依据挥发性污染物浓度变化划分土壤气相抽提过程的研究

土壤气相抽提（SVE）是去除包气带土壤中挥发性有机物（VOCs）经济快捷的原位土壤修复方法。VOCs饱和蒸汽压高,能在负压气流下被定向地带到地面收集处理。为了便于划分SVE过程,试验采用两种土壤污染方案：直接污染和间接污染。间接污染土壤的目的是为了避免在土壤中形成非水相液体（NAPLs）,方法是使用气相污染源长时间污染土壤。通过多次对土壤进行间接污染和通风净化,证明VOCs主要来源于NAPLs。试验表明,依据VOCs的浓度变化,SVE过程能被划分为两个阶段：（1）高效去除阶段,即污染土壤中含NAPLs阶段,液态的VOCs进入土壤间隙形成NAPLs或溶解在土壤水中,或被土壤和有机质吸附。SVE过程中VOCs气相浓度降低,停止抽提后浓度能够恢复;（2）低效率的拖尾阶段,即土壤中无NAPLs存在,通风能够快速地降低污染物浓度,并且VOCs浓度降低后不能恢复。试验同时显示出在不同的土质中VOCs浓度变化具有相似的规律。     

含有非水相液体(苯)的土壤气相抽提体系传质实验研究

选取砂土作为实验室一维土柱通风实验的研究对象,考察了不同含水量(0%、21.9%、36.6%及51.2%)条件下,苯在气-水-油-固4相共存的土壤气相抽提体系(Soil vapor extraction,SVE)体系中的相间传质过程。并用局部相平衡模型及非平衡动力学模型预测结果与实验结果进行了比较。干燥情况下,局部相平衡模型可以描述通风过程,随着含水量的增加实验结果严重偏离平衡模型。含水量为21.9%、36.6%及51.2%时,非平衡动力学模型与实验结果较为符合。结果表明,土壤含水量影响气-液(Non-aqueousphase liquid,NAPL)间的传质,干燥土壤中相平衡模型可以描述SVE修复过程。随含水量的增加修复进程偏离相平衡模型较严重,此时需要用非平衡动力学模型来描述。     

A re-examination of closed flux chamber methods for the measurement of trace gas emissions from soils to the atmosphere

The most widely used method for measuring the emission of a trace gas such as N₂O from soil to the atmosphere involves the accumulation of the gas under closed chambers followed by sampling and analysis (by gas chromatography or infrared methods). These chambers can affect the gas exchange, and so improved designs have been proposed. We have tested their performance. One design includes a vent tube to allow ambient pressure fluctuations to occur also inside the chamber. We tested it against a sealed version on two different grassland sites during N₂O peak emissions in spring 1997. On a welldrained soil with a fairly large air permeability vented chambers yielded fluxes as much as five times those of sealed chambers, depending on wind speed. By contrast, on a heavier and wetter soil with smaller air permeability vented chambers averaged only 88% of the fluxes observed with sealed chambers. The effects of venting cannot be explained solely on the basis of mean pressure differences inside and outside the chamber. It seems more likely that wind blowing over the vent depressurizes the chamber (Venturi effect), resulting in significant gas flow from the more permeable soil into the interior of the chamber. The opposite trend for the less permeable soil suggests that diffusion losses through the vent tube are greater than the increase in concentration due to soil gas flow. Venting can create larger errors than the ones it is supposed to overcome.     

乙醇柴油混合燃料发动机EGR系统的标定

对燃用乙醇柴油混合燃料的DL190-12发动机的废气再循环（EGR）系统进行标定。采用真空度控制EGR阀开度的方法,实现废气再循环量的调节。提出了发动机负荷特性试验获取最佳EGR阀真空度的线工况标定方法。运用价值工程原理对发动机台架试验标定数据进行优化处理,建立发动机性能评价模型,设定了发动机性能评价指标,设计了评价指标的权重,并采用二级评价方法得出EGR阀最佳真空度MAP图,结果合理,可用于EGR的控制。     

A Laboratory Column Study on the Biodegradation of Toluene and Methyl tert–Butyl Ether: The Effect of Substrate Interactions

Soil vapor extraction (SVE) is one of the most effective remediation technologies for soil and groundwater contamination. Soil particles can be mobilized by air perturbation during SVE, resulting in the differentiation of porous media, which has not been well addressed. This paper developed a numerical method to study the flow pattern and quantify the change of porous media for the first time. Based on the mass equilibrium and Darcy’s law, a two-phase water–air flow model was constructed with integration of saturation, relative permeability, and capillary pressure during SVE. Relationship between porosity and saturation was deduced and coupled with the two-phase flow model for quantifying change of porous media in real time. Results reveal that both porosity and permeability increase sharply in the early stage of SVE then gradually to a quasi-steady state. These increases in vadose zone tapered off with distance from the SVE screen and the steady period occurred later as well. The influence radius of a single SVE well and the change degree in porosity and permeability of media were proportional to the extraction vacuum and the driving coefficient C, which is more sensitive than extraction vacuum according to the simulation results. Knowledge from this modeling exercise provides a useful tool to estimate the change of remediated zone and assess the environmental risk of remedial activities at real-world contamination sites.     

通风速率对土壤中四氯化碳污染物去除效率的影响研究

某重要岩溶地下水源地受到四氯化碳的严重污染,为此采用土柱通风试验模拟土壤气相抽提（SVE）净化四氯化碳污染物的过程,对通风速率为40mL·min-1和70mL·min-1两种条件下土壤四氯化碳的去除过程进行了试验模拟研究。结果表明,土柱通风能有效去除土壤中的四氯化碳污染物,通风条件下土壤中四氯化碳的去除过程符合一级反应动力学,土壤中四氯化碳浓度C的对数值ln[C（/μg·L-1）]与时间t呈良好的线性关系,相关系数均在0.95以上。通风速率为40mL·min-1的土柱A各取样口四氯化碳去除反应速率常数k值在0.0132～0.0155h-1之间,通风速率为70mL·min-1的土柱B各取样口k值在0.0178～0.0222h-1之间,说明增大通风速率能提高土壤中四氯化碳污染物的去除效率。     

A Rapid and Simple Manifold to Study Exchangeable Cations and Cation Exchange Capacity in 24 Soil Samples Simultaneously

ABSTRACT

The outcomes of this work highlight the development and validation of a rapid and simple manifold for determination of exchangeable cations [calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K)] and cation exchange capacity (CEC) in soil. First, the performance of the manifold was evaluated to determine the best conditions to use: filter assembly, volume and number of aliquots of extracting solution, and the use of vacuum. Second, the analytical performance was study from trueness and precision analysis. For that, soil samples with assigned values, an in house reference material and unknown soil samples, were used, comparing their results with those obtained using the classical extraction method (agitation, centrifugation, and filtration). The performance study showed that a filter system assembled with S&S Nº859 type filter paper, cotton, and plastic piece is better to the other studied options. Four aliquots of 10 mL extracting solution and a few seconds of vacuum between additions is recommended to achieve the best recovery. The extraction procedure proposed using the manifold demonstrated to be accurate, and so can effectively replace the classical method for the extraction of exchangeable cations and CEC in soils. Regarding simplicity, rapidity, and simultaneity, the manifold method could be the method of choice for extraction up to 24 samples. Moreover, the manifold method significantly reduces the laboratory supplies and instrument used in the extraction steps in the classical method, attaining better efficiency and reducing costs associated to this stage of the analysis.     

Comparing forms and solutions of the single root soil water extraction model

Different forms and solutions of the single root model (SRM) arise from: assumed functional relationships between the radius of the SRM soil cylinder and the rooting density (L_r); averaging modes of hydraulic conductivity (K); steady-state or steady-rate flow assumption; and methods of evaluating the root geometry factor (B). SRM forms and solutions, in particular B approximations, were evaluated by analytical comparison and by performance, when incorporated into a water uptake simulation model for oats. The approximation of B as a constant, or as an exponential function of rooting density (B′), had only a small temporary effect on soil water extraction rates and potentials at the soil—root interface. A combination of B′ with exponential rooting profile estimation is proposed as an optimal SRM form for water uptake analysis. It is shown (in appendices) that: (1) assuming SRM steady-state flow to originate on average from the volumetric middle of the SRM soil cylinder is nearly equivalent to the assumption of a steady-rate flow; and (2) utilizing a geometric mean K for the SRM soil cylinder may cause soil water extraction rates to be underestimated.     

考虑灌溉参数空间变异的区域畦灌模拟与验证

精确评估区域畦田灌水质量有助于提高农田灌水管理水平,而具有空间变异性的灌溉参数如何有效表征是影响区域畦田灌水质量精确模拟评价的关键因素。为此,该研究的目的在于借助Monte-Carlo抽样,建立考虑畦灌参数空间变异性的区域畦灌模拟方法。采用Monte-Carlo抽样将具有空间变异性的区域灌溉参数(如入畦单宽流量、土壤砂粒含量、黏粒含量、土壤容重等)离散表征为若干个灌溉参数样本,依次输入田块尺度畦灌地表水流-土壤水动力学耦合模型,以模拟评价区域畦灌过程。基于3次区域畦灌试验的实测数据和1个对比的确定性畦灌模拟方法,验证建立的模型的模拟效果。结果表明,所建模拟方法与确定性模拟方法模拟计算的灌水效率和灌水均匀具一定差异,所建模型的模拟值与实测值间的灌溉定额和田间水利用系数相对误差分别为9.95%~12.23%和8.39%~10.21%,而基于现有模型的相对误差则分别为14.15%~16.78%和13.87%~15.88%,畦田平均土壤含水率实测值与所建模型模拟值的累积分布趋势表现出良好的一致性。上述指标表明所建模拟方法有效缩小了区域灌溉参数空间均化处理所带来的模拟误差范围较大等问题,为区域畦田灌溉优化设计和管理提供了技术支撑。     

A mathematical model for removing volatile subsurface hydrocarbons by miscible displacement

A mathematical model is developed for analyzing the forced venting method of controlling hazardous vapors escaping from underground spills. Equations for predicting concentration profiles are derived from the fundamental laws governing the isothermal flow and dispersion of two-component, miscible, compressible fluids in a porous medium. The resulting equations are solved numerically by finite difference methods to predict concentration profiles for a two-dimensional venting process. Concentration profiles were found to be more sensitive to the dispersion coefficient than to porosity or permeability for the flow rates examined. A comparison of the model profiles with laboratory measurements indicated that realistic predictions are feasible.     

强化生物通风修复柴油污染土壤影响因素的正交实验

生物通风是继SVE后又一项主要的生物修复技术,在石油污染土壤修复中拥有广阔的前景。为寻求最佳修复效果的最优组合,采用生物通风修复柴油污染土壤的正交土柱实验,对影响生物通风修复效果的5个主要因素（污染强度、土壤含水率、C：N：P、通风的孔隙体积数、通风方式）进行了定量化。结果表明,利用强化生物通风可以在柴油污染土壤的治理中取得较好的效果;方差分析各因素均无显著性影响;极差分析得到影响强化生物通风柴油去除效果的最主要因素为土壤含水率、污染强度,次主要因素为C：N：P、通风的孔隙体积数,而通风方式对去除率的影响很小;在实验的不同阶段有些因素的最优水平有不同程度的改变,总体来说各因素的最佳水平分别为：土壤含水率为4．88％,污染强度为40000mg·kg^-1,C：N：P为100：20：1,通风的孔隙体积数为4,而通风方式的两种水平对去除率的影响相差不大。     

A Facility to Investigate Effects of Elevated Soil Gas Concentration on Vegetation

A facility has been developed at the University of Nottingham at which natural gas can be injected into soil to investigate the effects on the soil ecology and on the growth and development of plants. The facility involves 18 plots, 12 of which are equipped with a regulated and metered gas supply. The gas is released from a diffusive point source 1 m below the centre of each plot. Permanent pasture grass, wheat and bean were gassed from October 2002 until July 2003 at a target flow rate of 100 L h^?1. From May 2003 until July 2003 gas was injected into additional plots of each species to determine the effects of a new leak on a fully established crop. Spatial and temporal variability of soil gas concentrations were determined by two complementary methods. First, by daily extraction of soil gas samples from permanently buried sample pipes that come to diffusive equilibrium with the adjacent soil gas concentration. Second, by intermittent extraction of soil gas samples from bar holes inserted on a 50-cm grid. Contour plots of spatial variation were then constructed from the bar hole data. Methane (CH₄) concentrations near the centres of the plots were variable. They could reach values of up to 80% gas, but decreased rapidly away from the area of peak concentration. No relationship was found between gas flow rate or soil gas concentration and atmospheric pressure or other meteorological parameters. Soil structure affected gas dispersion, and an inverse relationship was found between CH₄ and O₂ concentrations. The grass showed visible symptoms within 44 days, whereas wheat and bean developed symptoms after four months. These symptoms included a circle of chlorosis in grass and poor development and leaf chlorosis for the wheat and bean. When the same species were gassed from mid-May; the wheat and bean showed no visible symptoms but the late-gassed grass also developed a further circle of yellowing.     

挥发性有机物污染土壤蒸气抽排模型研究进展

土壤蒸气抽排是一种当前国外广泛应用的土壤现场修复技术,它能经济高效地去除非饱和带土壤中的挥发性有机污染物。本文详细叙述了土壤蒸气抽排中的地下抽排气体流场模型和污染物去除模型的发展过程和研究现状;描述了适合不同情况的一维、二维和三维抽排气体流场模型,以及不存在非水相液体和存在非水相液体的两类污染物去除模型的特点和适用条件;总结了运用各种模型,分析土壤气透性、污染物挥发性和抽排流速等主要因素对土壤蒸气抽排去污效果的影响及所取得的研究成果;对土壤蒸气抽排模型的研究和运用中目前需要解决的问题及发展前景进行了展望。     

Topographic modelling of soil moisture conditions: a comparison and verification of two models

Topography, as captured by a digital elevation model (DEM), can be used to model soil moisture conditions because water tends to flow and accumulate in response to gradients in gravitational potential energy. A widely used topographic index, the soil wetness index (SWI), was compared with a new algorithm that produces a cartographic depth-to-water (DTW) index based on distance to surface water and slope. Both models reflect the tendency for soil to be saturated. A 1 m resolution Light Detection and Ranging (LiDAR) DEM and a 10 m conventional photogrammetric DEM were used and results were compared with field-mapped wet soil areas for a 193 ha watershed in Alberta, Canada, for verification. The DTW model was closer to field-mapped conditions. Values of K_match90 (areal correspondence, smaller values indicating better performance) were 7.8% and 12.3% for the LiDAR and conventional DEM DTW models, respectively, and 88.5% and 86.7% for the SWI models. The two indices were poorly correlated spatially. Both DEMs were found to be useful for modelling soil moisture conditions using the DTW model, but the LiDAR DEM produced the better results. All major wet areas and flow connectivity were reproduced and a threshold value of 1.5 m DTW accounted for 71% of the observed wet areas. The poor performance of the SWI model is probably because of its over-dependence on flow accumulation. Incorporation of a flow accumulation algorithm that replicates the effects of dispersed flow showed some improvement in the SWI model for the conventional DEM but it still failed to replicate the full areal extent of wet areas. Local downslope topography and hydrologic conditions seemed to be more important in determining soil moisture conditions than is taken account of by the SWI. The DTW model has potential for application in distributed hydrologic modelling, precision forestry and agriculture and implementation of environmental soil management practices.     

不同温度下的土壤热导率模拟

土壤热导率是研究陆地表层水热盐耦合运动的基本物理参数。由于水汽潜热传热在高温下的显著作用,高温下的土壤热导率显著高于常温值。该研究的目的是建立能够有效预测高温下土壤热导率的模型。在气体扩散定律的基础上,该文结合常温土壤热导率模型,提出了一个计算高温土壤热导率的新方法。并利用热脉冲技术实际测定了不同温度、不同含水率下的土壤热导率,对新模型进行了测试验证。结果表明,Cass等的水汽运移促进因子参数依赖于土壤质地,且存在较大的不确定性。经过对该参数修正后,建立的热导率模型均能够较好地模拟出高温下的土壤热导率。     

土壤中土霉素残留的高效液相色谱检测方法

为有效测定土壤中土霉素残留量,建立了固相萃取－高效液相色谱法提取以及测定潮土、红壤、紫色土中土霉素残留量的方法。土壤中土霉素残留经提取缓冲溶液进行有效提取,经过DVB固相萃取小柱纯化、无水甲醇洗脱和氮气流浓缩后,经HPLC测定。对提取缓冲液、流动相以及流动相pH值、有机相与无机相的比例以及流速等测定条件进行优化研究。结果表明：提取液为Na2EDTA-Mcllvaine,流动相为乙腈∶0.01mol/L磷酸二氢钠（pH值2.5,V∶V=10∶90）,温度25℃,流速1.2ml/min,检测波长350nm对3种不同性质的土壤中土霉素残留量的测定最为合适。应用本方法进行土壤中土霉素残留量的测定,土霉素含量与峰面积具有良好的线性关系,相关系数（n=9）分别为红壤0.997,紫色土0.995,潮土0.987;检出限分别为红壤0.11mg/kg,紫色土0.17mg/kg,潮土0.09mg/kg;回收率(n=18)分别为红壤80.7%~128.8%,紫色土70.5%~100.0%,潮土61.5%~103.9%;相对标准偏差(RSD, n=18)分别为红壤7.1%~28.2%,紫色土11.9%~38.1%,潮土4.1%~17.0％。本方法简便、准确,适合于测定不同土壤中土霉素残留量,结果可靠。     

抽气方式与充气压力对盒式气调包装气体置换性能的影响

基于不同条件的气体置换流场分析是实现气体置换工艺参数与结构优化的基础。针对盒式气调包装机的关键装置—气体置换装置的物理模型进行流场分析,采用RNG k-ξ湍流模型对进行气流流场数值模拟,建立盒式气调包装气体置换结构内部三维流场;比较等效面积下3种抽气方式对包装内部气体置换性能的影响,确定抽气孔的优化布置方式;分析不同压差工况下的气体置换速度,确定充气压力适宜的工作范围。结果表明,当压强相对于极限真空处于粗真空时（0.04～ 0.1 MPa）,3种抽气方式的气体置换效率差异不显著,随着压强的减小（小于0.04 MPa）,中间抽气方式优于两边抽气方式;同时,采用中间抽气,两边四孔充气方式时,充气压力大于0.5 MPa,有利于获得较高的气体置换精度与置换效率。     

Uncertainty in the spatial prediction of soil texture: Comparison of regression tree and Random Forest models

Within the southern Ecuadorian Andes, landslides have an impact on landscape development. Landslide risk estimation as well as hydrological modelling requires physical soil data. Statistical models were adapted to predict the spatial distribution of soil texture from terrain parameters. For this purpose, 56 soil profiles were analysed horizon-wise by pipette and laser method. Results by pipette compared to laser method showed the expected shift to higher silt and lower clay contents. Linear regression equations were adapted. The performance of regression tree (RT) and Random Forest (RF) models was compared by hundredfold model runs on random Jackknife partitions. Digital soil maps of sand, silt and clay percentage mean and standard deviation indicate model variability and prediction uncertainty.RF models performed better than RT models. All terrain factors considered in the analysis influenced soil texture of the surface horizon, but altitude a.s.l. was assigned the highest variable importance during model construction. Shallow subsurface flow is considered responsible for increasing sand/clay ratios with increasing altitude, on steep slopes and with overland flow distance to the channel network by removing clay particles downslope. Deeper soil layers are not influenced by this process and therefore, did not show the same texture properties. However, the influence of parent material and landslides on the spatial distribution of soil texture cannot be neglected. Model performance, most probably, could be improved by a bigger dataset.     

气力滚筒式水稻直播精量排种器排种性能分析与田间试验

为了提高气力滚筒式水稻直播精量排种器的排种性能,该文运用单因素和中心组合试验设计理论,借助JPS-12型排种器性能检测试验台,研究了排种滚筒转速、负压气室真空度、清种气流速度及正压气室清堵正压4个主要运行参数对其排种性能的影响规律。单因素试验结果表明:排种滚筒转速、负压气室真空度、清种气流速度对排种器合格率、漏播率等指标的影响显著;正压气室清堵正压对排种器合格率、漏播率等指标的影响不显著;3个影响显著因素的三因素五水平回归正交旋转组合设计试验结果表明:各试验因素及因素交互作用对主要评价指标的影响主次顺序不同,影响排种器合格率的主次因素依次为:排种滚筒转速负压气室真空度清种气流速度;影响漏播率的主次因素依次为:负压气室真空度排种滚筒转速清种气流速度;对所建回归方程进行综合优化,得出排种器最佳工作参数组合为:排种滚筒转速10.00 r/min,负压气室真空度4.6 k Pa,清种气流速度21.88 m/s。此时,排种器的合格率为87.73%、漏播率为2.93%、空穴率为0.53%、重播率为9.34%、破损率为0.91%、穴距平均值为200.07 mm、穴距变异系数为4.75%、各行排量一致性变异系数为3.07%、总排量稳定性变异系数为2.08%。田间播种试验结果为合格率79.42%、漏播率15.11%、空穴率3.88、重播率5.47%、穴距平均值175.61 mm、穴距变异系数为20.03%。研究结果为气力滚筒式水稻直播精量排种器结构参数优化及排种性能提升提供参考。     

Aroma characteristics of stored tobacco cut leaves analyzed by a high vacuum distillation and canister system

An extraction method using a high vacuum distillation extraction apparatus coupled to a canister was newly developed for the analysis and sensory test of tobacco leaf volatiles. We extended the application of the canister that is used in environmental analysis, to the extraction of the aroma components in tobacco leaves. The volatile components with vapor pressures higher than 0.1 mmHg were easily evaporated under decompression and then trapped into the vacuumed canister. After the collection of volatiles, the canister was pressurized by a slow stream of inert gas in order to emit the whole aroma under a controlled flow. Applying a preconcentrator--gas chromatography/mass spectrometry (GC/MS) and sensory test to the headspace gas components, the aroma alteration between 0 and 2 weeks of storage was simultaneously or individually evaluated. As a result, after the storage, alcohols such as 1-hexanol, linalool, and benzyl alcohol decreased significantly. The amount of carotenoid derivatives that have the characteristic tobacco leaf aroma had not changed. Sensory evaluation of the same headspace gas with that used for GC/MS demonstrated the alternation of the aroma quality before and after storage. The main changes were the decrease of greenness and smoothness in aroma and the decrease of ethylbenzene, 2-pentylfuran, 1-hexanol, benzaldehyde, and linalool concentrations.