The natural (baseline) quality of groundwater: a UK pilot study

Knowledge of the natural baseline quality of groundwaters is an essential prerequisite for understanding pollution and for imposing regulatory limits. The natural baseline of groundwaters may show a range of concentrations depending on aquifer mineralogy, facies changes, flow paths and residence time. The geochemical controls on natural concentrations are discussed and an approach to defining baseline concentrations using geochemical and statistical tools is proposed. The approach is illustrated using a flowline from the Chalk aquifer in Berkshire, UK where aerobic and anaerobic sections of the aquifer are separately considered. The baseline concentrations for some elements are close to atmospheric values whereas others evolve through time-dependent water-rock interaction. Certain solutes (K, NH(4)(+)), often considered contaminants, reach naturally high concentrations due to geochemical controls; transition metal concentrations are generally low, although their concentrations may be modified by redox controls. It is recommended that the baseline approach be incorporated into future management strategies, notably monitoring.     

Explosions in buildings: modeling and interpretation of real accidents

Real explosions in domestic structures (Rasbash and Stretch, Struct. Eng 1969;47;403–11) and industrial plants (Howard, Loss Prevention 1972;6;68–73) have been analyzed. Deflagration dynamics are solved for enclosures of volumes of 130–8000 m³ for vent release overpressures in the range of 0–0.21 bar, and for different inertia of covers over the venting spaces in the range 0–15 kg/m². From comparisons of the real explosion data with the modeling of pressure-time behavior during vented gaseous deflagrations according to an earlier lumped parameter theory values of the main parameter, a turbulence factor, χ, are obtained. The results suggest the combustion is highly turbulent for real conditions in domestic structures (turbulence factor χ⩾8 with discharge coefficient μ=0.6) and especially in large-scale enclosures such as a plant, with internal obstacles (turbulence factor χ⩾17). On the basis of the devised effective turbulence factors (the ratio χ/μ) the design procedures for avoiding the development of excessive overpressures during deflagrations, in both domestic and industrial plant, can be improved.     

Numerical and experimental hydrodynamic studies of a lagoon pilot

The determination of residence time is of major interest in terms of the characterisation, design and modelling of most environmental engineering processes, where a proper and homogeneous fluid distribution is often essential, and especially in the domain of wastewater or waste material treatment. In this paper, two different numerical methods for obtaining theoretical predictions of residence time distributions using the finite volume method are used. The first one consists of solving a transport equation of the local mean age of the fluid, which is the average time that a fluid particle takes to reach any point of the domain from a supply inlet. The result obtained is a spatial distribution of the local mean age of the fluid, which may be displayed as isocontours in the space domain considered. The second one consists of injecting a virtual particle stream (i.e. a fluid particle having the same density as the surrounding fluid, and treated numerically as a tracer) and measuring the time elapsed between the injection and the termination of the trajectory using a Lagrangian reference frame. The result obtained is expressed as an exit time distribution and may be displayed as a histogram. Finally, a comparison with measurements of mean residence times of tracers in a lagoon is made in order to establish the relevance of this method in concrete form. The prediction enables the instantaneous determination of the geometrical characteristics of the flow that contribute actually to the residence time dispersion. Its appropriate use prior to the design of water treatment and waste material treatment installations should contribute to prevent undesirable flow patterns such as short-circuiting and dead spaces.     

Comparison of batch sorption tests, pilot studies, and modeling for estimating GAC bed life

Saint Paul Regional Water Services (SPRWS) in Saint Paul, MN experiences annual taste and odor episodes during the warm summer months. These episodes are attributed primarily to geosmin that is produced by cyanobacteria growing in the chain of lakes used to convey and store the source water pumped from the Mississippi River. Batch experiments, pilot-scale experiments, and model simulations were performed to determine the geosmin removal performance and bed life of a granular activated carbon (GAC) filter-sorber. Using batch adsorption isotherm parameters, the estimated bed life for the GAC filter-sorber ranged from 920 to 1241 days when challenged with a constant concentration of 100 ng/L of geosmin. The estimated bed life obtained using the AdDesignS model and the actual pilot-plant loading history was 594 days. Based on the pilot-scale GAC column data, the actual bed life (>714 days) was much longer than the simulated values because bed life was extended by biological degradation of geosmin. The continuous feeding of high concentrations of geosmin (100-400 ng/L) in the pilot-scale experiments enriched for a robust geosmin-degrading culture that was sustained when the geosmin feed was turned off for 40 days. It is unclear, however, whether a geosmin-degrading culture can be established in a full-scale filter that experiences taste and odor episodes for only 1 or 2 months per year. The results of this research indicate that care must be exercised in the design and interpretation of pilot-scale experiments and model simulations for predicting taste and odor removal in full-scale GAC filter-sorbers. Adsorption and the potential for biological degradation must be considered to estimate GAC bed life for the conditions of intermittent geosmin loading typically experienced by full-scale systems.     

Dynamic modeling of bacteria in a pilot drinking-water distribution system

Computer modeling can be a useful tool in understanding the dynamics of bacterial population growth. Yet, the variability and complexity of biological systems pose unique challenges in model building and adjustment. Recent tools from Bayesian statistical inference can be brought together to solve these problems. As an example, the authors modeled the development of biofilm in an industrial pilot drinking-water network. The relationship between chlorine disinfectant, organic carbon, and bacteria concentrations was described by differential equations. Using a Bayesian approach, they derived statistical distributions for the model parameters, on the basis of experimental data. The model was found to adequately fit both prior biological information and the data, particularly at chlorine concentrations between 0.1 and 2 mg/liter. Bacteria were found to have different characteristics in the different parts of the network. The model was used to analyze the effects of various scenarios of water quality at the inlet of the network. The biofilm appears to be very resistant to chlorine and confers a large inertia to the system. Free bacteria are efficiently inactivated by chlorine, particularly at low concentrations of dissolved organic carbon.     

Arsenic removal by zero-valent iron: field,laboratory and modeling studies

Field and laboratory studies were conducted to elucidate the design factors and mechanisms of arsenic removal from contaminated ground water using zero-valent iron. Large scale, field pilot experiments demonstrated for more than 8 months that iron filing filters can efficiently remove arsenite from aqueous solutions to levels less than 10 micro g/L. The maximum arsenic accumulation measured was 4.4 mg As/g of media. The iron filing filters leached significant quantities of iron (73% of the iron was leached). A critical design parameter of the system was found to be the hydraulic detention time of the water in the filter. TCLP analyses of the spent media indicated that the arsenic concentration in the leachate was two orders of magnitude lower than the 5mg/L of TCLP for arsenic. Spectroscopic and laboratory arsenic leaching studies (alkaline extraction and TCLP) suggest that the arsenic surface precipitate is related to sulfur. The aging process (due to the longevity of the removal mechanism) makes the precipitation process virtually irreversible. A mathematical model was developed to simulate the removal process using a partitioning coefficient and a mass transfer process. Calibration of these parameters using the data for three columns revealed that the equilibrium-partitioning coefficient was the same for all three columns while the mass transfer coefficient was a function of the flow rate. The calibrated mass transfer coefficients are similar to those reported in the literature if they are normalized to the surface area of the media.     

BAF工艺处理微污染含铁锰地下水试验研究

采用BAF工艺处理微污染含铁锰地下水,研究了其净化效能和适宜的运行条件.结果表明,在水力负荷为4-5 m3/(m2·h),气水比为3:1-4:1的试验条件下,BAF工艺能有效去除氨氮、锰、铁、CODMn.和浊度.当原水铁含量小于2 mg/L,滤层中部DO在4 mg/L左右时,对氨氮的去除效果最佳.微量Fe2+即可维系滤...     

西南喀斯特小流域地下水数值模拟

本文以位于西南典型喀斯特地区的贵州普定后寨河流域为研究对象,采用等效连续导水介质体概化方法建立喀斯特流域地下水数值计算模型.运用MODFLOW中的排水沟渠子程序包以及河流子程序包,构建考虑地表河与地下河系统与含水层地下水流交换水动力过程模拟方法,分析后寨河流域地下水流运动特征,估算含水层补排水量.模型计算的地下水位动态...     

地下水曝气修复过程离心模型试验研究

为了研究地下水曝气修复机理及其影响因素,采用离心模型试验模拟地下水曝气修复过程,其中土体用透明玻璃珠代替以便于图像观察和分析处理,同时由于模型能够提高土体的应力水平,从而可以在较大范围内研究曝气压力的影响。离心模型试验得到了气体运动规律和曝气影响区域的特征。研究表明：土体中的气体流速随曝气压力增加而逐渐增大;曝气影响范围在曝气压力较小时随曝气压力增加而增大,当曝气压力持续增大超过临界压力时,影响范围将保持稳定;曝气影响范围随土体粒径的增大而减小,随离心加速度增大而减小;曝气影响范围为锥形,可以采用虚拟曝气点和稳定渗气夹角定量描述。试验成果可以为曝气修复系统的设计和运行提供参考依据。     

地下水曝气修复技术的模型试验研究

地下水曝气法是修复土壤和地下水有机污染的有效方法。通过模型试验,探讨了地下水曝气法的工作机理,研究了气体不同类型土体中的运移方式和影响区域。研究表明,最小曝气压力的大小取决于土体毛细压力和静水压力;在孔隙较大的砾石体中,气体以独立气泡的方式运移,单井影响区域基本为抛物型,超过一定曝气压力值后其影响半径不再变化;在孔隙较小的细砂中,气体以稳定的微通道方式运移;当曝气压力相同时,细砂中空气流量小于砾石中的空气流量,但是单井影响范围较砾石体大,脉动曝气效果也较好。     

Treatment of dairy wastewater by inorganic coagulants: Parametric and disposal studies

Present study reports treatment of simulated dairy wastewater (SDW) by inorganic coagulants such as poly aluminum chloride (PAC), ferrous sulphate (FeSO₄) and potash alum (KAl(SO₄)₂·12H₂O). Batch coagulation experiments were conducted to evaluate the influence of initial pH (pH_i: 5–10) and coagulant dosage (m: 100–5000 mg/L) on chemical oxygen demand (COD) removal from SDW. Residual COD and system pH were observed as function of time. Optimum pH_i (pH_i,op) was found to be 8.0 for all the three coagulants. Optimum m (m_op) was found to be 300, 800 and 500 mg/L for PAC, FeSO₄ and KAl(SO₄)₂·12H₂O, respectively, giving 69.2, 66.5 and 63.8% COD removal efficiency in 30 min. Heating values of the sludge generated by the coagulants PAC, FeSO₄ and KAl(SO₄)₂·12H₂O were found to be 20.7, 29.6 and 17.3 MJ/kg, respectively.     

水井抽水引起地基沉降的离心模型试验研究

地下水的开采是引起地面沉降的重要因素之一.通过离心模型试验研究抽水引起的地基变形.研制一套离心场中地基抽水的模拟和测量系统.进行离心模型试验,测量抽水过程中粉土地基孔隙水压力和沉降的变化及分布规律,探讨渗透作用对地面沉降发展规律的影响.试验结果表明靠近抽水位置区域的地基变形大于远离抽水位置区域,排水引起的地基沉降量与其不均匀程度随着排水次数和沉降的增大有逐渐减小的趋势.在地下水开采过程中,地基侧向变形也是引起地面沉降的重要影响因素.地基渗流场变化强烈的发展阶段对于地基沉降的影响值得关注.     

基于颜色Petri网的再制造工艺过程建模与优化调度方法

针对再制造工艺过程的众多不确定性问题,建立了一个基于颜色Petri网的再制造工艺过程模型,引入颜色标识描述了再制造工艺路线的不确定性、再制造工艺时间的不确定性和再制造资源冲突不确定性。以最小化再制造工艺成本和延期交货惩罚成本为目标建立了再制造优化调度模型,并提出了一种基于模拟退火算法和最小松弛时间规则的优化调度方法。该混合算法结合概率突跳特性在解空间中随机寻优,确定最优的再制造工艺路线和零部件加工优先级。将所提出的优化模型和方法应用到某废旧机床再制造实践中,运用Matlab编程开展再制造调度仿真。仿真结果表明:所提出模型与方法与基准案例相比,可平均减少15%的再制造总成本。     

含水介质非均质概化对地下水数值模拟的影响分析

实际地下水系统的复杂程度远远超出目前人们可以用数学方法准确刻画的程度,地下水模型建立通常依赖于一系列对野外真实情况的假设和近似.由于观测资料的稀疏性以及观测误差等人为因素,导致含水介质非均质性参数分区不能准确地反映实际情况,存在不同程度的概化,便会引起数值模拟结果的不确定性.本文着重探讨了不同程度的含水介质非均质概化对...     

黑河流域地下水流数值模拟的研究进展

地下水在黑河流域水文过程和水资源转化中发挥着重要的作用。近20年来,研究者们专门针对黑河流域提出了一批地下水的数值模拟模型。这些模型在结构上可分为单层平面模型、双层准三维模型和多层三维模型。对包气带、河流与泉、开采井、季节性冻融等关键因素,现有模型采取了相似或不同的刻画方法,取得了一定的进展。未来的黑河流域地下水模型应加强与地表水、土壤水、水利工程等关联模型的耦合。     

长大隧道施工中地下水处理

介绍了几种地下水的探测和预报方法,针对施工中可能突发漏水的部位,依照“以堵为主,堵排结合”的处理原则,提出了地下水的处理方法,有效地防止了地下水对施工的危害,确保了长大隧道的施工质量。     

Air pollution and terrain aerodynamics: A review of fluid modeling studies at the EPA fluid modeling facility

Recent fluid modeling studies conducted at the EPA Fluid Modeling Facility of flow and diffusion in complex terrain are reviewed. Ratios of the maximum concentration on a hill surface to the maximum concentration in the absence of the hill are estimated. This ratio may be regarded as a terrain amplification factor and is a function of hill aspect ratio (two-versus three-dimensional), hill slope, atmospheric stability, etc. For upwind sources, terrain amplification factors are typically 1 to 2 for neutral flow over two-dimensional hills and 2 to 4 for three-dimensional hills. Terrain amplification factors as large as 10 or 15 were found for low sources placed downwind of two-dimensional hills of moderate to large slope. For strongly stable flow over three-dimensional hills, it is more useful to compare maximum surface concentrations with those at the centerline of the plume in the absence of the hill. These concentrations have been shown to be essentially equal.     

Study of signal-to-noise ratio driven by colored noise

This paper investigates the signal-to-noise ratio(SNR)driven by colored noise and weak input signals.Based on the Cauchy-Schwarz and Rayleigh quotients inequalities,an analytical expression of SNR is developed,and its upper band is closely related to the Fisher information of noise.For mimicking the colored noise,we adopt the first-order moving-average model and propose the optimal input signal waveform.The stochastic resonance effect in threshold systems is demonstrated for the Gaussian mixture colored noise.The obtained results will be interesting in the case of improving the nonlinear filter performance by adding noise to the weak signal corrupted by the colored noise.     

Clogging of a limestone fracture by stimulating groundwater microbes

Biological clogging is promoted in aquifers either to contain or to remediate groundwater. In this study, an apparatus able to detect small changes in hydraulic conductivity (K) was developed to measure the clogging of a single fracture in limestone, following microbial stimulation. The fracture had a 2.5 mm2 section and was 50 cm long. Prior to the inoculation of the limestone, the sequencing of representative clones from 16S rRNA genes isolated from groundwater, showed significant affiliation with Cytophaga spp., Arcobacter spp. and Rhizobium spp. These bacteria are known to secrete extracellular polymeric substances and form biofilms. When nutrients were added to the inoculated limestone, a decrease in K occurred after 8 days, reaching 0.8% of its initial value after 22 days (Kfi = 340 cm min-1). This study showed that a stimulation of indigenous microbes from groundwater effectively clogged a macrofracture in limestone, suggesting the potential application of biobarriers in fractured rock aquifers.     

Organic indicators of groundwater pollution by a sanitary landfill

The organic composition of leachate from the Barcelona sanitary landfill is described. According to the low degree of stabilization of the disposed garbage the acid fraction accounts for 80–90% of the total organic extract. More than 50 individual organic components have been identified, indicating catabolic degradation of lipids (e.g. C₄–C₁₁ carboxylic acids), proteins (e.g. indole derivatives) and lignins (e.g. p-hydroxyphenyl derivatives) or simply compounds originally present in the refuse that have been washed out by percolating waters (nicotine, caffeine, phthalates).To obtain a monitoring system for the groundwater pollution originated by this landfill leachate, an analytical method is proposed based on the GC-ECD fingerprinting of groundwater acidic extracts after derivatization with PFB bromide. The chromatogram contains carboxylic and phenolic components and the profiles exhibited by waters from several test wells in the downstream edge of the landfill were indicative of the suspected leachate pollution.