Adsorption of chromium (VI) by strong alkaline anion exchange fiber in a fixed-bed column: Experiments and models fitting and evaluating

Removal of perfluoroalkyl acids and common drinking water contaminants by weak-base anion exchange resins: Impacts of solution pH and resin properties

The underlying chemistry of weak-base (WB) anion exchange resins (AERs) for contaminant removal from water is not well documented in the literature. To address this, batch adsorption experiments were conducted at pH 4, 7, and 10 using two representative WB-AERs (polyacrylic IRA67 and polystyrene IRA96) and two representative strong-base (SB) AERs (polyacrylic IRA458 and polystyrene A520E), of differing polymer composition, for the removal of nitrate, sulfate, 3-phenylpropionic acid (3-PPA) as surrogate for natural organic matter, and six perfluoroalkyl acids (PFAAs). Under acidic (pH 4) and neutral (pH 7) conditions, the selectivity of AERs for each contaminant was predominantly influenced by polymer composition followed by the size of the resin functional group. This result reflected the WB-AERs being fully protonated and functioning identical to SB-AERs. Isotherm model parameters revealed WB-AER had higher capacity than SB-AER with analogous polymer composition and porosity regardless of resin selectivity for each contaminant. Under basic conditions (≥ pH 10), contaminant removal by WB-AERs declined due to deprotonation of the tertiary amine functional groups. Removal of PFAAs by the more hydrophobic polystyrene WB-AER (IRA96) remained approximately constant with changing pH, which was possibly due to electrostatic interactions with remaining protonated amine functional groups on the resin.

Use of COMSOL software for modeling and simulation of copper removal in a dynamic mode on a new biowaste

The main purpose of this investigation is to model the results related to biosorption using COMSOL (Multiphysics 4.3a), and to solve the advection-dispersion equation by using both linear and Langmuir models. A bidimensional model was then proposed to study the mass transfer in the process of copper ions sorption in a dynamic mode on cider vinegar residues. Sorption tests were realized by evaluating the influence of flow rate (0.75, 1, and 2.65 ml min^-1 ), bed height (3.5, 7 and 8.5 cm), and copper initial concentration (169 and 300 mg L^-1 ). For all cases, the mathematical formulation was solved by assuming that the column is homogeneous and the sorption is instantaneous. The corresponding results were exploited through breakthrough curve profiles, where it was shown that the solutions obtained by the "Langmuir COMSOL" model coincide with the experimental values. In contrast, the linear model has been unable to fit them. The optimal results were analyzed by Thomas, Adam-Bohart Yoon Nelson, and Ogata-Bank models, which proves that the Thomas method is well adapted with a satisfactory correlation coefficient (0.93). Further, the model validation was performed by determining the residual root mean square error, which was found less than 0.3, thereby indicating a reasonable concordance between the estimated and experimental points. The high sorption capacity obtained was around of 41.37 mg g^-1 , which suggests that the cider vinegar residues can be exploited as a low-cost, available, and effective sorbent biomass in the field of the treatment of industrial effluents. PRACTITIONER POINTS: Cider vinegar residues (CVR) as low cost biosorbent were studied for continuous biosorption. A successful COMSOL model was proposed and validated. CVR is an effective biosorbent for copper fixed bed biosorption. High sorption capacity was around of 41.37 mg g^-1 under optimal conditions.

Biosorptive Removal of Ethacridine Lactate from Aqueous Solutions by Saccharomyces pastorianus Residual Biomass/Calcium Alginate Composite Beads: Fixed-Bed Column Study

In this study, ethacridine lactate removal from aqueous solution using a biosorbent material based on residual microbial biomass and natural polymers in fixed-bed continuous column was investigated. Composite beads of Saccharomyces pastorianus residual biomass and calcium alginate were obtained by immobilization technique. The prepared biosorbent was characterized by Fourier transformed infrared spectroscopy, scanning electron microscopy, and analysis of point of zero charge value. Then, laboratory-scale experiments by fixed-bed column biosorption were conducted in continuous system. To this purpose, the column bed high (5 cm; 7.5 cm), initial pollutant concentration (20 mg/L; 40 mg/L), and solution flow through the column (0.6 mL/min; 1.5 mL/min) were considered the main parameters. Recorded breakthrough curves suggest that lower flow rates, greater bed heights, and a lower concentration of ethacridine lactate led to an increased biosorption of the target compound. The biosorption dynamic was investigated by nonlinear regression analysis using the Adams–Bohart, Yoon–Nelson, Clark, and Yan mathematical models. Conclusively, our research highlights, firstly, that the obtained biosorbent material has the required properties for retaining the ethacridine lactate from aqueous solution in continuous system. Secondly, it emphasizes that the modeling approach reveals an acceptable fitting with the experimental data for the Yoon–Nelson, Clark, and Yan models.

Modified dry bean pod waste (Phaseolus vulgaris) as a biosorbent for fluorescein removal from aqueous media: Batch and fixed bed studies

This study presents the use of dry bean pods as a solid phase for fluorescein removal from water. The non-pretreated solid phase did not display any sorption properties for the chosen dye. However, interesting sorption properties were observed following a chemical derivative treatment with nitric acid. The study was carried out using both batch and column approaches. Regarding the batch study, all parameters that influence sorption capacity, such, as pH, adsorbent mass, ionic strength, temperature and contact time, were evaluated. A sorptive capacity of 36.80 mg g^-1 was obtained in the optimized condition. In the fixed column bed study, the influence of particle size, flow rate and initial concentration of the dye were evaluated through breakthrough curves and a sorptive capacity of 4.35 mg g^-1 was obtained. Thermodynamic studies revealed that the adsorption is exothermic and spontaneous. Four different models, Langmuir, Freundlich, Temkin and Redlich-Patterson, were employed. The Akaike information criterion (AIC) was employed to rank the best equilibrium model, which was determined as the Freundlich isotherm. The method was applied to a real sample and the same removal rate was obtained, thus indicating its suitability to wastewater treatment.

An integrated active biochar filter and capacitive deionization system for high-performance removal of arsenic from groundwater

An integrated process of filtration and electrosorption was first applied to enable high-performance arsenic removal for groundwater remediation. An active manganese dioxide-rice husk biochar composite (active BC) filter was utilized for oxidization of As(III) to As(V) and initial removal of As(III, V). Subsequently, electrosorption by capacitive deionization (CDI) was applied as a posttreatment to improve arsenic removal. The active BC approach exhibited fast removal rates of 0.75 and 0.63 g mg^-1 h^-1 and high maximum removal capacities of 40.76 and 48.15 mg g^-1 for As(III) and As(V), respectively. Importantly, column experiments demonstrated that the arsenic removal capacity in the active BC filter was 2.88 mg g^-1, which was 72 times higher than that of BC. The results were due to the high efficiency (94%) of redox transformation of As(III) to As(V). The electrosorptive removal of arsenic was further controlled by changing the voltage in CDI. With a charging step of 1.2 V, the total arsenic concentration can be reduced to 0.001 mg L^-1 with a low energy consumption of 0.0066 kW h m^-3. Furthermore, the integrated system can remove As from real groundwater to achieve the World Health Organization guideline value for drinking water quality.

Artificial neural network (ANN) approach for prediction and modeling of breakthrough curve analysis of fixed-bed adsorption of iron ions from aqueous solution by activated carbon from Limonia acidissima shell

The present research article explored the potential of activated carbon prepared from Limonia acidissima shell to adsorb total Fe ions from aqueous solution in a packed bed up-flow column. The effect of essential factors such as bed height (3–5 cm), initial concentration (30–50 mg/L), and flow rate (3.32–5.4 mL/min) on the performance of the column bed was investigated. The adsorption capacity augmented with an increase in bed height and initial adsorbate concentration but declined with an increase in flow rate. The maximum uptake capacity of 209.6 mg/g was achieved at 5 cm bed height, 3.32 mL/min, and 50 mg/L initial concentration. The bed depth service time (BDST) model was used to analyze the experimental data and determine the characteristic parameters of the packed bed reactor suitable for designing large-scale column studies. The Adams–Bohart, Thomas, and Yoon–Nelson models were applied to the experimental data to predict breakthrough curves using non-linear regression. The artificial neural network (ANN) based model was able to efficaciously predict the column performance using the Levenberg–Marquardt (LM) algorithm. A comparison between the experimental data and model results contributed to a high degree of correlation, specifying that the preliminary information was in good agreement with the ANN predicted data.

Synthesis of Calcium Silicate Hydrate from Coal Gangue for Cr(VI) and Cu(II) Removal from Aqueous Solution

Both the accumulation of coal gangue and potentially toxic elements in aqueous solution have caused biological damage to the surrounding ecosystem of the Huainan coal mining field. In this study, coal gangue was used to synthesize calcium silicate hydrate (C-S-H) to remove Cr(VI) and Cu(II)from aqueous solutions and aqueous solution. The optimum parameters for C-S-H synthesis were 700 °C for 1 h and a Ca/Si molar ratio of 1.0. Quantitative sorption analysis was done at variable temperature, C-S-H dosages, solution pH, initial concentrations of metals, and reaction time. The solution pH was precisely controlled by a pH meter. The adsorption temperature was controlled by a thermostatic gas bath oscillator. The error of solution temperature was controlled at ± 0.3, compared with the adsorption temperature. For Cr(VI) and Cu(II), the optimum initial concentration, temperature, and reaction time were 200 mg/L, 40 °C and 90 min, pH 2 and 0.1 g C-S-H for Cr(VI), pH 6 and 0.07 g C-S-H for Cu(II), respectively. The maximum adsorption capacities of Cr(VI) and Cu(II) were 68.03 and 70.42 mg·g⁻¹, respectively. Furthermore, the concentrations of Cu(II) and Cr(VI) in aqueous solution could meet the surface water quality standards in China. The adsorption mechanism of Cu(II) and Cr(VI) onto C-S-H were reduction, electrostatic interaction, chelation interaction, and surface complexation. It was found that C-S-H is an environmentally friendly adsorbent for effective removal of metals from aqueous solution through different mechanisms.

Superior removal of inorganic and organic arsenic pollutants from water with MIL-88A(Fe) decorated on cotton fibers

Arsenic contamination has attracted worldwide concerns, owing to its toxicity and severe threat to human and environment. It is urgent to develop efficient adsorbents to remove arsenic pollutants. Within this paper, both pristine MIL-88A(Fe) and MIL-88A(Fe) decorated on cotton fibers were successfully fabricated using an eco-friendly method. The pristine MIL-88A(Fe) displayed outstanding adsorption performances towards four selected arsenic pollutants, in which the adsorption capacities toward As(III), As(V), ROX and ASA were 126.5, 164.0, 261.4 and 427.5 mg g^-1, respectively. Additionally, MIL-88A(Fe) exhibited excellent removal efficiencies in a wide pH range and with the presence of different co-existing ions. It was proposed that the coordinative interactions of As-O-Fe between arsenic pollutants and MIL-88A(Fe) contributed to the superior adsorption performances. Furthermore, two MIL-88A(Fe)/cotton fibers composites were synthesized by both post synthesis (MC-1) and in-situ synthesis (MC-2), which demonstrated identically outstanding adsorption activities toward four selected arsenic pollutants. MC-1 and MC-2 enhanced the stability and reusability of MIL-88A(Fe), which was challenging issues of pristine MIL-88A(Fe) powder. Additionally, the fixed-bed column packed by MC-1 or MC-2 can continuously eliminate arsenic pollutants from the water flow. This work provided a new possibility of metal-organic frameworks to accomplish potentially large-scale application to purify the arsenic-contaminated water.

Preparation of Carbon-Silicon Doping Composite Adsorbent Material for Removal of VOCs

The adsorption-desorption combined process has been considered as a promising method for the industrial VOCs (volatile organic compounds) treatment. Herein, a carbon-silicon composite adsorbent material has been prepared for the removal of VOCs at lower potential flammable risk. The preparation involves two main steps: Extrusion forming and thermal treatment. The carboxymethyl cellulose and silicate were adopted as binder and fire retardant respectively. The molding and inflaming retarding mechanisms were proposed and discussed. Results show that the newly prepared doping combined material is micro-mesoporous with a specific surface area of 729 m²/g. The maximum adsorption capacity of carbon-silicon doping combined material to p-xylene is observed to be 292 mg/g. The adsorption is found to be favorable, which is well described by the Yoon-Nelson model and Freundlich isotherm. The combined material is also found to possess reversible adsorption to p-xylene; without sacrificing (<2%) too much adsorption capacity after five adsorption-desorption cycles. The composite materials have an increased ignition temperature of at least 40 °C compared with raw carbon material. These findings suggest that the obtained composite material possesses good adsorption capacity and flame-retardant properties.

Fixed bed adsorption column studies and models for removal of ibuprofen from aqueous solution by strong adsorbent Nano-clay composite

In this study, ibuprofen was removed using a strong nano-clay-composite based on cloisite 15A, PVP and β-cyclodextrin (CD@clay-PVP) adsorbent through a fixed-bed column system. Chemically modified nano-clay was characterized by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and XRD. Different input situations were evaluated and included adsorbent bed height, initial concentrations, and the impact of the flow rate on the adsorbent. The various mathematical models employed to predict the breakthrough curve and model parameters include Thomas, bed-depth service time (BDST), Yoon-Nelson, and Clark. The characteristics of parameters related to the models were obtained by linear and nonlinear regression to design the process for the columns. Based on error analysis and adsorption conditions, all of the models are identical in describing the adsorption fixed-bed columns.

Adsorption removal of Cr(VI) by isomeric FeOOH

The aim of this work is to study the performances of isomeric α-, β-, and γ-FeOOH (goethite, akaganéite and lepidocrocite, including five samples named as Gth1 and Gth2, Aka1 and Aka2, and Lep, respectively) for removing hexavalent chromium (Cr(VI)) from aqueous solutions. The adsorption mechanisms were explored by kinetic and isothermal experiments. Adsorption efficiencies under the different pH values, anions, and the levels of adsorbate and adsorbent were also measured. Results showed that the Cr(VI) adsorption by isomeric FeOOH could be best described by pseudo-second-order kinetic model. The processes of Cr(VI) isothermal adsorption could be greatly fitted by the Langmuir and Freundlich equations with the high correlation coefficients of R² (>0.92). Also, there were the optimum pH values of 3.0-8.0 for FeOOH to adsorb Cr(VI), and their adsorption capacities were tightly related with the active sites of adsorbents. Cr(VI) adsorptions by these adsorbents were easily influenced by H₂PO₄ ^-, and then SO₄ ^2-, while there were little effects by Cl^-, CO₃ ^2- and NO₃ ^-. These obtained results could provide a potentially theoretical evidence for isomeric FeOOH materials applied in the engineering treatment of the polluted chromate-rich waters.

Adsorption of Lead on Lentil Husk in Fixed Bed Column Bioreactor

This study depicts successful employment of fixed bed column bioreactor for adsorption of lead in continuous mode using lentil husk as sorbent. Design parameters considerably controlled the reactor performance, amongst which height of the fixed bed and flow rate were crucial in generating cleaner effluent. Adsorption capacity was found to shoot up to the level of 205.87 mg g^-1 at 10 cm bed height, 100 mg L^-1 feed concentration and 20 mL min^-1 flow rate. Kinetic study done at regular intervals of time revealed high percentage removal of lead (99-96%) throughout entire span of reactor operation. Experimental data were well interpreted by Thomas model and Yoon-Nelson model. The reactor bed was regenerated after each adsorption and loaded metal was recovered up to the extent of ∼96%. The column reactor was efficient enough to treat lead containing actual industrial effluents.

Continuous column adsorption of naphthenic acids from synthetic and real oil sands process-affected water (OSPW) using carbon-based adsorbents

In this study, activated petroleum coke (APC) and commercial activated carbon (CAC) were used in a continuous adsorption column for removal of model naphthenic acids and organics from real oil sands process-affected water (OSPW). Diphenylacetic acid and 2-naphthoic acid, two model naphthenic acid (NA) compounds, were removed completely by the APC in a continuous column operation. Due to the complex nature of organics in OSPW, total organic carbon (TOC) was measured to determine the effectiveness of OSPW treatment by APC. The removal of TOC from OSPW at its natural pH 8 by APC was only 25%, whereas acidification at pH 4 followed by APC adsorption removed 96% of the initial TOC. When compared to a commercial activated carbon, the APC showed an average of 20% higher organics removal. The experimental breakthrough curves were better fitted by Thomas model in comparison to Adams-Bohart and Yoon-Nelson models. The regeneration of APC was conducted using methanol with 0.01 wt% NaOH (pH = 11.7) and a total of four cycles of adsorption and regeneration were conducted with marginal loss of adsorption sites.

Harmful weed to prospective adsorbent: low-temperature-carbonized Ipomoea carnea stem carbon coated with aluminum oxyhydroxide nanoparticles for defluoridation

Gainful utilization of stems of the pernicious weed, Ipomoea carnea, to prepare good quality carbon and its modification with aluminum oxyhydroxide (AlOOH) nanoparticles for efficient defluoridation from contaminated drinking water is discussed in this paper. Surface functional groups are enhanced by functionalization of the carbons under acid treatment which acted as anchor to the AlOOH nanoparticles. Formation of AlOOH particles over the carbon surface is confirmed from X-ray diffractometry analysis. The AlOOH-carbon nanocomposite showed higher fluoride removal capacity than the neat AlOOH nanoparticles with a maximum removal capacity in the range of 46.55-53.71 mg g^-1. Reaction kinetics and isotherm studies showed that fluoride adsorption is quite feasible on the adsorbent surface. The column study showed the possibility of the adsorbent for large-scale applications. The adsorbent can be regenerated by a mild treatment with 0.1 N NaOH solutions. The adsorbent is highly capable for defluoridation from synthetic as well as fluoride-contaminated natural water and, thus, can be used as an alternative for commercial defluoridation adsorbents. The use of Ipomoea carnea for defluoridation can be a way of producing low-cost adsorbent material, and the use for such purposes may also be helpful to control the weed up to a good extent.

Microwave irradiation and citric acid assisted seed germination and phytoextraction of nickel (Ni) by Brassica napus L.: morpho-physiological and biochemical alterations under Ni stress

The complex bio-geochemistry of soil allows pollutant to persist for a longer period of time which further decreased the fertility and natural composition of land. Nickel, an inorganic pollutant, coming from a wide range of industrial and manufacturing units possesses serious threat to soil degradation and crop productivity around the world. The present study was carried to evaluate the combined role of microwave irradiation (MR) and citric acid (CA) on the phytoextraction potential of Brassica napus L. under Ni stress. An initial seed germination test was conducted to select effective time scale of MR exposure. Highest seed germination was observed at exposure of 2.45 GHz frequency for 30 s. Healthy seeds of B. napus L. genotype Faisal Canola (RBN-03060) treated with MR at 2.45 GHz for 30 s were sown in plastic pots filled with 5 kg of soil. Nickel and CA applied exogenously in solution form with different combinations to both MR-treated and untreated B. napus plants. The MR-treated plants showed higher growth, biomass, photosynthetic pigments (Chl a, b, total, and carotenoids) and activities of antioxidant enzymes (SOD, POD, APX, CAT) as compared to untreated plants who showed higher reactive oxygen species (MDA, H₂O₂) and electrolyte leakage. Increasing Ni concentration significantly decreased the physiological and biochemical attributes of B. napus both in MR-treated and untreated plants. The addition of CA alleviated Ni-induced toxic effects in both MR-treated and untreated plants by improving antioxidant defense system. The degree of Ni stress mitigation was higher in MR-treated plants. The Ni concentration was higher in root, stem, and leaves of MR-treated plants under CA application as compared to untreated plants. The present study concluded that seeds treated with MR before sowing showed higher accumulation and concentration of Ni from soil, and this phenomenon boosted with the application of CA.

Hexavalent Chromium Removal from Model Water and Car Shock Absorber Factory Effluent by Nanofiltration and Reverse Osmosis Membrane

Nanofiltration and reverse osmosis are investigated as a possible alternative to the conventional methods of Cr(VI) removal from model water and industrial effluent. The influences of feed concentration, water recovery, pH, and the coexisting anions were studied. The results have shown that retention rates of hexavalent chromium can reach 99.7% using nanofiltration membrane (NF-HL) and vary from 85 to 99.9% using reverse osmosis membrane (RO-SG) depending upon the composition of the solution and operating conditions. This work was also extended to investigate the separation of Cr(VI) from car shock absorber factory effluent. The use of these membranes is very promising for Cr(VI) water treatment and desalting industry effluent. Spiegler-Kedem model was applied to experimental results in the aim to determine phenomenological parameters, the reflection coefficient of the membrane (σ), and the solute permeability coefficient (P_s). The convective and diffusive parts of the mass transfer were quantified with predominance of the diffusive contribution.

Study of the involved sorption mechanisms of Cr(VI) and Cr(III) species onto dried Salvinia auriculata biomass

Removal of Cr(VI) species by dried biomass of the aquatic macrophyte Salvinia auriculata was studied in order to understand the involved sorption mechanisms. Kinetic tests were carried out under the conditions such as concentration range of Cr(VI) from 50 to 250 mg L^-1 and a temperature of 30 °C. Modification of the biosorbent by the presence of Cr(VI) species was assessed by analysis of its porosity, density and infrared molecular absorption spectrum. A series of experimental approaches involving directed chemical modifications on the biosorbent surface was performed. The main functional groups involved in the sorption mechanisms were identified. The gas sorption analyser was applied and proved that a strong chemical effect of Cr(VI) species on the surface took place, resulting in a leaching organic matter with an obvious and significant increase in the porosity parameters. The intra-particle diffusion model revealed different mass transfer zones into the adsorbent during Cr(VI) removal. New combined Langmuir and Dubinin-Radushkevich isotherm was the best to fit the equilibrium data of Cr(VI) species removal. Finally, Cr(VI) removal was mainly mediated by a redox process where Cr(III) species were formed.

Packed-bed column biosorption of chromium(VI) and nickel(II) onto Fenton modified Hydrilla verticillata dried biomass

The present study represents the first attempt to investigate the biosorption potential of Fenton modified Hydrilla verticillata dried biomass (FMB) in removing chromium(VI) and nickel(II) ions from wastewater using up-flow packed-bed column reactor. Effects of different packed-bed column parameters such as bed height, flow rate, influent metal ion concentration and particle size were examined. The outcome of the column experiments illustrated that highest bed height (25cm); lowest flow rate (10mLmin(-1)), lowest influent metal concentration (5mgL(-1)) and smallest particle size range (0.25-0.50mm) are favourable for biosorption. The maximum biosorption capacity of FMB for chromium(VI) and nickel(II) removal were estimated to be 89.32 and 87.18mgg(-1) respectively. The breakthrough curves were analyzed using Bed Depth Service Time (BDST) and Thomas models. The experimental results obtained agree to both the models. Column regeneration experiments were also carried out using 0.1M HNO3. Results revealed good reusability of FMB during ten cycles of sorption and desorption. Performance of FMB-packed column in treating secondary effluent was also tested under identical experimental conditions. Results demonstrated significant reduction in chromium(VI) and nickel(II) ions concentration after the biosorption process.

Hexavalent chromium removal performance of anionic functionalized monolithic polymers: column adsorption, regeneration and modelling

Anionic functionalized monolithic macro-porous polymers were used for the removal of hexavalent chromium(VI) anions from aqueous solution in column experiments. At a flux of 1.0 cm min and 30 mg Cr(VI) L(-1) feed concentration, breakthrough capacity and apparent capacity were 0.066 g Cr(VI) g(-1) anionic monolith and 0.144 g Cr(VI) g(-1) anionic monolith, respectively. The degree of column utilization was found to lie in the range 41-46%. Two kinetic models, theoretical and Thomas models, were applied to experimental data to predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design. The simulation of the whole breakthrough curve was effective with the models. At a flux of 1.0 cm min and 30 mg Cr(VI) L(-1) feed concentration, the dispersion coefficient and adsorption equilibrium constant (K) were 3.14 × 10(-7) m s(-1) and 3,840, respectively. Also, Thomas model parameters k1 (rate constant of adsorption) and qm (equilibrium solid-phase concentration of sorbed solute) were 1.08 × 10(-3) L mg(-1) min(-1) and 0.124 g g(-1), respectively. After reaching equilibrium adsorption capacity, the monoliths were regenerated using 1 N HCl and were subsequently re-tested. It was found that the regeneration efficiency reduced from 98% after second usage to 97% after the third usage.

Facile preparation of amidoxime-functionalized fiber by microwave-assisted method for the enhanced adsorption of chromium(vi) from aqueous solution

In this study, a facile and highly efficient approach, the microwave-assisted (MW-aid) method, was applied for the synthesis of amidoxime-functionalized fibrous adsorbent, which exhibited enhanced adsorption capacities for Cr(vi) in aqueous solution.