增至30 g/L时,半速率常数逐渐减小;在厌氧污泥系统中,NaCl抑制作用下的盐抑制常数高于KCl,且颗粒污泥的盐抑制常数高于絮状污泥.     

固态排渣煤粉炉NOx产生浓度影响因素偏相关分析

利用第一次全国污染源普查“火力发电行业产排污系数核算”工作中现场监测得到的数据,首次采用偏相关分析的方法,对固态排渣煤粉炉中机组规模、空气过剩系数、煤中挥发分和发电负荷率等因素对NOx产生浓度的影响进行定性分析,结论：NOx产生浓度与前三种因素存在显著的相关。而与发电负荷率的关系受锅炉是否采用低氮燃烧技术的影响。空气过剩系数越大,煤的挥发分越高,NOx产生浓度越低;采用低氮燃烧装置的锅炉中,机组规模越大,产生的NOx越少,且对于同一锅炉来说,NOx产生浓度随着发电负荷率的升高而增大;未采用燃烧控制的锅炉中,机组规模越大,NOx产生浓度越高,且与发电负荷率不相关。根据分析结果,提出了控制燃煤电厂固态排渣煤粉炉NOx排放的优化措施和建议。     

Modelling vegetation greenness responses to climate variability in a Mediterranean terrestrial ecosystem

Accurate knowledge of the quality and environmental impact of the highway runoff in Pear River Delta, South China is required to assess this important non-point pollution source. This paper presents the quality characterization and environmental impact assessment of rainfall runoff from highways in urban and rural area of Guangzhou, the largest city of Pear River Delta over 1 year’s investigation. Multiple regression and Pearson correlation analysis were used to determine influence of the rainfall characteristics on water quality and correlations among the constituents in highway runoff. The results and analysis indicates that the runoff water is nearly neutral with low biodegradability. Oil and grease (O&G), suspended solids (SS) and heavy metals are the dominant pollutants in contrast to the low level of nutrient constituents in runoff. Quality of highway runoff at rural site is better than that of at urban site for most constituents. Depth and antecedent dry period are the main rainfall factors influencing quality of highway runoff. The correlation patterns among constituents in highway runoff at urban site are consistent with their dominant phases in water. Strong correlations (r ≥ 0.80) are found among chemical oxygen demand (COD), total phosphorus, Cu and Zn as well as conductivity, nitrate nitrogen and total nitrogen. O&G, COD, SS and Pb in highway runoff at urban site substantially exceed their concentrations in receiving water of Pear River. The soil directly discharged by highway runoff at rural site has contaminated seriously by heavy metals in surface layer accompanying with pH conversion from original acidic to alkaline at present.     

Physical Modeling of Emissions from Naturally Ventilated Underground Parking Garages

The dispersion of pollutants from naturally ventilated underground parking garages has been studied in a boundary layer wind tunnel. Two idealized model setups have been analysed, one was simulating pollutant dispersion around an isolated rectangular building and one was representing dispersion in a finite array of idealized building blocks. Flow and dispersion close to modelled ground level emission sources was measured. The results illustrate the complexity of the flow around buildings and provide insight in pollutant transport from ground level sources located directly on building surfaces. As a result, areas critical with respect to high pollutant concentrations could be visualized. Particularly, the results show high concentration gradients on the surface of the buildings equipped with modelled emission sources. Inside the boundary layers on the building walls, a significant amount of pollutants is transported to upwind locations on the surface of the building. The paper documents the potential of physical modelling to be used for the simulation and measurement of dispersion close to emission sources and within complex building arrangements.     

大气固定污染源低浓度颗粒物采样及分析技术研究进展

简述了我国现阶段大气固定污染源颗粒物监测中遇到的问题及低浓度颗粒物采样与分析技术研究的必要性,归纳了国外低浓度颗粒物采样分析技术要点,包括大体积采样、滤筒上游采样设备堆积颗粒物的回收、有效称重步骤的确立等,并对我国开展低浓度颗粒物采样及分析技术研究提出了相关建议.     

Physicochemical substance properties as indicators for unreliable exposure in microplate-based bioassays

In the last years many efforts were made to transform standardized algal test protocols into low-cost microplate assays. While advantages were pointed out frequently, limitations are not systematically addressed, thus hindering a widespread utilisation. In this study a group of organic substances with a wide distribution of volatility (log K_AW from −6.53 to −2.13) and lipophilicity (log K_OW from 1.26 to 4.92) was investigated with respect to the influence of these physicochemical properties on their algal toxicity in different assays. Therefore the EC₅₀ values were determined with a microplate assay based on ISO 8692 protocol and the results were compared with those of an established algal growth inhibition test conducted in air tight glass vessels. Using the ratio of the EC₅₀ values, a clear connection between biological response and volatility as well as lipophilicity of test substances could be detected. Chemicals with a log K_OW higher than 3 or a Henry coefficient log K_AW higher than −4 were identified as less effective in the microplate assay than in the comparative assay. The loss in nominal concentration due to physicochemical properties could be shown to contribute to this using HPLC analysis. Consequently, when using microplate assay’s one should be aware that lipophilic and volatile chemicals might be underestimated in their toxicity, which could be indicated from evaluating related physicochemical properties modelled from structural information prior to an experimental investigation.     

Laboratory longitudinal diffusion tests: 2. Parameter estimation by inverse analysis

This study focuses on the verification of test interpretations for different state analyses of diffusion experiments. Part 1 of this study identified that steady, quasi-steady and equilibrium state analyses for the through- and in-diffusion tests with solution reservoirs are generally feasible where the tracer is not highly sorptive. In Part 2 we investigate parameter identifiability in transient-state analysis of reservoir concentration variation using a numerical approach. For increased generality, the analytical models, objective functions and Jacobian matrix necessary for inverse analysis of transient-state data are reformulated using unified dimensionless parameters. In these dimensionless forms, the number of unknown parameters is reduced and a single dimensionless parameter represents the sorption property. The dimensionless objective functions are evaluated for individual test methods and parameter identifiability is discussed in relation to the sorption property. The effects of multiple minima and measurement error on parameter identifiability are also investigated. The main findings are that inverse problems for inlet and outlet reservoir concentration analyses are generally unstable and well-posed, respectively. Where the tracer is sorptive, the inverse problem for the inlet reservoir concentration analysis may have multiple minima. When insufficient measurement data is collected, multiple solutions may result and this should be taken into consideration when inversely analyzing data including that of inlet reservoir concentration. Verification of test interpretation by cross-checking different state analyses is feasible where the tracer is not highly sorptive. In an actual experiment, test interpretation validity is demonstrated through consistency between theory and practice for different state analyses.