Removal of hexavalent chromium from water by adsorption on mosambi (Citrus limetta) peel

Central composite design-assisted visual and non-invasive detection of sertraline by sweet lemon waste-derived core-shell AuNPs@CDs

This study reports a fast and visual detection method of antidepressant sertraline (SRT) drug by the core-shell AuNPs@CDs as the nanoprobes. The CDs has been eco-friendly synthesized from sweet lemon wastes to directly reduce Au+ to AuNPs without any external photoirradiation process or additional reductants. Optimizing key variables that impact the sensing process has been done using the central composite design (CCD) approach to simulate the assay condition before the analysis. Adding SRT with different concentrations to the nanoprobes under mildly acidic conditions presents an absorbance peak at 560 nm with purple color tonalities that differ from the behavior of alone nanoprobes (530 nm, pink color). The obtained absorption change is linearly proportional to the increase of SRT concentration from 1 μM to 35 μM with a limit of detection (LOD) value of 100 nM. The color changes with a vivid tonality from pink and purple to violet as the colorful fingerprint patterns are readily traceable by the naked eye, allowing the visual assay of SRT. The greenness of the developed approach is well evaluated by some international indexes including the complimentary green analytical procedure (ComplexGAPI) and also, the analytical greenness (AGREE) indexes. The proposed waste-derived nanoprobes based on the eco-friendly procedure not only conduct quantitative and qualitative non-invasive analysis of SRT by the naked eye but also, may widen for other applications in various fields.

Comprehensive distribution characteristics and factors affecting the migration of chromium in a typical chromium slag-contaminated site with a long history in China

The contamination of abandoned chromium slag-contaminated sites poses serious threats to human health and the environment. Therefore, improving the understanding of their distribution characteristics and health risks by multiple information is necessary. This study explored the distribution, accumulation characteristic, and the role in the migration process of chromium. The results showed that the contents of total Cr and Cr (VI) ranged from 12.00 to 7400.00 mg/kg, and 0.25 to 2160.00 mg/kg, respectively. The average contents of both total Cr and Cr (VI) reached the highest value at the depth of 7-9 m, where the silt layer retaining total Cr and Cr (VI) was. The spatial distribution analysis revealed that the total contamination area percentages of total Cr and Cr (VI) reached 7.87% and 90.02% in the mixed fill layer, and reduced to 1.21% and 34.53% in the silty layer, and the same heavily polluted areas were located in the open chromium residue storage. Soil pH and moisture content were the major factors controlling the migration of total Cr and Cr(VI) in soils. Results of probabilistic health risk assessment revealed that carcinogenic risk was negligible for adults and children, and the sensitive analysis implied that the content of Cr(VI) was the predominant contributor to carcinogenic risk. The combination of chemical reduction and microbial remediation could be the feasible remediation strategy for soil Cr(VI) pollution. Overall, this study provides scientific information into the chromium post-remediation and pollution management for various similar chromium-contaminated sites.

A critical review on the separation of heavy metal(loid)s from the contaminated water using various agricultural wastes

Wastewater contamination with heavy metal(loids)s has become a worldwide environmental and public health problem due to their toxic and non-degradable nature. Different methods and technologies have been applied for water/wastewater treatment to mitigate heavy metal(loid)-induced toxicity threat to humans. Among various treatment methods, adsorption is considered the most attractive method because of its high ability and efficiency to remove contaminants from wastewater. Agricultural waste-based adsorbents have gained great attention because of high efficiency to heavy metal(loids)s removal from contaminated water. Chemically modified biosorbents can significantly enhance the stability and adsorption ability of the sorbents. The two mathematical models of sorption, Freundlich and Langmuir isotherm models, have mostly been studied. In kinetic modeling, pseudo-second-order model proved better in most of the studies compared to pseudo-first-order model. The ion exchange and electrostatic attraction are the main mechanisms for adsorption of heavy metal(loid)s on biosorbents. The regeneration has allowed various biosorbents to be recycled and reused up to 4-5 time. Most effective eluents used for regeneration are dilute acids. For practical perspective, biosorbent removal efficiency has been elucidated using various types of wastewater and economic analysis studies. Economic analysis of adsorption process using agricultural waste-based biosorbents proved this approach cheaper compared to traditional commercial adsorbents, such as chemically activated carbon. The review also highlights key research gaps to advance the scope and application of waste peels for the remediation of heavy metal(loid)s-contaminated wastewater.

Ag2O@UiO-66 new thin film as p-n heterojunction: permanent photoreduction of hexavalent Cr

The new nanosphere Ag2O@UiO-66 thin-film was synthesized on a stainless steel mesh surface via an electrophoretic deposition method, and is used as an effective and low-cost photocatalyst using visible light. The synthesized nanocomposite was used to perform photo-reduction of Cr(vi) ions under white light irradiation. The best removal rate (72% after 15 minutes) was obtained by the film with 0.034 grams of deposited composite having relative percentages of Ag2O : UiO-66 of 70 : 30. The interesting obtained results confirm that the p-n heterojunction of the composite is the main cause of the desired charge separation and the photoreduction speed increase. In the following, the resulting compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmittance electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy diffraction X-ray spectroscopy (EDAX) and the Brunauer, Emmett, and Teller (BET) method. Scavenging studies performed in the presence of familiar scavengers confirmed that superoxide radicals (˙O2-) and dissolved oxygen gas have a significant role in the photocatalytic reduction process.

Improved reduction efficiency, cycling performance, and removal rate of hexavalent chromium by adding water-soluble salts

Recently, the reaction speed and cycle performance of hexavalent chromium reduction over microsized zero-valent iron (ZVI) with an Fe0 core and iron oxide (FeOx) shell structure have been improved by activating the Fe0-core electrons through electromagnetic coupling between Fe0-core electrons and charges (hexavalent chromium in solution, double-charge layers of the ZVI/solution interface). Herein, the abovementioned electromagnetic coupling was greatly increased by adding salt (CH3COONa, NaCl, NaNO3, and Na2SO4) in the hexavalent chromium solution to increase the charge response. Adding salt greatly improved the reaction speed and cycle performance of hexavalent chromium reduction. It took 8 min to reduce hexavalent chromium with CH3COONa to below the discharge standard of wastewater in the first cycle and 20 min after reducing for 20 cycles. The best apparent rate of constant value (0.416 (min)-1) is nearly four times larger than those without salts. X-ray diffraction and X-ray photoelectron spectroscopy revealed the production of amorphous iron oxide shell with salt. The salt improves the hexavalent chromium reduction speed and cycle performance and impedes the Fe0-core-electron transfer via the produced Fe2O3, resulting in existence of an optimized salt dosage. This work aims to provide an effective route for enhancing the removal efficiency and cycle performance of heavy-metal-ion reduction via Fe0. And this work also proposes a novel viewpoint that adding salt in waste water would increase the electromagnetic coupling between the charges in solution and Fe0-core electrons which could finally activate the redox reaction.

Reduction of hexavalent chromium using Bacillus safensis isolated from an abandoned mine

The present work focused on the isolation of a bacterial strain multi-resistant to heavy metals with a high potential for reducing hexavalent chromium (Cr(VI)) and studied its Cr(VI) removal performance in immobilized state and the mechanisms involved. Bacterial isolate was identified as Bacillus safensis CCMM B629 (B. safensis), is able to completely reduce 50, 100 and 200 mg/L of Cr(VI) after 24, 48 and 120 h, respectively under optimized conditions of pH 7 and 30°C. The coexistence of nitrates, cadmium and mercury inhibits reduction, while copper and iron significantly improve removal efficiencies. Additionally, the presence of electron donors such as glycerol, glucose and citrate significantly increases bioreduction rate. Cells immobilized in alginate beads successfully reduced Cr(VI) compared to free cells, showing the performance of biobeads in Cr(VI) reduction. Membrane fraction exhibited highest rate of Cr(VI) reduction (65%) compared to other cellular components, indicating that Cr(VI) reduction occurred primarily in cell membrane. Further characterization of Cr(VI) removal by B. safensis cells using scanning electron microscopy and energy-dispersive X-ray (SEM-EDX) analysis showed its ability to reduce and adsorb Cr(VI), confirming that hexavalent chromium was taken up successfully on bacterial cell surfaces. Based on Fourier transform infrared spectroscopy analysis (FTIR), hydroxyl, carboxyl, amide, and phosphoryl functional groups participated in combination with Cr(III). In conclusion, B. safensis is a bacterium with great potential for Cr(VI) removal, and it is a promising and competitive strain for use in bioremediation of Cr(VI) contaminated industrial effluents.

Preparation and evaluation of celite decorated iron nanoparticles for the sequestration performance of hexavalent chromium from aqueous solution

The increasing usage of an important heavy metal chromium for industrial purposes, such as metallurgy, electroplating, leather tanning, and other fields, has contributed to an augmented level of hexavalent chromium (Cr(VI)) in watercourses negatively impacting the ecosystems and significantly making Cr(VI) pollution a serious environmental issue. In this regard, iron nanoparticles exhibited great reactivity in remediation of Cr(VI)-polluted waters and soils, but, the persistence and dispersion of the raw iron should be improved. Herein, this article utilized an environment-friendly celite as a modifying reagent and described the preparation of a novel composites namaly celite decorated iron nanoparticles (C-Fe⁰) and evaluation of C-Fe⁰ for the sequestration performance of Cr(VI) from aqueous solution. The results indicated that initial Cr(VI) concentration, adsorbent dosage, and especially solution pH are all critical factors to control C-Fe⁰ performance in Cr(VI) sequestration. We demonstrated that C-Fe⁰ could achieve a high Cr(VI) sequestration efficiency with an optimized adsorbent dosage. Fitness of the pseudo-second-order kinetics model with data indicated that adsorption was the rate-controlling step and chemical interaction controlled Cr(VI) sequestration on C-Fe⁰. The adsorption isotherm of Cr(VI) could be the best depicted by Langmuir model with a monolayer adsorption. The underlying sequestration path of Cr(VI) by C-Fe⁰ was then put forward, and the combined effect of adsorption and reduction implied the potentials of C-Fe⁰ in Cr(VI) removal.

Removal of arsenic from semiarid area groundwater using a biosorbent from watermelon peel waste

Groundwater is one of the most important reservoirs in semi-arid and arid zones of the world, particularly in Mexico. The aims of this work were to produce a biosorbent from watermelon peel waste and a biosorbent with citric acid treatment and to evaluate both biosorbents with different concentrations of arsenic in groundwater. The biosorbents were produced with watermelon peel residues, which were observed by SEM microscopy to evaluate their physical morphology. Its removal potential was tested at concentrations of 0, 1, 13, 22, and 65 μg/L of arsenic, and both adsorption capacity and removal percentage were analyzed by final measurement obtained by atomic absorption spectrometry. The pH was measured throughout the experimentation maintaining ranges between 5.5 and 7.5. The biosorbent without treatment presented clearer and more compact flakes. At the microscopic level, the biosorbent without treatment presented pores with a more circular shape, and the biosorbent with treatment was more polygonal, similar to a honeycomb. The highest removal percentage was 99.99%, for both treatments at 4 h. The biosorbent without treatment at 4 h with arsenic concentrations of 65 μg/L presented the highest adsorption capacity (2.42 μg/g). It is concluded that watermelon peel biosorbent is a material that has the potential to remove arsenic from groundwater. This type of biosorbent is effective to remove arsenic and could be used in the field, however, it still needs to be optimized to convert it into a material completely suitable for large-scale use.

Simultaneous removal of ternary heavy metal ions by a newly isolated Microbacterium paraoxydans strain VSVM IIT(BHU) from coal washery effluent

In the present work, the removal of Cr (VI), Cd (II) and Pb (II) at 50 mg/L of each metal ion concentration was investigated by Microbacterium paraoxydans strain VSVM IIT(BHU). The heavy metal binding on the bacterial cell surface was confirmed through X-ray photoelectron spectroscopy and energy dispersive X-ray. X-ray photoelectron spectroscopy analysis also confirmed the reduction of Cr (VI) to Cr (III). Heavy metal removal dynamics was investigated by evaluating dimensionless, and the value of N_k (9.49 × 10^-3, 9.92 × 10^-3 and 1.23 × 10^-2 for Cr (VI), Cd (II) and Pb (II) ions) indicated that the removal of heavy metals by bacterial isolate was mixed diffusion and transfer controlled. It was found that both the experimental and predicted values for isolated bacterial strain coincided with each other with a good R² value in the L-M Algorithm range of 0.94-0.98 for the ternary metal ion system. The bacterial isolate presented a maximum heavy metal ion removal efficiency of 91.62% Cr (VI), 89.29% Pb (II), and 83.29% Cd (II) at 50 mg/L.

Citrus limetta fruit waste management by liquefaction using hydrogen-donor solvent

The liquefaction of Citrus limetta fruit waste (both pulp and peel) in a hydrogen-donor solvent has not been reported in the literature and authors considered the same as the objective of this work. Thus, results on waste management of this potential fruit wastes by liquefaction in hydrogen-donor methanol solvent at 260 °C temperature, residence time of 30 min, and 1 : 2, 1 : 3 and 1 : 4 biomass-to-solvent ratios were reported in this work. The aim was to achieve biofuels of high quantity and quality from this waste, which would otherwise be disposed of without any value addition. A maximum of 12.5 wt% of biocrude yield was found from Citrus limetta peel biomass, which was higher than that from the thermochemical conversion of other citrus fruit waste biomasses. Biocrude having higher heating value (HHV) of 26.76 MJ kg-1 from Citrus limetta pulp, when the feed biomass pulp-to-solvent ratio was 1 : 4, found to be the best outcome of this study. Biocrude and biochar have also been extremely characterized using several advanced techniques such as Gas Chromatography Mass Spectrometry (GC-MS), Fourier Transform Infrared Spectroscopy (FTIR), and Field Emission Scanning Electron Microscopy (FESEM), etc. Finally, the novelty of this work is not only obtaining higher yield of biocrude but also better HHV compared to other similar studies in the literature.

Removal of car battery heavy metals from wastewater by activated carbons: a brief review

Spent automobile batteries are one of the most significant secondary sources of harmful heavy metals for the environment. After being incorporated into the aquatic ecosystems, these metals disseminate to various plants, microorganisms, and the human body and cause multiple adverse effects. Activated carbons (ACs) have long been used as an effective adsorbent for different heavy metals in wastewater treatment processes. Although numerous research works have been published to date on this topic, they are scattered in the literature. In this review, we have assembled these works and provided an extensive overview of the application of ACs for treating spent car battery heavy metals (CBHMs) from aquatic systems. The preparation of ACs from different precursor materials, their application in the adsorption of CBHMs, the adsorption mechanism, kinetics, adsorption isotherms and various parameters that may affect the adsorption processes have been discussed in detail. A brief comparative analysis of the adsorption performances of ACs prepared from different precursor materials is also provided. Finally, recommendations for future research works are also offered.

Removal of lead and chromium from solution by organic peels: effect of particle size and bio-adsorbent

A variety of organic wastes can be used in innovative methods to treat water pollution through the adsorption process. In this work, we evaluated the effect of particle size (500–2000, 250–500, and less than 250 μm) and bio-adsorbent (orange, potato, and passion fruit peels) on the removal of lead and chromium from solution. The size and type of peels affected the capacity to adsorb metal ions (p < 0.05). Passion fruit peel had the highest metal adsorption, followed by orange and potato, since the cation exchange capacity (217.70 ± 39.57 cmol (+) kg⁻¹) and the specific surface area (141.10–1095.29 cm² g⁻¹) were higher in the passion fruit rind. The size of the adsorbent did not affect the organic matter, ash, exchange capacity, surface chemistry, or pH of the peels. However, these properties differed among the bio-adsorbents (p < 0.05). The Freundlich equation explained the adsorption of the metallic ions on the orange rind and of lead on the passion fruit. The linear model was the best fit for the adsorption isotherms of the metals on potato peel. The adsorption of chromium on the passion fruit had a maximum adsorption capacity of 3.3 mg g⁻¹. These results indicate that plant waste materials, especially passion fruit peel, have the potential as feasible and low-cost adsorbents in pilot studies for the treatment of polluted water.

Removal of inorganic toxic contaminants from wastewater using sustainable biomass: A review

Lignocellulosic biomass is most abundant, ecofriendly and sustainable material on this green planet which has received great attention due to exhaustion of petroleum reserves and various environmental complications. Due to its abundance and sustainability, it has been opted in number of advanced applications i.e. synthesis of green chemicals, biofuels, paper, packaging, biocomposite and for discharge of toxic contaminants from wastewaters. Utilization of sustainable biomass for removal of toxic pollutants from wastewater is robust technique due to its low-cost and easy availability. In this review, we have summarized removal of inorganic pollutants by sustainable lignocellulosic biomass in their natural as well as in chemically functionalized form. Various techniques for modification of sustainable biomass have been discussed and it was found that modified biomass showed better biosorption ability as compared to natural biomass. We conclude that modified biomass biosorbents are useful for removal of toxic inorganic pollutants to deficient levels. Several modification strategies can improve the qualities of biosorbent, however grafting is the most successful among them, as demonstrated in this work. The numerous grafting methods using a free radical grafting process are also summarized in this review article. This review also gathers studies comparing sorption capabilities with and without modification using modified and unmodified biosorbents. Chemically modified cellulosic biomass is favoured over untreated biomass because it has a higher adsorption efficiency, which is favoured by a large number of reactive binding sites, improved ion-exchange characteristics, and more functional groups available after modification.

Research progress in the removal of heavy metals by modified chitosan

Chitosan and its modifiers have been widely studied for their good biocompatibility and excellent adsorption properties for heavy metal ions. The synthesis and application of modified chitosan, the effects of process variables (such as pH, amount of adsorbent, temperature, contact time, etc.), adsorption kinetics, thermodynamics and the adsorption mechanism on the removal of heavy metal ions are reviewed. The purpose is to provide the latest information about chitosan as adsorbent and to promote the synthesis of modified chitosan and its application in the removal of heavy metals.

Statistical optimization for simultaneous removal of methyl red and production of fatty acid methyl esters using fresh alga Scenedesmus obliquus

Microalgae are a diverse group of microorganisms, the majority of which are photosynthetic in nature. Microalgae have different applications, the most important of which is the biological treatment of wastewater. Microalgae grow in various types of wastewater, such as wastewater polluted by Azo dyes, due to microalgae using wastewater as a culture medium, which contains many nutrients like nitrogen, phosphate, and carbon sources. Microalgae grow in various types of wastewater, such as wastewater polluted by Azo dyes, due to microalgae using wastewater as a culture medium, which contains many nutrients like nitrogen, phosphate, and carbon sources. So, microalgae are used for bioremediation of wastewater due to the efficiency of growing in wastewater and for the high production of lipids followed by trans-esterification to biodiesel. Face-centered central composite design (FCCCD) was used to determine the factors that have the most significant impact on the simultaneous decolorization of methyl red and lipid production by the fresh green alga Scenedesmus obliquus. The predicted results indicated that the alga decolorized 70.15% methyl red and produced 20.91% lipids by using 1 g/L nitrogen, an incubation time of 10 days, a pH of 8, and the concentration of methyl red is 17.65 mg/L. The dry biomasses of S. obliquus were also examined by SEM and FTIR before and after treatment with methyl red. SEM and FTIR showed that the properties of dry S. obliquus were altered after the biosorption of methyl red. According to GC-MS analysis of hexane extracts of S. obliquus, the lipid profile differed before and after methyl red decolorization. The results proved that it is possible to use S. obliquus to remove dyes and produce renewable fuels such as biodiesel. The novelty of this study is that this is the first time in which the effect of nitrogen concentrations in the medium used for algal growth on the removal of dye has been studied.

Appealing Renewable Materials in Green Chemistry

In just a few years, chemists have significantly changed their approach to the synthesis of organic molecules in the laboratory and industry. Researchers are encouraged to approach “greener” reagents, solvents, and methodologies, to go hand in hand with the world’s environmental matter, such as water, soil, and air pollution. The employment of plant and animal derivates that are commonly regarded as “waste material” has paved the way for the development of new green strategies. In this review, the most important innovations in this field have been highlighted, paying due attention to those materials that have played a crucial role in organic reactions: wool, silk, and feather. Moreover, we decided to focus on the other most important supports and catalysts in green syntheses, such as proteins and their derivates. Different materials have shown prominent activity in the adsorption of metals and organic dyes, which has constituted a relevant scope in the last two decades. We intend to furnish a complete screening of the application given to these materials and contribute to their potential future utilization.

A systematic review on adsorptive removal of hexavalent chromium from aqueous solutions: Recent advances

The contamination of natural resources by hexavalent chromium (Cr(VI)) originating from natural and anthropogenic activities is a serious environmental concern. Although many articles on chromium remediation have been published, a comprehensive understanding of the mechanisms involved in remediation with different sorbents is not yet available. In this systematic review, the performance and applicability of several adsorptive materials for Cr(VI) removal from aqueous media are discussed, along with a detailed analysis of the mechanisms involved. Statistical analysis is applied to compare the efficacies of different adsorbents, while a similar approach is used to determine the effects of sorbent properties and experimental conditions on the adsorption capacity. A detailed analysis of the factors involved in fixed-bed column studies is also presented. A suitable desorption approach to the regeneration of the spent adsorbent and its adsorption performance in reuse is also examined. Among the different sorbents, nanoparticles and mineral-doped biochar were found to be the most effective sorbents, while the adsorption was higher at low pH (~4.0) than that at intermediate pH (6-8). Contrary to our expectation, adsorption was high for sorbents with low specific surface areas, suggesting that the adsorption of Cr(VI) is largely influenced by the chemical properties of the sorbents. The optimum adsorption in fixed-bed column systems is obtained at a lower Cr(VI) ion concentration, a lower influent flow rate, and a higher bed height. Since most of the studies reviewed herein were merely experimental and utilized ideal conditions with the presence of a single contaminant, i.e. Cr(VI) in water, further studies on adsorption dynamics with the presence of other interfering ions are suggested. This review is promising for the further development of Cr(VI) removal strategies and closes the research gaps pertaining to their challenges.

Eco-Friendly Adsorbent from Waste of Mint: Application for the Removal of Hexavalent Chromium

A serious environmental disaster is looming on the horizon due to the indiscriminate release of heavy metals into the soil and wastewater from human industrial practices. In this study, waste mint (WM) was used to remove chromium(VI) from aqueous solution using batch experiments. The adsorbent material (WM) was characterized using scanning electron microscopy coupled with energy dispersive analysis of X-ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). The adsorption parameters optimized were as follows: pH solution (2–11), initial concentration of Cr(VI) (10–50 mg/L), adsorbent dose (0.1–10 g/L), and temperature conditions (298 K, 308 K, and 318 K). The experimental data fitted well to the fractional power kinetic model (0.97≤R2≤ 0.99) and Langmuir isotherm (R2 = 0.984) with a maximum adsorption capacity Qmax = 172.41 mg/g. The thermodynamic parameters for Cr(VI) sorption were also calculated, confirming that the adsorption process was spontaneous and accompanied by an exothermic adsorption (−4.83 ≤ ΔG ≤ −3.22 kJ/mol and ΔH = −28.93 kJ/mol). The Cr(VI) removal percentage was within the range of 41–98%, and the highest removal was noted at pH = 2. The results of the present study suggest that WM is a potential low-cost adsorbent for the removal of chromium(VI) from aqueous solutions.

Removal of Lead(II) from Synthetic Wastewater by Lavandula pubescens Decne Biosorbent: Insight into Composition–Adsorption Relationship

In this work, the widely-abundant, cheap, wild plant Lavandula pubescens Decne was evaluated as an adsorbent for removing Pb(II) ions from wastewater. The chemical composition of the plant was partially isolated and characterized by the corresponding techniques, including gas chromatography–mass spectrometry, gas liquid chromatography, and FTIR spectroscopy. The adsorption capacity of the dried plant material for Pb(II) ions increased with increasing contact time, initial ion concentration, and temperature, while it decreased with increasing adsorbent dosage. The optimum condition for Pb(II) adsorption was determined as 550 mg/L initial metal concentration, pH ≤ 7, and 90 min of contact. The best fit for Pb(II) adsorption isotherms was the linear form of the Freundlich model; however, the maximum capacity indicated by Langmuir was 91.32 mg/g. The experimental data fit better the pseudo-second-order kinetic model (R2 = 0.969), suggesting chemisorption process. Thermodynamic data revealed an endothermic, nonspontaneous, and adsorption process favored at higher concentrations.

Utilización de subproductos agroindustriales para la bioadsorción de metales pesados

La contaminación por metales pesados es un problema que afecta a los ambientes acuáticos y terrestres, y cuya principal fuente son las actividades antrópicas. Para atender este problema, la comunidad científica ha desarrollado métodos físico-químicos para la remoción de metales pesados en efluentes contaminados: sin embargo, la mayoría no son económicamente favorables, ya que presentan elevados costos de operación y mantenimiento, además de que algunos generan residuos difíciles de manejar. Sin embargo, existe un método de bajo costo, altamente eficiente y sin formación de contaminantes secundarios, denominado bioadsorción. La bioadsorción utiliza subproductos agroindustriales con el objetivo de utilizar la excesiva generación de estos residuos como bioadsorbentes, para la remoción de metales pesados en aguas residuales. La utilización de subproductos agroindustriales como bioadsorbentes ha mostrado ser una alternativa para su aprovechamiento, consecuentemente, México tiene potencial en la producción de bioadsorbentes. El objetivo de esta revisión es proporcionar información sistematizada del método de remoción de metales pesados por bioadsorción a través del uso de subproductos agroindustriales.

Inexpensive Organic Materials and Their Applications towards Heavy Metal Attenuation in Waters from Southern Peru

There is interest in using locally available, low cost organic materials to attenuate heavy metals such as Cd, Cr, Cu, Hg, Ni, Pb, and Zn found in surface waters in Peru and other developing regions. Here we mesh Spanish language publications, archived theses, and prior globally available literature to provide a tabulated synthesis of organic materials that hold promise for this application in the developing world. In total, nearly 200 materials were grouped into source categories such as algae and seashells, bacteria and fungi, terrestrial plant-derived materials, and other agricultural and processing materials. This curation was complemented by an assessment of removal potential that can serve as a resource for future studies. We also identified a subset of Peruvian materials that hold particular promise for further investigation, including seashell-based mixed media, fungal blends, lignocellulose-based substrates including sawdust, corn and rice husks, and food residuals including peels from potatoes and avocadoes. Many studies reported percent removal and/or lacked consistent protocols for solid to liquid ratios and defined aqueous concentrations, which limits direct application. However, they hold value as an initial screening methodology informed by local knowledge and insights that could enable adoption for agriculture and other non-potable water reuse applications. While underlying removal mechanisms were presumed to rely on sorptive processes, this should be confirmed in promising materials with subsequent experimentation to quantify active sites and capacities by generating sorption isotherms with a focus on environmental conditions and specific contaminated water properties (pH, temperature, ionic strength, etc.). These organics also hold promise for the pairing of sorption to indirect microbial respiratory processes such as biogenic sulfide complexation. Conversely, there is a need to quantify unwanted contaminant release that could include soluble organic matter and nutrients. In addition to local availability and treatment efficacy, social, technical, economic, and environmental applicability of those materials for large-scale application must be considered to further refine material selection.

Characteristics and long-term effects of stabilized nanoscale ferrous sulfide immobilized hexavalent chromium in soil

Based on the phenomenon of soil polluted by Hexavalent chromium (Cr(VI)), this study systematically examined the efficiency, stability and feasibility of using sodium carboxymethyl cellulose-stabilized nanoscale ferrous sulfide (CMC-nFeS) to immobilize Cr(VI) in contaminated soil. The experiments described herein showed CMC-nFeS exhibited superior dispersity and a higher antioxidative effect than nFeS alone. Batch tests indicated the nanoparticles could effectively immobilize Cr(VI) in soil. At Cr(VI) concentrations of 56.01-502.21 mg/kg, the reducing capacity of CMC-nFeS was 54.68-198.74 mg Cr(VI)/g FeS. Following treatment with CMC-nFeS, the leachabilities of Cr(VI) and Cr_total determined by the Toxicity Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP) and Physiologically Based Extraction Test (PBET) decreased significantly after 24 h and remained stable for 90 days. Column tests with water and simulated acid rain showed the injection of CMC-nFeS significantly increased the fixed Cr concentration and the procedure was environmentally friendly. Furthermore, analysis of the reaction mechanism demonstrated the best removal obtained in a neutral environment and Cr(VI) was reduced and immobilized in the form of Cr(OH)₃ and Fe_0.75Cr_0.25OOH confirmed by SEM-EDS and XPS analysis.

Kinetic and thermodynamic studies on biosorption of Cr(VI) on raw and chemically modified Datura stramonium fruit

Biosorption of Cr(VI) on sulfuric and phosphoric acid-treated Datura stramonium fruit was investigated in batch mode. The various parameters that influence the biosorption process such as Cr(VI) initial concentration, biosorbent dosage, contact time, temperature, and pH value were optimized. Both linear and non-linear regression analysis of isotherm data suggest that Langmuir isotherm model mimics the behavior of Cr(VI) ion biosorption onto Datura stramonium fruit biosorbent. The maximum Cr(VI) ions adsorption capacity of 138.074 mg/g at pH 2 is achieved with phosphoric acid treated Datura stramonium (PDSF). The kinetics of adsorption process is well described by pseudo-second-order model with high R² and low χ² value. The estimated activation energy of < 8 kJ/mol obtained for both raw and chemically modified adsorbents suggests that the adsorption occurs mainly via physisorption. Besides, thermodynamic results reveal that biosorption of Cr(VI) on both treated and untreated Datura stramonium was endothermic, spontaneous, and randomness in nature.

Application of molecular biological tools for monitoring efficiency of trichloroethylene remediation

Trichloroethylene (TCE) is one of the most ubiquitous halogenated organic compounds of concerns of carcinogens in groundwater in Taiwan. Bioremediation has been recognized as a cost-effective approach in reducing TCE concentration. Five pilot-scale wells were constructed to monitor TCE concentrations in contaminated groundwater. With injection of EOS^®, TCE was effectively degraded to 42%-93% by the end of 175 days. The biostimulation with EOS^® was useful in establishing a micro-site anaerobic but with limited contribution. Dilution of the aquifer movement also caused the TCE reduction among injection and monitoring wells. The degradability was affected by the location and the proximity from the injection well. TCE concentrations found to be negatively correlated with the associated Dehalococcoides spp. and functional genes levels. Dhc concentration of 10⁸ copies L^-1 caused the initial 40% of TCE degradation. The well with the optimal degradation owned tceA of 10⁹ cells L^-1_. T-RFLP results indicate the wells with the superior TCE degradability also performed the highest Shannon index number (means the highest diversity), which occurred on the same day that Dhc levels started to enlarge. Desulfovibrio desulfuricans and Desulfuromonas chloroethenica were predominant species identified in the T-RFLP fingerprint profile. In brief, a variety of different factors including well locations, geochemical indicators, and microbial contribution were useful to explain the site-specific optimal TCE remediation approach. The consistence among TCE degradation, Dhc growing pattern, functional gene levels, and the dynamics of the microbial community structure present the novelty of this study.

Chitosan-coated black sesame (Sesamum indicum L.) seed pulp as a novel candidate adsorbent for Cr(VI) elimination

This study evaluates the application of Cr(VI) adsorption from the prepared synthetic solution by black sesame (Sesamum indicum L.) seed pulp (BSSP) and chitosan (Cts)-coated black sesame seed pulp beads (Cts-BSSP). BSSP and Cts-BSSP were used as an adsorbent without any chemical or physical treatment to remove Cr(VI) from an aqueous medium. The results indicated that the Cr(VI) removal was pH-dependent and reached an optimum at pH 2.0. It has been observed that the percentage of adsorption increased from 62% to 95% when the amount of Cts-BSSP increased from 0.0125 g to 0.0250 g. The required adsorbent amount for the maximum removal was 0.05 g and 0.1 g for Cst-BSSP and BSSP, respectively. The contact time for the adsorption was 120 min and 90 min for BSSP and Cst-BSSP, respectively. Scanning electron microscopy and Fourier transform infrared spectroscopy were used to explore the possible adsorption mechanism for Cr(VI). The equilibrium data for the BSSP and Cts-BSSP were used with the Langmuir and Freundlich adsorption isotherm models to assess the adsorption capacity and relevant mechanism. The adsorption capacity of the Cts-BSSP for Cr(VI) is relatively high compared to BSSP. The monolayer maximum adsorption capacities for Cr(VI) ions were 31.44 and 18.32 mg/g for Cts-BSSP and BSSP, respectively.

Extraction of Natural Surfactant Saponin from Soapnut (Sapindus mukorossi) and its Utilization in the Remediation of Hexavalent Chromium from Contaminated Water

In this study optimization of extraction conditions for saponin from soapnut (Sapindus mukorossi) has been investigated. This investigation showed that a better extraction of saponin can be achieved with increasing the dielectric constant of solvent employed. The best yield was attained in a 50% v/v aqueous ethanol medium. Another objective of the present study is to assess the thermodynamics of the uptake-reduction of hexavalent chromium in contaminated water samples using saponin. Pyrene has been employed to determine the critical micellar concentration (CMC) (in the UV-vis method of determination) of saponin as a spectroscopic probe. Thus, the effectiveness of the bio-surfactant as a self-motivated adsorbent for hexavalent chromium is investigated. Several physico-chemical parameters like contact time, sorbate concentration, pH and temperature have been determined. The findings of the investigation invoked a very efficient uptake of 213.48 mg g−1 of hexavalent chromium from the contaminated water sample at a lower value of pH 2 and temperature 35°C. It is observed that the method followed a pseudo-first order kinetics, where the evaluated ΔG0 has supported the sorption as a feasible and spontaneous process. The HR-MS, FTIR, steady state Fluorescence spectroscopy, HR-TEM and UV-Vis spectroscopy have been employed for the current scientific studies.

Optimization of Cr(VI) biosorption onto Aspergillus niger using 3-level Box-Behnken design: Equilibrium, kinetic, thermodynamic and regeneration studies

Heavy metal biosorption is an efficient technology for the decontamination of metal from industrial waste water. The present study focused on exploration of Aspergillus niger towards removal of Cr(VI) from aqueous solution. The influence of different experimental parameters-initial pH, adsorbent dose, initial concentration, contact time, shaking speed, temperature, and their combined effect during Cr(VI) adsorption-was investigated by means of response surface methodology based on four factorial Box-Behnken experimental design. Optimized values of initial Cr(VI) concentration, pH, adsorbent dose, and contact time were found as 33.33 mg/L, 4.6, 1.0 g/L, and 48.45 min, respectively. A. niger showed the highest adsorption capacity 11.792 mg/g at initial pH 2.0. Equilibrium data fitted well to the Temkin and Freundlich isotherms. Cr(VI) biosorption showed Pseudo-second order rate kinetics. The activation energy of the adsorption was estimated as 2.9 × 10^-3 kJ/mol. Thermodynamics properties of the Cr(VI) biosorption was spontaneous in nature. Desorption study showed that nearly 94% of the Cr(VI) adsorbed on A. niger could be desorbed using 0.5 M EDTA.

New approach in modeling Cr(VI) sorption onto biomass from metal binary mixtures solutions

In the last decades Cr(VI) sorption equilibrium and kinetic studies have been carried out using several types of biomasses. However there are few researchers that consider all the simultaneous processes that take place during Cr(VI) sorption (i.e., sorption/reduction of Cr(VI) and simultaneous formation and binding of reduced Cr(III)) when formulating a model that describes the overall sorption process. On the other hand Cr(VI) scarcely exists alone in wastewaters, it is usually found in mixtures with divalent metals. Therefore, the simultaneous removal of Cr(VI) and divalent metals in binary mixtures and the interactive mechanism governing Cr(VI) elimination have gained more and more attention. In the present work, kinetics of Cr(VI) sorption onto exhausted coffee from Cr(VI)-Cu(II) binary mixtures has been studied in a stirred batch reactor. A model including Cr(VI) sorption and reduction, Cr(III) sorption and the effect of the presence of Cu(II) in these processes has been developed and validated. This study constitutes an important advance in modeling Cr(VI) sorption kinetics especially when chromium sorption is in part based on the sorbent capacity of reducing hexavalent chromium and a metal cation is present in the binary mixture.

A review on progress of heavy metal removal using adsorbents of microbial and plant origin

Heavy metals released into the water bodies and on land surfaces by industries are highly toxic and carcinogenic in nature. These heavy metals create serious threats to all the flora and fauna due to their bioaccumulatory and biomagnifying nature at various levels of food chain. Existing conventional technologies for heavy metal removal are witnessing a downfall due to high operational cost and generation of huge quantity of chemical sludge. Adsorption by various adsorbents appears to be a potential alternative of conventional technologies. Its low cost, high efficiency, and possibility of adsorbent regeneration for reuse and recovery of metal ions for various purposes have allured the scientists to work on this technique. The present review compiles the exhaustive information available on the utilization of bacteria, algae, fungi, endophytes, aquatic plants, and agrowastes as source of adsorbent in adsorption process for removal of heavy metals from aquatic medium. During the last few years, a lot of work has been conducted on development of adsorbents after modification with various chemical and physical techniques. Adsorption of heavy metal ions is a complex process affected by operating conditions. As evident from the literature, Langmuir and Freundlich are the most widely used isotherm models, while pseudo first and second order are popularly studied kinetic models. Further, more researches are required in continuous column system and its practical application in wastewater treatment.

Synthesis of copper–isonicotinate metal–organic frameworks simply by mixing solid reactants and investigation of their adsorptive properties for the removal of the fluorescein dye

The copper–isonicotinate metal–organic frameworks [Cu(INA)₂] (INA = isonicotinate) (MOFs) has been prepared by a highly efficient and environmentally benign technique involving mixing and heating of solid reactants without milling. The adsorption of fluorescein dye on the as-synthesised [Cu(INA)₂] was also investigated.