Biosorption of metal ions from aqueous solution and tannery effluent by Bacillus sp. FM1

Microbial Removal of Heavy Metals from Contaminated Environments Using Metal-Resistant Indigenous Strains

Contamination of soil with heavy metals has become a matter of global importance due to its impact on agriculture, environmental integrity, and therefore human health and safety. Several microbial strains isolated from soil contaminated by long-term chemical and petrochemical activities were found to manifest various levels of tolerance to Cr, Pb, and Zn, out of which Bacillus marisflavi and Trichoderma longibrachiatum exhibited above-moderate tolerance. The concentrations of target heavy metals before and after bioremediation were determined using electrochemical screen-printed electrodes (SPE) modified with different nanomaterials. The morpho-structural SEM/EDX analyses confirmed the presence of metal ions on the surface of the cell, with metal uptake being mediated by biosorption with hydroxyl, carboxyl, and amino groups as per FTIR observations. T. longibrachiatum was observed to pose a higher bioremediation potential compared to B. marisflavi, removing 87% of Cr and 67% of Zn, respectively. Conversely, B. marisflavi removed 86% of Pb from the solution, compared to 48% by T. longibrachiatum. Therefore, the fungal strain T. longibrachiatum could represent a viable option for Cr and Zn bioremediation strategies, whereas the bacterial strain B. marisflavi may be used in Pb bioremediation applications.

Effect of pretreatment of Bacillus subtilis biomass on biosorption and its real time application

The research study investigated the biosorption behavior of Pb(II) ions by treated and untreated biomass of B. subtilis. At initial biosorption conditions, the biosorption efficiency was found to be 36.75%. At the optimized experimental conditions, control biomass showed maximum biosorption efficiency of 58.04% where the biomass was treated with different chemicals. The biomass treated with formaldehyde showed the highest efficiency of 80.9% which was further optimized and attained maximum efficiency of 89.8% for Pb(II) ions. SEM (Scanning Electron Microscope) and EDX (Energy dispersive X- ray) analysis evaluates the structural and elemental changes that occurred as a result of biosorption. Functional groups that are involved in biosorption were revealed by FTIR (Fourier Transform Infrared spectroscopy). Kinetic data showed the best fit with the pseudo second-order model. Effective removal of lead ions from industrial contaminated water sources by pretreatment biomass of B. subtilis elucidates its potential use as biosorbent for metal remediation..

Novel Green Biosynthesis of 5-Fluorouracil Chromium Nanoparticles Using Harpullia pendula Extract for Treatment of Colorectal Cancer

Colorectal cancer (CRC) is the third highest major cause of morbidity and mortality worldwide. Hence, many strategies and approaches have been widely developed for cancer treatment. This work prepared and evaluated the antitumor activity of 5-Fluorouracil (5-Fu) loaded chromium nanoparticles (5-FuCrNPs). The green biosynthesis approach using Harpullia (H) pendula aqueous extract was used for CrNPs preparation, which was further loaded with 5-Fu. The prepared NPs were characterized for morphology using scanning and transmission electron microscopes (SEM and TEM). The results revealed the formation of uniform, mono-dispersive, and highly stable CrNPs with a mean size of 23 nm. Encapsulation of 5-Fu over CrNPs, with a higher drug loading efficiency, was successful with a mean size of 29 nm being produced. In addition, Fourier transform infrared (FTIR) and X-ray diffraction pattern (XRD) were also used for the investigation. The drug 5-Fu was adsorbed on the surface of biosynthesized CrNPs in order to overcome its clinical resistance and increase its activity against CRC cells. Box–Behnken Design (BBD) and response surface methodology (RSM) were used to characterize and optimize the formulation factors (5-Fu concentration, CrNP weight, and temperature). Furthermore, the antitumor activity of the prepared 5-FuCrNPs was tested against CRC cells (CACO-2). This in vitro antitumor study demonstrated that 5-Fu-loaded CrNPs markedly decreased the IC50 of 5-Fu and exerted more cytotoxicity at nearly all concentrations than 5-Fu alone. In conclusion, 5-FuCrNPs is a promising drug delivery system for the effective treatment of CRC.

Current and Emerging Adsorbent Technologies for Wastewater Treatment: Trends, Limitations, and Environmental Implications

Wastewater generation and treatment is an ever-increasing concern in the current century due to increased urbanization and industrialization. To tackle the situation of increasing environmental hazards, numerous wastewater treatment approaches are used—i.e., physical, chemical, and biological (primary to tertiary treatment) methods. Various treatment techniques being used have the risks of producing secondary pollutants. The most promising technique is the use of different materials as adsorbents that have a higher efficacy in treating wastewater, with a minimal production of secondary pollutants. Biosorption is a key process that is highly efficient and cost-effective. This method majorly uses the adsorption process/mechanism for toxicant removal from wastewater. This review elaborates the major agricultural and non-agricultural materials-based sorbents that have been used with their possible mechanisms of pollutant removal. Moreover, this creates a better understanding of how the efficacy of these sorbents can be enhanced by modification or treatments with other substances. This review also explains the re-usability and mechanisms of the used adsorbents and/or their disposal in a safe and environmentally friendly way, along with highlighting the major research gaps and potential future research directions. Additionally, the cost benefit ratio of adsorbents is elucidated.

Characterization of the copper resistance mechanism and bioremediation potential of an Acinetobacter calcoaceticus strain isolated from copper mine sludge

Bioremediation is one of the most effective ways for removal of heavy metals and restoration of contaminated sites. This study investigated the copper (Cu) resistance mechanism and bioremediation potential of an Acinetobacter calcoaceticus strain KW3 isolated from sludge of Cu mine. The effect of Cu concentrations on the bacterial growth, biomass, and adsorption capacity, as well as the effect of contact time on the adsorption process was evaluated in a batch biosorption test. The strain exhibited strong tolerance of Cu, and the minimal inhibitory concentration was around 400 mg Cu²⁺ L^-1, at which the maximum adsorption capacity was 14.1 mg g^-1 dry cell mass. Cell walls and intracellular soluble components adsorbed 51.2% and 46.6% of Cu²⁺, respectively, suggesting that the strain not only adsorbed Cu²⁺ on the surface but also metastasized ions into cells. The adsorption and kinetic data were well fitted with Freundlich isotherm and Pseudo-second-order models, suggesting that cell surface had a high affinity for Cu²⁺ and the chemisorption could be the main adsorption mechanism. Scanning electron microscope and Fourier transform infrared spectroscopy analysis revealed that hydroxyl, carboxylic, amide, sulfate, and phosphate on cell walls might be involved in the biosorption process. Two-dimensional gel electrophoresis and MALDI-TOF/TOF mass spectrometry revealed that some oxidoreductases, in particular Cu resistance protein A (CopA) expression levels, were upregulated. Antioxidant defense and P_1B-type ATPases CopA efflux might play a crucial role in maintaining cellular homeostasis and intracellular detoxification. To our knowledge, this is the first time that Cu resistance mechanisms, especially intracellular enzymatic mechanisms, were identified in an A. calcoaceticus KW3 strain.

A comprehensive study on the bacterial biosorption of heavy metals: materials, performances, mechanisms, and mathematical modellings

Discharges of waste containing heavy metals (HMs) have been a challenging problem for years because of their adverse effects in the environment. This article provides a comprehensive review of recent findings on bacterial biosorption and their performances for sequestration of HMs. It highlights the significance of HM removal and presents a brief overview on bacterial functionality and biosorption technology. It also discusses the achievements towards utilisation of bacterial biomass with biosorption of HMs from aqueous solutions. This article includes different types of kinetic, equilibrium, and thermodynamic models used for HM treatments using different bacterial species, as well as biosorption mechanisms along with desorption of metal ions and regeneration of bacterial biosorbents. Its fast kinetics of metal biosorption and desorption, low operational cost, and no production of toxic by-products provide attraction to many researchers. Bacteria can easily be produced using inexpensive growth media or obtained as a by-product from industries. A systematic comparison of the literature for a metal-binding capacity of bacterial biomass under different conditions is provided here. The properties of the cell wall constituents such as peptidoglycan and the role of functional groups for metal sorption are presented on the basis of their biosorption potential. Many bacterial biosorbents as reported in scientific literature have a high biosorption capacity, where some are better than commercial adsorbents. Based on the reported results, it seems that most bacteria have the potential for industrial applications for detoxification of HMs.

Biosorption technology for removal of toxic metals: a review of commercial biosorbents and patents

In last decades, the biosorption process has become one of the main alternative treatment technologies for the removal of pollutants from dilute aqueous solution. Among these pollutants, toxic metals have drawn attention due to their negative effects in human body and food chain. Even though biosorption is considered a cost-effective and eco-friendly technology to remove toxic metals from dilute wastewaters, there are still obstacles that restrain its commercialization. For this reason, various scientific articles and patents have been published each year to make more effective and economical this technology. This review reports an overview of past achievements, current research of biosorption studies, and future trends for the development of the biosorption as sustainable cleaner technology. Mechanisms of metal uptake, recovery and biosorbent regeneration, process design, commercial application of biosorbents, and patents registered are presented. Finally, future aspects in biosorption research and suggestions for its application will be discussed.

Acetate biostimulation as an effective treatment for cleaning up alkaline soil highly contaminated with Cr(VI)

Stimulation of microbial reduction of Cr(VI) to the less toxic and less soluble Cr(III) through electron donor addition has been regarded as a promising approach for the remediation of chromium-contaminated soil and groundwater sites. However, each site presents different challenges; local physicochemical characteristics and indigenous microbial communities influence the effectiveness of the biostimulation processes. Here, we show microcosm assays stimulation of microbial reduction of Cr(VI) in highly alkaline and saline soil samples from a long-term contaminated site in Guanajuato, Mexico. Acetate was effective promoting anaerobic microbial reduction of 15 mM of Cr(VI) in 25 days accompanied by an increase in pH from 9 to 10. Our analyses showed the presence of Halomonas, Herbaspirillum, Nesterenkonia/Arthrobacter, and Bacillus species in the soil sample collected. Moreover, from biostimulated soil samples, it was possible to isolate Halomonas spp. strains able to grow at 32 mM of Cr(VI). Additionally, we found that polluted groundwater has bacterial species different to those found in soil samples with the ability to resist and reduce chromate using acetate and yeast extract as electron donors.

Ni(II) and Cu(II) removal from aqueous solution by a heavy metal-resistance bacterium: kinetic, isotherm and mechanism studies

The potentiality of a heavy metal-resistance bacterium Acinetobacter sp. HK-1 for removing Ni(II) and Cu(II) ions from aqueous solution and the biosorption mechanism were investigated in this study. The effects of pH, contact time and Ni(II)/Cu(II) concentration on the adsorption process were evaluated and the maximum biosorption capacity of strain HK-1 was found to be 56.65 mg/g for Ni(II) and 157.2 mg/g for Cu(II), respectively. The experimental kinetic data fit well with the pseudo-second-order model (R² > 0.98) and the biosorption process was best explained by the Langmuir-Freundlich dual model (R² > 0.97). The morphologies of HK-1 before and after adsorption in a Ni(II)/Cu(II) supplemented system were compared using a scanning electron microscope. After adsorption, the valence state of Ni(II)/Cu(II) was not changed and the formation of nickel/copper phosphate was observed using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. The results of Fourier transform infrared spectroscopy and XPS further indicated that amine, phosphate and carboxyl groups were involved in the biosorption process. Cu(II) biosorption by Acinetobacter sp. was firstly reported. Based on the above results, it can be concluded that Acinetobacter sp. HK-1 has a promising application in Ni(II) and Cu(II) ion removal from industrial wastewater.

Effect of trace metals and electron shuttle on simultaneous reduction of reactive black-5 azo dye and hexavalent chromium in liquid medium by Pseudomonas sp

This study demonstrates the role of electron shuttles and trace metals in the biotransformation of azo dye reactive black-5 and hexavalent chromium (CrVI) that are released simultaneously in tannery effluent. Previously isolated bacterial strain Pseudomonas putida KI was used for the simultaneous reduction of the dye (100 mg L(-1)) and CrVI (2 mg L(-1)) in a mineral salts medium (MSM). Among various trace metals, only Cu(II) had a stimulating effect on the bacterial-mediated reduction process. Application of electron shuttles such as hydroquinone and uric acid at a low concentration (1mM) had a positive effect on the reduction process and caused simultaneous reduction of 100% dye and 97% CrVI in 12-18 h. Mannitol, EDTA and sodium benzoate at all concentrations (ranging from 1 to 9 mM) showed an inhibitory effect on the reduction of reactive black-5 and CrVI. An inverse linear relationship between the velocity of reaction (V) and the concentration [S] of electron shuttles was observed. The results imply that both types and concentration of an electron shuttle and trace metals can affect the simultaneous reduction of reactive black-5 and CrVI.

Is biosorption suitable for decontamination of metal-bearing wastewaters? A critical review on the state-of-the-art of biosorption processes and future directions

For the past few decades, biosorption has been widely investigated for the removal of different contaminants in aqueous media. A number of biomasses of different genre have been identified to possess good biosorption capacity. Insights into biosorption mechanisms have been provided by various researchers in order to develop a fundamental scientific understanding of the biosorption process. However, biosorption has not been employed widely for its large-scale commercial applications. The key factors that affect the growth and evolution of biosorption as a practical technology for decontamination of wastewaters include, (1) lack of investigations on multi-component solutions and wastewaters with complex matrix effects, (2) incomplete understanding of physico-chemical characteristics of biomasses of different types, (3) lack of studies to improve the performance of biosorbents through surface functionalization, and (4) non-integration of biosorption in wastewater/water treatment plants. This critical review aims to identify and discuss the practical limitations of biosorption and provide future research directions to make biosorption a technologically viable process with emphasis on selection and modification of biomasses to suit desired treatment applications, identify appropriate operation modes for large-scale applications of biosorption, and perform techno-economic evaluation of overall biosorption processes.

Bioremoval of heavy metals by bacterial biomass

Heavy metals are among the most common pollutants found in the environment. Health problems due to the heavy metal pollution become a major concern throughout the world, and therefore, various treatment technologies such as reverse osmosis, ion exchange, solvent extraction, chemical precipitation, and adsorption are adopted to reduce or eliminate their concentration in the environment. Biosorption is a cost-effective and environmental friendly technique, and it can be used for detoxification of heavy metals in industrial effluents as an alternative treatment technology. Biosorption characteristics of various bacterial species are reviewed here with respect to the results reported so far. The role of physical, chemical, and biological modification of bacterial cells for heavy metal removal is presented. The paper evaluates the different kinetic, equilibrium, and thermodynamic models used in bacterial sorption of heavy metals. Biomass characterization and sorption mechanisms as well as elution of metal ions and regeneration of biomass are also discussed.