Green synthesis of novel biochar from Abelmoschus esculentus seeds for direct blue 86 dye removal: Characterization, RSM optimization, isotherms, kinetics, and fixed bed column studies

The presence of Direct blue 86 dye (DB86) in water can lead to various health hazards to the humans and animals. The study explored efficacy of biochar derived from Abelmoschus Esculentus seeds (AESB) to remove DB86 from an aqueous solution. BET analysis of AESB delineated H4 classification with the predominance of micropores and mesopores spread throughout the surface. FTIR study demonstrated the presence of the alkyl (C-H), Alkene (C]C), Carbonyl (C]O) and O-H bond of the sulphonic group which helped in adsorption of DB86 molecules through various mechanisms i.e., pore filling, π-π interactions, and hydrogen bonding interactions. Response surface methodology (RSM) was used for designing the adsorption experiment and analysing the optimum operating parameters. Batch experiments demonstrated excellent adsorption capacity (277.04 mg/g) of AESB and was efficient in 98.06% removal of DB86 at optimal conditions i.e., dye conc. = 300 mg/L, dose = 2.5 g/L, pH = 2, time of 120 min. Adsorption followed nonlinear Sips model (R2 = 0.999) with an error (X2 = 0.13, RMSE = 0.83, MAPE 0.56 and MSRE = 0.0006). The kinetic analysis revealed intra-particle diffusion being the rate-determining step and followed nonlinear pseudo-first-order kinetics (R2 = 0.997). Thermodynamic study revealed that the adsorption of DB-86 proceeded spontaneously and exhibited endothermic characteristics, with the enthalpy change primarily governed by the physisorption mechanism. Thomas model revealed inverse relation of breakthrough and exhaustion time with flow while it was proportional to bed height. The sorption capacity (N0) (2.2493 mg/l min) and rate constant (Ka) (0.028 L/min. mg) of BDST model can accurately be used for predicting the performance of AESB in full scale column.

Continuous fixed-bed adsorption of reactive azo dye on activated red mud for wastewater treatment-Evaluation of column dynamics and design parameters

Continuous adsorption of Remazol Brilliant Blue (RBB) dye in water onto sulfuric acid activated red mud (CATRM) in a fixed bed column was investigated. Breakthrough curves were obtained experimentally by varying the bed height (Z), influent flow rate (Q), and dye concentration(C₀). The adsorption efficiency in the removal of RBB was favored at lower C₀, higher Z, and lower Q. The maximum adsorption capacity of the activated red mud bed in the column was obtained at C₀ = 70 mg/L, Z = 8 cm, and Q = 5 mL/min and found to be 106 mg/g. Important parameters of column dynamics and design such as mass transfer zone (MTZ) and length of unused bed (LUB) were evaluated from the breakthrough curves. The MTZ and LUB have varied with varying Z, which indicated the existence of nonideal conditions. Thomas model was found to be valid to predict the column dynamics and the model parameters were evaluated. Bed depth service time (BDST) model parameters were evaluated to facilitate the determination of packed bed height for the design of packed bed adsorption column. The bed could be regenerated with NaOH solution with desorption efficiency decreasing from 83.8 to 55.72% from the first to third cycle. A fixed bed of CATRM can be effectively used for continuous dye removal from industrial wastewater.

Natural Zeolites for the Sorption of Ammonium: Breakthrough Curve Evaluation and Modeling

The excessive use of ammonium fertilizer and its associated leakage threatens aquatic environments around the world. With a focus on the treatment of drinking water, the scope of this study was to evaluate and model the breakthrough curves for NH₄⁺ in zeolite-filled, fixed-bed columns. Breakthrough experiments were performed in single- and multi-sorbate systems with the initial K⁺ and NH₄⁺ concentrations set to 0.7 mmol/L. Breakthrough curves were successfully modeled by applying the linear driving force (LDF) and Thomas models. Batch experiments revealed that a good description of NH₄⁺ sorption was provided by the Freundlich sorption model (R² = 0.99), while unfavorable sorption was determined for K⁺ (n_F = 2.19). Intraparticle diffusion was identified as the rate limiting step for NH₄⁺ and K⁺ during breakthrough. Compared to ultrapure water, the use of tap, river, and groundwater matrices decreased the treated bed volumes by between 25% and 69%-as measured at a NH₄⁺ breakthrough level of 50%. The concentrations of K⁺ and of dissolved organic carbon (DOC) were identified as the main parameters that determine NH₄⁺ sorption in zeolite-filled, fixed-bed columns. Based on our results, the LDF and Thomas models are promising tools to predict the breakthrough curves of NH₄⁺ in zeolite-filled, fixed-bed columns.

Application of Granulated Nickel-Aluminum-Zirconium Complex Hydroxide in the Flow Method for Recovery of Chromium(VI) Ions

A colloidal silicate granulated nickel-aluminum-zirconium (CSG-NAZ) was prepared, and the chromium(VI) (Cr(VI)) ions recovery capacity was evaluated using a sodium sulfate solution in a column experiment. The amount adsorbed and breakthrough time were enhanced by decreasing the flow rate (flow rate is in the order of 3.0 > 2.0 > 0.5 mL). The breakthrough curves and model parameters were estimated using the Thomas and Yoon-Nelson models. The obtained data confirmed to fit both the Yoon-Nelson model (0.858-0.906) and the Thomas model (0.813-0.906). Additionally, Cr(VI) ions that adsorbed onto CSG-NAZ could be desorbed using a sodium sulfate solution in a column experiment. The total recovery percentage of Cr(VI) ions was 80.9% after six repetitions of adsorption/desorption. Finally, the obtained results revealed that CSG-NAZ was a candidate adsorbent for the recovery of Cr(VI) ions owing to its applicability toward a continuous system.

Dynamic Adsorption Properties of Insoluble Humic Acid/Tourmaline Composite Particles for Iron and Manganese in Mine Wastewater

Iron- and manganese-contaminated mine water is widespread around the world, and economical and efficient remediation has become a priority. Insoluble humic acid/tourmaline composite particles (IHA/TM) were prepared by combining inorganic tourmaline (TM) with the natural organic polymer humic acid (HA), and the effects of different calcination temperatures and calcination times of TM and IHA on the adsorption of Fe²⁺ and Mn²⁺ were analyzed. Based on the microscopic characterization of Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Brunnauer–Emmet–Teller (BET), X-ray diffractometer (XRD) and Fourier transform infrared (FTIR), the simultaneous adsorption performance of IHA/TM on Fe²⁺ and Mn²⁺ was studied through dynamic adsorption tests, and a dynamic adsorption model was established. Adsorption regeneration experiments were carried out to further investigate the effectiveness of the composite particles in practical applications. The results show that, when the calcination temperature was 330 °C and the calcination time was 90 min, the removal rates of iron and manganese by the IHA/TM composite particles reached 99.85% and 99.51%, respectively. The curves for penetration of Fe²⁺ and Mn²⁺ ions into the IHA/TM composite particles were affected by the bed height, flow rate and influent concentration. Decreasing the flow rate, decreasing the influent concentration, or increasing the bed height prolonged the operation time of the dynamic column. If the bed height was too low, the penetration point was reached before the expected treatment was achieved, and when the bed height was too high, the removal of Fe²⁺ and Mn²⁺ was slow, and the utilization rate of the adsorbent was also reduced. If the flow rate was too low, longitudinal remixing easily occurred in the column. However, when the flow rate was too high, the speed of Fe²⁺ and Mn²⁺ ions passing through the adsorption layer increased, which reduced the total amount of adsorption. The increase in influent concentration not only reduces the removal rate, but also greatly shortens the total operation time of the dynamic column and reduces the treatment water. The dynamic process for the adsorption of Fe²⁺ and Mn²⁺ by IHA/TM was fitted best by the Thomas model. The adsorption column was continuously regenerated five times, and the results show that the IHA/TM composite particles were suitable for iron and manganese removal from mine wastewater. The research results will provide a reference for the effectiveness of the IHA/TM composite particles in practical applications.

Fixed-bed column study of phosphate adsorption using immobilized phosphate-binding protein

Bio-adsorption using high-affinity phosphate-binding proteins (PBP) has demonstrated effective phosphorus removal and recovery in batch-scale tests. Subsequent optimization of design and performance of fixed-bed column systems is essential for scaling up and implementation. Here, continuous-flow fixed-bed column tests were used to investigate the adsorption of inorganic phosphate (orthophosphate, P_i) using phosphate-binding proteins immobilized on resin (PBP-NHS) targeting P_i removal to ultra-low levels followed by recovery. Time to breakthrough decreased with higher influent P_i concentration, smaller bed volume, and higher influent flow rates. The Thomas and Yoon-Nelson breakthrough models adequately described PBP-NHS resin performance with a correlation coefficient of R² > 0.95. The sharp S-shape of the breakthrough curves for both P_i-only solution and multi-ion solution indicated highly favorable and selective separation of P_i using PBP-NHS resin, beyond that achieved using LayneRT™, a commercial ion exchange resin. The P_i adsorption capacity of the PBP-NHS column was unaffected by competing anions, whereas capacity of the LayneRT™ column dropped by 20%. Tertiary wastewater effluent was also successfully treated in PBP-NHS column tests with a typical S-shaped breakthrough curve. Operating the fixed-bed column in multi-cycle mode evidenced the reusability of PBP-NHS resin with no significant decline in column performance. The results of this study contribute to efforts to scale up designs of PBP-NHS adsorption systems.

Batch and continuous adsorption of Cu(II) and Zn(II) ions from aqueous solution on bi-functionalized sugarcane-based biosorbent

A new one-pot synthesis method optimized by a 2³ experimental design was developed to prepare a biosorbent, sugarcane bagasse cellulose succinate pyromellitate (SBSPy), for the removal of Cu(II) and Zn(II) from single-component aqueous solutions, in batch and continuous modes. The bi-functionalization of the biosorbent with ligands of different chemical structures increased its selectivity, improving its performance for removing pollutants from contaminated water. The succinate moiety favored Cu(II) adsorption, while the pyromellitate moiety favored Zn(II) adsorption. Sugarcane bagasse (SB) and SBSPy were characterized using several techniques. Analysis by ¹³C Multi-CP SS NMR and FTIR revealed the best order of addition of each anhydride that maximized the chemical modification of SB. The maximum adsorption capacities of SBSPy for Cu(II) and Zn(II), in batch mode, were 1.19 and 0.95 mmol g^-1, respectively. Homogeneous surface diffusion, intraparticle diffusion, and Boyd models were used to determine the steps involved in the adsorption process. Isothermal titration calorimetry was used to assess changes in enthalpy of adsorption as a function of SBSPy surface coverage. Fixed-bed column adsorption of Cu(II) and Zn(II) was performed in three cycles, showing that SBSPy has potential to be used in water treatment. Breakthrough curves were well fitted by the Thomas and Bohart-Adams models.

Arsenic adsorption study in acid mine drainage using fixed bed column by novel beaded adsorbent

The downflow fixed-bed column adsorption-desorption of arsenic by the beaded coal mine drainage sludge-Youngdong (BCMDS-YD) adsorbent was experimentally studied. The specific surface area of BCMDS-YD synthesized using inorganic binding was 178 m² g^-1, and the pH_IEP was 5.32. The XRD analysis revealed that it was composed of calcite and schwertmannite. As a result, an increase in the inflow rate resulted in an earlier column exhaustion. The breakthrough curve indicated that a smaller adsorbent particle size and lower influent pH prolonged the column life span. Thomas logistic model was applied to fit the breakthrough curve by linear and nonlinear regression. Under the condition of an influent flow rate of 2.65 mL min^-1 (EBCT 40 min), an influent arsenic average concentration of 0.5-1 mg L^-1, an influent pH of 7.6, an adsorbent mass of 100 g, an adsorbent grain size of 1.40-1.70 mm, and an operating temperature of 25 °C, the equilibrium adsorption capacity reached 4.56 mg g^-1. The mechanism of arsenic adsorption is adsorption and precipitation. As a result of the adsorbent reuse experiment, it was judged that it could be reused with good results in all three cycle experiments. The cost of treating arsenic with the BCMDS-YD adsorbent was 0.145 $ per m^-3. The results of this study show examples of sustainable development concepts in mining drainage, and BCMDS-YD can effectively remove arsenic and other heavy metals from acid mine drainage.

Fixed-Bed Adsorption of Lead from Aqueous Solution Using Chitosan-Coated Bentonite

In this study, fixed-bed adsorption of Pb(II) from an aqueous solution using chitosan-coated bentonite (CCB) was investigated. Characterization of CCB was performed using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The effects of varying bed height (1.3 to 4.3 cm), flow rate (0.20 to 0.60 mL/min), and initial concentration (500 to 1500 mg/L) on the length of mass transfer zone (Z_m) and adsorption capacity at breakthrough (q_b) and exhaustion (q_e) were examined. Low flow rate and high bed height were determined to cause a longer time to reach breakthrough and exhaustion. Meanwhile, the fixed-bed system was observed to quickly attain breakthrough and exhaustion under high initial concentrations. Kinetic column models such as the Thomas, Yoon-Nelson, and Clark models were used to predict the breakthrough curves. High R² values (0.9758 ≤ R² ≤ 0.8087) were attained for the Thomas model, which indicates that there is good agreement between experimental data and linear plots generated by the Thomas model. Moreover, the Thomas model is best in describing the breakthrough curves of Pb(II) removal under a fixed-bed system.

Fixed-bed column dynamics of ultrasound and Na-functionalized diatomite to remove phosphate from water

A continuous fixed-bed column study was used to evaluate phosphate adsorption performance of U-D-Na which was functionalized by the cheap NaCl reagent after simple ultrasonic purification of diatomite. In this work, various effect factors, including flow rate, initial phosphate concentration, and the bed height, on breakthrough performance of fixed column were investigated. Experimental results demonstrated that the breakthrough time declined with the increase of inlet phosphate concentration and feed rate, whereas the increase of bed height turned out to significantly extend the breakthrough time. The dynamic adsorption process could be well fitted by the Thomas model, with a correlation coefficient R² > 0.9000 under main operating conditions. A thrice loop of effective regeneration was achieved with 0.1 M hydrochloric acid eluent and deionized water. The maximum removal rate for phosphate was more than 95% in the column adsorption process. The results proved that U-D-Na could be used as a better alternative phosphate adsorbent for wastewater in a continuous column sorption process.

Cadmium Removal from Giant Squid (Dosidicus gigas) Hydrolysate in Fixed-Bed Columns Packed with Iminodiacetic Resin: Tools for Scaling up the Process

Giant squid hydrolysate (GSH) elaborated from different batches from a fishing company was evaluated for cadmium removal. Fixed-bed column packed with iminodiacetic resin as adsorbent was used. GSH solution at different cadmium concentrations were fed in the fixed-bed column and breakthrough curves were evaluated. A high degree of metal removal from the solution was achieved and the saturation point (C_e/C₀ ≤ 0.8) was achieved more quickly at higher concentrations of cadmium. The maximum capacity of adsorption (q₀) was obtained using the Thomas model, where 1137.4, 860.4, 557.4, and 203.1 mg g^-1 were achieved using GSH with concentrations of 48.37, 20.97, 12.13, and 3.26 mg L^-1, respectively. Five cycles of desorption of the resin with HCl (1 M) backflow and regeneration with NaOH (0.5 M) were also evaluated, where no significant differences (p-value > 0.05) were observed between each cycle, with an average of 935.9 mg g^-1 of q_max. The in-series columns evaluated reached a total efficiency of 90% on average after the third column in GSH with a cadmium concentration of 20.97 mg L^-1. This kind of configuration should be considered the best alternative for cadmium removal from GSH. Additionally, the chemical composition of GSH, which was considered a quality parameter, was not affected by cadmium adsorption.

Lab-scale continuous flow studies for comparative biosorption of cadmium (II) on untreated and xanthated Ficus religiosa biomass

The present studies report the use of an ecofriendly biomass Ficus religiosa in untreated (UFR) and xanthate treated (XFR) forms for the Cd (II) ions removal in a fixed bed column. FTIR, SEM-EDS, BET surface area, and elemental analysis (CHNS) techniques were used to characterize the biosorbents. The acquired data supported FTIR findings regarding the nature of functional groups present in the materials. Packed bed continuous flow studies explored the effects of various parameters such as Cd (II) ion concentration (100 mg/L-300 mg/L), bed heights (5 cm-30 cm), pH (3-5), at a constant linear flow rate (~1.13 cm/min). The obtained S-shaped breakthrough curves indicated the efficiency of the packed bed for the Cd (II) removal. Breakthrough time and exhaust times increased (67.5 min-390 min and 292.5 min-1852.5 min) (97.5 min-442.5 min and 345 min-1920 min) for unmodified and modified respectively with bed heights. The BDST, Thomas, and Yoon-Nelson models were used to evaluate the experimental results. The Yoon-Nelson model describes the breakthrough data more efficiently compared to other models. Under similar conditions, the modified material exhibited 400% increased capacity (55.20 mg/g) than that of unmodified material (13.33 mg/g). Thus, xanthate modification significantly enhanced the capacity for Cd (II) ions from aqueous solutions. PRACTITIONER POINTS: Xanthate modification of Ficus religiosa is an environmentally friendly process. Modified and unmodified materials were utilized for Cd (II) removal in fixed bed column process which is industrially viable process. Low inlet Cd (II) concentration at pH 5 and higher bed height favored the continuous flow process at fixed flow rate. Modification caused an increase of about 400% in the capacity of material.

Comments on "Treatment of malachite green dye containing solution using bio-degradable sodium alginate/NaOH treated activated sugarcane baggsse charcoal beads: Batch, optimization using response surface methodology and continuous fixed bed column study" and "Adsorption and oxidation of ciprofloxacin in a fixed bed column using activated sludge derived activated carbon"

This comment analyses the results of the fixed-bed column modeling from the studies published by Gupta and Garg (2019), and Das et al. (2020), which are the last two papers on this topic published in this journal.

Comments on "Dynamic Adsorption of Sulfamethoxazole from Aqueous Solution by Lignite Activated Coke"

This paper presents a brief discussion with regard to the fixed-bed modeling results of a recent paper by Li et al. published in this journal.

L-Ascorbic Acid-g-Polyaniline Mesoporous Silica Nanocomposite for Efficient Removal of Crystal Violet: A Batch and Fixed Bed Breakthrough Studies

In the present study, mesoporous silica nanoparticles (MSNs) synthesized through sol-gel process and calcined at 600 °C were further surface functionalized by a copolymer chain of L-ascorbic acid (AS) and polyaniline (PAni) by in situ free radical oxidative polymerization reaction. The surface modification of MSNs by AS-g-PAni was confirmed by using various analytical techniques, namely FTIR, XRD, SEM-EDX, TEM and AFM. The composition of AS-g-PAni@MS was found to be composed of C (52.53%), N (20.30%), O (25.69%) and Si (1.49%), with 26.42 nm as the particle size. Further, it was applied for the adsorption of crystal violet (CV) dye under batch, as well as fixed bed method. RSM-BBD was taken into consideration, to optimize the various operational parameters effecting the adsorption through batch method. To explore maximum efficiency of the material, it was further subjected to adsorption of CV under fixed bed method, using the variable bed heights of 3.7, 5.4 and 8.1 cm. Based on high value of regression coefficient (R2) and low value of RMSE given as (0.99, 0.02) for 3.7 cm, (0.99, 0.03), the breakthrough data were very well defined by the Thomas model, with optimum concurrence of stoichiometric adsorption capacity values. The external mass transfer equilibrium data were well fitted by the Langmuir model, with maximum monolayer adsorption capacity of 88.42 mg g-1 at 303K, 92.51 mg g-1 at 313 K, 107.41 mg g-1 at 313 K and 113.25 mg g-1 at 333 K. The uptake of CV by AS-g-PAni@MS was well defined by pseudo second order model with rate constant K2 = 0.003 L mg-1 min-1 for 50 and 0.003 L mg-1 min-1 for 60 mg L-1 CV. The adsorption reaction was endothermic with enthalpy (ΔH) value of 3.62 KJ mol-1 and highly efficient for treatment of CV-contaminated water for more the five consecutive cycles.

Sisal xylem fibre-based activated carbon fibres for fuel adsorption: effect of thermal stabilization of diammonium phosphate

Activated carbon fibres (ACFs) are considered as the next generation of activated carbon products. However, lack of structural diversity in pore structure and high prices of raw materials for ACFs has restrained the development of ACF materials. In this paper, a sisal-based activated carbon fibre (SACF) material was prepared from sisal wastes with a unique thermal stabilization treatment to maintain fibrous shapes of SACFs while dispersing in solutions, and the SACFs were prepared as raw fibre materials for fuel evaporation emissions controlling products. Experimental results of N₂ adsorption showed that SACF has a typical I-type adsorption isotherm, with specific surface area of SACF samples of approximately 1200 m² g^-1, and mainly microporous pore structure. Compared with commercial samples (specific surface area, 1841.29 m² g^-1), the butane working capacities of SACF for advanced fuel evaporation emissions controlling product was 0.4 g/100 ml higher. Furthermore, two dynamic models, Thomas model and Clark model, were applied to adsorption breakthrough data, which showed excellent fit. And it indicated from the adsorption breakthrough curves and parameters of both models that the SACF has better performance in fuel adsorption and desorption process than the commercial samples.

Fixed-bed adsorption of copper from aqueous media using chitosan-coated bentonite, chitosan-coated sand, and chitosan-coated kaolinite

Fixed-bed studies were performed to evaluate the removal efficiency of copper (Cu(II)) from aqueous solution using chitosan-coated bentonite (CCB), chitosan-coated sand (CCS), and chitosan-coated kaolinite (CCK). The thermal and morphological properties of CCB, CCK, and CCS were characterized using thermogravimetric analysis, Fourier transform infrared spectroscopy, and the Brunauer-Emmett-Teller method. Dynamic experiments were carried out to investigate the effect of solution pH (3.0 to 5.0) and initial Cu(II) concentration (200 to 1000 mg/L) on the time to reach breakthrough (t_b), total volume of treated effluent (V_eff), and adsorption capacity at breakthrough (q_b). Results show that increasing the initial Cu(II) concentration inhibits the column performance where lower V_eff, t_b, and q_b were obtained. Decreasing the pH from 5.0 to 3.0 led to improved removal efficiency with higher values of V_eff, t_b, and q_b. Under pH 3.0 and 200 mg/L, the maximum removal efficiency of 68.60%, 56.10%, and 58.90% for Cu(II) was attained using CCB, CCS, and CCK, respectively. The Thomas model was determined to adequately predict the breakthrough curves based on high values of coefficient of determination (R² ≥ 0.8503). Regeneration studies were carried out using 0.1 M HCl and 0.1 M NaOH solution in the saturated column of CCB, CCK, and CCS.

Modified Biopolymer Adsorbents for Column Treatment of Sulfate Species in Saline Aquifers

In the present study, variable forms of pelletized chitosan adsorbents were prepared and their sulfate uptake properties in aqueous solution was studied in a fixed-bed column system. Unmodified chitosan pellets (CP), cross-linked chitosan pellets with glutaraldehyde (CL-CP), and calcium-doped forms of these pellets (Ca-CP, Ca-CL-CP) were prepared, where the removal efficiencies and breakthrough curves were studied. Dynamic adsorption experiments were conducted at pH 4.5 and 6.5 with a specific flow rate of 3 mL/min, fixed-bed height of 200 mm, and an initial sulfate concentration of 1000 mg/L. Breakthrough parameters demonstrated that Ca-CP had the best sulfate removal among the adsorbents, where the following adsorption parameters were obtained: breakthrough time (75 min), exhaust time (300 min), maximum sulfate adsorption capacity (q_max; 46.6 mg/g), and sulfate removal (57%) at pH 4.5. Two well-known kinetic adsorption models, Thomas and Yoon-Nelson, were fitted to the experimental kinetic data to characterize the breakthrough curves. The fixed-bed column experimental results were well-fitted by both models and the maximum adsorption capacity (46.9 mg/g) obtained was for the Ca-CP adsorbent. A regeneration study over four adsorption-desorption cycles suggested that Ca-CP is a promising adsorbent for sulfate removal in a fixed-bed column system.

Comment on "removal of hexavalent chromium by biochar supported nZVI composite: Batch and fixed-bed column evaluations, mechanisms, and secondary contamination prevention"

This article aims to discuss (1) the incorrect identification of Cr(III) and Cr(VI) binding energies in the Cr 2p XPS (X-ray photoelectron spectroscopy) spectra of the laden adsorbent (the nZVI-BC sample after Cr(VI) adsorption), (2) misconception regarding the Weber-Morris intraparticle diffusion model, and (3) inconsistency between the experiential data and the Thomas adsorption rate constants. The authors hope that our comments are beneficial for other researchers to avoid the undesirable mistakes.

A breakthrough column study for removal of malachite green using coco-peat

A continuous adsorption study in a fixed bed column using coco-peat (CP) as an adsorbent was carried out for the removal of toxic malachite green (MG) from contaminated water. Fixed bed column studies were carried out to check field application viability. Various parameters like particle size, pH, concentration, dose and interference were exercised to optimize dye removal. Data obtained from breakthrough column studies were evaluated using Thomas and BDST model. Thomas rate constants K_t (0.22 ml min^-1 mg^-1) and adsorption capacity q_o (181.04 mg g^-1) were estimated and found to favor efficiency of CP. Thomas model was tested with several parameters like flow rate, concentration, and bed depth. Upon increase in input dye concentration, flow rate and bed height, adsorption coefficients increased. According to BDST model, maximum dye uptake of 468.26 mg/l was obtained with an input dye concentration of 5 mg/l. HYBRID and MPSD error functions were tested and found that Thomas model fits best. Dilute hydrochloric acid was found best for desorption. Real wastewater from textile industry was analyzed and confirmed the prospect of large-scale industrial application. In conclusion, coco-peat can be used as a promising bio-sorbent in column bed for scavenging of MG from contaminated water.

Arsenic adsorption on Fe-Mn modified granular activated carbon (GAC-FeMn): batch and fixed-bed column studies

Granular activated carbon (GAC) was modified with Fe-Mn binary oxide to produce a novel effective hybrid adsorbent (GAC-FeMn) for simultaneous removal of As(III) and As(V) from water. After characterization (including BET, SEM/EDS and XRD analyses) of the raw and modified GAC, FTIR analysis before and after As removal showed that ligand exchange was the major mechanism for As removal on GAC-FeMn. Sorption kinetics followed pseudo-second order kinetics for both As(III) and As(V) and were not controlled by intraparticle diffusion. Batch equilibrium experiments yielded adsorption capacities for As(III) and As(V) of 2.87 and 2.30 mg/g, and demonstrated that better sorption was achieved at low pH. Of the competitive anions investigated (PO₄^3-, SiO₃^2-, CO₃^2-, SO₄^2-, NO₃^-, Cl^-), phosphate had the greatest negative effect on As(III) and As(V) adsorption. Three sorption/desorption cycles were conducted in continuous column tests with a real arsenic contaminated groundwater, with subsequent TCLP leaching tests confirming the stability of the spent sorbent. In the column tests, breakthrough curves were also obtained for phosphates, which were present at a relatively high concentration (1.33 mg/L) in the investigated groundwater. The phosphates limited the effective operational bed life of GAC-FeMn for arsenic removal. Nonetheless, the maximum arsenic adsorption capacities for GAC-FeMn obtained by the Thomas model during the three sorption cycles were high, ranging from 18.8 to 29.8 mg/g, demonstrating that even under high phosphate loads, with further process improvements, GAC-FeMn may provide an excellent solution for the economic removal of arsenic from real groundwaters.

Evaluation of zeolite-supported microscale zero-valent iron as a potential adsorbent for Cd2+ and Pb2+ removal in permeable reactive barriers

A new composite adsorbent, zeolite-supported microscale zero-valent iron (Z-mZVI) was evaluated as a potential adsorbent for the removal of Cd²⁺ and Pb²⁺ from aqueous solution using batch and column experiments. Adsorption isotherms were well fitted by Langmuir model, and the maximum adsorption capacity was 63.14 mg/g for Cd²⁺ and 154.61 mg/g for Pb²⁺, respectively. Both adsorption processes followed the pseudo-second-order model which indicated that the rate-limiting step for different initial concentration was dominated by chemical adsorption process. The coexistence of Cd²⁺ and Pb²⁺ caused the reduction of Cd²⁺ removal efficiency, but not for Pb²⁺. Z-mZVI has a high removal capacity for Cd²⁺ and Pb²⁺ over a wide pH range (3.0-6.8) as well as in the presence of competitive Ca²⁺ or Mg²⁺ ions (<2 mmol/L). Moreover, Z-mZVI shows a high immobilization capacity for the adsorbed Cd²⁺ and Pb²⁺ products, even at the acid solution (pH = 3.95). Column experiment confirmed that Z-mZVI could simultaneously remove Cd²⁺ and Pb²⁺ from solution efficiently. Thomas model can simulate the equilibrium adsorption capacity of Cd²⁺ and Pb²⁺ of the Z-mZVI column well. This study demonstrates that Z-mZVI is an efficient and promising reactive material in permeable reactive barriers for Cd²⁺ and Pb²⁺ removal from aqueous solution.

Removal of heavy metals from acid mine drainage using chicken eggshells in column mode

Chicken eggshells (ES) as alkaline sorbent were immobilized in a fixed bed to remove typical heavy metals from acid mine drainage (AMD). The obtained breakthrough curves showed that the breakthrough time increased with increasing bed height, but decreased with increasing flow rate and increasing particle size. The Thomas model and bed depth service time model could accurately predict the bed dynamic behavior. At a bed height of 10 cm, a flow rate of 10 mL/min, and with ES particle sizes of 0.18-0.425 mm, for a multi-component heavy metal solution containing Cd²⁺, Pb²⁺ and Cu²⁺, the ES capacities were found to be 1.57, 146.44 and 387.51 mg/g, respectively. The acidity of AMD effluent clearly decreased. The ES fixed-bed showed the highest removal efficiency for Pb with a better adsorption potential. Because of the high concentration in AMD and high removal efficiency in ES fixed-bed of iron ions, iron floccules (Fe₂(OH)₂CO₃) formed and obstructed the bed to develop the overall effectiveness. The removal process was dominated by precipitation under the alkaline reaction of ES, and the co-precipitation of heavy metals with iron ions. The findings of this work will aid in guiding and optimizing pilot-scale application of ES to AMD treatment.

Removal of Pb(II) ions from aqueous solution using water hyacinth root by fixed-bed column and ANN modeling

Hyacinth root was used as a biosorbent for generating adsorption data in fixed-bed glass column. The influence of different operating parameters like inlet Pb(II) ion concentration, liquid flow rate and bed height on the breakthrough curves and the performance of the column was studied. The result showed that the adsorption efficiency increased with increase in bed height and decreased with increase in inlet Pb(II) ion concentration and flow rate. Increasing the flow rate resulted in shorter time for bed saturation. The result showed that as the bed height increased the availability of more number of adsorption sites in the bed increased, hence the throughput volume of the aqueous solution also increased. The adsorption kinetics was analyzed using different models. It was observed that maximum adsorption capacity increased with increase in flow rate and initial Pb(II) ion concentration but decreased with increase in bed height. Applicability of artificial neural network (ANN) modeling for the prediction of Pb(II) ion removal was also reported by using multilayer perceptron with backpropagation, Levenberg-Marquardt and scaled conjugate algorithms and four different transfer functions in a hidden layer and a linear output transfer function.