Batch and column adsorption of herbicide fluroxypyr on different types of activated carbons from water with varied degrees of hardness and alkalinity

There has been little research into the effects of the water hardness and alkalinity of surface waters on the adsorption of herbicides on activated carbons. The aim of this study was to determine the influence of these water characteristics on fluroxypyr adsorption on different activated carbons. At low fluroxypyr surface concentrations, the amount adsorbed from distilled water was related to the surface hydrophobicity. Surface area of carbons covered by fluroxypyr molecules ranged from 60 to 65%. Variations in fluroxypyr solubility with water hardness and alkalinity showed a salting-in effect. Calcium, magnesium and bicarbonate ions were adsorbed to a varied extent on the activated carbons. The presence of fluroxypyr in solution decreased their adsorption due to a competition effect. K_F from the Freundlich equation linearly increased with water hardness due to salt-screened electrostatic repulsions between charged fluroxypyr molecules. The amount adsorbed from distilled water was largest at high fluroxypyr solution concentrations, because there was no competition between inorganic ions and fluroxypyr molecules. The column breakthrough volume and the amount adsorbed at breakthrough were smaller in tap versus distilled water. Carbon consumption was lower with activated carbon cloth than with the use of granular activated carbon.     

Study of mathematical models for the removal of Ni2+ from aqueous solutions using Citrullus lanatus rind,an agro‐based waste

The defilement of water bodies is going on increasing due to the use of noxious chemicals. In the present study, to alleviate the deadly effects of the heavy metal, the agricultural solid waste Citrullus lanatus rind was used as the precursor for the Nickel ion removal. To remove Nickel from synthetic solution, adsorption studies were conducted. Characterization was done using TGA, SEM and FT‐IR analysis. Various parameters on the adsorption capacity of the adsorbent, isotherm and kinetic studies were carried out. The maximum loading capacity of Ni²⁺ was found to be 38.98 mg/g from Langmuir model. Error analyses were also studied to validate the best fit of the curve for isotherm models. The kinetic models were studied to understand the adsorption mechanism. The dynamic behaviour of the fixed column and the modelling of the breakthrough curves were carried out. Desorption studies were performed to consider the reusability of the rind.     

太阳能固体吸附式转轮制冷机性能分析

针对活性炭纤维-乙醇太阳能固体吸附式转轮制冷系统,采用沿吸附床周向的一维均匀压力场数学模型,对转轮吸附床温度场进行了静态模拟计算;从吸附床的内、外部特性参数出发,全面而系统地分析了这些参数的改变对系统性能、平衡脱附率以及吸附量的影响。结果表明,在转轮吸附床的内部参数中,转轮吸附床的转速、吸附剂的填充密度对系统的性能有着较大的影响;在其外部参数中,冷却气体入口流速、蒸发温度等因素对系统影响比较大。     

Dynamic and static adsorption and desorption of Hg(II) ions on chitosan membranes and spheres

The adsorption and desorption of Hg(II) ions was studied using static and dynamic methods, employing membranes and spheres of chitosan as the adsorbent. The quantity of adsorption was influenced by chitosan crosslinking and by the adsorbent shape. The Langmuir model was applied to fit the experimental equilibrium data. Glutaraldehyde-crosslinked membranes presented a lower desorption capacity, when compared to natural membranes, but could be regenerated for use in successive cycles. Dynamic adsorption experiments suggested that the adsorption capacity depended mainly on adsorbent geometry, due to differences between surface area to mass ratio and initial concentration of Hg(II) ions. The adsorption capacity determined by the dynamic method was 65% and 77% for membranes and spheres, respectively of the value obtained static method results. A process combining dynamic adsorption and static desorption can be used to concentrate the Hg(II) ions by a factor of nearly seven (7x), when compared to the initially treated volume.     

Adsorption isotherms: illusive capacity and role of oxygen

This paper examines the influence of molecular oxygen on the adsorptive capacity of GAC. A new experimental procedure for determining adsorption isotherms is introduced. This procedure, denoted as “anaerobic”, differs from the currently used techniques, denoted as “aerobic”, in that oxygen is repeatedly purged from the test environment. The results show that the capacity of GAC for the retention of o-cresol can increase up to 3-fold in the presence of oxygen when compared to the anaerobic capacity. The same trend is observed for the adsorption of phenol and 3-ethylphenol. It is shown that this increase in capacity cannot be attributed to biological degradation of these adsorbates in the presence of oxygen. It is speculated that this phenomenon is due to some chemical reactions between the adsorbates and molecular oxygen that are catalyzed by the activated carbon surface and occur at a different time scale than physical adsorption. Initial portions of breakthrough curves for o-cresol are very accurately predicted using capacities depicted by the anaerobic isotherm, while the total GAC adsorptive capacity for o-cresol, as determined from breakthrough experiments, appears to agree closely with the capacity predicted from the aerobic isotherm.     

Experimental study on adsorption capacity of an activated carbon-based adsorption water chiller

The objective of this study was to evaluate the adsorption capacity of a working pair for an adsorption water chiller. Activated carbon fibre–methanol, activated carbon fibre–ethanol and activated carbon pallet–ethanol were used as an adsorbent–adsorbate pair in this study. The experiment was conducted using a stainless steel adsorber, 110?mm diameter by 150?mm height, filled with adsorbent and transparent plastic evaporator, 100?ml capacity, filled with adsorbate. The experiment was performed by isobaric adsorption in the temperature range of 10–100°C at the evaporator temperature of 20°C (water chiller). An experimental investigation showed that the activated carbon fibre–methanol pair has the highest adsorption capacity (0.44?kg/kg) compared to the activated carbon fibre–ethanol and activated carbon pallet–ethanol pairs. The finding revealed that uniform structure and large surface area of adsorbent as well as low boiling point and large latent heat of adsorbate had highly significant effects on adsorption capacity. The effect of time and adsorber temperature on adsorption capacity is also discussed in this study.     

Enhanced mitigation of para-chlorophenol using stratified activated carbon adsorption columns

The adsorptive removal of toxic para-chlorophenol using activated carbon adsorption columns is a proven effective engineering process. This paper examined the possibility to stratify an adsorbent bed into layers, in order to enhance the adsorption process performance in terms of increased column service time and adsorbent bed saturation. Four different types of fixed-bed adsorption columns are used and compared under the same operating conditions, but with the variation of column geometry and activated carbon particle size stratification. The Type 3 column - a cylindrical column with particle stratification packing, is found to be the most efficient choice, as the extent of column service time and adsorbent bed saturation are the largest. This could eventually decrease the frequency of adsorbent replacement/regeneration and hence reduce the operating cost of the fixed-bed adsorption process. The Homogeneous Surface Diffusion Model (HSDM) was applied successfully to describe the dynamic adsorption of para-chlorophenol onto Filtrasorb 400 (F400) activated carbon in different types of columns. The Redlich-Peterson isotherm model equation, an experimentally derived external mass transfer correlation and a constant surface diffusivity are used in the HSDM. The optimised surface diffusivity of para-chlorophenol is found to be 1.20E-8 cm²/s, which is in good agreement with other phenolics/F400 carbon diffusing systems in literature.     

Combined effect of carbon dosage and initial adsorbate concentration on the adsorption isotherm of heavy metals on activated carbon

The adsorption of dissolved chromium and lead ions by powdered activated carbons significantly depends on the pH, initial adsorbate concentration and carbon dosage. Freundlich and Langmuir equations were unable to describe adequately the observed isotherms under the combined influence of both the carbon dosage and initial adsorbate concentration. These equations were modified and the resulting equations were found to correlate well with the experimental equilibrium data. The modified Langmuir equation gave an overall mean ratio of calculated to experimental adsorptive capacity of 1.001 compared with 1.046 given by the modified Freundlich equation for a total of 135 sets of equilibrium data obtained at different carbon dosages and initial adsorbate concentrations.     

Mechanism of adsorption and electrosorption of bentazone on activated carbon cloth in aqueous solutions

An electrochemical technique has been applied to enhance the removal of a common herbicide (bentazone) from aqueous solutions using an activated carbon cloth as electrode. A pH increase from acidic to basic reduces the uptake, with capacities going from 127 down to 80 mg/g at pH 2 and 7, respectively. Increasing the oxygen content of the carbon cloth causes a decrease in the bentazone loading capacity at all pH values. This indicates that adsorption is governed by both dispersive and electrostatic interactions, the extent of which is controlled by the solution pH and the nature of the adsorbent. Anodic polarization of the carbon cloth noticeably enhances the adsorption of bentazone, to an extent depending on the current applied to the carbon electrode. The electrosorption is promoted by a local pH decrease provoked by anodic decomposition of water in the pores of the carbon cloth.     

Single and competitive adsorption of Cd and Zn onto a granular activated carbon

Single and competitive adsorption of cadmium and zinc onto granular activated carbon DARCO 12–20 mesh has been investigated. This activated carbon has been shown as an effective adsorbent for both metals. Cadmium and zinc removals increased with pH and decreased with molar metal/carbon ratio. Surface precipitation phenomena have been detected for the higher pHs and molar ratios. The adsorption process has been modelled on the surface complexation Triple Layer Model (TLM). For this purpose, the amphoteric nature of the activated carbon has been studied. Single metal adsorption data have been used to calibrate TLM parameters. A dependence of the adsorption constants on pH and molar metal/carbon ratio has been observed, and a correlation for log K_ads has been determined. In the competitive system, the removal efficiency of the activated carbon decreased for both metals. The TLM model, using surface complexation constants determined from single adsorption experiments, successfully predicted cadmium and zinc removal from the two metal solutions.     

Interactions of diuron with dissolved organic matter from organic amendments

Diuron is frequently detected in some drinking water reservoirs under the Burgundy vineyards, where organic amendments are applied. The environmental effect of these amendments on pesticide transport is ambiguous: on the one hand it could enhance their retention by increasing soil organic carbon content; on the other hand, dissolved organic matter (DOM) could facilitate their transport. Elutions were performed using columns packed with glass beads in order to investigate DOM-diuron interactions, and the possible co-transport of diuron and DOM. Four organic amendments (A, B, C and D) were tested; C and D were sampled at fresh (F) and mature (M) stages. An increase in diuron leaching was observed only for A and D_F amendments (up to 16% compared to the DOM-free blank samples), suggesting a DOM effect on diuron transport. These results could be explained by the higher DOM leaching for A and D_F compared to B, C_F, C_M and D_M increasing diuron-DOM interactions. These interactions seem to be related to the aromatic and aliphatic content of the DOM, determining formation of hydrogen and non-covalent bonds. The degree of organic matter maturity does not seem to have any effect with amendment C, while a reduction in diuron leaching is observed between D_F and D_M. After equilibrium dialysis measurement of diuron-DOM complexes, it appeared that less than 3% of the diuron applied corresponded to complexes with a molecular weight > 1000 Da. Complexes < 1000 Da could also take part in this facilitated transport.     

Characteristics of competitive adsorption between 2-methylisoborneol and natural organic matter on superfine and conventionally sized powdered activated carbons

When treating water with activated carbon, natural organic matter (NOM) is not only a target for adsorptive removal but also an inhibitory substance that reduces the removal efficiency of trace compounds, such as 2-methylisoborneol (MIB), through adsorption competition. Recently, superfine (submicron-sized) activated carbon (SPAC) was developed by wet-milling commercially available powdered activated carbon (PAC) to a smaller particle size. It was reported that SPAC has a larger NOM adsorption capacity than PAC because NOM mainly adsorbs close to the external adsorbent particle surface (shell adsorption mechanism). Thus, SPAC with its larger specific external surface area can adsorb more NOM than PAC. The effect of higher NOM uptake on the adsorptive removal of MIB has, however, not been investigated. Results of this study show that adsorption competition between NOM and MIB did not increase when NOM uptake increased due to carbon size reduction; i.e., the increased NOM uptake by SPAC did not result in a decrease in MIB adsorption capacity beyond that obtained as a result of NOM adsorption by PAC. A simple estimation method for determining the adsorbed amount of competing NOM (NOM that reduces MIB adsorption) is presented based on the simplified equivalent background compound (EBC) method. Furthermore, the mechanism of adsorption competition is discussed based on results obtained with the simplified EBC method and the shell adsorption mechanism. Competing NOM, which likely comprises a small portion of NOM, adsorbs in internal pores of activated carbon particles as MIB does, thereby reducing the MIB adsorption capacity to a similar extent regardless of adsorbent particle size. SPAC application can be advantageous because enhanced NOM removal does not translate into less effective removal of MIB. Molecular size distribution data of NOM suggest that the competing NOM has a molecular weight similar to that of the target compound.     

Modelling biocide leaching from facades

Biocides leach from facades during rain events and subsequently enter the aquatic environment with storm water. Little is known about the losses of an entire settlement, since most studies referred to wash-off experiments conducted under laboratory conditions. Their results show a fast decrease of concentrations in the beginning, which subsequently slows down. The aim of this study is to develop a simple model to understand the mechanisms leading to these losses as well as to simulate losses under various rainfall and application conditions.We developed a four-box model based on the knowledge gained from fits of an exponential function to an existing experimental data set of a wash-off experiment. The model consists of two mobile stocks from which biocides are washed off during a rain event. These mobile stocks are supplied with biocides from storage stocks by diffusion-type processes. The model accurately reproduced the measured data of wash-off during single cycles as well as peak wash-offs over all cycles.Our model results for diuron losses showed that a large proportion (∼70%) of the applied biocides are still in the stocks even after a rain volume corresponding to several years (1100 mm y⁻¹, Swiss Plateau). Applications to realistic outdoor conditions showed that losses can not be neglected for urban environments and that knowledge about the amount of rainfall turned into runoff and the decay constants of the biocides in the facades are crucial. The model increased our understanding of the processes leading to the observed dynamic in laboratory experiments and was used to simulate losses for various rainfall and application conditions.     

活性氧化铝吸附水中砷的动态试验研究

近年来,饮用水砷污染事件层出不穷,选择高效合适的除砷方法,已成为全球关注的问题.试验采用逆流式单床吸附柱的吸附方式,对活性氧化铝吸附砷做了动态试验研究.研究结果显示,当初始砷浓度为10mg/L时,砷的去除率均在90%以上;当初始砷浓度为50mg/L时,以5mg/L为穿透点,穿透体积为110L,动态吸附量为3.43mg/g.结果表明,在水中砷的去除方面,活性氧化铝可作为一种有效吸附剂.该研究对实际应用中的活性氧化铝改性及饮用水处理具有重要意义.     

Adsorption of tri- and tetra-chloroethylene from aqueous solutions on activated carbon fibers

Recently the contamination of groundwater by trichloroethylene and related compounds have become a new environmental problem. As the first step to clarify the feasibility of applying newly developed adsorbent, activated carbon fiber (ACF), to adsorption treatments of water taken from such a contaminated groundwater source, the adsorption equilibrium and the adsorption rate of trichloroethylene and tetrachloroethylene from aqueous solutions on four ACFs with different pore-size distribution were investigated. The adsorption capacities of ACFs having larger volume of micropores are larger than those of granular activated carbons (GACs) usually used at present. Also, the adsorption rate on ACFs is far more rapid in comparison with GAC adsorption because of smaller diffusion path.     

Immobilization of Hg(II) in water with polysulfide-rubber (PSR) polymer-coated activated carbon

An effective mercury removal method using polymer-coated activated carbon was studied for possible use in water treatment. In order to increase the affinity of activated carbon for mercury, a sulfur-rich compound, polysulfide-rubber (PSR) polymer, was effectively coated onto the activated carbon. The polymer was synthesized by condensation polymerization between sodium tetrasulfide and 1,2-dichloroethane in water. PSR-mercury interactions and Hg-S bonding were elucidated from x-ray photoelectron spectroscopy, and Fourier transform infra-red spectroscopy analyses. The sulfur loading levels were controlled by the polymer dose during the coating process and the total surface area of the activated carbon was maintained for the sulfur loading less than 2 wt%. Sorption kinetic studies showed that PSR-coated activated carbon facilitates fast reaction by providing a greater reactive surface area than PSR alone. High sulfur loading on activated carbon enhanced mercury adsorption contributing to a three orders of magnitude reduction in mercury concentration. μ-X-ray absorption near edge spectroscopic analyses of the mercury bound to activated carbon and to PSR on activated carbon suggests the chemical bond with mercury on the surface is a combination of Hg-Cl and Hg-S interaction. The pH effect on mercury removal and adsorption isotherm results indicate competition between protons and mercury for binding to sulfur at low pH.     

Dynamic pesticide removal with activated carbon fibers

Rapid small-scale minicolumn tests were carried out to simulate the atrazine adsorption in water phase with three pelletized pitch-based activated carbon fibers (ACF) and one commercial granular activated carbon (GAC). Initial atrazine solutions were prepared with pretreated ground water. Minicolumn tests showed that the performance of highly activated carbon fibers (surface area of 1700 m2/g) is around 7 times better than the commercial GAC (with surface area at around 1100 m2/g), whereas carbon fibers with medium activation degree (surface area of 1500 m2/g) had a removal efficiency worse than the commercial carbon. The high removal efficiency of the highly activated ACF is due to the wide-opened microstructure of the material, with an appreciable contribution of the low size mesopores, maintaining at these conditions a fast kinetic adsorption rate rather than a selective adsorbent for micropollutants vs. natural organic matter.     

碳纤维布和钢板在旧桥加固中的应用

介绍采用粘贴碳纤维布和粘贴钢板加固桁架拱的方法，并对其进行了静动载试验，试验结果表明，加固后桥梁的整体刚度和承载力得到了一定程度的提高，说明采用粘贴碳纤维布加固拉弯构件、粘贴钢板加固受压构件的综合加固方法是有效的。     

天然气液化厂站脱汞的探讨

分析了吸附脱汞和氧化型吸收剂的脱汞效果,吸附脱汞的吸附剂包括煤基活性炭、活性炭纤维、活性焦、钙基吸附剂、壳聚糖类吸附剂.介绍了天然气脱汞的国内外工程实例.     

Structural and sorption properties of activated carbon modified with iron oxides

The structural and sorption characteristics of activated carbon modified with iron oxides were investigated and static exchange capacity of its surface functional groups of basic and acidic nature was determined. The modification of carbon with iron oxides was found to result in insignificant (7–13%) reduction of micropore and mesopore volume and in basification increase of the sorbent surface. The modified activated carbon is highly efficient in removing phenolic compounds from water.