Surface reaction of Bacillus cereus biomass and its biosorption for lead and copper ions

Simultaneous removal of malachite green and lead from water by consortium dry-biomasses of Bacillus licheniformis AG3 and Bacillus cereus M116

Synthetic textile dye malachite green (MG) and heavy metals present in industrial wastewater are hazardous to the ecosystem. Bioremediation of dyes and heavy metals using dry-biomasses has advantages over chemical methods. This study screened an acclimatized, heavy metal-resistant, and dye-degrading Gram positive Bacillus licheniformis AG3 strain from the textile wastewater near Kolkata, West Bengal. The EDXRF analysis of this colored wastewater effluent showed 36.33 mg/L lead, significantly higher than the WHO recommendation. Previously, Bag et al. showed bioremediation of synthetic dyes using dry-biomass of Bacillus cereus M116 from an aqueous solution (Bag et al. Arch Microbiol 203(7):3811-3823, 2021). Here, a consortium of dry-biomasses of B. licheniformis AG3 and B. cereus M116 strains (1:1 w/w ratio) was prepared for the simultaneous removal of lead and MG from wastewater. Statistical optimization determines that the pH, initial concentration of contaminants, and dry-biomass concentrations are critical for bioremediation under batch procedures. Further, optimization using the response surface methodology showed that 0.01% consortium dry-biomasses eliminated a maximum of 99.35% MG and 96.01% lead (II) within 6 h. SEM-EDS and FTIR confirmed a strong surface biosorption. Furthermore, a fixed-bed biofilter column of the consortium dry-biomasses was prepared, which was able to remove 98.1% MG and 98.5% lead at the 0.5-1 mL/min flow rate. Together, this study developed a biofilter with a consortium dry biomasses of B. licheniformis AG3 and B. cereus M116 for the simultaneous removal of MG and lead from wastewater.

Innovative optimization for enhancing Pb2+ biosorption from aqueous solutions using Bacillus subtilis

Introduction

Toxic heavy metal pollution has been considered a major ecosystem pollution source. Unceasing or rare performance of Pb2+ to the surrounding environment causes damage to the kidney, nervous, and liver systems. Microbial remediation has acquired prominence in recent decades due to its high efficiency, environment-friendliness, and cost-effectiveness.

Methods

The lead biosorption by Bacillus subtilis was optimized by two successive paradigms, namely, a definitive screening design (DSD) and an artificial neural network (ANN), to maximize the sorption process.

Results

Five physicochemical variables showed a significant influence (p < 0.05) on the Pb2+ biosorption with optimal levels of pH 6.1, temperature 30°C, glucose 1.5%, yeast extract 1.7%, and MgSO4.7H2O 0.2, resulting in a 96.12% removal rate. The Pb2+ biosorption mechanism using B. subtilis biomass was investigated by performing several analyses before and after Pb2+ biosorption. The maximum Pb2+ biosorption capacity of B. subtilis was 61.8 mg/g at a 0.3 g biosorbent dose, pH 6.0, temperature 30°C, and contact time 60 min. Langmuir's isotherm and pseudo-second-order model with R2 of 0.991 and 0.999 were suitable for the biosorption data, predicting a monolayer adsorption and chemisorption mechanism, respectively.

Discussion

The outcome of the present research seems to be a first attempt to apply intelligence paradigms in the optimization of low-cost Pb2+ biosorption using B. subtilis biomass, justifying their promising application for enhancing the removal efficiency of heavy metal ions using biosorbents from contaminated aqueous systems.

Metal tolerance and biosorption of Pb ions by Bacillus cereus RMN 1 (MK521259) isolated from metal contaminated sites

Recent years, metal pollution is an alarming factor to know about protects the environmental ecosystem due to the toxic, persistent and abundant in nature. Metals are present everywhere in the biotic and abiotic samples including soil, water, and microbes. The rate of bioaccumulation and biotransformation are very high. The excess concentration of the metals causes heavy metal pollution or contamination. Due to these defects, the removal of metals using biological sources is heightened in the current research. In this current investigation, the biosorption potential ability of the metal tolerable Bacillus cereus on Pb and Cu rich environment was chosen and thoroughly monitored. The 16s rRNA of the Bacillus cereus was sequenced, and named as Bacillus cereus RMN 1 (MK521259). The various test concentration (10-60 mg/mL) of Pb and Cu was exhibited the maximum removal percentages of 85.2% and 60.2%. The result of bisorption factors exhibited, 300 mg/mL of the biosorbent potency, 60 min contact time and pH 7, and they found to be optimal to remove the maximum of Pb ion from the solution. In the regression coefficients, the Freundlich and Langmuir isotherm models were used to study the adsorption kinetics of metal ions. In addition, the isotherm model confirmed that the of B. cereus biomass medicated metal adsorption was more favourable reaction for metal degradation. With the above evidences, the results of the present investigation proved that B. cereus derived biomass was actively adsorbing the metals ions. Thus we are recommending for the implementation of effective waste water treatment.

Biosorption efficiency of nickel by various endophytic bacterial strains for removal of nickel from electroplating industry effluents: an operational study

Realising the hazardous effect of nickel on human health, microbes and plants are effectively used for bioremediation. The endophytic microorganisms have an important role in the phytoremediation of nickel using Vigna radiata. Therefore, in order to harness the potential of microbial strains, the present study was designed to examine the metal biosorption ability of endophytic bacterial strains isolated from plants growing in nickel-contaminated soil. A total of six endophytic nickel resistance bacteria were isolated from the plant Vigna radiata. The metal tolerant bacterial strains were identified following 16 S rRNA gene sequence analysis. Nickel biosorption estimation and plant growth-promoting (PGP) activities of isolated strains were performed and found high nickel biosorption efficiency of 91.3 ± 0.72% at 600 mg L^-1 using Bacillus safensis an isolated endophytic strain from Vigna radiata. Furthermore, high indole acetic acid (IAA) and exopolysaccharide (EPS) production were obtained in all the strains as compared to without nickel-containing medium used as control. Moreover, the production of high EPS suggests improved biosorption ability of isolated endophytic strains. In addition, a kinetic study was also performed to evaluate different adsorptions isotherms and support the nickel biosorption ability of endophytic strains. The treatment of nickel electroplating industrial effluent was also demonstrated by isolated endophytic strains. Among six (6) strains, B. cereus showed maximum 57.2 ± 0.62% biosorption efficiency of nickel which resulted in the removal of 1003.50 ± 0.90 mg L^-1 of nickel from the electroplating industry effluents containing initial 1791 ± 0.90 mg L^-1 of nickel. All other strains were also capable of significant nickel biosorption from electroplating industry effluents as well. Thus, isolated endophytic nickel tolerant strains can be further used at large-scale biosorption of nickel from electroplating industry effluent.

Unraveling the Underlying Heavy Metal Detoxification Mechanisms of Bacillus Species

The rise of anthropogenic activities has resulted in the increasing release of various contaminants into the environment, jeopardizing fragile ecosystems in the process. Heavy metals are one of the major pollutants that contribute to the escalating problem of environmental pollution, being primarily introduced in sensitive ecological habitats through industrial effluents, wastewater, as well as sewage of various industries. Where heavy metals like zinc, copper, manganese, and nickel serve key roles in regulating different biological processes in living systems, many heavy metals can be toxic even at low concentrations, such as mercury, arsenic, cadmium, chromium, and lead, and can accumulate in intricate food chains resulting in health concerns. Over the years, many physical and chemical methods of heavy metal removal have essentially been investigated, but their disadvantages like the generation of chemical waste, complex downstream processing, and the uneconomical cost of both methods, have rendered them inefficient,. Since then, microbial bioremediation, particularly the use of bacteria, has gained attention due to the feasibility and efficiency of using them in removing heavy metals from contaminated environments. Bacteria have several methods of processing heavy metals through general resistance mechanisms, biosorption, adsorption, and efflux mechanisms. Bacillus spp. are model Gram-positive bacteria that have been studied extensively for their biosorption abilities and molecular mechanisms that enable their survival as well as their ability to remove and detoxify heavy metals. This review aims to highlight the molecular methods of Bacillus spp. in removing various heavy metals ions from contaminated environments.

Lead metal biosorption and isotherms studies by metal-resistant Bacillus strain MRS-2 bacterium

In this study, lead (Pb) biosorption studies in aqueous solution were performed with metal-resistant Bacillus strain MRS-2 (ATCC 55674) bacterium which was previously isolated from wastewater plant. It showed minimum inhibition concentration of 300 ppm Pb on the nutrient agar plates. Pb biosorption using MRS-2 bacteria was investigated under different parameters such as pH, temperature, biomass dosage, initial Pb concentration, contact time, and type of biomass by batch experiments. Pb concentration was analyzed through Inductively coupled plasma-optical emission spectrometry. The rate of biosorption (Q) and Pb biosorption capacity (q_e ) were calculated for above mentioned parameters. It was observed that Pb precipitates by itself from the solution at pH 2 and 8 or above without bacteria and precipitation did not increase even in the presence of bacteria. The results showed that the highest biosorption rate and biosorption capacity (mg/g) were observed at pH 7, 25°C, 2-h contact time with live bacteria. The highest biosorption rate was observed at 1.5 g/L biomass dose and 5 ppm initial Pb concentration, whereas the highest Pb biosorption capacity was observed at 0.25 g/L biomass dose and 12.5 ppm initial Pb concentration. It was observed that Pb biosorption by live bacteria occurred through adsorption on cell surface. In this study, the biosorption isotherm analysis favored the Langmuir isotherm model indicating monolayer biosorption. This Bacillus strain showed higher Pb biosorption capacity than most of the previously reported Bacillus strains. In conclusion, this study indicates that the Bacillus MRS-2 strain can be used to remove Pb from industrial wastewaters in an ecofriendly approach.

Biosorption of organic dye Acridine orange from aqueous solution using dry biomass of Bacillus cereus M116

Acridine orange (AO), a basic carcinogenic fluorochrome dye, is used in the industry for staining. In this study, Gram-positive bacteria, Bacillus cereus M¹₁₆ (MTCC 5521) dry biomass was tested as an eco-friendly, easily available, and cheap biosorbent for the AO dye removal. We obtained optimum biosorption of AO at a biomass concentration of 0.25 g/L and initial dye concentrations of 50-400 mg/L at neutral to basic pH within the 300 min contact time. Kinetics analysis of the biosorption process was best fitted with the pseudo-second-order reaction type. We also performed the isotherm analysis to predict the nature of the reaction taking place, which was found to follow the Redlich Peterson isotherm model with high determination coefficients. The maximum sorption capacity was 210.46 mg/g of dry biomass. The differential FTIR spectroscopic analysis of pristine and AO-treated Bacillus cereus M¹₁₆ cells suggested the potential involvement of carbonyl, hydroxyl, and amine groups in the biosorption process. Also, the scanning electron microscopy of the cells after AO removal confirmed a gross surface alteration compared to the untreated cells. Furthermore, Response Surface Model (RSM) analysis with the three-way ANOVA test confirms statistically significant interactions between the dye concentration, pH, and temperature with the biosorption capacity (p < 0.001). Hence, the dry biomass of Bacillus cereus M¹₁₆ was found to be an effective bio-remedial for the AO removal.

Exploring of toxic Pb(II) removal by low-cost bio-adsorbent of camphor leaf forestry waste after camphor oil extraction

Camphor leaf (CL) was widely used to extract camphor oil and thus led to abundant forestry waste. In order to reduce pollution, the waste CL was used to prepare bio-adsorbent for Pb(II) removal after alkali treatment and functional modification. The effects of solution pH, initial Pb(II) concentration, contact time and solution temperature were investigated on adsorption process to evaluate the potential application in heavy metal ions' removal. It was found that the massive hydroxyl groups released and plenty of micro-pores formed after the alkali treatment of CL bio-adsorbent, which obviously increased the Pb(II) adsorption. And the adsorption performance promoted continually after further functional modification by ionized 1,2,3,4-butanetetracarboxylic acid (BTCA). The increase of pH was favourable for the adsorption even though the precipitation effect was deducted. Linear fitting method was more suitable to describe the adsorption process than nonlinear fitting method, including adsorption isotherms and adsorption kinetics research. The adsorption thermodynamics was better to be described by nonlinear fitting method due to its lower root mean square error (RMSE) value and higher R² value. Among which, the adsorption isotherm and adsorption kinetics were fitted well to Langmuir model and pseudo-second-order model, respectively. The adsorption thermodynamics was exothermic in nature and the process was spontaneous at low solution temperature. The adsorption mechanism was revealed as the combination of dominant chemical adsorption and assistant physical adsorption.

The Synthesis of PbS NPs and Biosorption of Pb(II) by Shinella Zoogloeoides PQ7 in Aqueous Conditions

Increasing heavy metal pollution in water continues to endanger human health. The genus Shinella has potential for heavy metal bioremediation but has rarely been studied. In this study, we report that Shinella zoogloeoides PQ7 turns black in the presence of lead ions. Transmission electron microscopy (TEM), Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) indicated that PbS nanoparticles (NPs) were synthesized by PQ7. Moreover, PQ7 was used as a biosorbent to remove Pb(II) from aqueous solutions. Biosorption performance was evaluated in terms of contact time, pH, biomass dosage and initial Pb(II) concentration. The equilibrium and kinetic data were consistent with the Freundlich isotherm model (R2 = 0.986) and pseudo-second-order model (R2 = 0.977), respectively. The maximum (qmax) Pb(II) adsorption reached 222.22 mg/g, which was higher than that of other bacteria reported in previous literature. SEM–EDS, XRD and Fourier transform infrared (FTIR) analyses also confirmed the adsorption of Pb(II) by the PQ7 cells. In conclusion, PQ7 is a promising strain in removing and recovering Pb(II) from wastewater.

Magnetic metal organic frameworks/graphene oxide adsorbent for the removal of U(VI) from aqueous solution

A well-defined magnetic metal organic frameworks (MOFs)/graphene oxide (Fe₃O₄@HKUST-1/GO) consisting of magnetic Fe₃O₄ nanoparticles, HKUST-1 nanocrystal and GO was synthesized through a simple and environmentally friendly approach. Characterizations of Fe₃O₄@HKUST-1/GO adsorbing U(VI) with high-resolution transmission electron microscopy suggested that the Fe₃O₄@HKUST-1/GO possessed good stability. The introduction of GO enhanced the ability of particles to uptake U(VI) from aqueous solution. The effects of solution pH, contact time and temperature on U(VI) adsorption were systematically tested by intermittent experiments. The adsorption process can be better described by the Langmuir model and the pseudo-second-order kinetic model. The results showed that the Fe₃O₄@HKUST-1/GO exhibited good adsorption capacity towards U(VI) at the initial solution pH value of 4.0 and T = 318 K. The X-ray photoelectron spectroscopy was used to analyze the U(VI) removal mechanism. This work represents the application of Fe₃O₄@HKUST-1/GO as a novel adsorbent to extract U(VI) from contaminated water.

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.

Bacterial resistance to lead: Chemical basis and environmental relevance

Natural bacterial isolates from heavily contaminated sites may evolve diverse tolerance strategies, including biosorption, efflux mechanism, and intracellular precipitation under the continually increased stress of toxic lead (Pb) from anthropogenic activities. These strategies utilize a large variety of functional groups in biological macromolecules (e.g., exopolysaccharides (EPSs) and metalloproteins) and inorganic ligands, including carboxyl, phosphate and amide groups, for capturing Pb. The amount and type of binding sites carried by biologically originated materials essentially determines their performance and potential for Pb removal and remediation. Many factors, e.g., metal ion radius, electronegativity, the shape of the cell surface sheath, temperature and pH, are thought to exert significant influences on the abovementioned interactions with Pb. Conclusively, understanding the chemical basis of Pb-binding in these bacteria can allow for the development of effective microbial Pb remediation technologies and further elucidation of Pb cycling in the environment.

Bioaccumulation of potentially toxic elements by submerged plants and biofilms: A critical review

The accumulation of potentially toxic elements (PTEs) in aquatic ecosystems has become a global concern, as PTEs may exert a wide range of toxicological impacts on aquatic organisms. Submerged plants and the microorganisms attached to their surfaces, however, have displayed great potential as a means of coping with such pollution. Therefore, it is crucial to understand the transport pathways of PTEs across sediment and organisms as well as their accumulation mechanisms in the presence of submerged plants and their biofilms. The majority of previous studies have demonstrated that submerged plants and their biofilms are indicators of PTE pollution in the aquatic environment, yet relatively little is known about PTE accumulation in epiphytic biofilms. In this review, we describe the transport pathways of PTEs in the aquatic environment in order to offer remarkable insights into bioaccumulation mechanisms in submerged plants and their biofilms. Based on the literature cited in this review, the roles of epiphytic biofilms in bioaccumulation and as an indicator of ecosystem health are discussed.

Multiple Transcriptional Mechanisms Collectively Mediate Copper Resistance in Cupriavidus gilardii CR3

Bacteria resist copper (Cu) stress by implementing several metabolic mechanisms. However, these mechanisms are not fully understood. We investigated the mechanism of Cu resistance in Cupriavidus gilardii CR3, a Cu-resistant bacterium with a fully sequenced, annotated genome. The growth of CR3 was inhibited by higher Cu concentrations (≥1.0 mM) but not by lower ones (≤0.5 mM). CR3 accumulated Cu intracellularly (ratios of intercellular to extracellular Cu were 11.6, 4.24, and 3.9 in 0.1, 0.5, and 1.5 mM Cu treatments, respectively). A comparative transcriptome analysis of CR3 respectively revealed 310 and 413 differentially expressed genes under 0.5 and 1.5 mM Cu stress, most of which were up-regulated under Cu treatment. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes functional enrichment analyses uncovered several genotype-specific biological processes related to Cu stress. Besides revealing known Cu resistance-related genes, our global transcriptomics approach indicated that sulfur metabolism, iron-sulfur cluster, and cell secretion systems are involved in mediating Cu resistance in strain CR3. These results suggest that bacteria collectively use multiple systems to cope with Cu stress. Our findings concerning the global transcriptome response to Cu stress in CR3 provide new information for understanding the intricate regulatory network of Cu homeostasis in prokaryotes.

Bioimmobilization of lead by Bacillus subtilis X3 biomass isolated from lead mine soil under promotion of multiple adsorption mechanisms

In this study, a lead-resistant bacterium, Bacillus subtilis X3, was used to prepare a lead bioadsorbent for immobilization and removal of lead in lead solution. The lead shot precipitate was analysed by scanning electron microscopy combined with energy dispersive X-ray fluorescence microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The adsorbed lead was mainly mineralized to form Pb₅(PO₄)₃OH, Pb₁₀(PO₄)₆(OH)₂ and Pb₅(PO₄)₃Cl; however, other mechanisms that can also promote the mineralization of lead should not be ignored. For example, Na⁺ and Ca²⁺ on the cell wall surface were exchanged with Pb²⁺ in solution, which confirmed that the ion-exchange process occurred before mineralization. Moreover, adsorption bridging caused by extracellular polymeric substances also accelerated the further aggregation of lead, and the biomass was encapsulated by lead gradually. Hydroxyl, carbonyl, carboxyl and amine groups were not observed in lead mineral crystals, but the complexation between lead and these groups still benefited the mineralization of lead. The valence of Pb(II) was not changed after mineralization, which indicated that the biosorption process was not a redox reaction. Finally, biosorption occurred on the outer surface of the cell, but its specific surface area was relatively small, limiting the amount and efficiency of biosorption.

Organophosphorus flame retardants and heavy metals in municipal landfill leachate treatment system in Guangzhou, China

The occurrence, distribution and removal efficiencies of organophosphorus flame retardants (OPFRs) and metals were examined in a municipal landfill leachate treatment system in Guangzhou, China. Five OPFRs and thirty-five metals were detected in wastewater samples collected at different treatment stages. ∑OPFRs was reduced from 4807.02 ng L^-1 to 103.91 ng L^-1 through the treatment system, with close to 98% removed from the dissolved phase. Tris(clorisopropyl) phosphates (TCPPs) dominated through the treatment process and accounted for over 80% and 50% of ∑OPFRs at the influent and the effluent, respectively. TCPPs were most efficiently removed (98.6%) followed by tris(2-chloroethyl) phosphate (TCEP) (96.6%) and triphenyl phosphate (TPP) (88.5%). For metals, Fe, Cr, and Rb were dominant in the raw leachate, detected at 7.55, 2.82, and 4.50 mg L^-1, respectively. Thirteen regulated heavy metals - including eight major pollutants (i.e., As. Cd, Cr, Cu, Hg, Ni, Pb, and Zn) - have been detected in all wastewater samples at sub-mg L^-1 levels. Over 99.5% removal was achieved for Cr, Ni, and Fe, and close to 95% removal efficiency was observed for Rb. For the eight major heavy metals, over 99% removal was observed; the only exception was Cu, which was removed at 89%. It was found that microfiltration/reverse osmosis was critical for the removal of OPFRs and heavy metals while the core biological treatment played a minor role towards their removal. Remobilization of Co, Cu, Fe, Hg, Mn, Ni, Sb, and Sr from the returned sludge occurred during the second denitrification, indicating the need for additional post-biological process for effective removal of both contaminants. This study highlights the critical need to develop cheap, effective treatment technologies for contaminants-laden leachate generated from open dumps and under-designed landfills.

A Novel Pb-Resistant Bacillus subtilis Bacterium Isolate for Co-Biosorption of Hazardous Sb(III) and Pb(II): Thermodynamics and Application Strategy

The present work is the first to study co-biosorption of Pb(II) and Sb(III) by a novel bacterium and its application strategy. The biosorption characteristics of Pb(II) and Sb(III) ions from aqueous solution using B. subtilis were investigated. Optimum pH, biomass dosage, contact time and temperature were determined to be 5.00, 6.00 mg/L, 45 min and 35 °C, respectively. Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) models were applied to describe the biosorption isotherm of the metal ions by B. subtilis. Results showed that Langmuir model fitted the equilibrium data of Pb(II) better than others, while biosorption of Sb(III) obeyed the Freundlich model well. The biosorption capacity of B. subtilis biomass for Pb(II) and Sb(III) ions was found to be 17.34 ± 0.14 and 2.32 ± 0.30 mg/g, respectively. Kinetic data showed the biosorption process of Pb(II) and Sb(III) ions both followed the pseudo-second-order kinetic model, with R² ranging from 0.974 to 0.999 for Pb(II) and from 0.967 to 0.979 for Sb(III). The calculated thermodynamic parameters, negative ∆G and positive ∆H and ∆S values, indicated the biosorption of Pb(II) and Sb(III) ions onto B. subtilis biomass in water was feasible, endothermic, and spontaneous. Bacterial bioleaching experiment revealed B. subtilis can increase the mobility of Pb(II) and Sb(III) in polluted soil when pH was close to 6 at low temperature. Consequently, B. subtilis, as a cheap and original bacterial material, could be a promising biomass to remove Pb or isolate Sb from industrial wastewater and to assist phytoremediation of Pb and Sb from weak acid or near neutral pH polluted soils at low temperature.

Adsorption of heavy metals on conventional and nanostructured materials for wastewater treatment purposes: A review

The problem of water pollution is of a great concern. Adsorption is one of the most efficient techniques for removing noxious heavy metals from the solvent phase. This paper presents a detailed information and review on the adsorption of noxious heavy metal ions from wastewater effluents using various adsorbents - i.e., conventional (activated carbons, zeolites, clays, biosorbents, and industrial by-products) and nanostructured (fullerenes, carbon nanotubes, graphenes). In addition to this, the efficiency of developed materials for adsorption of the heavy metals is discussed in detail along with the comparison of their maximum adsorption capacity in tabular form. A special focus is made on the perspectives of further wider applications of nanostructured adsorbents (especially, carbon nanotubes and graphenes) in wastewater treatment.

Adsorption and Desorption Characteristics of Cd2+ and Pb2+ by Micro and Nano-sized Biogenic CaCO3

The purpose of this study was to elucidate the characteristics and mechanisms of adsorption and desorption for heavy metals by micro and nano-sized biogenic CaCO3 induced by Bacillus subtilis, and the pH effect on adsorption was investigated. The results showed that the adsorption characteristics of Cd2+ and Pb2+ are well described by the Langmuir adsorption isothermal equation, and the maximum adsorption amounts for Cd2+ and Pb2+ were 94.340 and 416.667 mg/g, respectively. The maximum removal efficiencies were 97% for Cd2+, 100% for Pb2+, and the desorption rate was smaller than 3%. Further experiments revealed that the biogenic CaCO3 could maintain its high adsorption capability for heavy metals within wide pH ranges (3-8). The FTIR and XRD results showed that, after the biogenic CaCO3 adsorbed Cd2+ or Pb2+, it did not produce a new phase, which indicated that biogenic CaCO3 and heavy metal ions were governed by a physical adsorption process, and the high adsorptive capacity of biogenic CaCO3 for Cd2+ and Pb2+ were mainly attributed to its large total specific surface area. The findings could improve the state of knowledge about biogenic CaCO3 formation in the environment and its potential roles in the biogeochemical cycles of heavy metals.

Adsorption of cadmium by live and dead biomass of plant growth-promoting rhizobacteria

Plant growth-promoting rhizobacteria (PGPR) have been extensively investigated in combination remediation with plants in heavy metal contaminated soil. However, being biosorbent, few studies of live and dead cells of PGPR have been undertaken. Meanwhile, the application of live or dead biomass for the removal of heavy metals continues to be debated. Therefore, this study uses living and non-living biosorbents of Cupriavidus necator GX_5, Sphingomonas sp. GX_15, and Curtobacterium sp. GX_31 to compare their Cd(ii) adsorption capacities by SEM-EDX, FTIR, and adsorption experiments. In the present study, whether the cells were living or dead and whatever the initial Cd(ii) concentration was, removal efficiency and adsorption capacity can be arranged as GX_31 > GX_15 > GX_5 (p < 0.05). However, removal efficiency in live and dead biosorbents was quite different and it greatly affected by the initial Cd(ii) concentrations. The dead cells exhibited a higher adsorption capacity than the live cells of GX_31. Nevertheless, for GX_5 and GX_15, the loading capacity of the non-living biomass was stronger than that of the living biomass at 20 mg L⁻¹ of Cd(ii), but the capacity was similar at 100 mg L⁻¹ of Cd(ii). Minor changes of spectra were found after autoclaving and it seemed that more functional groups of the dead biosorbent were involved in Cd(ii) binding by FTIR analysis, which also illustrated that the hydroxyl, amino, amide, and carboxyl groups played an important role in complexation with Cd(ii). Based on these findings, we concluded that the dead cells were more potent for Cd(ii) remediation, especially for GX_31.

Plant growth-promoting rhizobacteria (PGPR) have been extensively investigated in combination remediation with plants in heavy metal contaminated soil.

Sorption of Cu by humic acid from the decomposition of rice straw in the absence and presence of clay minerals

The sorption of Cu on humic acid (HA) from the decomposition of rice straw in the absence (Ck-HA) and presence of montmorillonite (M-HA), kaolinite (K-HA), gibbsite (Gi-HA) and goethite (Go-HA) was investigated at pH 5.0 by using batch studies combined with isothermal titration calorimetry (ITC) and atomic force microscopy (AFM). Characterization by elemental analysis and potentiometric titration showed the composition difference among these five HA. The sorption capacity and rate increased in the order: M-HA < K-HA < Gi-HA < Ck-HA < Go-HA. ITC results revealed that the sorption process was spontaneous and endothermic. The aggregation of HA particles after sorption were observed by AFM images. The influence of pH and positive correlations between the sorption capacity and the content of acidic functional groups of HA indicated that the dissociated acidic functional groups, especially the dissociation of carboxylic groups in HA played an important role in Cu sorption. Sequential desorption of sorbed Cu showed that the surface bonded fraction (97.6-99.0%) was significantly higher than the ion exchanged fraction (1.0-2.4%). Markedly positive entropies (ΔS, 94.4-104.3 J mol^-1 K^-1) further demonstrated that Cu binding to HA by forming inner-sphere complexes. The findings of this study would promote the understanding on the environmental impact of the decomposition of organic waste from agricultural production.

Biosorption characteristic of Alcaligenes sp. BAPb.1 for removal of lead(II) from aqueous solution

In this study, strain BAPb.1 was isolated from lead mining area and used as an adsorbent to remove lead(II) ions from aqueous solution. The physicochemical characteristics, heavy metal resistance and antibiotic sensitivity of strain BAPb.1 were investigated. Biosorption capacity was evaluated by batch biosorption experiments, and isothermal characteristics were discussed. Atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectrometry (FTIR) were conducted to explore the mechanism for lead(II) adsorption. Based on morphological and physiological characteristics as well as the phylogenetic analysis of 16S rDNA sequences, strain BAPb.1 was identified as a member of the genus Alcaligenes. It exhibited high resistances to multiple heavy metals such as lead(II), copper(II), zinc(II), nickel(II) and chromium(VI), and to antibiotics such as kanamycin, ampicillin, streptomycin, chloramphenicol, and tetracycline. The optimum conditions for maximum biosorption rate of 85.2% and maximum capacity of 56.8 mg g^-1 were found at pH of 5, adsorbent dosage of 1.5 g L^-1 (dry weight), initial lead(II) concentration of 100 mg L^-1, and contact time of 30 min at 30 °C. Biosorption isotherms were well fitted with Langmuir isotherm model. Mechanism analysis reveals that the lead(II) ions may exchange with sodium and potassium ions, and the hydroxyl, carbonyl and phosphate groups on the cell surface can chelate the lead(II) ions, therefore, surface adsorption play significant role in the biosorption process.

Microbial strategy for potential lead remediation: a review study

The extensive exploitation and usage of lead compounds result in severe lead(II) pollution in water and soil environments, even in agricultural land, threatening the health of animals and humans via food chains. The recovery and remediation of lead(II) from water and soil environments have been intensively concerned in recent years. Compared with the traditional physic-chemistry treatment, microbial remediation strategy is a promising alternative to remediate lead(II)-contaminated environments due to its cost-effective and environmentally-friendly properties. Various microorganisms are capable of removing or immobilizing lead(II) from water and soil environments through bioaccumulation, precipitation or accelerated transformation of lead(II) into a very stable mineral, resulting in significant effects on lead(II) mobility and bioavailability. In the present review, we investigated a wide diversity of lead(II) bioremediation induced by different microbes and its multi-mechanisms. Moreover, we also discussed the progress and limitations, summarized the common rules of lead(II)-microbe interaction, and evaluated the environmental significance of microbes in lead biogeochemistry process. In addition, we further deliberated the feasibility and potential application of microbes in developing cost-effective, eco-friendly bioremediation or long-term management strategy for lead(II) contaminated repositories.

Copper Oxide Nanoparticles Impact Several Toxicological Endpoints and Cause Neurodegeneration in Caenorhabditis elegans

Engineered nanoparticles are becoming increasingly incorporated into technology and consumer products. In 2014, over 300 tons of copper oxide nanoparticles were manufactured in the United States. The increased production of nanoparticles raises concerns regarding the potential introduction into the environment or human exposure. Copper oxide nanoparticles commonly release copper ions into solutions, which contribute to their toxicity. We quantified the inhibitory effects of both copper oxide nanoparticles and copper sulfate on C. elegans toxicological endpoints to elucidate their biological effects. Several toxicological endpoints were analyzed in C. elegans, including nematode reproduction, feeding behavior, and average body length. We examined three wild C. elegans isolates together with the Bristol N2 laboratory strain to explore the influence of different genotypic backgrounds on the physiological response to copper challenge. All strains exhibited greater sensitivity to copper oxide nanoparticles compared to copper sulfate, as indicated by reduction of average body length and feeding behavior. Reproduction was significantly reduced only at the highest copper dose, though still more pronounced with copper oxide nanoparticles compared to copper sulfate treatment. Furthermore, we investigated the effects of copper oxide nanoparticles and copper sulfate on neurons, cells with known vulnerability to heavy metal toxicity. Degeneration of dopaminergic neurons was observed in up to 10% of the population after copper oxide nanoparticle exposure. Additionally, mutants in the divalent-metal transporters, smf-1 or smf-2, showed increased tolerance to copper exposure, implicating both transporters in copper-induced neurodegeneration. These results highlight the complex nature of CuO nanoparticle toxicity, in which a nanoparticle-specific effect was observed in some traits (average body length, feeding behavior) and a copper ion specific effect was observed for other traits (neurodegeneration, response to stress).

Elucidation of impact of heavy metal pollution on soil bacterial growth and extracellular polymeric substances flexibility

Metal bioaccessibility is an alarming issue in croplands of mining sites due to overloading of toxic metals. Hence, the present study is aimed to determine the overloading of toxic metal in croplands across the Tawag village, Hutti, Raichur, India. Correspondingly, to identify the soil bacterial growth, physiological oxidative stress enzyme activity and surface macromolecular functional group evolution were analysed in and around the toxic metal contaminated sites through FT-IR and FT-Raman spectrometry. The evaluated results attribute that the study area is heavily polluted with the toxic metals such as arsenic, cadmium, chromium, lead and zinc. However, biochemical and 16S rRNA gene sequence homology tree confirmed that the arsenic and cadmium-resistant isolate belongs to Bacillus sp. MDPMK-02 and retrieved unique Gene Bank ID KT596811 (accession number) at National Centre for Biotechnology information (NCBI), India. Additionally, sodium arsenite-amended culture media possessing reduced biomass and enhanced the activity of oxidative stress defence enzymes such as superoxide dismutase (SOD) and catalase (CAT) than cadmium chloride-amended medium and control. Subsequently, the infrared (IR) and Raman spectral analytical assessment distinguish that arsenic-treated Gram-positive isolate membrane fetched high percentage of hydration, elevation of surface polysaccharides, proteins and polyhydroxybutyric acid (PHBA) molecular specific stretch intensity compared to cadmium exposures. From these results, the study concluded that the mining wastes significantly pollute the surrounding croplands, and also Bacillus sp. MDPMK-02 possesses good chemosensing for cross-protection and bio-adaptation of toxic metal ions. Hence, these isolates can be compiled and implemented in environmental hazardous management techniques such as bioremediation, bioleaching and biodegradation.

Phycoremediation and adsorption isotherms of cadmium and copper ions by Merismopedia tenuissima and their effect on growth and metabolism

The current study tends to investigate the removal of cadmium and copper ions by Merismopedia tenuissima, grown in different concentrations of cadmium and copper ions, as well to investigate their effects on growth and metabolism. Sorption isotherms of Langmuir and Freundlich were obtained for the quantitative description of cadmium and copper uptake by M. tenuissima. Langmuir model adequately to describe the data of biosorption for these metals. However, the Freundlich model could work well in case of Cu(2+) only. M. tenuissima appears to be more efficient for removing Cd(2+) ions than Cu(2+). However, the affinity constant of Cu(2+) on the biomass of M. tenuissima was higher than Cd(2+) indicating that M. tenuissima is more tolerant to Cd(2+) phytotoxicity than Cu(2+). FTIR analysis of algae with and without biosorption revealed the presence of carboxyl, amino, amide and hydroxyl groups, which were responsible for biosorption of Cd(+2) and Cu(+2) ions.

Surface Modification of Naturally Available Biomass for Enhancement of Heavy Metal Removal Efficiency, Upscaling Prospects, and Management Aspects of Spent Biosorbents: A Review

Heavy metal pollution in water emerges as a severe socio-environmental problem originating primarily from the discharge of industrial wastewater. In view of the toxic, non-biodegradable, and persistent nature of most of the heavy metal ions, remediation of such components becomes an absolute necessity. Biosorption is an emerging tool for bioremediation that has gained momentum for employing low-cost biological materials with effective metal binding capacities. Even though biological materials possess excellent metal adsorption abilities, they show poor mechanical strength and low rigidity. Other disadvantages include solid-liquid separation problems, possible biomass swelling, lower efficiency for regeneration or reuse, and frequent development of high pressure drop in the column mode that limits its applications under real conditions. To improve the biosorption efficiency, biomasses need to be modified with a simple technique for selective/multi-metal adsorption. This review is intended to cover discussion on biomass modification for enhanced biosorption efficiency, mechanism studies using various instrumental/analytical techniques, and future direction for research and development including the fate of spent biosorbent. In most of the previously published researches, difficulty of the process in scaling up has not been addressed. The current article outlines the application potential of biosorbents in the development of hybrid technology integrated with membrane processes for water and wastewater treatment in industrial scale.

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.

Biosorption mechanisms involved in immobilization of soil Pb by Bacillus subtilis DBM in a multi-metal-contaminated soil

Mechanisms of soil Pb immobilization by Bacillus subtilis DBM, a bacterial strain isolated from a heavy-metal-contaminated soil, were investigated. Adsorption and desorption experiments with living bacterial cells as well as dead cells revealed that both extracellular adsorption and intracellular accumulation were involved in the Pb(2+) removal from the liquid phase. Of the sequestered Pb(II), 8.5% was held by physical entrapment within the cell wall, 43.3% was held by ion-exchange, 9.7% was complexed with cell surface functional groups or precipitated on the cell surface, and 38.5% was intracellularly accumulated. Complexation of Pb(2+) with carboxyl, hydroxyl, carbonyl, amido, and phosphate groups was demonstrated by Fourier transform infrared spectroscopic analysis. Precipitates of Pb5(PO4)3OH, Pb5(PO4)3Cl and Pb10(PO4)6(OH)2 that formed on the cell surface during the biosorption process were identified by X-ray diffraction analysis. Transmission electron microscopy-energy dispersive spectroscopic analysis confirmed the presence of the Pb(II) precipitates and that Pb(II) could be sequestered both extracellularly and intracellularly. Incubation with B. subtilis DBM significantly decreased the amount of the weak-acid-soluble Pb fraction in a heavy-metal-contaminated soil, resulting in a reduction in Pb bioavailability, but increased the amount of its organic-matter-bound fraction by 71%. The ability of B. subtilis DBM to reduce the bioavailability of soil Pb makes it potentially useful for bacteria-assisted phytostabilization of multi-heavy-metal-contaminated soil.

Application of Taguchi L32 orthogonal array design to optimize copper biosorption by using Spaghnum moss

In this work, Taguchi L32 experimental design was applied to optimize biosorption of Cu(2+) ions by an easily available biosorbent, Spaghnum moss. With this aim, batch biosorption tests were performed to achieve targeted experimental design with five factors (concentration, pH, biosorbent dosage, temperature and agitation time) at two different levels. Optimal experimental conditions were determined by calculated signal-to-noise ratios. "Higher is better" approach was followed to calculate signal-to-noise ratios as it was aimed to obtain high metal removal efficiencies. The impact ratios of factors were determined by the model. Within the study, Cu(2+) biosorption efficiencies were also predicted by using Taguchi method. Results of the model showed that experimental and predicted values were close to each other demonstrating the success of Taguchi approach. Furthermore, thermodynamic, isotherm and kinetic studies were performed to explain the biosorption mechanism. Calculated thermodynamic parameters were in good accordance with the results of Taguchi model.

Biosorption of uranium on Bacillus sp. dwc-2: preliminary investigation on mechanism

In this paper, the biosorption mechanisms of uranium on an aerobic Bacillus sp. dwc-2, isolated from a potential disposal site for (ultra-) low uraniferous radioactive waste in Southwest China, was explored by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, FT-IR spectroscopy, proton induced X-ray emission (PIXE) and enhanced proton backscattering spectrometry (EPBS). The biosorption experiments for uranium were carried out at a low pH (pH 3.0), where the uranium solution speciation is dominated by highly mobile uranyl ions. The bioaccumulation was found to be the potential mechanism involved in uranium biosorption by Bacillus sp. dwc-2, and the bioaccumulated uranium was deposited in the cell interior as needle shaped particles at pH 3.0, as revealed by TEM analysis as well as EDX spectra. FTIR analysis further suggested that the absorbed uranium was bound to amino, phosphate and carboxyl groups of bacterial cells. Additionally, PIXE and EPBS results confirmed that ion-exchange also contributed to the adsorption process of uranium. All the results implied that the biosorption mechanism of uranium on Bacillus sp. is complicated and at least involves bioaccumulation, ion exchange and complexation process.

Biodegradation of decabromodiphenyl ether (BDE-209) by a metal resistant strain, Bacillus cereus JP12

A metal resistant bacterial strain, Bacillus cereus JP12, could use decabromodiphenyl ether (BDE-209) as the sole carbon and energy source for growth in mineral salt medium. Under the conditions of pH 6.0, 30°C, 150 rpm and an inoculum of OD600=0.6, more than 88% of the initial BDE-209 (1mg/L) was degraded after 12 days. The addition of appropriate surfactants and additional carbon sources could enhance the biodegradation efficiency of BDE-209. The presence of Cu(2+) (≤ 8 mg/L) and Zn(2+) (≤ 15 mg/L) provided a slight stimulating effect on BDE-209 removal. However, BDE-209 biodegradation efficiency was decreased when adding higher levels of metals due to reduced substrate availability caused by excess metal adsorption into the cell surface. Biosorption of heavy metals by JP12 led to release of light metals such as K(+) and Na(+). A BDE-209 biodegradation pathway was proposed on the basis of metabolite identification.

Isotherm kinetics of Cr(III) removal by non-viable cells of Acinetobacter haemolyticus

The potential use of non-viable biomass of a Gram negative bacterium i.e. Acinetobacter haemolyticus to remove Cr(III) species from aqueous environment was investigated. Highest Cr(III) removal of 198.80 mg g(-1) was obtained at pH 5, biomass dosage of 15 mg cell dry weight, initial Cr(III) of 100 mg L(-1) and 30 min of contact time. The Langmuir and Freundlich models fit the experimental data (R(2)>0.95) while the kinetic data was best described using the pseudo second-order kinetic model (R(2)>0.99). Cr(III) was successfully recovered from the bacterial biomass using either 1M of CH(3)COOH, HNO(3) or H(2)SO(4) with 90% recovery. TEM and FTIR suggested the involvement of amine, carboxyl, hydroxyl and phosphate groups during the biosorption of Cr(III) onto the cell surface of A. haemolyticus. A. haemolyticus was also capable to remove 79.87 mg g(-1) Cr(III) (around 22.75%) from raw leather tanning wastewater. This study demonstrates the potential of using A. haemolyticus as biosorbent to remove Cr(III) from both synthetic and industrial wastewater.