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Due to the worldwide concern about emerging contaminants in aqueous systems, the main objective of the present study is the adsorption of gemifloxacin (GMF), a fluoroquinolone‐type antibiotic, by rice straw‐based activated carbon. The rice straw chemically activated with K2CO3 (RSAC) had very high carbon content (>80%) and low silica content (due to the extraction step after activation), high specific surface area (1668 m2/g), and oxygenated functional groups. The GMF adsorption capacity of RSAC was relatively dependent on the initial pH of the solution and highly dependent on the adsorbent dose. The pseudo‐second order model and the BET isotherm models were the best models for predicting adsorption's kinetic and equilibrium behaviors. The maximum monolayer adsorption capacities of RSAC at 25, 35, and 45°C were 565.6, 552.4, and 525.8 mg/g, respectively. The thermodynamic parameters indicated a spontaneous and exothermic character of the GMF adsorption process. n–π, π–π, electrostatic interactions, and hydrogen bonding were demonstrated as probable mechanisms involved. Thermal regeneration of GMF‐saturated RSAC at 550°C resulted in perfect adsorbent regeneration in the second cycle and reasonable performance in the third cycle. [ABSTRACT FROM AUTHOR]

Air humidification systems are in demand in many industrial and municipal sectors. Bubble columns are one of the most common forms of laboratory-scale humidifiers. Many operating parameters affect the performance of these systems, such as bubbler geometry, gas flow rate, temperature, the water level in the bubbler, and nozzle type. Since considering all these factors in an experimental system is costly, predicting performance by a computational fluid dynamics model is essential. In the present study, a laboratory-scale bubble column was simulated, and the effect of operating parameters was determined in terms of relative humidity at the outlet. In addition, the hydrodynamic fluid transfer from the nozzle to the outlet was thoroughly evaluated. An acceptable agreement was obtained between the experimental and model data, allowing further investigation on other important variables. Among the geometrical parameters, the ratio of water height to column diameter and nozzle type affected system performance by about 4 % and 20 %. Changing the flow rate and water temperature also affected the humidification process by 15 % and 16 %. The model scheme can be useful in developing and performing humidification systems before practical application. [ABSTRACT FROM AUTHOR]

In the search for new adsorbents for wastewater treatment, a modified clay-based adsorbent for the adsorption of Ni(II) was proposed in the present study. Silica pillared clays (SPCs) are adsorbents with high specific surface area and thermal stability, which have not been thoroughly investigated for their metal adsorption capacity. SPC was prepared by intercalating tetraethoxysilane (TEOS) as a silica source and a cationic surfactant (ethyl hexadecyl dimethylammonium bromide) between layers of a Na-saturated Iranian clay, followed by calcination. In order to make SPC a more efficient adsorbent for use in large-scale commercial applications, the present study addresses the conversion of a powdered SPC adsorbent into a granular one (ALG-SPC) by entrapping it in a polymeric matrix of calcium alginate and then using it for the adsorption of Ni(II) from aqueous solutions. The process of pillarization/granulation increased the specific surface area of the clay from 40 m2/g to 506 m2/g. A strong pH dependence of Ni(II) adsorption on pH was observed, showing the role of electrostatic interaction as the dominant mechanism in Ni(II) adsorption. The pseudo-second order model was the most appropriate kinetic model to describe Ni(II) adsorption. The isotherm models of Sips and Freundlich fit the equilibrium data best. According to the isotherm model of Sips, the maximum adsorption capacity was 52.58 mg/g. Some preliminary binary adsorption experiments were performed, which showed the negative effect of the presence of aniline in the solution on Ni(II) adsorption. Further investigations on multicomponent and continuous adsorption can be carried out. [ABSTRACT FROM AUTHOR]

Decreasing the concentration of pollutants in wastewater is a necessary issue particularly in the third-world countries. Mercury is known as one of the most important metal contaminants with harmful impacts on the environment. The present work is based on the lab-scale Hg elimination from synthetic wastewater. For this purpose, adsorption application in continuous mode has been chosen and a modified activated carbon which is sulphurised via dimethyl-disulphide was applied as adsorbent. Thus, the original activated carbon performance in Hg2+ adsorption was compared with the sulphurised sorbent. Investigation of the dynamic behaviour of adsorption fixed bed system which is highly demanded prior to industrialisation, was studied in the present work to predict the mass transfer coefficients and diffusional properties of adsorbent-adsorbate system. Therefore, a diffusional model namely Axial-dispersion Film Pore-Surface Diffusion model including all the main mass transfer mechanisms in porous beds was implemented. Apart from the mathematical model, one of the most common shortcut approaches (Thomas model) was applied to describe the adsorption behaviour in fixed beds for comparison with the mathematical model results. Based on the Thomas model and experimental results, several important properties of both adsorbate/adsorbent system such as equilibrium adsorption capacity and exhaustion rate were calculated and explained. According to the results of mathematical modelling, the factors and mechanisms with the lowest degree of importance were determined in each system, and the more appropriate/simpler mathematical models were suggested. [ABSTRACT FROM AUTHOR]