Adsorption Breakthrough of Benzene in the Fixed Bed of Modified Activated Carbon under Different Humidity Conditions

The breakthrough curves of benzene and water on modified activated carbons（ACs） were investigated.Temperature-programmed desorption（TPD） experiments were conducted to measure the TPD curves of benzene and water on modified and unmodified ACs and to estimate the activation energy for the desorption of benzene on the modified ACs.Starting with unmodified ACs,two modified ACs were prepared by using two different types of silane,designated by KH560 and 1706.The results showed that the activation energy for the desorption of benzene on KH560/AC and 1706/AC was higher than that on unmodified AC.In addition,the activation energy for the desorption of water on KH560/AC and 1706/AC was lower than that on unmodified AC.The breakthrough curves of benzene obtained from the experimental observations under different humidity conditions were compared with the results of the TPD experiments.The results show that the modified ACs are less affected by water,whereas the unmodified ACs are more affected by water,indicating that surface modification by organosilane compounds can improve the adsorption of benzene on the activated carbo,which weakens the adsorption of water.

Modeling Date Palm Trunk Fibers (DPTF) Packed Bed Adsorption Performances for Cadmium Removal from Aqueous Wastewater

In this study,the potential of a low-cost bio-adsorbent,taken directly from Date Palm Trunk Fibers(DPTF)agricultural wastes,for cadmium ions removal from wastewaters is examined.The performances of this adsorbent are evaluated by building breakthrough curves at different bed heights and flow rates while keeping other parameters,such as the initial feed concentration,pH,and particle size,constant.The results indicate that the maximum cadmium adsorption capacity of DTPF can be obtained from the Thomas model as 51.5 mg/g with the most extended mass transfer zone of 83 min at the lowest flow rate at 5 ml/min.The saturation concentrations(NO)and the rate constant(kab)obtained from the BDST(bed depth service time)model are 7022.16 mg/l and 0.0536 l/mg.min,respectively.Using the Yon-Nelsen Model,it is found that operating at a lower flow rate leads to a larger value of the elapsed needed time to reach a 50%breakthrough.The Wolborska model indicates that the bed capacity increases with decreasing the flow rate,and the adsorbent can achieve a greater external mass transfer kinetic coefficient(2.271/min)at a higher flow rate.

Modeling atrazine transport in soil columns with HYDRUS-1D

Both physical and chemical processes affect the fate and transport of herbicides. It is useful to simulate these processes with computer programs to predict solute movement. Simulations were run with HYDRUS- 1 D to identify the sorption and degradation parameters of atrazine through calibration from the breakthrough curves （BTCs）. Data from undisturbed and disturbed soil column experiments were compared and analyzed using the dual-porosity model. The study results show that the values of dispersivity are slightly lower in disturbed columns, suggesting that the more heterogeneous the structure is, the higher the dispersivity. Sorption parameters also show slight variability, which is attributed to the differences in soil properties, experimental conditions and methods, or other ecological factors. For both of the columns, the degradation rates were similar. Potassium bromide was used as a conservative non-reactive tracer to characterize the water movement in columns. Atrazine BTCs exhibited significant tailing and asymmetry, indicating non-equilibrium sorption during solute transport. The dual-porosity model was verified to best fit the BTCs of the column experiments. Greater or lesser concentration of atrazine spreading to the bottom of the columns indicated risk of groundwater contamination. Overall, HYDRUS-1D successfully simulated the atrazine transport in soil columns.

A comparative study of adsorption and regeneration with different agricultural wastes as adsorbents for the removal of methylene blue from aqueous solution

Removal of dye from the industrial wastewater is one of the most important subjects in water pollution regulation.Successive adsorption/desorption cycles of a basic dye, methylene blue, on the internal almond shell, sheep manure waste and sawdust were investigated using fixed bed column experiments in order to study the adsorption capacity to remove MB and adsorbent regeneration efficiency. The adsorption breakthrough curves were predicted by the Thomas model, Yoon Nelson model, and Wolborska model and modified dose–response model using non-linear regression analysis. The results showed that the modified dose–response model was more suitable for the description of breakthrough curves for three adsorbents only in the first cycle. Although sheep manure waste presents the highest adsorption capacity, it is hard to regenerate and needs more time regeneration. Conversely, the internal almond shell presents lower adsorption capacity, but they are more readily regenerated.

Gas phase tricholoethylene removal at low concentration using activated carbon fiber

The breakthrough adsorption behaviors of gas phase trichloroethylene in a packed bed of activated carbon fibers(ACF) were investigated. The specific surface area of the ACF was 600 m 2/g, 1400 m 2/g and 1600 m 2/g, respectively, and the concentration of trichloroethylene ranged from 270 mg/m 3 to 2700 mg/m 3. Results showed that the capacity of adsorption increased with increasing specific surface area, the relationship between the logarithms of 10% breakthrough time and concentration was approximately linear over the experimental range, the breakthrough time decreased with increasing temperature and humidity. The breakthrough curves at different inlet concentration or different temperature can be predicted by several simple theoretical models with good agreements.

Lattice Boltzmann simulation of solute transport in a single rough fracture

In this study, the lattice Boltzmann method （LBM） was used to simulate the solute transport in a single rough fracture. The self-affine rough fracture wall was generated with the successive random addition method. The ability of the developed LBM to simulate the solute transport was validated by Taylor dispersion. The effect of fluid velocity on the solute transport in a single rough fracture was investigated using the LBM. The breakthrough curves （BTCs） for continuous injection sources in rough fractures were analyzed and discussed with different Reynolds numbers （Re）. The results show that the rough frac~＇e wall leads to a large fluid velocity gradient across the aperture. Consequently, there is a broad distribution of the immobile region along the rough fracture wall. This distribution of the immobile region is very sensitive to the Re and fracture geometry, and the immobile region is enlarged with the increase of Re and roughness. The concentration of the solute front in the mobile region increases with the Re. Furthermore, the Re and roughness have significant effects on BTCs, and the slow solute molecule exchange between the mobile and immobile regions results in a long breakthrough tail for the rough fracture. This study also demonstrates that the developed LBM can be effective in studying the solute transport in a rough fracture.

Batch and fixed-bed column studies of selenite removal from contaminated water by orange peel-based sorbent

Orange peel is a biomass derived from citrus processing with desirable properties for metal sorption.In recent years,orange peel has been used to remove various heavy metals and toxic oxyanions.Selenium(Se)is an essential trace element for mammals.However,when the concentration of selenium exceeds an umbral limit,it becomes toxic.In this study,orange peel was used to treat Se(IV)-contaminated water.A high sorption capacity of 32.5 mg/g was obtained at a temperature of 20℃and a pH of 2.0.Hydroxyl groups bound Se(IV)to the surface of the orange peel.The sorption process was spontaneous and endothermic.A chemical sorption mechanism was involved in the removal of Se(IV).The Thomas and modified dose-response models were used to simulate the experimental breakthrough curves.The bed depth service time model was used to calculate the critical bed depth(Z0),and the calculated Z0 value was 1.6 cm.This study reveals that orange peel is a useful sorbent for Se(IV),and can be used for the purification of Se(IV)-contaminated water.©2020 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Synthesis and Evaluation of Microporous Metal Organic Frameworks for Light Hydrocarbon Adsorption

Five microporous MOFs were synthesized and their static adsorption properties for light hydrocarbons were experimentally investigated at 298 K and 150 kPa.Among the five MOFs,HKUST-1 and Ni(bdc)(ted)0.5 exhibited much higher uptakes of ethane and propane than PCN-250,UiO-66,and ZIF-8.Breakthrough experiments were carried out at 298 K and atmospheric pressure on HKUST-1 and two commercially used adsorbents.HKUST-1 exhibited a much lower dynamic than static adsorption capacity.Moreover,HKUST-1 and the two traditional adsorbents could effectively separate binary(ethane/propane)and ternary(ethane/propane/toluene)mixtures.

Analysis of solute preferential transport in a dark coniferous forest ecosystem of Gongga Mountain,Sichuan Province,southwestern China

We selected a dark coniferous forest ecosystem of Gongga Mountain in the upper reaches of the Yangtze River as our research area to study the preferential flow and solute preferential transport by adding the tracers KNO3 and KBr to the self-made soil column equipment in different ways to examine density and volume changes of inflows and outflows of a mass input （impulse input） and a stable, well-distributed input （step input））. The results showed that this dark coniferous forest ecosystem of Gongga Mountain is a typical area of preferential flow and solute preferential transport, a process that can be classified into five parts. A great amount of solute was transported at high speed as the result of preferential flow in the soil and caused the density of the solute in both deep water and in groundwater to rise rapidly, which definitely increased pollution in the deep soil layer.

Effect of Rock Fragments on Tracer Transport in Broadleaved and Coniferous Forest Soils: Column Study

This study investigated the effect of rock fragments on tracer transport in broadleaved and coniferous forest soils from the 0 - 100 cm depth of Gongga Mountain in eastern margin of Qinghai Tibetan Plateau. Using repacked soil columns (20 cm in height and 10 cm in diameter) with different rock fragments contents (0%, 5%, and 15% in v/v), breakthrough curves of bromide (as non-reactive tracer) were obtained under saturated condition. A two-region model was applied and the parameters were estimated by inverse modeling. Results show that with increasing rock fragment content the dispersivity (λ) generally increased while the mobile-immobile partition coefficient (β) and the mass transfer coefficient (ω) decreased. The presence of rock fragments led to an increase in the fraction of immobile domain as well as soil tortuosity. A plausible explanation is that the soil beneath the rock fragments behaved as immobile domain and soil-rock interfaces could serve as preferential flow paths.

Review:Mathematically modeling fixed-bed adsorption in aqueous systems

Adsorption is one of the widely used processes in the chemical industry environmental application.As compared to mathematical models proposed to describe batch adsorption in terms of isotherm and kinetic behavior,insufficient models are available to describe and predict fixed-bed or column adsorption,though the latter one is the main option in practical application.The present review first provides a brief summary on basic concepts and mathematic models to describe the mass transfer and isotherm behavior of batch adsorption,which dominate the column adsorption behavior in nature.Afterwards,the widely used models developed to predict the breakthrough curve,i.e.,the general rate models,linear driving force(LDF) model,wave propagation theory model,constant pattern model,Clark model,Thomas model,Bohart-Adams model,Yoon-Nelson model,Wang model,Wolborska model,and modified dose-response model,are briefly introduced from the mechanism and mathematical viewpoint.Their basic characteristics,including the advantages and inherit shortcomings,are also discussed.This review could help those interested in column adsorption to reasonably choose or develop an accurate and convenient model for their study and practical application.