Removal of Pyridine from Aqueous Solution by Adsorption on an Activated Carbon Cloth

Pyridine is a very toxic pollutant that has to be removed from wastewater. In this work, adsorption of pyridine on activated carbon cloth (ACC) is studied as a possible alternative for eliminating pyridine from aqueous solution. The ACC was produced from polyacrylonitrile. The adsorption equilibrium data of pyridine on ACC was obtained in a batch adsorber. The experimental data was interpreted with the isotherms of Langmuir, Freundlich, and Prausnitz‐Radke (PR), and the PR isotherm better represented the experimental data. The capacity of ACC for adsorbing pyridine was favored increasing the solution pH from 3 to 6, and this effect was due to the π–π dispersive and electrostatic interactions between the pyridine species in solution and the surface complexes of ACC. The modified Langmuir model fitted reasonably well the influence of pH on the adsorption capacity. In this model was assumed that both neutral pyridine and pyridinium were simultaneously adsorbed on ACC accordingly to the experimental results. The adsorption capacity was almost independent of temperature. The reversibility study revealed that 75% of the pyridine can be desorbed from ACC indicating that part of the pyridine was irreversibly adsorbed, and possibly chemisorbed.     

Removal of Basic Textile Dyes in Single and Multi‐Dye Solutions by Adsorption: Statistical Optimization and Equilibrium Isotherm Studies

The removal of three basic dyes by adsorption onto bentonite was investigated for single, binary, and ternary solutions in a batch system. Before and after dye adsorption, bentonite samples were analyzed by using X‐ray fluorescence spectrometer, SEM, and Fourier transform IR spectrometry. The D‐optimal design and response surface methodology were applied in designing the experiments for evaluating the interactive effects of each initial concentrations variable of the dyes in binary systems. Predicted values were found to be in good agreement with experimental values, which defined propriety of the model and the achievement of D‐optimal in optimization of adsorption of binary dye systems. The competitive adsorption results showed that the adsorption amount of a dye was suppressed in the presence and increasing concentrations of second or third dye. For mono‐component isotherm modeling, Langmuir and Freundlich models were applied to equilibrium data of single, binary, and ternary dye solutions, while modified Langmuir, Sheindrof–Rebhun–Sheintuch and modified extended Freundlich models were also applied to equilibrium data of binary dye solutions for multi‐component isotherm modeling. The results showed that the Langmuir was the more suitable model for single dye systems while extended Freundlich model fitted best to the experimental data with the lowest error values for multi‐dye systems.     

Studies on Adsorptive Desulfurization by Activated Carbon

Sulfur removal using adsorption requires a proper process parametric study to determine its optimal performance characteristics. In this study, response surface methodology was employed for sulfur removal from model oil (dibenzothiophene; DBT dissolved in iso‐octane) using commercial activated carbon (CAC) as an adsorbent. Experiments were carried out as per central composite design with four input parameters such as initial concentration (C₀: 100–900 mg/L), adsorbent dosage (m: 2–22 g/L), time of adsorption (t: 15–735 min), and temperature (T: 10–50°C). Regression analysis showed good fit of the experimental data to the second‐order polynomial model with coefficient of determination R²‐value of 0.9390 and Fisher F‐value of 16.5. The highest removal of sulfur by CAC was obtained with m = 20 g/L, t = 6 h, and T = 30°C.     

Adsorption of Cadmium Ions from Aqueous Solution Using Granular Activated Carbon and Activated Clay

The present study was aimed at removing cadmium ions from aqueous solution through batch studies using adsorbents, such as, granular activated carbon (GAC) and activated clay (A‐clay). GAC was of commercial grade where as the A‐clay was prepared by acid treatment of clay with 1 mol/L of H₂SO₄. Bulk densities of A‐clay and GAC were 1132 and 599 kg/m³, respectively. The surface areas were 358 m²/g for GAC and 90 m²/g for A‐clay. The adsorption studies were carried out to optimize the process parameters, such as, pH, adsorbent dosage, and contact time. The results obtained were analyzed for kinetics and adsorption isotherm studies. The pH value was optimized at pH 6 giving maximum Cd removal of 84 and 75.2% with GAC and A‐clay, respectively. The adsorbent dosage was optimized and was found to be 5 g/L for GAC and 10 g/L for A‐clay. Batch adsorption studies were carried out with initial adsorbate (Cd) concentration of 100 mg/L and adsorbent dosage of 10 g/L at pH 6. The optimum contact time was found to be 5 h for both the adsorbents. Kinetic studies showed Cd removal a pseudo second order process. The isotherm studies revealed Langmuir isotherm to better fit the data than Freundlich isotherm.     

Response Surface Optimization of Acid Red 119 Dye Adsorption by Mixtures of Dried Sewage Sludge and Sewage Sludge Ash

The mixtures of dried sewage sludge (DSS) and sewage sludge ash were studied for removal of acid red 119 (AR119) dye as a new, more environmental friendly, and low cost adsorbent. For this purpose, response surface methodology was applied to optimize the dye removal efficiency and turbidity of treated dye solutions as two individual responses. Results revealed that an optimum condition under specified constraints (dye removal efficiency >95% and turbidity <50 NTU) was obtained at a contact time of 60 min, 40 wt% DSS in the mixture, an initial pH of 6, and an initial dye concentration of 200 mg dye/L in distilled water. Under the optimal condition, dye removal efficiency of 94.98% and effluent turbidity of 24.9 NTU was observed. In further studies, at optimum condition, the effect of some additives on adsorption process and desorption/reusability of adsorbent was investigated. It was observed that removal efficiency was significantly decreased to 83.76% when a simulated dye wastewater (containing the selected dye, acetic acid, and Glauber's salt dissolved in tap water) was used. Desorption studies revealed that AR119 dye could be well removed from dye‐loaded adsorbent by 0.3 M NaOH solution.     

Removal of Selenium by Adsorption onto Granular Activated Carbon (GAC) and Powdered Activated Carbon (PAC)

The present work involves the study of Se(IV) adsorption onto granular activated carbon (GAC) and powdered activated carbon (PAC). The adsorbents are coated with ferric chloride solution for the effective removal of selenium. The physico-chemical characterization of the adsorbents is carried out using standard methods, e. g., proximate analysis, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), thermo-gravimetric (TGA) and differential thermal analysis (DTA), etc. The FTIR spectra of the GAC and PAC indicate the presence of various types of functional groups, e. g., free and hydrogen bonded OH groups, silanol groups (Si-OH), alkenes, and CO group stretching from aldehydes and ketones on the surface of adsorbents. Batch experiments are carried out to determine the effect of various factors such as adsorbent dose (w), initial pH, contact time (t), and temperature (T) on the adsorption process. The optimum GAC and PAC dosage is found to be 10 g/L and 8 g/L, respectively, for Se(IV) removal with C₀ = 100 mg/L. The percent removal of Se(IV) increases with increasing adsorbent concentration, while removal per unit weight of adsorbent increases with decreasing adsorbent concentration. Se(IV) adsorption onto both the GAC and PAC adsorbents is high at low pH values, and decreases with increased initial pH. The results obtained are analyzed by various kinetic models. The parameters of pseudo-first order, pseudo-second order kinetics, and Weber-Morris intra particle kinetics are determined. It is seen that the sorption kinetics of Se(IV) onto GAC and PAC can be best represented by the pseudo-second order kinetic model.     

Removal of Cadmium from Aqueous Solution Using Castor Seed Hull: A Kinetic and Equilibrium Study

The effects of various parameters such as initial concentration, adsorbent loading, pH, and contact time on kinetics and equilibrium of adsorption of Cd²⁺ metal ion from its aqueous solution by castor seed hull (CSH) and also by activated carbon have been investigated by batch adsorption experiments. The amount of adsorption increases with initial metal ion concentration, contact time, solution pH, and the loading of adsorbent for both the systems. Kinetic experiments indicate that adsorption of cadmium metal ion on both CSH and on activated carbon consists of three steps – a rapid adsorption of cadmium metal ion, a transition phase, and an almost flat plateau region. This has also been confirmed by the intraparticle diffusion model. The lumped kinetic results show that the cadmium adsorption process follows a pseudo‐second order rate law. The kinetic parameters including the rate constant are determined at different initial metal ion concentrations, pH, amount, and type of adsorbent, respectively. The Langmuir and Freundlich adsorption isotherm models are used to describe the experimental data. The Langmuir model yields a better correlation coefficient than the other model. A comparison of the monolayer adsorption capacity (q_m) of CSH, activated carbon, and several other reported adsorbents has been provided. The value of separation factor (R_L) calculated from the Langmuir equation also gives an indication of favorable adsorption of the metal ion. From comparative studies, it has been found that CSH is a potentially attractive adsorbent than commercial activated carbon for cadmium metal ion (Cd²⁺) removal.     

Dye Removal from Colored Textile Wastewater by Poly(propylene imine) Dendrimer: Operational Parameters and Isotherm Studies

This paper deals with the removal of textile dyes from aqueous solutions by poly(propylene imine) dendrimer (PPI). Direct red 80 (DR80), Acid Green 25 (AG25), Acid Blue 7 (AB7), and Direct Red 23 (DR23) were used as model dyes. The effects of operational parameters on dye removal such as dendrimer concentration, dye concentration, salt (inorganic anions), and pH have been studied at 25°C. The Langmuir and Freundlich isotherm models were investigated. In addition, dye desorption of dendrimer was studied. The results indicated that acidic pH supported the adsorption of dyes by dendrimer. Furthermore studies of dye concentration and salt effects exhibited that dye removal percentage by dendrimer was decreased. It was found that the isotherm data of DR80, AG25, and DR23 followed Langmuir isotherm and isotherm data of AB7 followed Freundlich isotherm models. Desorption tests showed that maximum dye releasing of 76.5% for DR80, 84.5% for AG25, 87% for AB7, and 93% for DR23 were achieved in aqueous solution at pH 12. Based on the data of present study, one could conclude that the dendrimer being an environmentally friendly adsorbent with relatively large adsorption capacity might be a suitable alternative for elimination of dyes from colored textile wastewater.     

Removal of EDTA from Aqueous Solutions Using Activated Carbon Prepared from Rubber Wood Sawdust: Kinetic and Equilibrium Modeling

Adsorptive removal of EDTA (ethylenediaminetetraacetic acid) from aqueous solution was studied using steam pyrolyzed activated carbon. Rubber wood sawdust, obtained from a local timber facility at Kodangavila, Trivandrum, Kerala, India was used as the precursor for the production of the activated carbon. Batch adsorption experiments were employed to monitor and optimize the removal process. The experimental parameters, i. e., solution pH, agitation time, initial EDTA concentration and adsorbent dosage, affecting the adsorption of EDTA onto sawdust activated carbon (SDAC) were optimized. The inner core mechanism for the interaction between EDTA and SDAC, which resulted in the adsorption process, was also discussed. The change in amount of EDTA adsorbed onto SDAC and CAC (commercial activated carbon) was compared over a wide range of pH (2.0–8.0). The maximum removal of EDTA took place in the pH range of 4.0–6.0 for SDAC and 5.0–5.5 for CAC, which demonstrates the effectiveness of the former adsorbent. Kinetic as well as equilibrium studies were performed to determine the rate constant and adsorption capacity, respectively. The adsorption kinetic data was fitted with pseudo‐first‐order kinetics and the equilibrium data was shown to follow the Langmuir isotherm model. These observations explain the formation of a monolayer of EDTA on the surface of SDAC as confirmed by the slow approach to equilibrium after 4 h of contact time. The adsorption capacity of SDAC for the removal of EDTA was 0.526 mmol/g and is seen to be greater than that of CAC and other reported adsorbents (0.193–0.439 mmol/g). Finally, it is clear that the production of steam pyrolyzed activated carbon in the presence of K₂CO₃ greatly enhanced EDTA removal and resulted in a product with possible commercial value for wastewater treatment strategies.     

Improved Removal of Indoor Volatile Organic Compounds by Activated Carbon Fiber Filters Calcined with Copper Oxide Catalyst

Heating, ventilating, and air‐conditioning (HVAC) systems ensure indoor air quality and provide a comfortable environment. However, the conventional HVAC systems only provide indoor ventilation and adjust temperature and humidity. This work removes indoor volatile organic compounds (VOCs) using a feasible and novel air‐cleaning for an HVAC system, to remove indoor VOCs. An activated carbon‐fiber (ACF) filter calcined with copper oxide (CuO) catalyst, called a CuO/ACF catalyst filter, was the developed kit. Formaldehyde, a major VOC, was chosen as the target pollutant. Experiments were performed to confirm the filtration ability of the CuO/ACF catalyst filter in removing formaldehyde in a stainless‐steel chamber equipped with a simplified HVAC system. Total air exchange rate (ACH) was controlled at 0.5 and 1.0 h⁻¹, the fresh ACH was 0.15 and 0.30 h⁻¹, and relative humidity (RH) was set at 30 and 70%. A first‐order decay of formaldehyde existed in the controlled chamber when the two pretreated CuO/ACF catalyst filters were employed. Experimental results demonstrate that the CuO/ACF catalyst filters removed formaldehyde effectively. The decay constant was 0.425 and 0.618 h⁻¹ for 0.5 and 2.0 ppm formaldehyde, respectively. Moreover, the formaldehyde decay rate increased as total ACH, fresh ACH, RH, and the Cu(NO₃)₂ concentration for calcination of CuO/ACF catalyst filter increased.     

Adsorption of Chromium(III), Nickel(II), and Copper(II) from Aqueous Solution by Activated Alumina

The possible use of activated alumina powder (AAP) as adsorbent for Cr(III), Ni(II), and Cu(II) from synthetic solutions was investigated. The effect of various parameters on batch adsorption process such as pH, contact time, adsorbent dosage, particle size, temperature, and initial metal ions concentration were studied to optimize the conditions for maximum metal ion removal. Both higher (molar) and lower (ppm) initial metal ion concentration sets were subjected to adsorption on AAP. Adsorption process revealed that equilibrium was established in 50 min for Cr(III) at pH 4.70, 80 min for Ni(II) at pH 7.00, and 40 min for Cu(II) at pH 3.02. Percentage removal was found to be highest at 55°C for Cr(III) and Ni(II) with 420 µm and 45°C for Cu(II) with 250‐µm particle size AAP. A dosage of 2 g for Cr(III), 8 g for Ni(II), and 10 g Cu(II) gave promising data in the metal ion removal. The adsorption process followed Langmuir as well as Freundlich models. The thermodynamics of adsorption of these metal ions on activated aluminum indicated that the adsorption was spontaneous and endothermic in nature. Present study indicates that AAP can act as a promising adsorbent for industrial wastewater treatment.     

Response Surface Optimization for Removal of Cadmium from Aqueous Solution by Waste Agricultural Biosorbent Psidium guvajava L. Leaf Powder

Response surface methodology (RSM) was applied to study the combined effects of the various parameters namely, pH, biosorbent dosage, cadmium concentration and temperature, and to optimize the process conditions for the maximum removal of cadmium using Psidium guvajava L. leaf powder. In order to obtain the mutual interactions between the variables and to optimize these variables, a 2⁴ full factorial central composite design using RSM was employed. The analysis of variance (ANOVA) of the quadratic model demonstrates that the model was highly significant. The model was statistically tested and verified by experimentation. A maximum cadmium removal of 93.2% was obtained under the following optimum conditions: aqueous cadmium concentration 40.15 mg/L, adsorbent dosage 0.5 g/50 mL solution, pH 5.0, and temperature (35°C). The value of desirability factor obtained was 1.     

Ionic Liquid Modified Resin for the Adsorptive Removal of Dibutyl Phthalate: Equilibrium,Kinetic, and Thermodynamic Studies

This study evaluated the adsorptive properties of dibutyl phthalate (DBP) on room temperature ionic liquid (RTIL) modified XAD‐4 resin. The modified RTIL‐XAD 4 sorbent was characterized by FTIR. Effect of varying experimental conditions such as pH, contact time, temperature, shaking speed, concentrations, and interfering species were investigated by batch adsorption experiments. Adsorption was found to be most favorable at pH 6 within 30 min. Experimental data were evaluated in terms of kinetic, equilibrium, and thermodynamic modeling. Kinetics of the sorption was found to follow pseudo second order rate equation whereas Freundlich and D–R isotherms were the most suitable models to explain sorption phenomenon. Thermodynamically sorption was endothermic, irreversible, and spontaneous in nature.     

Parameter Optimization of Activated Carbon Production from Agave sisalana and Punica granatum Peel: Adsorbents for C.I. Reactive Orange 4 Removal from Aqueous Solution

In the present study, activated carbons were prepared from sisal fiber (Agave sisalana sp.) and pomegranate peel (Punica granatum sp.) using phosphoric acid as the activating agent. Both sisal fiber activated carbon (SFAC) and pomegranate peel activated carbon (PPAC) were characterized using methylene blue number, iodine number, BET surface area, SEM, and FTIR. The BET surface area of the SFAC and PPAC were 885 and 686 m²/g, respectively. The adsorption studies using C.I. Reactive Orange 4 dye on the SFAC and PPAC were carried out. The effects of time, initial adsorbate concentration, pH, and temperature on the adsorption were studied. The isotherm studies were carried and it was found that the Langmuir and Freundlich isotherms fit well for the adsorption of RO 4 on SFAC, while adsorption of RO 4 on PPAC is better represented by the Langmuir and Temkin isotherms. Adsorption kinetics of adsorption was determined using pseudo first order, pseudo second order, Elovich and intraparticle diffusion models and it was found that the adsorption process follows pseudo second order model. Thermodynamics parameters such as changes in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) were determined by using van't Hoff equation. The positive ΔH value indicates that RO 4 dye adsorption on SFAC and PPAC is endothermic in nature.     

Biosorption of Cd(II), Ni(II) and Pb(II) from Aqueous Solution by Dried Biomass of Aspergillus niger: Application of Response Surface Methodology to the Optimization of Process Parameters

In this study, the biosorption of Cd(II), Ni(II) and Pb(II) on Aspergillus niger in a batch system was investigated, and optimal condition determined by means of central composite design (CCD) under response surface methodology (RSM). Biomass inactivated by heat and pretreated by alkali solution was used in the determination of optimal conditions. The effect of initial solution pH, biomass dose and initial ion concentration on the removal efficiency of metal ions by A. niger was optimized using a design of experiment (DOE) method. Experimental results indicated that the optimal conditions for biosorption were 5.22 g/L, 89.93 mg/L and 6.01 for biomass dose, initial ion concentration and solution pH, respectively. Enhancement of metal biosorption capacity of the dried biomass by pretreatment with sodium hydroxide was observed. Maximal removal efficiencies for Cd(II), Ni(III) and Pb(II) ions of 98, 80 and 99% were achieved, respectively. The biosorption capacity of A. niger biomass obtained for Cd(II), Ni(II) and Pb(II) ions was 2.2, 1.6 and 4.7 mg/g, respectively. According to these observations the fungal biomass of A. niger is a suitable biosorbent for the removal of heavy metals from aqueous solutions. Multiple response optimization was applied to the experimental data to discover the optimal conditions for a set of responses, simultaneously, by using a desirability function.     

A Study: Removal of Cu(II), Cd(II), and Pb(II) Ions from Real Industrial Water and Contaminated Water Using Activated Sludge Biomass

This study aims to remove of Cu²⁺, Cd²⁺, and Pb²⁺ ions from solution and to investigate the adsorption isotherms, adsorption kinetics, and ion‐exchange affinities of these metals using waste activated sludge (AS) biomass. The adsorptions of the metals on biomass were optimal at an acidic pH value of 6.0 based on its monolayer capacities. Maximum monolayer capacities of AS biomass (q_max) were calculated as 0.478, 0.358, and 0.280 mmol g^?1 for Cu²⁺, Cd²⁺, and Pb²⁺, respectively, and the adsorption equilibrium time was found as 60 min for each metal. The adsorbed amount of metal rose with increasing of initial metal ion concentration. The equilibrium adsorption capacity of AS for initial 0.25 mmol L^?1 metal concentration was determined as 0.200, 0.167, and 0.155 mmol g^?1 for Cu²⁺, Cd²⁺, and Pb²⁺ ions, respectively. These relevant values were determined as 0.420, 0.305, and 0.282 mmol g^?1 for Cu²⁺, Cd²⁺, and Pb²⁺ ions, respectively, when initial metal concentration was 0.50 mmol L^?1. In the multi‐metal sorption system, the adsorption capacity of AS biomass was observed in the order of Cu²⁺ > Cd²⁺ > Pb²⁺. In the presence of 100 mmol L^?1 H⁺ ion, the order of ion‐exchange affinity with H⁺ was found as Cu²⁺ > Cd²⁺ > Pb²⁺. The adsorption kinetics were also found to be well described by the pseudo‐second‐order and intraparticle diffusion models. Two different rate constants were obtained as k_i1 and k_i2 and k_i1 (first stage) was found to be higher than k_i2 (second stage).