Behavior of the mass transfer zone in a biosorption column

Removal of V(V) from a Mixed Solution Containing Vanadium and Chromium Using a Micropocrous Resin in a Column: Migration Regularity of the Mass Transfer Zone and Analysis of Dynamic Properties

In China, both vanadium(V) and chromium(VI) are present in wastewater resulting from vanadate precipitation (AVP wastewater) and from leaching vanadium-chromium reduction slag. Addressing environmental preservation and the comprehensive utilization of metal resources necessitates the extraction and separation of V(V) and Cr(VI) from these mixed solutions. However, their separation is complicated by very similar physicochemical properties. This study establishes a method for the dynamic selective adsorption of V(V) from such mixtures. It evaluates the impact of various operating conditions in columns on dynamic adsorption behavior. This study examines the migration patterns of the mass transfer zone (MTZ) and forecasts its effective adsorption capacity through multivariate polynomial regression and a neural network (NN) model. The NN model's outcomes are notably more precise. Its analysis reveals that C 0 is the most critical factor, with Q and H following in importance. Furthermore, the dynamic properties were analyzed using two established models, Thomas and Klinkenberg, revealing that both intraparticle and liquid film diffusion influence the rates of exchange adsorption, with intraparticle diffusion being the more significant factor. Using 3 wt % sodium hydroxide as the eluent to elute V(V)-loaded resin at a flow rate of 4 mL/min resulted in a chromium concentration of less than 3 mg/L in the V(V) eluate, indicating high vanadium-chromium separation efficiency in this method. These findings offer theoretical insights and economic analysis data that are crucial for optimizing column operation processes.

Arsenic removal adsorbent using limonite-polyethersulfone composite fiber via continuous flow column process

This research introduces an enhanced limonite-based composite fiber adsorbent for arsenic (As) removal. The modification involves creating polyethersulfone (PES)-limonite composite fibers loaded with 60 wt% limonite powders, designed to be applicable in water flow environments. The fibers were prepared using a wet-spinning process based on phase inversion, with varying concentrations (10, 20, and 30 wt%) of PES in NMP solution. The composite fiber with 10 wt% NMP exhibited a porous structure and demonstrated efficient absorption of both As(III) and As(V). Adsorption followed the Langmuir model, with qm values of 1.5 mg/g for As(III) and 3.2 mg/g for As(V) at pH 6. In column experiments, As removal rates increased with contact time, attributed to decreased flow rates (1 mL/min). Moreover, increasing fiber column height led to enhanced removal rates, as indicated by the Adams-Bohart model. The mechanism for As(V) removal involved the formation of an inner-sphere complex through ion exchange between α-FeOOH and HAsO4 - and H2 AsO4 2- in an aqueous solution at pH 6.8. PRACTITIONER POINTS: Changing the polyethersulfone ratio in the composite leads to variations in the appearance of limonite within each composite fiber. Limonite composite fibers effectively remove As(III) and As(V) at neutral pH. The adsorption behavior follows Langmuir kinetic model, the qm of 1.5 mg/g for As(III) and 3.2 mg/g for As(V). Longer columns and contact times enhance arsenic (As) removal in practical water treatment systems. Adam-Bohart model aids in predicting breakthrough and saturation time in As adsorption column design.

Removal of Arsenate by Fixed-Bed Columns Using Chitosan-Magnetite Hydrogel Beads and Chitosan Hydrogel Beads: Effect of the Operating Conditions on Column Efficiency

Fixed-bed columns packed with chitosan-magnetite (ChM) hydrogel and chitosan (Ch) hydrogel were used for the removal of arsenate ions from aqueous solutions at a pH of 7.0. The effect of flow rate (13, 20, and 25 mL/h), height of the columns (13 and 33 cm), and initial arsenate concentration (2, 5 and 10 mg/L) on the column's efficiency for the removal of As(V) is reported. The maximum adsorption capacity (qb), obtained before the allowed concentration of contaminant is exceeded, the adsorption capacity (qe) when the column is exhausted, and the mass transfer zone were determined. With this information, the efficiency of the column was calculated, which is given by the HL/HLUB ratio. The higher this ratio, the higher the efficiency of the column. The highest efficiency and the highest uptake capacity value at breakthrough point were obtained when using the lower flow rate, lower initial arsenate concentration, and longer bed length. When 33 cm-high columns were fed with a 10 mg As(V)/L solution at 13 mL/h, the maximum uptake capacity values at exhaustion obtained for Ch and ChM were 1.24 and 3.84 mg/g, respectively. A pH increase of the solution at the column's exit was observed and is attributed to the proton transfer from the aqueous solution to the amino and hydroxyl groups of chitosan. The incorporation of magnetite into Ch hydrogels significantly increases their capacity to remove As(V) due to the formation of complexes between arsenic and the magnetite surface. Experimental data were fitted to the Thomas model, the Yoon-Nelson model and the Bohart-Adams model using non-linear regression analysis.

Bioengineered magnetic graphene oxide microcomposites for bioremediation of chromium in ex situ - A novel strategy for aggrandized recovery by electromagnetic gadgetry

Novel magnetic microcomposites consisting of graphene oxide and iron oxide was synthesized to immobilize metabolically versatile Paracoccus sp. MKU1 and Leucobacter sp. AA7 and tested for the simultaneous adsorption and enhanced biological detoxification of hexavalent chromium (Cr(VI)) from tannery wastewater. This study reports highest chromium adsorption of 272.6 mg/g and 179.3 mg/g with complete reduction of Cr(VI) to Cr(III) by the microcomposites of AA7 and MKU1 from wastewater in a bioreactor (10 L) at large-scale for first time in ex situ. Furthermore, both the microcomposites displayed an enhanced detoxification of tannery wastewater by reducing various physicochemical conditions such as ammonia, nitrate, TDS, fluoride, CaCO_3, Ca, Mg, NO₃ and SO₂ under the permissible limits. Use of electromagnetic device for magnetic microcomposites recovery from bioreactor yielded a maximum of 88% and 80.6% recovery for AA7 and MKU1, respectively. The rate of chromium recuperation achieved following desorption from the microcomposites of AA7 and MKU1 was 90.71% and 93.97%, respectively. Thus, the multifarious benefits including adsorption, metabolic detoxification, recovery, and recuperation by single functional microcomposites seems to be an intriguing and profitable approach for practicing in real-time operations to effectively remove heavy metals from the contaminated wastewater for environmental protection.

The Dynamic Behaviour of a Binary Adsorbent in a Fixed Bed Column for the Removal of Pb2+ Ions from Contaminated Water Bodies

In the search for a technically efficient and abundant adsorbent in water treatment processes, a bio-composite adsorbent derived from agricultural wastes has been identified as a potential candidate. In this study, eggshells and sugarcane bagasse were combined in varied proportions (1:0, 1:3, 1:1, 3:1 and 0:1) and applied as biosorbents in a lab-scale adsorption column. The effect of bed depth (4–12 cm) of the biosorbents was investigated which enabled the prediction of breakthrough curves for the removal of Pb (II) ions. The life span of the column was extended by increasing the bed depth of the column. The binary adsorbent of 1:3 weight ratio of <75 µm particle size showcased the highest removal efficiency of 91% at a bed depth of 12 cm. The mass transfer zone (MTZ) increased with increasing bed depth with a minor portion of the bed left unused, signifying that the process was highly efficient. The Thomas model constant, KTh, decreased with increasing bed depth with the maximum amount of Pb adsorbed being 28.27 mg/g. With the Yoon–Nelson model, KYN decreased with an increase in τ as the bed height increased. In this study, a novel approach was adopted where the proposed methodology enabled the use of a bio-composite adsorbent in heavy metal removal. The findings of this research will aid in the design and optimisation of the pilot-scale operation of environmentally friendly treatment options for metal laden effluent.

Efficient Fluoride Removal by a Fixed-Bed Column of Self-Assembled Zr(IV)-, Fe(III)-, Cu(II)-Complexed Polyvinyl Alcohol Hydrogel Beads

Fixed-bed column adsorption studies are performed with metal-complexed polyvinyl alcohol (PVA) hydrogel beads to remove fluoride from groundwater. The fixed-bed column (bed height = 8 ± 0.2 cm) of copper-zirconium-PVA (PCZH), zirconium-PVA (PZH), and iron-zirconium-PVA (PFZH) hydrogel beads have equilibrium fluoride removal capacities of 17.26 ± 0.05, 31.67 ± 0.05, and 11.84 ± 0.05 mg g^-1 from a 10 ± 0.20 mg L^-1 fluoride solution of pH 6.5 maintained at a flow rate of 1 ± 0.01 mL min^-1. The breakthrough curves for fluoride adsorption are analyzed by non-linear empirical models of Thomas, Bohart-Adams, Yoon-Nelson, and semi-empirical bed depth service time models. The maximum fluoride adsorption capacities obtained from the Thomas model are 25.66 ± 0.05, 38.17 ± 0.05, and 13.75 ± 0.05 mg g^-1 for PCZH, PZH, and PFZH. Moreover, the column of PZH (bed height = 4 ± 0.2 cm) removes about 1.67 ± 0.05 mg g^-1 of fluoride from the alkaline groundwater sample with high total dissolved solids containing 2.84 ± 0.20 mg L^-1 fluoride maintained at a flow rate of 0.5 ± 0.01 mL min^-1. The fluoride removal efficiency decreases marginally (<1 ± 0.02%) in the presence of interfering ions such as chlorides, sulfates, phosphates, bicarbonates, and nitrates. Furthermore, the fixed-bed column (bed height = 4 ± 0.2 cm) of PCZH, PZH, and PFZH remove 7.40 ± 0.05, 14.85 ± 0.05, and 6.53 ± 0.05 mg g^-1 fluoride, respectively, even after the third regeneration cycle. Additionally, the hydrogel beads are effective in the removal of arsenate (≤90 ± 0.02%) and chromate ions (≤96 ± 0.02%) from 100 ± 0.20 mg L^-1 solution in batch adsorption studies. Therefore, the hydrogel beads could be used as potent filters for the removal of fluoride, chromate, and arsenate ions from water.

Extending granular activated carbon (GAC) bed life: A column study of in-situ chemical regeneration of pesticide loaded activated carbon for water treatment

In-situ chemical regeneration of granular activated carbon (GAC) may represent an advantageous alternative to conventional off-site thermal regeneration in water treatment applications. The performance of chemical regeneration of carbon exhausted by metaldehyde and isoproturon was investigated using rapid small-scale column tests, performed using a sequence of pesticide adsorption and chemical regeneration cycles with a novel alkaline-organic regenerant solution. A fresh regenerant solution was able to achieve 82% and 45% regeneration of carbon exhausted by metaldehyde and isoproturon, respectively. After the first regeneration, the performance declined slightly to 79%, and to 36% after the fourth regeneration. A comparison using a thermally regenerated (operational) carbon suggested that chemical regeneration was more beneficial for carbon exhausted by metaldehyde. The regenerant solution has a potential to be re-used multiple times, thereby minimizing the amount of waste chemicals generated. A series of carbon characterization tests showed that chemical regeneration did not alter the surface area, pore size distribution and surface chemistry of the carbon. As part of the evaluation, the adsorption thermodynamics of virgin and chemically regenerated carbons were determined using isothermal titration calorimetry to evaluate the adsorption behaviour of the pesticides on the carbon samples. The relatively high regeneration efficiency achieved by chemical regeneration, and minimal deleterious effect to the physico-chemical properties of the carbon, demonstrated the beneficial potential of this process as an alternative to conventional thermal regeneration of GAC.

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.

The potentials of biofilm reactor as recourse for the recuperation of rare earth metals/elements from wastewater: a review

Wastewater is nowadays increasingly receiving global attention as a resource much more than a problem due to its potential so serve as a resource recovery channel. In this regard, wastewater is gradually been transformed from being a cesspool to a "treasure pool." Among notable resources in the treasure pool, rare earth metals/elements (REEs) warrant focal investigation, both in terms of environmental abundance and biorecovery, due to their environmental impacts. The ineffectiveness or cost intensiveness of extant physicochemical and advanced wastewater resource recovery techniques warrants the investigation of natural phenomenons in the treasure pools. Bacteria are able to cleverly secrete certain biochemicals to help trap and aggregate nutrients for their metabolism-the biofilms. In this regard, there is increased espousal of biofilm-enabled reactors, especially for the application of the recovery of invaluable feedstock in wastewater as well as other aqueous media due to high production rates and stability of cells. Furthermore, it anticipated that this technology will be translated to recovery of rare earth elements, due to their increased demand across the globe. This piece reiterates the nitty-gritty of biofilm-enhanced biorecovery and also keeps the scientific readership abreast of the multifarious aspects regarding the successful biofilm affected biorecovery of REEs at reactor scale.

Continuous and selective copper recovery by multi-modified and granulated SBA-15

Continuous and selective recovery of copper (Cu) from heavy metal wastewater not only mitigates the pollution of environment but also can be applied for industrial field. Due to several advantages such as large pore size, easy modification, physical and chemical stabilities, mesoporous silica material, SBA-15, has been synthesized via hydrothermal reaction in this study. For enhancing the adsorption capacity and selectivity for Cu ions, prepared SBA-15 was modified with manganese loading and amine-grafting (MN-SBA) then granulated by alginic-acid (GMN-SBA), successfully. Adsorption capacities for heavy metals such as Cu, Zn, Ni and Mn were 2.11, 1.24, 1.74 and 1.25 mmol/g on MN-SBA and decreased to 1.23, 0.68, 0.86 and 0.65 when it was granulated. Even though the adsorption capacities of GMN-SBA for heavy metals decreased by 40-50%, it enabled easy regeneration and separation process when applied for continuous fixed-bed column adsorption mode. Specifically, the results demonstrated that GMN-SBA was able to be reused for 5 times while maintaining over 80% adsorption capacities. Fixed-bed adsorption results were well explained by dynamic adsorption model incorporated with linear driving force approximation (LDFA) model. The simulation of fixed-bed adsorption tests was proceeded in terms of bed length, feeding concentration and flow rate, and it showed the breakthrough times were shifted in the axis of time. In multi-component adsorption, LDFA model showed a high overshoot phenomenon of the breakthrough curves for Zn, Ni and Mn compared to Cu. This reflected the high affinity of Cu towards GMN-SBA compared to other heavy metals.

Performance of biochar-based filtration bed for the removal of Cr(VI) from pre-treated synthetic tannery wastewater

In the present study, the performance of biochar-based filtration bed was assessed to enhance the removal efficiency of Cr(VI), from the pre-treated synthetic tannery wastewater. The pre-treatment of wastewater was carried out with aluminium formate (AF) as a coagulant and 80% Cr(VI) removal was observed which might be due to the formation of carboxylic complexation reaction. The purity of coagulant and the sludge components were validated with XRD analysis and the results revealed the formation of pure aluminium formate compound as well as a clear change in the crystalline structure in the treated sludge. FT-IR spectra demonstrated the carboxylic compound participated in the removal of Cr(VI) during the coagulation process. The pre-treated wastewater having 20 mg/L (residual) Cr(VI) was passed through a three-layered filtration bed containing biochar, which showed complete removal of Cr(VI) ∼ 99.99% by precipitating into bind form under the influence of CaCO₃ and formate ions. The possible mechanistic approach might be due to the presence of formate ions in the pre-treated wastewater, the precipitation of Cr(VI) occurred in the form of Cr(OH)₂ by the release of bicarbonate (HCO^3-)^, carbonate ion (CO₃ ^2-) and hydroxide (OH^-) ions in the filtration bed. The properties of the biochar were investigated by XRD and FTIR analysis and the results revealed the existence of hydroxyl, carboxyl and carbonyl groups, which participated during the removal of Cr(VI). The results suggest that biochar-based filtration bed could be a promising method for the treatment of pre-treated tannery wastewater.

Removal of Cu(II) by Fixed-Bed Columns Using Alg-Ch and Alg-ChS Hydrogel Beads: Effect of Operating Conditions on the Mass Transfer Zone

The removal of Cu(II) ions from aqueous solutions at a pH of 5.0 was carried out using fixed-bed columns packed with alginate-chitosan (Alg-Ch) or alginate-chitosan sulfate (Alg-ChS) hydrogel beads. The effect of the initial Cu(II) concentration, flow rate, pH, and height of the column on the amount of Cu removed by the column at the breakpoint and at the exhaustion point is reported. The pH of the solution at the column's exit was initially higher than that at the entrance, and then decreased slowly. This pH increase was attributed to proton transfer from the aqueous solution to the amino and COO^- groups of the hydrogel. The effect of operating conditions on the mass transfer zone (MTZ) and the length of the unused bed (H_LUB) is reported. At the lower flow rate and lower Cu(II) concentration used, the MTZ was completely developed and the column operated efficiently; by increasing column height, the MTZ has a better opportunity to develop fully. Experimental data were fitted to the fixed-bed Thomas model using a non-linear regression analysis and a good correspondence between experimental and Thomas model curves was observed.

Modification of Lignocellulosic Materials with a Mixture of m-DMDHEU/Choline Chloride to Remove CrO4 2-, NO3 -, and H2AsO4 - in Aqueous Solution

A new denaturation agent is the mixture of 4,5-dihydroxy-1,3-bis(methoxymethyl)imidazolidin-2-one (m-DMDHEU)/choline chloride (CC) introduced to modify three kinds of lignocellulosic materials containing different lignin contents in the following order: cotton used in medicine < sawdust from acacia auriculiformis wood < powder from the coconut shell. The modification process is carried out through two main steps: 0.2 N NaOH solution with 70% v/v ethanol and 30% v/v water was applied to remove lignin and activate the initial raw materials, and then delignified materials were modified with m-DMDHEU/CC by using a parched heat supply method after chemical impregnation. Structural characterictics and physicochemical properties of modified materials were tested and dissected by scanning electron microscopy, Fourier transform infrared spectroscopy, solid-state ¹³C nuclear magnetic resonance spectroscopy (solid-state ¹³C CP-MAS NMR), specific surface area, and pH at the point of zero charge (pH_PZC). The ability to adsorb and exchange anions of modified materials was referred and examined by using aqueous solutions containing CrO₄ ^2-, NO₃ ^-, and H₂AsO₄ ^- anions in different conditions. The results revealed that anionite lignocellulosic materials could separate these anions with very good efficiency and better than strong anion exchange resin (GA-13) in the same conditions; outlet water could meet the permissible drinking and living water standards; and the m-DMDHEU cross-link bridge also was a good bridge to connect CC to cellulose chain beside other common urea cross-link bridges.

DFT and MD simulation supplemented experiments for isotopic fractionation of zinc compounds using a macrocyclic crown ether appended polymeric resin

Isotope effect is a quantum mechanical phenomenon and thus poses a challenge for the separation of isotopes of an element of interest, especially for heavy elements. Isotopic fractionation of zinc is also quite difficult and challenging but is necessitated due to various applications of its isotopes ranging from nuclear medicine to nuclear power reactors. Here, we developed the dibenzo-18-crown-6 (DB18C6) ether-functionalized poly(methacrylic acid) (PMA) resin by exploiting the ion and isotope recognition ability of the crown ether using DFT/MD simulations followed by experiments for isotopic fractionation of zinc. The PMADB18C6 adsorbent was prepared and suitably characterized. Both computational and experimental findings demonstrate that the adsorption and isotope separation of zinc with PMADB18C6 are due to the molecular recognition effect of the "O" dipole of the crown ether. Furthermore, both MD simulations and experiments suggest Langmuir type adsorption isotherms. The adsorption of Zn2+ ions on the PMA resin is predicted to be endothermic, whereas it is exothermic on the PMADB18C6 resin, as revealed from the experimentally observed enthalpy change. A small scale fixed bed column study was demonstrated to test the scale-up application. The values of the experimental separation factors: 1.0013 for 66/64 and 1.0027 for 68/64 confirm the computationally predicted results of 1.00088 and 1.0010, respectively, thus establishing the combined strength of the theory and experiments for the identification of efficient fractionating agents for a complex quantum isotope effect which eventually helps in planning further experiments in view of medicinal and technological applications of zinc isotopes.

Freeze Granulated Zeolites X and A for Biogas Upgrading

Biogas is a potential renewable energy resource that can reduce the current energy dependency on fossil fuels. The major limitation of utilizing biogas fully in the various applications is the presence of a significant volume fraction of carbon dioxide in biogas. Here, we used adsorption-driven CO2 separation using the most prominent adsorbents, NaX (faujasite) and CaA (Linde Type A) zeolites. The NaX and CaA zeolites were structured into hierarchically porous granules using a low-cost freeze granulation technique to achieve better mass transfer kinetics. The freeze granulation processing parameters and the rheological properties of suspensions were optimized to obtain homogenous granules of NaX and CaA zeolites 2-3 mm in diameter with macroporosity of 77.9% and 68.6%, respectively. The NaX and CaA granules kept their individual morphologies, crystallinities with a CO2 uptake of 5.8 mmol/g and 4 mmol/g, respectively. The CO2 separation performance and the kinetic behavior were estimated by breakthrough experiments, where the NaX zeolite showed a 16% higher CO2 uptake rate than CaA granules with a high mass transfer coefficient, 1.3 m/s, compared to commercial granules, suggesting that freeze-granulated zeolites could be used to improve adsorption kinetics and reduce cycle time for biogas upgrading in the adsorption swing technology.

Two physical processes enhanced the performance of Auricularia auricula dreg in Cd(II) adsorption: composting and pyrolysis

This study aims to discover the impact of composting and pyrolysis on the adsorption performance of Auricularia auricula dreg (AAD) for Cd(II) in aqueous solution. Auricularia auricula dreg (AAD), Auricularia auricula dreg biochar (AADB) and Auricularia auricula dreg compost (AADC) were used to remove Cd(II) from aqueous solution, and their adsorption conditions and mechanisms were compared. The adsorption quantity of three adsorbents reached the maximum (AAD: 80.0 mg/g, AADB: 91.7 mg/g, AADC: 93.5 mg/g) under same conditions (adsorbent dosage of 1 g/L, pH 5.0, biosorption temperature of 25 °C, and biosorption time of 120 min). All Cd(II) biosorption processes onto three adsorbents complied with the Langmuir isotherm model and the pseudo-second-order kinetic equation, and spontaneously occurred in an order of AADC > AADB > AAD. The difference in biosorption quantity relied on variation in surface structure, crystal species and element content caused by composting or pyrolysis. Composting enhanced the changes in surface structure, crystal species, functional groups and ion exchange capacity of the AAD, resulting in AAD had greatly improved the biosorption quantity of Cd(II). Pyrolysis increased the adsorption of Cd(II) mainly by increasing the Brunauer-Emmett-Teller (BET) surface area, the particle size and pH, in the same time, providing more oxygen-containing functional groups.

Recovery of Rare Earth Elements from Wastewater Towards a Circular Economy

The use of rare earth elements is a growing trend in diverse industrial activities, leading to the need for eco-friendly approaches to their efficient recovery and reuse. The aim of this work is the development of an environmentally friendly and competitive technology for the recovery of those elements from wastewater. Kinetic and equilibria batch assays were performed with zeolite, with and without bacterial biofilm, to entrap rare earth ions from aqueous solution. Continuous assays were also performed in column setups. Over 90% removal of lanthanum and cerium was achieved using zeolite as sorbent, with and without biofilm, decreasing to 70% and 80%, respectively, when suspended Bacillus cereus was used. Desorption from the zeolite reached over 60%, regardless of the tested conditions. When in continuous flow in columns, the removal yield was similar for all of the rare earth elements tested. Lanthanum and cerium were the elements most easily removed by all tested sorbents when tested in single- or multi-solute solutions, in batch and column assays. Rare earth removal from wastewater in open setups is possible, as well as their recovery by desorption processes, allowing a continuous mode of operation.

Ammonium removal from aqueous solutions by fixed-bed column using corncob-based modified biochar

This study investigated the potential of removing ammonium ([Formula: see text]) from aqueous solutions using corncob based on modified biochar (MBCC) in the fixed-bed column. Corncob biochar was soaked in a mixture of HNO₃ 6.0 M and NaOH 0.3 M to prepare active binding sites for ammonium removal. The effect of initial ammonium concentrations (10-40 mg/L), flow rates (1-9 mL/min) and MBCC fixed-bed heights (8-24 cm) on the breakthrough characteristics of the adsorption system were studied. The results showed that the highest adsorption capacity of fix-bed column, the breakthrough time and value of C_t/C_o were 12.83 mg/g, 480 min and 0.862 ± 0.025 at 10 mg/L of initial ammonium concentration, 8 cm of MBCC fixed-bed height and 3 mL/min of flow rate, respectively. The breakthrough curve model in this study also indicated that all Yoon-Nelson, Thomas and Adam-Bohart models well fit with the experimental data with a high R². The results also proved that MBCC can be used as a potential adsorbent for eliminating [Formula: see text] in the fixed-bed column. The saturated MBCC was also regenerated and reused consecutively for four cycles. The usage of mixture of NaOH and NaCl in recovering MBCC was better than NaCl only.

Evaluating the reliability of equilibrium dissolution assumption from residual gasoline in contact with water saturated sands

Understanding dissolution dynamics of hazardous compounds from complex gasoline mixtures is a key to long-term predictions of groundwater risks. The aim of this study was to investigate if the local equilibrium assumption for BTEX and TMBs (trimethylbenzenes) dissolution was valid under variable saturation in two dimensional flow conditions and evaluate the impact of local heterogeneities when equilibrium is verified at the scale of investigation. An initial residual gasoline saturation was established over the upper two-thirds of a water saturated sand pack. A constant horizontal pore velocity was maintained and water samples were recovered across 38 sampling ports over 141days. Inside the residual NAPL zone, BTEX and TMBs dissolution curves were in agreement with the TMVOC model based on the local equilibrium assumption. Results compared to previous numerical studies suggest the presence of small scale dissolution fingering created perpendicular to the horizontal dissolution front, mainly triggered by heterogeneities in the medium structure and the local NAPL residual saturation. In the transition zone, TMVOC was able to represent a range of behaviours exhibited by the data, confirming equilibrium or near-equilibrium dissolution at the scale of investigation. The model locally showed discrepancies with the most soluble compounds, i.e. benzene and toluene, due to local heterogeneities exhibiting that at lower scale flow bypassing and channelling may have occurred. In these conditions mass transfer rates were still high enough to fall under the equilibrium assumption in TMVOC at the scale of investigation. Comparisons with other models involving upscaled mass transfer rates demonstrated that such approximations with TMVOC could lead to overestimate BTEX dissolution rates and underestimate the total remediation time.

Evaluation of ammonium adsorption in biochar-fixed beds for treatment of anaerobically digested swine slurry: Experimental optimization and modeling

Fixed-bed column experiments were performed to investigate the effect of influent concentration, flow rate, and adsorbent bed depth on ammonium adsorption from anaerobically digested swine slurry using three types of biochar made from corncobs (MCB), hardwood (WB), and mixed sawdust pellets (MSB). WB performed better than the other two biochar types with a maximum sorption capacity of 67-114mg/g due to its superior surface area and larger pore volume. Ammonium adsorption kinetics and dynamics depended on the influent NH4(+)-N concentration, applied inflow flow rate, and the depth of the fixed bed. Maximum sorption capacities under influent NH4(+)-N concentration of 500mg/L, were identified to be 114.2mg/g, 108.9mg/g, and 24.7mg/g at inflow rate of 15mL/min for WB, MCB, and MSB, respectively. The data shows that using deeper beds and applying lower flow rates could be a better strategy to increase ammonium adsorption in biochar-fixed beds. Moreover, three kinetic models (Thomas, Adams-Bohart (BDST), and Yoon-Nelson) were applied to the experimental data to predict breakthrough curves and determine characteristic adsorption parameters for process design. The applied models fitted data in the order: Thomas (R(2)=0.971)>BDST (R(2)=0.960)>Yoon-Nelson (R(2)=0.940). It was concluded that ammonium adsorption in biochar-fixed beds could be an effective method for routine cyclic treatment of slurry. However, further effluent polishing is required to meet discharge requirements.

Treatment influence on green coconut shells for removal of metal ions: pilot-scale fixed-bed column

This work investigates copper, nickel and zinc ion biosorption in single- and multi-component systems in a fixed-bed column using green coconut shells (CS). Approximately 85% of biosorbents are in a particle size ranging from 0.25 to 2 mm. Operational parameters selected include a flow rate of 200 mL min-1 and a bed height of 100 cm, which were selected for a shorter execution time and good adsorption capacity. Empty-bed contact time and Thomas models were applied, showing a good fit with the experimental data. The column adsorption capacity increased after the green CS powder was treated in a column with NaOH at a concentration of 0.1 mol L-1. The highest values of adsorption capacities founded were 0.69, 0.45 and 0.39 mmol L-1 for Cu(II), Ni(II) and Zn(Il), respectively, using green CS treated inside a column with NaOH of 0.1 M. The pH and chemical oxygen demand were monitored in the treatment solution and indicated that the adjustment of these parameters is necessary before disposal of these solutions. A study of desorption using an acid solution was carried out for recovery of metal ions.

Competitive biosorption of lead, cadmium, copper, and arsenic ions using algae

The present study aims to evaluate the competitive biosorption of lead, cadmium, copper, and arsenic ions by using native algae. A series of experiments were carried out in a batch reactor to obtain equilibrium data for adsorption of single, binary, ternary, and quaternary metal solutions. The biosorption of these metals is based on ion exchange mechanism accompanied by the release of light metals such as calcium, magnesium, and sodium. Experimental parameters such as pH, initial metal concentrations, and temperature were studied. The optimum pH found for removal were 5 for Cd(2+) and As(3+) and 3 and 4 for Pb(2+) and Cu(2+), respectively. Fourier transformation infrared spectroscopy analysis was used to find the effects of functional groups of algae in biosorption process. The results showed that Pb(2+) made a greater change in the functional groups of algal biomass due to high affinity to this metal. An ion exchange model was found suitable for describing the biosorption process. The affinity constants sequence calculated for single system was K Pb > K Cu > K Cd > K As; these values reduced in binary, ternary, and quaternary systems. In addition, the experimental data showed that the biosorption of the four metals fitted well the pseudo-second-order kinetics model.

Breakthrough Curve Analysis for Column Dynamics Sorption of Mn(II) Ions from Wastewater by UsingMangostana garciniaPeel-Based Granular-Activated Carbon

The potential of granular-activated carbon (GAC) derived from agrowaste of Mangostene (Mangostana garcinia) fruit peel was investigated in batch and fixed bed system as a replacement of current expensive methods for treating wastewater contaminated by manganese, Mn(II) cations. Batch equilibrium data was analyzed by Langmuir, Freundlich, and Temkin isotherm models at different temperatures. The effect of inlet metal ion concentration (50 mg/L, 70 mg/L, and 100 mg/L), feed flow rate (1 mL/min and 3 mL/min), and activated carbon bed height (4.5 cm and 3 cm) on the breakthrough characteristics of the fixed bed sorption system were determined. The adsorption data were fitted with well-established column models, namely, Thomas, Yoon-Nelson, and Adams-Bohart. The results were best-fitted with Thomas and Yoon-Nelson models rather than Adams-Bohart model for all conditions. The column had been regenerated and reused consecutively for five cycles. The results demonstrated that the prepared activated carbon was suitable for removal of Mn(II) ions from wastewater using batch as well as fixed bed sorption system.

Removal of hexavalent chromium by biosorption process in rotating packed bed

Removal of hexavalent chromium ions from an aqueous solution by crude tamarind (Tamarindus indica) fruit shell was examined in a rotating packed bed contactor by continuously recirculating a given volume of solution through the bed. Reduction of Cr(VI) to Cr(III) within the biosorbent appeared to be the removal mechanism. Depletion rate of Cr(VI) from, and release of reduced Cr(III) ions into the aqueous phase, was influenced by mass transfer resistance besides pH and packing depth. A mathematical model considering the reduction reaction to be irreversible and incorporating intraparticle and external phase mass transfer resistances represented the experimental data adequately. The study indicated that the limitations of fixed bed contactor operating under terrestrial gravity in intensifying mass transfer rates for this system can be overcome with rotating packed bed due to liquid flow under centrifugal acceleration.

Fungal biosorption--an alternative to meet the challenges of heavy metal pollution in aqueous solutions

The removal of heavy metal from the environment, especially wastewater, is now shifting from the use of conventional methods to the use of biosorption, which may be defined as the binding and concentration of selected heavy metal ions or other molecules on to certain biological material. Although most biosorption research concerns metal and related pollutants, including radionuclides, the term is now applied for particulates and all manner of organic pollutants as well. Such pollutants can be in gaseous, soluble and insoluble forms. Biosorption is a physical process carried out through mechanisms such as ion exchange, surface complexation and precipitation. It is a property of both living and dead organisms (and their components) and has been heralded as a promising biotechnology for pollutant removal from solution. Various biomasses such as plant products (tree bark, peanut skin, sawdust, plant weeds etc.) have been tested for metal biosorption with very encouraging results. In this comprehensive review, biosorptive ability of fungal biomass toward heavy metals is emphasized. A detailed description of adsorption properties and mode of action of fungal biosorbents is offered in order to explain the heavy metal selectivity displayed by these biosorbents. The cell structure and cell wall of the fungal cell is evaluated in terms of metal sequestration. The parameters influencing the passive uptake of pollutants are analysed. The binding mechanism is discussed, including the key functional groups involved in the process. Quantification of metal-biomass interactions is fundamental to evaluation of potential implementation strategies; hence sorption isotherms and sorption kinetics, as well as models used to characterize fungal biosorbent sorption, are reviewed. Despite the continuing dramatic increase in published research on biosorption, there has been little or no exploitation in an industrial context. Thus, the current status and future directions regarding biosorption at an industrial level are discussed. A systematic comparative review of the literature, based on the metal-binding capacity of fungal biomass under different conditions, is also provided. The problems associated with fungal biosorption are analysed and suitable remedies are discussed. Thus, this article reviews the achievements and current status of fungal biosorption technology and hopes to provide insights into future research.

Modeling the adsorption of Cr(III) from aqueous solution onto Agave lechuguilla biomass: study of the advective and dispersive transport

The biosorption of Cr(III) onto packed columns of Agave lechuguilla was analyzed using an advective-dispersive (AD) model and its analytical solution. Characteristic parameters such as axial dispersion coefficients, retardation factors, and distribution coefficients were predicted as functions of inlet ion metal concentration, time, flow rate, bed density, cross-sectional column area, and bed length. The root-mean-square-error (RMSE) values 0.122, 0.232, and 0.285 corresponding to the flow rates of 1, 2, and 3 (10(-3))dm3min(-1), respectively, indicated that the AD model provides an excellent approximation of the simulation of lumped breakthrough curves for the adsorption of Cr(III) by lechuguilla biomass. Therefore, the model can be used for design purposes to predict the effect of varying operational conditions.

Cadmium removal from simulated wastewater to biomass byproduct of Lentinus edodes

A kind of agricultural waste, the byproduct of brown-rot fungus Lentinus edodes, was used as an efficient biosorbent for the removal of cadmium from water in this paper. The sorption conditions, such as pH, the dose of biomass and the initial concentration of cadmium were examined. Three kinds of adsorption models were applied to simulate the biosorption data. Uptake of cadmium was higher in weak acid condition than in strong acid condition. Nearly no sorption of cadmium occurred when the pH value was lower than 2.5. Biosorption isothermal data could be well simulated by Freundlich model, and then Langmuir and Temkin model. Langmuir simulation of the biosorption showed that the maximum uptake of cadmium was 5.58mmol/g in weak acid condition, which was much higher than many other biosorbents. The exchanged proton was highly related to the uptake of cadmium in weak acid condition. Fourier transform infrared spectrums and energy-dispersive X-ray microanalyzer were used to reveal ion-exchange mechanism between cadmium and the functional groups or participated inorganic metal ions during biosorption.

Optimization of a biosorption column performance

The dynamics of copper and zinc biosorption by Sargassum fluitans was analyzed under variable column operating conditions including different column lengths (15 and 45 cm), metal-feed solution concentrations (1 and 6 meq L(-1)), metal-sorbent affinities (2.01 and 0.45), and interstitial velocities (12 and 4 cm min(-1)). The experimental breakthrough curves obtained under these varying conditions were also simulated using a mathematical model taking into account the mass transfer as well as the axial dispersion phenomena. The column performance was evaluated using two performance indicators: the service time (t(s)) and the unused portion of the column as reflected in the area under the breakthrough curve (A(c)). Sensitivity analysis results indicated that the feed stream concentration, mass transfer coefficient, column length, and interstitial velocity had the most important effect on the column performance. Applying chromatography theories, the optimization of the biosorption process for productivity and sorption performance, in terms of operating conditions (interstitial velocity) and design parameters (column length), was outlined. The corresponding optimum curve relating the interstitial velocity and the column length resulted with the pressure drop limitations recognized. As an example, a laboratory column 100 cm long will necessitate an interstitial velocity of 19 cm min(-1) to yield the best sorption results.

Biosorption of Cr(VI) by three different bacterial species supported on granular activated carbon: a comparative study

The ability of three different bacterial species supported on granular activated carbon (GAC) to remove hexavalent chromium from low concentration liquid solutions was investigated, in batch and column studies. The microorganisms tested were Cr(VI) reducing types: Streptococcus equisimilis (CECT 926), Bacillus coagulans (CECT 12) and Escherichia coli (CECT 515). The results showed metal uptake values of 5.82, 5.35 and 4.12 mg/g(bios.), respectively, for S. equisimilis, B. coagulans and E. coli, for an initial metal concentration of 100 mg/l. In the same order and for the initial concentration of 50 mg/l, metal uptake values were 2.33, 1.98 and 3.60 mg/g(bios.). Finally, for the initial metal concentration of 10 mg/l, those values were, respectively, 0.66, 1.51 and 1.12 mg/g(bios.). Studies made with an industrial effluent, with the aim of testing these biofilms in a real situation, showed values of Cr uptake of 0.083, 0.090 and 0.110 mg/g(bios.), respectively, for S. equisimilis, B. coagulans and E. coli, for an initial concentration of 4.2 mg/l of total Cr. The quantification of polysaccharides, playing a key role in the whole process, was made and it was concluded that the production of polysaccharides is higher for B. coagulans followed by S. equisimilis and E. coli (9.19, 7.24 and 4.77 mg/g(bios.)). The batch studies data were described using the Freundlich, Langmuir, Redlich-Peterson, Dubinin-Radushkevich, Sips and Toth model isotherms. The best fit was obtained with Sips and Toth model isotherms, respectively, for the S. equisimilis and for the B. coagulans biofilms. For the E. coli biofilm the Freundlich, Redlich-Peterson, Sips and Toth models fitted very well to the experimental data. The Adams-Bohart, Wolborska and Yoon and Nelson models were applied to column studies data. Those models were found suitable for describing the dynamic behaviour of the columns with respect to the inlet chromium concentration. Obtained results showed that the biofilms tested are very promising for the removal of Cr(VI) in diluted industrial wastewater. Despite differences in the cell wall structure and composition, the three bacteria exhibit comparable sorption affinities towards chromium, in the open systems studies. The Gram-positive bacteria tested (B. coagulans and S. equisimilis) presented best metal removal percentages in batch studies.

Column biosorption of lanthanum and europium by Sargassum

Batch and column biosorption of La(3+) (lanthanum) and Eu(3+) (europium) was studied using protonated Sargassum polycystum biomass. The ion exchange sorption mechanism was confirmed by the proportional release of protons and by the total normality of the solution, which remained constant during the process. Equilibrium isotherms were determined for the binary systems, La/H and Eu/H for a total normality of 3 meq g(-1), which produced separation factors of 2.7 and 4.7, respectively, demonstrating a higher affinity of the biomass towards europium. Column runs with a single metal feed were used to estimate the intra-particle mass transfer coefficients for La and Eu (6.0 x 10(-4) and 3.7 x 10(-4) min(-1), respectively). Modeling batch and column binary systems with proton as the common ion was able to predict reasonably well the behavior of a ternary system containing protons. The software FEMLAB was used for solving the set of coupled partial differential equations. Moreover, a series of consecutive sorption/desorption runs demonstrated that the metal could be recovered and the biomass reused in multiple cycles by using 0.1N HCl with no apparent loss in the biosorbent metal uptake capacity.

Biosorption of hexavalent chromium onto raw and chemically modified Sargassum sp

Hexavalent chromium biosorption by raw algae is always accompanied with significantly high organic leaching. In this study, hydrochloric acid, sodium hydroxide, calcium chloride, formaldehyde, and glutaraldehyde were used for modification of raw Sargassum sp. seaweed (RSW), in order that the modified seaweed (MSW) has a lower organic leaching while the metal biosorption capacity is comparable to the RSW. The result shows that the chemical modification by 0.2% formaldehyde achieves such goals. The biosorption of both RSW and MSW is highly pH dependent. At the optimal pH of 2.0, the maximum biosorption capacities of MSW and RSW are 1.123 and 0.601 mmol g(-1), respectively. The surface treatment improves the reduction capacity of the biosorbents. The instrumental analysis demonstrates that the Cr(VI) biosorption is controlled by redox, ion exchange and coordination reactions, of which alcohol, carboxyl, amino and sulphonic groups play important roles. The complete uptake of hexavalent chromium is achieved in 20 h. The chemical reduction for Cr(VI) to Cr(III) is pH dependent and controls the overall chromium removal kinetics.