Biosorption Of Cr Research Articles

Binary Biosorption of Cu(II) and Cr(VI) by Naturally Formed Biofilm Matrices

Water pollution poses a significant ecological threat, contributing to the widespread degradation of aquatic ecosystems. Among the pollutants, heavy metals pose severe risks to both organisms and human health, emphasizing the urgent need for effective pollution control technologies. Biosorption presents a promising, cost-effective, and environmentally friendly solution to mitigate heavy metal contamination. Biofilms, consisting of microbial communities, have emerged as potential biosorbents for heavy metals. Since heavy metals can exist as cations and anions concurrently in aquatic environments, understanding their behavior in binary systems is essential for biosorption strategies. This study focuses on the binary biosorption of Cu(II) and Cr(VI), representing cationic and anionic heavy metals. Specific adsorption sites are identified by analyzing adsorption kinetics, isotherms, and IR spectra of biofilms. The results indicate that biofilms, in a binary scenario, demonstrate nearly identical adsorption capacities for Cu(II) and Cr(VI). Moreover, the adsorption process follows the Langmuir adsorption model, emphasizing the potential of biofilms as effective biosorbents for the simultaneous removal of cationic and anionic heavy metals. This study advocates for a sustainable approach to heavy metal remediation through the utilization of biofilms.

Biosorption of Cr(VI) by Theobroma cacao pericarp.

This paper reports a comprehensive study of Theobroma cacao pericarp (TCP) residues, which has been prepared, characterized, and tested as an inexpensive and efficient biosorbent of Cr(VI) from aqueous solutions. The maximum adsorption capacity of TCP obtained at optimal conditions (pH = 2, dose = 0.5g L-1, C0 = 100mg L-1) was qmax = 48.5mgg-1, which is one of the highest values reported by the literature. Structural and morphological characterization has been performed by FTIR, SEM/EDX, and pHPZC measurements. FTIR analysis revealed the presence of O-H, -NH, -NH2, C = H, C = O, C = C, C-O, and C-C functional groups that would be involved in the Cr(VI) biosorption processes. The experimental equilibrium data of biosorption process were successfully fitted to non-linear Langmuir (R2 = 0.95, χ2 = 11.0), Freundlich (R2 = 0.93, χ2 = 14.8), and Temkin (R2 = 0.93, χ2 = 14.7) isotherm models. Kinetics experimental data were well adjustment to non-linear pseudo-2nd (R2 = 0.99, χ2 = 2.08)- and pseudo-1st-order kinetic models (R2 = 0.98, χ2 = 2.25) and also to intra-particle Weber-Morris (R2 = 0.98) and liquid film diffusion (R2 = 0.99) models. These results indicate that Cr(VI) biosorption on heterogeneous surfaces as well as on monolayers of TCP would be a complex process controlled by chemisorption and physisorption mechanisms. The thermodynamic results indicate that the Cr(VI) biosorption on TCP is a feasible, spontaneous, and endothermic process. TCP can be regenerated with NaOH and reused up to 3 times.

Simultaneous biosorption of chromium and zinc from aqueous solution by Lactobacillus plantarum exopolysaccharides and biofilm characterized by structural and functional analysis

AbstractHeavy metals represent significant environmental pollutants in today's world. The primary sources of human exposure to these heavy metals are through food and water, which can lead to various life‐threatening diseases. Therefore, it is imperative to focus on the removal of these contaminants to safeguard human health. The study describes the optimization of biosorption conditions of chromium [Cr(III)] and zinc [Zn(II)] through biofilm and exopolysaacharides (EPS) of Lactobacillus plantarum. The strain was tested for minimum inhibitory concentration and assessed at 100–350 ppm for Cr (III) and Zn (II) in terms of log cfu/mL. Metal adsorption capacity of biofilm was slightly higher as compared to EPS. Biosorption of Cr (III) at pH 2 showed 90% biosorption through biofilms and 88% through EPS. Zn (II) showed maximum binding of about 86% and 78% by biofilm and EPS, respectively, at pH 8 at 37°C for 24 h. The binding of metal is mostly dependent upon the functional group present, the surface morphology of biofilm, and the EPS of strain.

Sorption of chromium from aqueous solutions using Fucus vesiculosus algae biosorbent

The presence of heavy metals in wastewater is an environmental concern and the current treatment procedures are very expensive so it is necessary to find effective and inexpensive biosorbents. In this study, Fucus vesiculosus was used as a biosorbent for the biosorption of Cr(III) ions from the aqueous solutions. Biosorption parameters, such as pH, adsorbent dose, contact time, and initial concentrations of Cr(III) had the most impact on the sorption process. The required pH value for sorption was 5, the biosorbent dose was 4.0 g/L, the contact time was seen to occur after 90 min, and the Cr(III) removal decreased from 98.9 to 92%. The maximum biosorption capacity of chromium was 14.12 mg/g. FTIR analysis of Fucus vesiculosus biomass before the sorption process contains carboxyl, amino, hydroxyl, alkyne, and carbonyl groups, and according to the analysis after the sorption process, it was found that Cr(III) metal ions were incorporated within the sorbent during the interaction with (=C–H) active functional groups. The biosorption data were found to be perfectly suited by Langmuir equilibrium isotherm model. According to the results of this study, Fucus vesiculosus is an effective biosorbent for the removal of Cr(III) from aqueous solutions.

Chitosan-Fe3O4 Membranes for Biosorption of Cr(VI) in Water, and Study of its Degradation Using Entomopathogenic Fungi (Beauveria sp and Nomureae sp)

Chitosan-Fe3O4 Membranes for Biosorption of Cr(VI) in Water, and Study of its Degradation Using Entomopathogenic Fungi (Beauveria sp and Nomureae sp)

The Potential of Fungal Biomass as Agents for Biosorption of Chromium (VI) Ion from Tannery Effluent

Biosorption and bioaccumulation are the overall process by which microorganism tolerate toxic levels of heavy metals in the environment. Thus, filamentous fungi are able to accumulate significant amount of metals from their environment. The potential of fungal biomass as agents for biosorption of chromium (VI) ion from tannery effluent is currently receiving attention. In the present study a total of four isolate of filamentous fungi and Candida sp, were obtained from tannery effluent Mario Jose locate at Challawa industrial estate Kano. These fungi were characterized morphologically, microscopically and screened for their tolerance and uptake capability of chromium (VI) ion in medium. The isolates were identified as viz; Rhizopus nigrican Aspergillus niger and Penicillium sp. Only three of these species were able to survived at 4% concentration of chromium ion solution on modified rice husk medium (MRHM). The results showed that Rhizopus nigricans and Aspergillus niger have better uptake capacity for chromium (VI) ion by these filamentous fungi from aqueous solution. The present study was also determined the maximum removal of chromium (VI) ion that performed by Rhizopus nigricans, Aspergillus niger, Penicillium sp and mixed culture organisms. The chromium (VI) removal with initial concentration ranging from 1.517mg/l – 0.067, 1.517mg/l – 0.072mg/l and Penicillium sp 1.517mg/l – 0.73mg/l and mixed culture 1.517mg/l – 0.874mg/l. The above studies show Rhizopus nigricans and Aspergillus niger organisms appear to be more effective in biosorption of Cr6+ in effluent using modified agricultural waste in comparison with conventional one’s base on time duration of absorption.

Removal of Chromium (VI) from Water Using Orange peel as the Biosorbent: Experimental, Modeling, and Kinetic Studies on Adsorption Isotherms and Chemical Structure

The present work aims to assess the effectiveness and efficiency of orange peels as a low-cost biosorbent for removing Cr(VI) from an aqueous solution by the biosorbent process. The orange peels as adsorbent was characterized using different methods, such as FTIR, pHpzc, equilibrium pH, TGA, XRD, SEM, and (BET). The tests were conducted in the batch mode, and the effects of different parameters, such as the pH, dosage of the bioadsorbent, influent Cr(VI), and time, on the biosorption of Cr(VI) were investigated. The adsorption kinetics proved that a contact time of 90 min resulted in the highest (approximately 97.8%) Cr(VI) removal, with an adsorption capacity of 4.96 mg/g. Moreover, the increase in the biosorbent dosage (from 1 to 10 g/L) resulted in the enhancement in the Cr(VI) removal effectiveness. Moreover, the pH of the solution also affected significantly the effectiveness of the removal. The tests were conducted under acidic pH solution conditions, and the prediction of the pH value at a zero charge (pH pzc) was confirmed experimentally. Furthermore, the results from the batch-mode assays were successfully tested by an experimental design (full factorial design). The biosorption of Cr(VI) on orange peels occurred mostly according to the pseudo-second-order kinetic model and the uptake of Cr(VI) was satisfactorily described by the Langmuir model.

Biosorption of Hexavalent Chromium by Freshwater Microalgae Craticula subminuscula from Aqueous Solutions

Recently, microalgae have tended to be used as a biological treatment for wastewater decontamination. The present study aimed to investigate the Cr(VI) removal using the freshwater microalgae ‘Craticula subminuscula’ and their biobased adsorbant, isolated from a Moroccan river in the High Atlas Mountain. The optimum operational conditions for maximum Cr(VI) biosorption by the biobased adsorbent form (95.32%) were determined at (pH = 1.09, adsorbent dose = 10.91 mg L−1, and treatment duration = 129.47 min) using response surface methodology (RSM). Under those optimal conditions, the biosorption process of Cr(VI) by C. subminuscula is endothermic, spontaneous and follows Langmuir and a pseudo-second-order model with a constant rate; the theoretical and experimental biosorption capacity of 0.0004 g/mg/min was 289.01 mg g−1 and 277.57 mg g−1, respectively. Fourier Transform Infrared Spectroscopy (FTIR) analyses of the biomass and scanning electron microscopy (SEM) revealed that the principal mechanism to remove Cr(VI) by C. subminuscula was the affinity of Cr(VI) by the cell walls of microalgae. Thus, the positive results of desorption cycles promise increased potential utilization of these algae in continuous systems within industrial processes. The findings contribute valuable insights into the effectiveness of C. subminuscula as a biobased remediation agent for Cr(VI) in wastewater treatment.

Biosorption and desorption of chromium using hybrid microalgae-activated sludge treatment system

This study utilised a mixed culture of Chlorella vulgaris and bacteria from sludge to treat synthetic tannery wastewater (STWW) in modified stirred-tank photobioreactors (MSTPBRs). The MSTPBRs were fabricated locally and operated at irradiance value of 580 µmol/m2s supplied by red light-emitting diodes at 12:12 light–dark cycles and 100 ± 1 rpm continuous stirring. In each case, 50, 100 and 150 mg/L concentrations of STWW were inoculated with mixed culture of microalgae and bacteria in three MSTPBRs, with the control MSTPBR operating at 50 mg/L of STWW. Chromium concentrations were measured using colorimeter whilst Fourier transform infrared spectroscopy (FTIR) indicated possible Cr biosorption. Maximum Cr (VI) and total Cr removal efficiencies of 93 and 94% were achieved, with more than 78% total Cr recovery. Results from FTIR suggested involvement of Chlorella vulgaris in the Cr biosorption. The hybrid microalgae-bacteria system efficiently treated tannery wastewater with considerable Cr removal efficiencies. The potentials of the system in treating tannery wastewater in larger scale may require further investigation.

Biosorption of hexavalent chromium by biochar prepared from the Ceratonia siliqua pod: Kinetic, equilibrium, and thermodynamics studies

Ceratonia siliqua pod biochar sample (CBC) was generated in this work from C. siliqua (carob pod waste) biomass (CBM) by slow pyrolysis for 5h at 400°C as an alternative low-cost biosorbent for the removal of Cr(VI). The biosorption parameters that were adjusted were the initial pH (2.0–10.0), temperature (30°C, 40°C, and 50°C), biosorbent dose (0.01–0.03 g/50 mL), initial Cr(VI) concentration (10–100 mg/L), and contact period (0–360 min). The interaction between the surface functional groups on the CBM and CBC and the Cr(VI) ions was found to be the primary mechanism for Cr(VI) sorption via surface complexation and electrostatic interactions, according to the investigation of the pH influence. The Langmuir isotherm was shown to be more well-fitting than the Freundlich and Dubinin-Radushkevich isotherms for the concentration range of 10 to 100 mg/L. The testing results indicated a sorption capacity of 90.909 mg/g of CBM and 131.579 mg/g of CBC. According to kinetic investigations, the absorption of Cr(VI) ions onto CBM and CBC was defined in pseudo-second order. The findings of thermodynamic investigations showed that the biosorption of Cr(VI) ions onto CBM and CBC was an exothermic, spontaneous process. These findings demonstrated that, even for high concentrations of Cr(VI) in industrial wastewater, CBM and CBC could be viable, affordable alternatives as adsorbents.

Potentials of surface modified biochar for removal of Cr from tannery effluent and its regeneration to ensure circular economy

Industries play a substantial role in contaminating the freshwater sources. This study was performed to appraise the potential of biochar activated with 85% phosphoric acid was used as chemisorbent for the removal of Chromium III and VI (Cr III and VI)) and desorbed chromium was utilized for replacing the conventional basic chromium sulfate to ensure circular economy. In our previous studies, the factors for biosorption of Cr were optimized through Box–Behnken model under Response Surface Methodology. Batch adsorption studies revealed that the optimum conditions for maximum Cr (VI) biosorption by activated biochar is pH = 2, biosorbent dose: 1%, biosorbent size: 1 mm, solute concentration: 985 mg L−1 and reaction time 35 h. Based on these results a column experiments were carried out and flow rate was optimized as 0.5 ml m−1 where prominent “S” shaped breakthrough curves were noticed. The predicted values under Thomas model for the adsorption of Cr was 3827.2 µg g−1, which was in close agreement with experimental value of 3566.1 µg g−1. The percent Cr sorption varied from 70.05 to 88.75% in first cycle and showed decreasing trend in the subsequent cycles. The elutant 0.5 M H2SO4 desorbed 89.56% of chromium furthermore eluted chromium was utilized for leather tanning. Reusing of recovered chromium for tanning experiments does not alter the leather Tensile (240.82 kg cm−2) and tear strengths (32.41 kg mm−1). This study suggested that recovered chromium from biosorbent can be well utilized for leather tanning to attain the leather of equivalent qualities as that of conventional methods which could save 20–22% of the production cost besides defending the environment from Cr contamination.

A Comparative Study of Cr(VI) Sorption by Aureobasidium pullulans AKW Biomass and Its Extracellular Melanin: Complementary Modeling with Equilibrium Isotherms, Kinetic Studies, and Decision Tree Modeling.

Melanin as a natural polymer is found in all living organisms, and plays an important role in protecting the body from harmful UV rays from the sun. The efficiency of fungal biomass (Aureobasidium pullulans) and its extracellular melanin as Cr(VI) biosorbents was comparatively considered. The efficiency of Cr(VI) biosorption by the two sorbents used was augmented up to 240 min. The maximum sorption capacities were 485.747 (fungus biomass) and 595.974 (melanin) mg/g. The practical data were merely fitted to both Langmuir and Freundlich isotherms. The kinetics of the biosorption process obeyed the pseudo-first-order. Melanin was superior in Cr(VI) sorption than fungal biomass. Furthermore, four independent variables (contact time, initial concentration of Cr(VI), biosorbent dosage, and pH,) were modeled by the two decision trees (DTs). Conversely, to equilibrium isotherms and kinetic studies, DT of fungal biomass had lower errors compared to DT of melanin. Lately, the DTs improved the efficacy of the Cr(VI) removal process, thus introducing complementary and alternative solutions to equilibrium isotherms and kinetic studies. The Cr(VI) biosorption onto the biosorbents was confirmed and elucidated through FTIR, SEM, and EDX investigations. Conclusively, this is the first report study attaining the biosorption of Cr(VI) by biomass of A. pullulans and its extracellular melanin among equilibrium isotherms, kinetic study, and algorithmic decision tree modeling.

Applicability of Natural Coffee Husk as a Mesoporous Adsorbent for Removal of Chromium (VI) from Aquatic Environments

Chromium (Cr) is an essential element in plant and animal metabolism, but high accumulation of this metal ion in soil and water from industrial sources has caused concern. This study investigated the removal of Cr (VI), the most mobile and toxic species, using coffee husk biosorption from aqueous solutions. Coffee husk was characterized using Brunauer Emmett Teller (BET) and Fourier Transform Infrared (FTIR) analysis. The effects of pH, adsorbent dosage, contact time, effect of KNO3 concentration, and temperature during the adsorption of Cr (VI) were studied. Infrared spectral studies revealed the presence of functional groups, such as hydroxyl and carboxyl groups, which facilitated the biosorption of Cr (VI). The maximum adsorption capacity reached 87 % at pH~2. Moreover, maximum adsorption capacity of Cr (VI) onto coffee husk 0.660 mg g-1 was recorded after 60 min of using 40 mg L-1 of Cr (VI) with no addition of KNO3 at 40 0C. The kinetic data followed the pseudo-second-order model with regression coefficients R2 = 0.99. The equilibrium data for the adsorption of Cr (VI) onto coffee husk biosorption were fitted into Langmuir and Temkin adsorption isotherm models with R2 = 0.98 corresponding to each model. Thermodynamic studies showed that the coffee husk-Cr (VI) adsorption system was spontaneous and endothermic because negative and positive values were obtained for ΔG° and Δ°H, respectively. The coffee husk was applicable to remove Cr (VI) after three recycling and using different environmental water samples. In conclusion, coffee husk can be used effectively as an adsorption system for Cr (VI) at different polluted sites.

Adsorption of Hexavalent Chromium Ions Using Pine Sawdust Cellulose Fibres

In developing countries, agriculture generates not only income but also waste. Therefore, it is essential to recycle this waste for different purposes. This study explored an affordable way to modify pine sawdust to treat chromium-containing wastewater, with successful outcomes. The biosorbent’s surface area was enhanced through pretreatment steps, including NaOH treatment, bleaching, and acid hydrolysis for cellulose fibre extraction. SEM–EDS, TEM, and XRD were used to study the chemical composition and morphology. XRD measurements also revealed a rise in the sizes of crystallites. FTIR results revealed shifts in bands (-OH), (-C-H), and (-COOH), suggesting their involvement in Cr (VI) ion adsorption. TGA/DTA indicated enhanced thermal stability for cellulose extracted from pine sawdust compared to untreated pine sawdust. The adsorption parameters for Cr (VI) ions were investigated through mass, pH, stirring time, and temperature studies. The optimal Cr (VI) adsorption conditions were 2.0 g mass, pH 6, 90 min stirring, 100 mg/L concentration, and 313 K temperature. The adsorption of Cr (VI) ions was best-fit to the Langmuir isotherm model (R2 = 0.9991, kL = 0.09). Pseudo-second-order kinetics (R2 = 0.9999) provided the best description for Cr (VI) biosorption on cellulose fibres (CF). The analysis results confirmed the isotherm and kinetics models. The negative thermodynamic parameters (ΔG° and ΔH°) indicated that the uptake of Cr (VI) ions on the adsorbent was exothermic and spontaneous.

Bioremediation Potential of Cr(VI) by Lysinibacillus cavernae CR-2 Isolated from Chromite-Polluted Soil: A Promising Approach for Cr(VI) Detoxification

The present study focuses on an efficient Cr(VI)-reducing bacterial strain (CR-2) isolated from an abandoned chromate plant in Qinghai Province, China. CR-2 was confirmed as Lysinibacillus cavernae using 16S rRNA gene sequencing. CR-2 could survive at 500 mg L−1 Cr(VI) and effectively reduce Cr(VI) at concentrations of <50 mg L−1, a pH of 5–9, a temperature of 20–40 °C, and a salinity of 5–15 g L−1. According to the Box–Behnken experimental design, the maximum Cr(VI) removal efficiency by L. cavernae CR-2 was 76.21% under optimum conditions, which comprised a pH of 6.68, a temperature of 28.90 °C, and a salinity of 9.85 g L−1. With regard to Cr(VI) reduction mediated by L. cavernae CR-2, enhancement in efficiency was observed in the presence of Cu2+ and Ca2+, while significant inhibition in the reduction capacity occurred upon exposure to Mg2+, Ba2+, Ni2+, Pb2+, or Cd2+. Moreover, L. cavernae CR-2 tends to use glucose as an electron donor for the reduction of Cr(VI). Results of cell fraction separation and degeneration indicated that the Cr(VI) removal was primarily due to the reduction of Cr(VI) via chromium reductase in the cytoplasm. In addition, bioanalysis of L. cavernae CR-2 by SEM-EDS and TEM-EDS suggested that Cr was distributed both on the surface and in the cell cytoplasm. FT-IR analyses established that multiple functional groups (hydroxyl, carbonyl, amide, amino, and aldehyde groups) participated in the Cr(VI) biosorption on the cell surface. XPS and HPLC also showed that the Cr(III) end-products could be present as Cr(III) hydroxides or as organic–Cr(III) complexes. This study yields insights into the Cr(VI) bioreduction mechanism of L. cavernae CR-2.

Dynamic Behavior of Pb(II) and Cr(III) Biosorption onto Dead Anaerobic Biomass in Fixed-Bed Column, Single and Binary Systems

The biosorption of lead (II) and chromium (III) onto dead anaerobic biomass (DAB) in single and binary systems has been studied using fixed bed adsorber. A general rate multi- component model (GRM) has been utilized to predict the fixed bed breakthrough curves for single and dual- component system. This model considers both external and internal mass transfer resistances as well as axial dispersion with non-liner multi-component isotherm (Langmuir model). The effects of important parameters, such as flow rate, initial concentration and bed height on the behavior of breakthrough curves have been studied. The equilibrium isotherm model parameters such as maximum uptake capacities for lead (II) and chromium (III) were found to be 35.12 and 23.84 mg g-1 respectively. While pore diffusion coefficients (Dp) were obtained to be 7.23×10-11 and 3.15×10-11 m2 s-1 for lead (II) and chromium (III) respectively from batch experiments. The results show that the general rate model was found correct for describing the biosorption process of the dynamic behavior of the DAB adsorber column.

Biomass application as a sorbent for adsorption of heavy metals from aqueous solutions

The increase of the population and the industrial development, lead to enormous environmental pollution. Various types of waste containing heavy metals are produced and discharged into water resources. Heavy metals are considered to be the main source of contamination that causes serious environmental problems. The polluted water becomes unusable and threatens the human health and the ecosystem. Toxicity and non-biodegradability of heavy metals, as well as their tendency to accumulate in soils, water resources and living organisms, makes them significant environmental pollutants. Removing heavy metal ions from water resources has been a challenge for a long time. Modern eco-process engineering emphasizes the need for appropriate and sophisticated methods for the natural and wastewater treatment, regardless of the geogenic or anthropogenic origin of the source of pollution. The most commonly used methods for elimination of heavy metals from aqueous solutions are: chemical deposition, membrane processes, electrodialysis and adsorption. Most of these methods are significantly expensive when treating large amounts of water, ineffective at low concentrations of metals, and produce large amounts of other toxic products that require adequate removal and disposal. Among these proposed processes, adsorption is the most commonly used and is considered to be an effective, efficient and economical method for water purification. The sustainable development of separation processes is focused on development of modern, bioseparation techniques for elimination of toxic metals from wastewater using unconventional sorbents with low commercial cost. Bisorption is an environmentally friendly alternative method that has advantages over conventional methods. Large quantities of natural waste materials, such as agro-waste and food industry by-products, can be applied as a potential biosorbents for the removal of heavy metals. In order to increase their adsorption capacity, biosorbents can be physically or chemically modified. Modelling and optimization of the process of biosorption of heavy metals (Mn(II), Fe(II), Ni(II), Cr(VI) and Pb(II)) from water resources through application of natural and modified biosorbents of domestic origin, has been performed in the frame of this work, as an alternative bioseparation technique. From theexamined potential biosorbents, rice husks and peanut husks, as well as their modified forms, showed the best biosorption affinity for the analyzed heavy metals. On the efficiency of removal of heavy metals from aqueous solutions, the influence of the following operating parameters has been investigated: pH value, initial adsorbate concentration and biosorption time. This work contains a detailed literary review, optimal biomass selection, characterization of the used natural and modified biosorbents.Modeling and analysis of the equilibrium, kinetics and dynamics of the investigated systems, was aslo conducted, using sophisticated computing tools and process simulators.

Hybrid biosorbents from exopolymeric substances immobilized in Ca-alginate and their biosorption mechanisms in single and multi-metal systems

ABSTRACT This study developed a hybrid biosorbent consisting of exopolymeric substances (EPS) from Bacillus cereus immobilized in the gelling agent Ca-alginate. Metal removal tests revealed that the hybrid EPS beads showed significantly higher metal removal compared to plain alginate beads. This higher removal efficacy in hybrid biosorbents was attributed to the increased number of functional groups detected via FTIR analysis. Hybrid EPS beads bind metals via the formation of strong covalent bonds (chemisorption), rather than through weak van der Waals forces (physisorption), complying with the pseudo-second order model. This was consistent in both single and multi-metal systems. For adsorption isotherm, metal removal (pH 5, 25ºC, 120 rpm) by hybrid biosorbents in single metal systems fits the Langmuir isotherm (monolayer adsorption). In multi-metal systems, however, the removal of Zn and Cd demonstrated a better fit to the Freundlich isotherm (multilayer adsorption) compared to the typical Langmuir isotherm (for Cu, Pb and Cr). The isotherm models indicated that the maximum biosorption capacity for Cu, Pb, Zn, Cd and Cr was at 34.97, 156.24, 19.19, 11.66 and 38.61 mg g−1, respectively. The hybrid EPS beads are superior for the biosorption of Cu, Pb and Cr compared to existing biosorbents.

Comparison of biosorption efficiency for hexavalent chromium remediation in synthetic wastewater using unmodified and chemically modified chicken feathers

The aim of the present study was to compare the effectiveness of raw chicken feathers (RCFs), NaOH and ethylenediamine-modified chicken feathers (MCFs), and xanthate-modified chicken feathers (XMCFs), treated with both NaOH, ethylenediamine, and carbon disulfide. The physicochemical characteristics of the biosorbents were analyzed using attenuated total reflection Fourier transform infrared spectrophotometry (ATR-FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), adsorption of N2 at −196°C and point of zero charge determination (pHpzc). The biosorption of Cr(VI) using MCFs and XMCFs was evaluated through various parameters, namely, pH, biosorbent amount, and contact time in batch experiments. The results showed a significant increase in the biosorption capacities of MCFs (90.90 mg/g) and XMCFs (100 mg/g) compared to RCFs (52.63 mg/g). The batch adsorption experiments indicated that the optimal conditions for biosorption were pH 2.0, with an equilibrium contact time of 90 min for RCFs, and 60 min for both MCFs and XMCFs. The optimal biosorbent concentrations were 16 g L−1 for RCFs and 12 g L−1 for both MCFs and XMCFs. The biosorption behavior was well described by the Langmuir isotherm and pseudo-second-order kinetic models. The thermodynamic parameters indicated that the biosorption of Cr(VI) onto the biosorbents was a spontaneous and endothermic process. Desorption analysis was carried out using a 0.1 M NaOH solution.

Ecotoxicity study of reduced-Cr(III) generated by Cr(VI) biosorption

Hexavalent chromium (Cr(VI)) is a known carcinogen in living organisms, and many studies have investigated Cr(VI) removal methods. Biosorption, one of the Cr(VI) removal methods, is dominated by chemical binding, ion exchange, physisorption, chelation and oxidation-reduction. Among these mechanisms, Cr(VI) can be removed by nonliving biomass through a redox reaction, which has been recognized as ‘adsorption-coupled reduction’. Cr(VI) is reduced to Cr(III) during biosorption, but there are no studies on the property and toxicity of the reduced-Cr(III). In this study, the harmfulness of reduced-Cr(III) was identified through assessment of mobility and toxicity in nature. Pine bark, a low-cost biomass, was used to remove Cr(VI) from aqueous solution. Reduced-Cr(III) was characterized by structural features using X-ray Absorption Near Edge Structure (XANES) spectra, mobility assessed using precipitation, adsorption and soil column test, and toxicity using radish sprouts and water flea. XANES analysis confirmed that reduced-Cr(III) has an unsymmetrical structure, and the reduced-Cr(III) showed low mobility and was virtually non-toxic, and helpful for plant growth. Our findings demonstrate that Cr(VI) biosorption technology using pine bark is a groundbreaking technology for Cr(VI) detoxification.