Treatment of secondary effluents by infiltration-percolation process using sand fortified with activated charcoal

The main purpose of this study was to investigate the ability of sand/granular activated charcoal mixture medium to treat urban wastewater effluents. Several laboratory experiments were conducted to determine the best combination ratio of sand/activated charcoal which would allow the optimum water purification. A comparative study was undertaken to evaluate the effect of the addition of activated charcoal on infiltration-percolation efficiency. Experiments demonstrated that fortifying sand medium with granular activated charcoal improved the pollutants removal efficiencies. Results showed that a combination ratio of 3:1 (by volume) of sand and granular activated charcoal gave the best depuration efficiency regarding organic matter, nitrogen and orthophosphorous. The mean removal rates of COD, NH₄–N and PO₄–P were 83.29, 95.85 and 65.21%, respectively. Furthermore, experiments demonstrated that a mixture of sand/activated charcoal in a 3:1 ratio resulted in the optimum oxidation capacity.     

Bioregeneration of granular activated carbon loaded with phenolic compounds: effects of biological and physico-chemical factors

Bioregeneration is a process of restoring the adsorptive capacity of the spent adsorbents through microbial action. In this study, the effects of acclimated biomass concentration, biomass acclimation concentration, dosage of granular activated carbon (GAC) and type of GAC on the bioregeneration efficiency (BE) of GAC loaded with phenol and p-nitrophenol (PNP), respectively, were investigated. The quantification was conducted by monitoring the time courses of adsorbed substrate amount during bioregeneration under the sequential adsorption and biodegradation approach. The mean BEs of phenol- and PNP-loaded GAC were found to be 78 ± 2 and 77 ± 1%, respectively. The results revealed that increasing acclimated biomass concentration and adsorbent dosage did not have an observable effect on the BEs of phenol- and PNP-loaded GAC. Additionally, the BEs were found to be almost the same for the bioregeneration of phenol-loaded GAC using biomass acclimated to 350 and 600 mg/L of phenol, respectively. The BEs of phenol-loaded GAC 830 (thermal-activated) and GAC 1240+ (thermal- and acid-activated) did not show any observable difference, but the BE of PNP-loaded GAC 1240+ was found to be greater than that of PNP-loaded GAC 830 indicating that the improvement of BE of spent GAC through further chemical activation was dependent on the type of adsorbate.     

Adsorption of methyl tert-butyl ether using granular activated carbon: Equilibrium and kinetic analysis

The adsorption of methyl tert-butyl ether by granular activated carbon was investigated. The experimental data were analyzed using the Freundlich isotherm and the Langmuir isotherm. Although equilibrium data were found to follow Freundlich isotherm model, it were fitted better by the Langmuir model with a maximum adsorption capacity of 204.1 mg/g. The kinetic data obtained at different concentrations were analyzed to predict the constant rate of adsorption using three common kinetic models: pseudo-first-order, pseudo-second-order equation and intraparticle diffusion equation. The pseudo-second-order model was suitable for describing the adsorption kinetics for the removal of methyl tert-butyl ether from aqueous solution onto granular activated carbon. Both the Lagergren first-order rate constant k ₁ and pseudo-second-order rate constant k ₂ decrease with increasing initial concentrations of methyl tert-butyl ether and the intraparticle diffusion rate constant k _p shows the reverse characteristic. Analysis of sorption data using a boyd plot confirmed that external mass transfer is the main rate-limiting step at the initial stage of adsorption. Results illustrate that granular activated carbon is an effective adsorbent for methyl tert-butyl ether and also provide specific guidance into adsorption of methyl tert-butyl ether on granular activated carbon in contaminated groundwater.     

Removal of copper ions from aqueous solution using silica derived from rice straw: comparison with activated charcoal

The batch removal of copper(II) ions from aqueous solution under different experimental conditions using alkali-leached silica and activated charcoal was investigated in this study. The copper(II) uptake was dependent on varying time, pH, copper concentration and temperature. Copper sorption was found fast reaching equilibrium within 1 h with better performance for alkali-leached silica than charcoal. Copper sorption was low at low pH values and increased with rise in initial pH-value until 6.7. Sorption fits well the Langmuir and Freundlich equations with higher uptake by increasing temperature. According to Langmuir equation, the maximum uptake of Cu(II) ions by alkali-leached SiO₂ and charcoal was found to be 242.5 and 94.4 mmol/g at temperature 60 °C and pH 6. Thermodynamic studies confirm that the process was spontaneous and endothermic nature. Kinetic data for Cu(II) sorption was found to follow pseudo-second-order model.     

活性炭测氡法在地热勘探中的应用——以张掖—民乐盆地为例

地热的运移和聚集主要沿断裂带进行,查明勘查区的断裂构造是地热勘探的重要目标。张掖—民乐盆地内断裂众多,且埋藏深,地表难以发现,特殊的地质条件使得传统物探方法的优势无法得到有效发挥。活性炭测氡法抗干扰性强、探测深度大、成本低,在探测隐伏构造方面具有独特优势。本次勘查在张掖—民乐盆地应用活性炭测氡法进行隐伏构造研究,通过对氡浓度测量值的趋势分析,提取局部异常,确定了研究区地下热水勘查有利部位,并为进一步进行钻探和浅层人工地震勘探创造了条件。     

The study of indoor radon in the urban dwellings using plastic track detectors

Radon and its progeny have been recognized as one of the major contributors to the natural radiation and health hazards in the human dwellings. Even lung cancer is expected if it is present in enhanced levels beyond maximum permissible limit. This paper reports the measurements of indoor radon and its progeny in the urban dwellings of the Etah district of Uttar Pradesh province in Northern India using the cellulose nitrate (LR-115 type-II) plastic track detectors. It is found that the values of radon concentration vary from 3.52 to 248.64 Bq m⁻³ with a standard deviation of 69.19. The values of radon progeny concentration vary from 0.38 to 26.88 mWL with a standard deviation of 7.48. The effective dose has been calculated and found to vary from 0.05 to 3.76 mSv year⁻¹ with a standard deviation of 1.05. The lifetime fatality risk is found to vary from 0.04 × 10⁻⁴ to 2.90 × 10⁻⁴. The results have been compared with the results reported in the rural areas of the same district.     

Removal of cyanide from aqueous solutions by plain and metal-impregnated granular activated carbons

In this study, the removal of free cyanide from aqueous solutions by activated carbon was investigated. Effects of metal impregnation (Cu and Ag), aeration, and concentrations of adsorbent and cyanide on the rate and extent of the removal of cyanide were studied. The results have shown that the capacity of activated carbon for the removal of cyanide can be significantly improved (up to 6.3-fold) via impregnation of activated carbon with metals such as copper and silver. Silver-impregnated activated carbon was found to be the most effective at the reduction of cyanide level in solution. This appeared to be coupled with its comparatively high metal content after impregnation process where silver (5.07%) could be more readily loaded on activated carbon than copper (0.43%). Kinetics and equilibrium data for cyanide removal by plain and metal-impregnated activated carbons were determined to be consistent with the pseudo second-order kinetics and the Langmuir adsorption isotherms, respectively. Aeration (0.27 l/min) was found to exert a profound effect on the process leading to a 5.5–49.1% enhancement in the performances of plain and metal-impregnated activated carbons. This enhancement could be attributed to the increase in the availability of active sites on activated carbon for adsorption and the catalytic oxidising activity of activated carbon in the presence of oxygen. Practical limiting capacity of plain, copper- and silver-impregnated activated carbons for the removal of cyanide were experimentally determined to be 19.7, 22.4 and 29.6 mg/g, respectively.     

Field and laboratory procedures for determining gold in natural waters: Relative merits of preconcentration with activated charcoal

The critical parameters and merits of a method to determine Au in waters by initial adsorption on to activated charcoal, and measurement by graphite furnace atomic absorption spectrometry (GFAAS) have been examined. Neutron activation analysis of the filtered charcoal substrate has been the prevalent methodology employed in recent years to determine Au in waters.Results of this study show that pH adjustment and intense mixing of the activated charcoal in the sample are prerequisites to complete adsorption of the Au. Thus, provided that such preparation facilities exist in the field area, this method would enable low-cost shipment of filtered activated charcoal discs to the laboratory where they would be analyzed relatively inexpensively and rapidly by GFAAS. A determination limit of 0.5 ng L⁻¹ (parts per trillion), based on adsorption from a 1-L sample, is achieved with a relative standard deviation of about ± 10% at the 5 ng L⁻¹ level. However, if acidification and filtration are not possible in the field or within a one-day delay period, then an alternate method is proposed. The litre sample would be sent to the laboratory where bromine-hydrochloric acid would be added to desorb the Au lost to the container walls and the water evaporated, the extract obtained and analysed by GFAAS. This approach is more time-consuming in the laboratory and entails costly shipment of bulky samples but may be the only feasible choice for some field situations.Application of this methodology to a small study area in British Columbia indicates the potential of analyzing surface waters for Au for geochemical exploration purposes.     

Adsorption of lead, ethylenediaminetetraacetic acid and lead-ethylenediaminetetraacetic acid complex onto granular activated carbon

This study investigated simultaneous removal of lead and ethylenediaminetetraacetic acid from synthetic wastewater samples using granular activated carbon adsorption. Data from a 1 × 10^?4 M lead-ethylenediaminetetraacetic acid adsorption isotherm study fitted well to Freundlich isotherm. Furthermore, for the pH-dependent 1 × 10?4 M lead-ethylenediaminetetraacetic acid study both lead and ethylenediaminetetraacetic acid adsorptions increased reaching values of 82 % and 93 % respectively at pH 5.8. However, a further increase in pH resulted in decreasing but near equal lead and ethylenediaminetetraacetic acid removals. Results for the 2 × ^10?4 M lead-ethylenediaminetetraacetic acid system showed a behavior that was qualitatively similar to the 1 × ^10?4 M lead-ethylenediaminetetraacetic acid findings. However, the 1×10^?3 M lead-ethylenediaminetetraacetic acid study showed only a decreasing adsorption trend. An increasing-decreasing type lead/ethylenediaminetetraacetic acid adsorption behavior was also noted for the 1× 10^?4 M lead/2 × 10^?4 M ethylenediaminetetraacetic acid system. Nevertheless for the 2×10^?4 M lead/1×10^?4 M ethylenediaminetetraacetic acid system, lead removal at increased pH was comparatively higher. Furthermore, results from a continuous column study completed at 1 × 10^?4 M lead and 0.75 × 10^?4 M ethylenediaminetetraacetic acid showed high saturation times both for lead and ethylenediaminetetraacetic acid. Results from the present work show that a notable removal of aqueous phase lead and ethylenediaminetetraacetic acid could be achieved using activated carbon adsorption. The details related to the effect of pH and pollutants’ concentration on the overall adsorption efficiency, as reported in the present work, would be of much use for an effective carbon adsorption process design for the treatment of respective wastewaters.     

Simulations of realistic granular soils in oedometer tests using physics engine

Discrete element method (DEM) has become a preeminent numerical tool for investigating the mechanical behavior of granular soils. However, traditional DEM uses sphere clusters to approximate realistic particles, which is computationally demanding when simulating many particles. This paper demonstrates the potential of using a physics engine technique to simulate realistic particles. The physics engines are originally developed for video games for simulating physical and mechanical processes that occur in the real world to produce realistic game experiences. The simulation accuracy and efficiency of physics engines have been significantly improved in the last two decades allowing them to be used as a scientific tool in many disciplines. This paper introduces modeling methodologies of physics engine including realistic particle representation and the contact model. Then, oedometer tests are simulated using realistic particles scanned by X-ray computed tomography (X-ray CT). The simulation results agree well with experimental results. This paper demonstrates that physics engines can output contact parameters for geotechnical analysis and force chains for visualization.     

Analysis of wave propagation in dry granular soils using DEM simulations

In this paper, a three-dimensional particle-based technique utilizing the discrete element method (DEM) is proposed to study wave propagation in a dry granular soil column. Computational simulations were conducted to investigate the soil response to sinusoidal motions with different amplitudes and frequencies. Three types of soil deposits with different void ratios were employed in these simulations. Different boundary conditions at the base such as rigid bedrock, elastic bedrock, and infinite medium were also considered. Analysis is done in time domain while taking into account the effects of soil nonlinear behavior. The computational approach is able to capture a number of essential characteristics of wave propagation including motion amplification and resonance. Dynamic soil properties were then extracted from conducted simulations and used to predict the response of the soil using the widely used equivalent linear method program SHAKE and compare its predictions to DEM results. Generally, there was a good agreement between SHAKE and DEM results except when the exciting frequency was close to the resonance frequency of the deposit where significant discrepancy in computed shear strains between SHAKE predictions and DEM results was observed.     

Penetration test in coarse granular material using Contact Dynamics Method

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. Indeed, the data are considerably more sensitive in this case to various parameters such as fabric structure, particle shapes or the applied impact energy. In order to achieve a better understanding of the penetration process into a coarse granular material, a numerical study was performed by means of contact dynamics simulations. The penetration of a moving tip in a sample composed of irregular grain shapes was studied and the influence of the driving velocity and input energy on the penetration strength was analyzed. The results show that the latter grows with both the penetration rate and energy, despite the strong fluctuations occur due to a jamming–unjamming process in which the contact network connectivity evolves intermittently in correlation with the penetration strength. This analysis suggests that the time-averaged data provided by a penetrometer is reliable information from which the bulk strength properties of coarse granular materials can be evaluated.     

辽西地区红山文化时期林木资源利用和生态环境研究

辽西地区是研究中国文明起源及早期文明化进程的重要区域。红山文化是辽西地区6.5~5.0 ka B.P. 的新石器时代晚期重要的考古学文化。本研究对辽西地区红山文化时期的魏家窝铺遗址、彩陶坡遗址、兴隆沟遗址第二地点和牛河梁遗址第一地点这4个遗址点中浮选和采集的134份样品中大于2 mm的940块木炭进行鉴定,分别是栎属(Quercus L.)、榆属(Ulmus L.)、朴属(Celtis L.)、李属(Prunus L.)、槭树属(Acer L.)、黄檗属(Phellodendron Rupr.)、椴属(Tilia L.)、梣属(Fraxinus L.)、胡桃属(Juglans L.)、松属(Pinus L.)、柳属(Salix L.)、侧柏属(Platycladus L.)等12种木本植物,以及2种未知的炭化植物遗存。研究表明遗址周围分布着桃、杏、胡桃楸等果树,生长着以栎属为建群种的暖温带落叶阔叶林及榆属、槭树属和朴属等阔叶树;山地上可能分布着由松属、侧柏属和黄檗属、椴属、梣属等组成的温性针阔混交林。利用共存生态因子法进行气候重建的结果表明,当时遗址周围的环境较现今温暖湿润。先民用栎属木材建造房屋、薪柴选用栎属、松属和槭树属木材。通过对牛河梁遗址第一地点出土的木炭推测当时祭祀时可能使用栎属木材。除了遗址中出土的炭化果核,核果类木材的出土,进一步佐证了先民会采集核果类木材的果实、种子作为食物,为探索红山文化时期先民生业方式提供了新视角。本研究为解读红山文化时期的先民对林木资源利用策略,了解当时生态环境与生业模式提供了新资料。

     

First results derived from a drop-tower testing system for granular flow in a microgravity environment

Because of the low-gravity on the Moon and Mars, landslides there have characteristics that are very different from those observed in a conventional gravity environment. These include highly marked dynamic characteristics, evidence of fierce movement at high speed and on a large scale. One of the key problems in extra-planetary exploration is understanding the behavior of granular material flows under the influence of low gravity. A drop-tower testing system situated in Beijing has been developed and used to investigate granular flow in a microgravity environment. A set of granular flow tests was performed in both normal and microgravity environments, during which the configurations of sand flows were captured by the monitoring system. Preliminary results provide fundamental information for the future exploration of planetary landscapes.     

Stress distribution in granular heaps using multi‐slip formulation

Many experiments on conical piles of granular materials have indicated, contrary to simple intuition that the maximum vertical stress does not occur directly beneath the sand‐pile vertex but rather at some distance from the apex resulting in a ring of maximum vertical stress. Some recent experiments have shown that the observed stress dip is very much dependent on construction history. A multi‐slip model has been proposed to investigate the stress dip phenomenon in granular heaps. The double‐slip version of the model was implemented into ABAQUS and used to study the vertical stress distribution along the base of a granular pile. The numerical simulations show that plastic deformation is confined within the localized region around the apex while the rest of the pile is in an elastic state of deformation. Within the plastic region the stress distribution differs significantly depending on the initial active slip orientation. The results show that for homogenous state of granular materials such as those produced by a raining procedure the vertical stress profile along the base reached its peak at the apex (i.e. no dip was observed). On the contrary, granular heaps constructed by the use of a localized source such as a funnel resulted in a significant reduction in the stress distribution within the ring with the minimum attained beneath the peak (i.e. a dip). Therefore, we believe that the initial microstructure and thus the initial slip orientation resulting from sand deposition is the source of the stress dip phenomenon. Copyright © 2005 John Wiley & Sons, Ltd.     

Characterization of mesoscale instabilities in localized granular shear using digital image correlation

Within shear bands in sands, deformation is largely non-affine, stemming primarily from buckling of well-known force chains and also from vortex-like structures. In the spirit of current trends toward multiscale modeling, understanding the links between these mesoscale deformational entities and corresponding macroscale response will form the basis for the next generation of sand behavioral models and may also aid in efforts to understand jamming–unjamming transitions in dense granular flows in general. Experimental methods to quantify and characterize such subscale kinematics, in particular in real sands, will play critical roles in these efforts. Digital Image Correlation (DIC) is a fast growing experimental technique to nondestructively measure surface displacements from digital images. Here, DIC has been employed to identify and characterize the development of vortex structures inside shear bands formed in dense sands during plane strain compression. A rigorous assessment of the DIC method has been performed, in particular for subscale behavioral characterization in unbonded granular solids, and guidelines are offered for accurate implementation. While DIC systematically overestimates shear band thickness, a methodology has been devised to compensate for this overestimation. Shear band thickness for four different uniform sands were found to range between 6 and 9 grain diameters, and for a well-graded sand between 8 and 9.5 grain diameters. These determinations agree with visual inspections of grain kinematics from the image data, as well as recent theoretical predictions.     

Determination of the aromaticity and the degree of aromatic condensation of a thermosequence of wood charcoal using NMR

Quantifying the role of black carbon (BC) in geochemical processes is difficult due to the heterogeneous character of its chemical structure. Chestnut wood charcoal samples produced at heat treatment temperatures (HTT) from 200-1000 °C were analysed using two different solid state ¹³C NMR techniques. First, aromaticity was determined as the percentage of total signal present in the aromatic region of ¹³C direct polarisation (DP) spectra. This was found to increase through the low temperature range of 200-400 °C; at higher temperatures, aromaticity was found to be >90%. Second, aromatic condensation was determined through the measurement of the chemical shift of ¹³C_benzene sorbed to the charcoals, which is influenced by the presence of “ring currents” in the aromatic domains of the charcoals. This technique was less sensitive to molecular changes through the lower temperature range, but showed there was a smooth increase in the degree of condensation of the aromatic structures with increasing temperature through the temperature range 400-1000 °C. Ab initio molecular modelling was used to estimate the size of aromatic domains in the charcoals based on the strength of the ring currents detected. These calculations indicated that charcoals produced at temperatures below 500 °C contain aromatic domains no larger than coronene (7 ring). At higher temperatures the size of these domains rapidly increases, with structures larger than a 19 ring symmetrical PAH being predominant in charcoals produced at temperatures above 700 °C. Data from this study were found to be generally consistent with previously published measurements using the benzenepolycarboxylic acid (BPCA) molecular marker method on the same set of samples.     

Prediction of the unconfined compressive strength of compacted granular soils by using inference systems

Adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) models have been extensively used to predict different soil properties in geotechnical applications. In this study, it was aimed to develop ANFIS and ANN models to predict the unconfined compressive strength (UCS) of compacted soils. For this purpose, 84 soil samples with different grain-size distribution compacted at optimum water content were subjected to the unconfined compressive tests to determine their UCS values. Many of the test results (for 64 samples) were used to train the ANFIS and the ANN models, and the rest of the experimental results (for 20 samples) were used to predict the UCS of compacted samples. To train these models, the clay content, fine silt content, coarse silt content, fine sand content, middle sand content, coarse sand content, and gravel content of the total soil mass were used as input data for these models. The UCS values of compacted soils were output data in these models. The ANFIS model results were compared with those of the ANN model and it was seen that the ANFIS model results were very encouraging. Consequently, the results of this study have important findings indicating reliable and simple prediction tools for the UCS of compacted soils.     

Modelling strain localization in granular materials using micropolar theory: mathematical formulations

It has been known that classical continuum mechanics laws fail to describe strain localization in granular materials due to the mathematical ill‐posedness and mesh dependency. Therefore, a non‐local theory with internal length scales is needed to overcome such problems. The micropolar and high‐order gradient theories can be considered as good examples to characterize the strain localization in granular materials. The fact that internal length scales are needed requires micromechanical models or laws; however, the classical constitutive models can be enhanced through the stress invariants to incorporate the Micropolar effects. In this paper, Lade's single hardening model is enhanced to account for the couple stress and Cosserat rotation and the internal length scales are incorporated accordingly. The enhanced Lade's model and its material properties are discussed in detail; then the finite element formulations in the Updated Lagrangian Frame (UL) are used. The finite element formulations were implemented into a user element subroutine for ABAQUS (UEL) and the solution method is discussed in the companion paper. The model was found to predict the strain localization in granular materials with low dependency on the finite element mesh size. The shear band was found to reflect on a certain angle when it hit a rigid boundary. Applications for the model on plane strain specimens tested in the laboratory are discussed in the companion paper. Copyright © 2006 John Wiley & Sons, Ltd.