Alginate-immobilized Aspergillus niger: Characterization and biosorption removal of thorium ions from radioactive wastewater

Advancements in microbial-mediated radioactive waste bioremediation: A review

The global production of radioactive wastes is expected to increase in the coming years as more countries have resorted to adopting nuclear power to decrease their reliance on fossil-fuel-generated energy. Discoveries of remediation methods that can remove radionuclides from radioactive wastes, including those discharged to the environment, are therefore vital to reduce risks-upon-exposure radionuclides posed to humans and wildlife. Among various remediation approaches available, microbe-mediated radionuclide remediation have limited reviews regarding their advances. This review provides an overview of the sources and existing classification of radioactive wastes, followed by a brief introduction to existing radionuclide remediation (physical, chemical, and electrochemical) approaches. Microbe-mediated radionuclide remediation (bacterial, myco-, and phycoremediation) is then extensively discussed. Bacterial remediation involves biological processes like bioreduction, biosorption, and bioprecipitation. Bioreduction involves the reduction of water-soluble, mobile radionuclides to water-insoluble, immobile lower oxidation states by ferric iron-reducing, sulfate-reducing, and certain extremophilic bacteria, and in situ remediation has become possible by adding electron donors to contaminated waters to enrich indigenous iron- and sulfate-reducing bacteria populations. In biosorption, radionuclides are associated with functional groups on the microbial cell surface, followed by getting reduced to immobilized forms or precipitated intracellularly or extracellularly. Myco- and phycoremediation often involve processes like biosorption and bioaccumulation, where the former is influenced by pH and cell concentration. A Strengths, Weaknesses, Opportunities, and Threats (SWOT) analysis on microbial remediation is also performed. It is suggested that two research directions: genetic engineering of radiation-resistant microorganisms and co-application of microbe-mediated remediation with other remediation methods could potentially result in the discovery of in situ or ex situ microbe-involving radioactive waste remediation applications with high practicability. Finally, a comparison between the strengths and weaknesses of each approach is provided.

Recent Developments in the Adsorption of Heavy Metal Ions from Aqueous Solutions Using Various Nanomaterials

Water pollution is caused by heavy metals, minerals, and dyes. It has become a global environmental problem. There are numerous methods for removing different types of pollutants from wastewater. Adsorption is viewed as the most promising and financially viable option. Nanostructured materials are used as effective materials for adsorption techniques to extract metal ions from wastewater. Many types of nanomaterials, such as zero-valent metals, metal oxides, carbon nanomaterials, and magnetic nanocomposites, are used as adsorbents. Magnetic nanocomposites as adsorbents have magnetic properties and abundant active functional groups, and unique nanomaterials endow them with better properties than nonmagnetic materials (classic adsorbents). Nonmagnetic materials (classic adsorbents) typically have limitations such as limited adsorption capacity, adsorbent recovery, poor selective adsorption, and secondary treatment. Magnetic nanocomposites are easy to recover, have strong selectivity and high adsorption capacity, are safe and economical, and have always been a hotspot for research. A large amount of data has been collected in this review, which is based on an extensive study of the synthesis, characterization, and adsorption capacity for the elimination of ions from wastewater and their separation from water. The effects of several experimental parameters on metal ion removal, including contact duration, temperature, adsorbent dose, pH, starting ion concentration, and ionic strength, have also been investigated. In addition, a variety of illustrations are used to describe the various adsorption kinetics and adsorption isotherm models, providing insight into the adsorption process.

Recent advances of application of bentonite-based composites in the environmental remediation

Bentonite-based composites have been widely utilized in the removal of various pollutants due to low cost, environmentally friendly, ease-to-operate, whereas the recent advances concerning the application of bentonite-based composites in environmental remediation were not available. Herein, the modification (i.e., acid/alkaline washing, thermal treatment and hybrids) of bentonite was firstly reviewed; Then the recent advances of adsorption of environmental concomitants (e.g., organic (dyes, microplastics, phenolic and other organics) and inorganic pollutants (heavy metals, radionuclides and other inorganic pollutants)) on various bentonite-based composites were summarized in details. Meanwhile, the effect of environmental factors and interaction mechanism between bentonite-based composites and contaminants were also investigated. Finally, the conclusions and prospective of bentonite-based composites in the environmental remediation were proposed. It is demonstrated that various bentonite-based composites exhibited the high adsorption/degradation capacity towards environmental pollutants under the specific conditions. The interaction mechanism involved the mineralization, physical/chemical adsorption, co-precipitation and complexation. This review highlights the effect of different functionalization of bentonite-based composites on their adsorption capacity and interaction mechanism, which is expected to be helpful to environmental scientists for applying bentonite-based composites into practical environmental remediation.

A review of remediation technologies for uranium-contaminated water

Uranium is a naturally existing radioactive element present in the Earth's crust. It exhibits lithophilic characteristics, indicating its tendency to be located near the surface of the Earth and tightly bound to oxygen. It is ecotoxic, hence the need for its removal from the aqueous environment. This paper focuses on the variety of water treatment processes for the removal of uranium from water and this includes physical (membrane separation, adsorption and electrocoagulation), chemical (ion exchange, photocatalysis and persulfate reduction), and biological (bio-reduction and biosorption) approaches. It was observed that membrane filtration and ion exchange are the most popular and promising processes for this application. Membrane processes have high throughput but with the challenge of high power requirements and fouling. Besides high pH sensitivity, ion exchange does not have any major challenges related to its application. Several other unique observations were derived from this review. Chitosan/Chlorella pyrenoidosa composite adsorbent bearing phosphate ligand, hydroxyapatite aerogel and MXene/graphene oxide composite has shown super-adsorbent performance (>1000 mg/g uptake capacity) for uranium. Ultrafiltration (UF) membranes, reverse osmosis (RO) membranes and electrocoagulation have been observed not to go below 97% uranium removal/conversion efficiency for most cases reported in the literature. Heat persulfate reduction has been explored quite recently and shown to achieve as high as 86% uranium reduction efficiency. We anticipate that future studies would explore hybrid processes (which are any combinations of multiple conventional techniques) to solve various aspects of the process design and performance challenges.

Eco-friendly and cost-effective adsorbent derived from blast furnace slag with black liquor waste for hazardous remediation

The current investigation concerns with preparation eco-friendly and cost-effective adsorbent (mesoporous silica nanoparticles (SBL)) based on black liquor (BL) containing lignin derived from sugarcane bagasse and combining it with sodium silicate derived from blast furnace slag (BFS) for thorium adsorption. Thorium ions were adsorbed from an aqueous solution using the synthesized bio-sorbent (SBL), which was then assessed by X-ray diffraction, BET surface area analysis, scanning electron microscopy with energy dispersive X-ray spectroscopy (EDX), and Fourier transforms infrared spectroscopy (FTIR). Th(IV) sorption properties, including the pH effect, uptake rate, and sorption isotherms across various temperatures were investigated. The maximum sorption capacity of Th(IV) on SBL is 158.88 mg/L at pH value of 4328 K, and 60 min contact time. We demonstrated that the adsorption processes comport well with pseudo-second-order and Langmuir adsorption models considering the kinetics and equilibrium data. According to thermodynamic inspections results, the Th(IV) adsorption process exhibited endothermic and random behavior suggested by positive ΔH° and ΔS° values, while the negative ΔG° values indicated a spontaneous sorption process. The maximum Th(IV) desorption from the loaded SBL (Th/SBL) was carried out at 0.25 M of NaHCO3 and 60 min of contact. Sorption/desorption processes have five successive cycles. Finally, this study suggests that the recycling of BFS and BL can be exploited for the procurement of a promising Th(IV) adsorbents.

Ability of Cupriavidus necator H16 to resist, bioremove, and accumulate some hazardous metal ions in water

Bacterial biomasses are suitable and inexpensive biosorbents for the removal of metal ions. The Gram-negative betaproteobacterium Cupriavidus necator H16 is found in soil and freshwater environments. In this study, C. necator H16 was used to remove chromium (Cr), arsenic (As), aluminum (Al), and cadmium (Cd) ions from water. Minimum inhibition concentration (MIC) values of C. necator to Cr, As, Al, and Cd were found as 76, 69, 341, and 275 mg/L, respectively. The highest rates of Cr, As, Al, and Cd bioremoval were 45, 60, 54, and 78%, respectively. pH levels between 6.0 and 8.0 and an average temperature of 30 °C were optimum for the most efficient bioremoval. Scanning electron microscopy (SEM) images of Cd-treated cells showed that the morphology of the cells was significantly impaired compared to the control. Shifts in the Fourier transform infrared spectroscopy analysis (FTIR) spectra of the Cd-treated cell walls also confirmed the presence of active groups. As a result, it can be said that C. necator H16 has a moderate bioremoval efficiency for Cr, As, and Al and a high bioremoval efficiency for Cd.

Potential Application of Innovative Aspergillus terreus/ Sodium Alginate Composite Beads as Eco-Friendly and Sustainable Adsorbents for Alizarin Red S Dye: Isotherms and Kinetics Models

Fungi were used as one of the most common bioremediation methods. From this perspective, our study highlights the optimization of Alizarin Red S (ARS) dye adsorption performance for the sodium alginate (SA) by using the fungus Aspergillus terreus (A. terreus) to form a composite bead and the possibility of its reusability. This was accomplished by mixing SA with different ratios of biomass powder of A. terreus, including 0%, 10%, 20%, 30%, and 40%, to form composite beads of A. terreus/SA-0%, A. terreus/SA-10%, A. terreus/SA-20%, A. terreus/SA-30%, and A. terreus/SA-40%, respectively. The ARS adsorption characteristics of these composite mixtures were analyzed at various mass ratios, temperatures, pH values, and initial concentrations. Moreover, sophisticated techniques, such as scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR), were employed to detect the morphological and chemical properties of this composite, respectively. The experimental results revealed that A. terreus/SA-20% composite beads have the highest adsorption capacity of 188 mg/g. Its optimum adsorption conditions were achieved at 45 ∘C and pH 3. Moreover, the ARS adsorption was well explained by the Langmuir isotherm (q_m = 192.30 mg/g) and pseudo-second-order and intra-particle diffusion kinetics. The SEM and FTIR findings corroborated the superior uptake of A. terreus/SA-20% composite beads. Lastly, the A. terreus/SA-20% composite beads can be employed as an eco-friendly and sustainable alternative to other common adsorbents for ARS.

Optimization and adsorption characteristics of beads based on heat-inactivated bacterial biomaterial towards the pesticide Cypermethrin

AIMS

Beads containing heat-inactivated bacterial biomaterial (BBBs) were prepared for removal of cypermethrin (CPM) and the conditions for this removal were evaluated and optimized via single-factor coupled orthogonal experiments based on five factors. The adsorption characteristics of BBBs and the binding mechanism were then explored.

METHODS AND RESULTS

Results showed that the adsorption rate of CPM could reach 98% with beads prepared under optimized conditions: equal volumes of Lactobacillus cell debris derived from 1×1011 CFU; 2% hydroxypropyl-β-cyclodextrin and 2.5% activated carbon concentration, were mixed to give mixture TM, and this and SA, was mixed 1:4 with sodium alginate (SA) and beads were prepared using a 26-Gauge needle). The best adsorption conditions were initial CPM concentration of 10 mg l-1, incubation time of 24 h, and rotational speed of 180 rpm. BBBs have a well-formed structure and abundant surface functional groups, such as -COOH, -OH, -NH, -CH, -CO, -C=C. The adsorption process conformed to pseudo-second-order kinetic, and it was also a Freundlich monolayer adsorption, and the calculated maximum adsorption capacity was 9.69 mg g-1 under optimized conditions.

CONCLUSIONS

BBBs showed the highest CPM removal capacity and a good tolerance ability.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results provided a theoretical foundation for developing an adsorbent with heat-inactivated Lactobacillus plantarum (L. plantarum) RS60 for removing CPM in wastewater or drinks.

Effect of extracellular proteins on Cd(II) adsorption in fungus and algae symbiotic system

Fungus-algae symbiotic systems (FASS) are typically used to assist in the immobilization of algae and strengthen the adsorption of heavy metals. However, the adsorption behavior of the symbiotic system and the molecular regulation mechanism of extracellular proteins in the adsorption of heavy metals have not been reported in detail. In this study, a stable FCSS (fungus-cyanobacterium symbiotic system) was used to study Cd(II) adsorption behavior. The fixation efficiency of fungus to cyanobacterium reached more than 95% at pH7.0, 30 °C, 150 rpm, and a medium ratio of 100%. The biomass, chlorophyll content, and total fatty acid content of the symbiotic system were much higher than those of cyanobacterium and fungus alone. The photosynthetic fluorescence parameters showed that the presence of fungus enhanced the light tolerance of cyanobacterium. The original light energy conversion efficiency and potential activity of PSII were enhanced, indicating that symbiosis could promote the photosynthetic process of cyanobacterium. The Cd(II) adsorption efficiency can achieve 90%. The system maintained excellent adsorption after six adsorption cycles. Differential proteins were mainly enriched in areas such as metabolism, ABC transport system, and pressure response. Cd(II) stress promotes an increase in efflux proteins. Moreover, cadmium can be fixed as much as possible by secreting extracellular proteins, and the toxicity of cadmium to cells can be alleviated by regulating the metabolism of glutathione, reducing oxidative phosphorylation level, and reducing oxidative stress, thus improving the resistance to Cd(II). Meanwhile, the expression of enzymes involved in glycolysis and the pentose phosphate pathway was upregulated, while the expression of those in the TCA cycle was downregulated. The expression of substances related to PSI and PSII in the photosynthetic system and rubisco, a key enzyme in the Calvin cycle, was significantly upregulated, indicating that the glucose metabolism and photosynthetic pathways of the symbiotic system were involved in resistance to Cd toxicity. This revealed the response mechanism of the fungus-algal symbiotic system in the process of Cd adsorption, and also provided reference value for industrial application in water treatment.

Response of soil microbial communities to natural radionuclides along specific-activity gradients

Understanding the response of soil microbial community to abnormal natural radionuclides is important to maintain soil ecological function, but the underlying mechanism of tolerance and survival of microbes is poorly studied. The effects of natural radionuclides on the topsoil microbial communities in anomalous natural radiation area were investigated in this work, and it was found that microbial community composition was significantly influenced by the specific-activities of natural radionuclides. The results revealed that relative abundances of 10 major microbial phyla and genera displayed different patterns along specific-activity gradients, including decreasing, increasing, hump-shaped, U-shaped, and similar sinusoidal or cosine wave trends, which indicated that the natural radionuclides were the predominant driver for change of microbial community structure. At the phylum and genus level, microbial communities were divided into two special groups according to the tolerance to natural radionuclides, such as ²³⁸U and ²³²Th, including tolerant and sensitive groups. Taken together, our findings suggest that the high specific-activities of natural radionuclides can obviously drive changes in microbial communities, providing a possibility for future studies on the microbial tolerance genes and bioremediation strains.

Continuous Systems Bioremediation of Wastewaters Loaded with Heavy Metals Using Microorganisms

Heavy metal pollution is a serious concern of the modern era due to its widespread negative effects on human health and to the environment. Conventional technologies applied for the uptake of this category of persistent pollutants are complex, often expensive, and inefficient at low metal concentrations. In the last few years, non-conventional alternatives have been studied in search of better solutions in terms of costs and sustainability. Microbial adsorbents are one of the biomass-based sorbents that have extensively demonstrated excellent heavy metals removal capacity even at low concentrations. However, most of the carried-out research regarding their application in wastewater treatment has been performed in discontinuous systems. The use of microorganisms for the uptake of metal ions in continuous systems could be an important step for the upscale of the remediation processes since it facilitates a faster remediation of higher quantities of wastewaters loaded with heavy metals, in comparison with batch systems removal. Thus, the current research aims to analyze the available studies focusing on the removal of metal ions from wastewaters using microorganisms, in continuous systems, with a focus on obtained performances, optimized experimental conditions, and the sustainability of the bioremoval process. The present work found that microbial-based remediation processes have demonstrated very good performances in continuous systems. Further sustainability analyses are required in order to apply the bioremediation technology in an optimized environmentally friendly way in large-scale facilities.

Potentiality of phosphorus-accumulating organisms biomasses in biosorption of Cd(II), Pb(II), Cu(II) and Zn(II) from aqueous solutions: Behaviors and mechanisms

Heavy metal pollution is consistently a critical global issue, and bioremediation is regarded as one of the most promising approaches. In this work, the biosorption characteristics of Cd(II), Pb(II), Cu(II) and Zn(II) from aqueous solutions using three phosphorus-accumulating organisms (PAOs) biomasses, Ochrobactrum cicero (PAB-006), Stenotrophomonas maltophilia (PAB-009), and Pseudomonas putida (PAB-0031), as biosorbents were investigated. Results indicated that the equilibrium biosorption capacities of biosorbents to heavy metal ions were sensitive to the solution pH, and increased with increasing pH values. The experimental data of Cd(II), Pb(II), Cu(II) and Zn(II) biosorption were in good agreement with the Pseudo-second-order, Redlich-Peterson and Temkin models, implying that the biosorption was a hybrid chemical reaction-biosorption process. In addition, the theoretical maximum biosorption capacities of Cd(II), Pb(II), Cu(II) and Zn(II) were calculated to be 67.84, 80.23, 50.56 and 63.07 mg/g for PAB-006, 59.99, 87.71, 39.26 and 64.00 mg/g for PAB-009 and 68.31, 85.43, 38.97 and 62.85 mg/g for PAB-031, respectively (pH = 5.0 ± 0.1, T = 25 °C), according to the parameters of the Langmuir model. Moreover, ionic strength had negligible influences or slight promoting effects, while humic acid exhibited positive effects on the removal of heavy metals. Further, PABs were stable and displayed excellent reusability. Characterization techniques of FTIR and XPS revealed that surface complexation, ion exchange, hydrogen bonding and electrostatic interaction were the main mechanisms involved in the biosorption process. In summary, the biosorbent PABs possessed high biosorption performance with excellent reusability, and which hold the great application prospect in the treatment of heavy metal contaminated water.

Revealing the role of oxygen-containing functional groups on graphene oxide for the highly efficient adsorption of thorium ions

Oxygen-containing functional groups on the surface of carbon materials can promote the adsorption capacity of radioactive thorium ions (Th(IV)), but their effect on the adsorption of Th(IV) has not been systematically revealed. Herein, to elucidate the nature of oxygen-containing group-mediated Th(IV) adsorption, a series of graphene oxide nanoflakes (GONFs) with different contents of oxygen-containing groups on the surface were prepared. The experimental results showed that the high adsorption of Th(IV) not only resulted from the oxygen content, but also was related to the type of oxygen-containing functional groups on GONFs. Subsequent density functional theory (DFT) calculations revealed that the high adsorption capacity for Th(IV) originated from the oxygen-containing groups and their adjacent activated sp2 carbon atoms. More importantly, the coordination of Th(IV) with oxygen functional groups induced the aggregation of GONFs, leading to the sedimentation of GONFs, which facilitated the separation of adsorbents and enabled the GONFs to be a more practical adsorbent for Th(IV). This work deepens our understanding of the role of oxygen-containing groups on Th(IV) adsorption and provides a new strategy for the design and synthesis of high-performance surface oxygen-containing carbon-based adsorbents with practical application potential.

A review on mycelial pellets as biological carriers: Wastewater treatment and recovery for resource and energy

Mycelial pellets, a new environment friendly biological carrier, have received wide attention from researchers due to porosity, stability and unique biocompatibility. In this article, the theoretical basis and mechanism of mycelial pellets as a biological carrier were analyzed from the properties of mycelial pellets and the interaction between mycelial pellets and other microorganisms. This article aims to collate and present the current application and development trend of mycelial pellets as biological carriers in wastewater treatment, resource and energy recovery, especially the symbiotic particle system formed by mycelial pellets and microalgae is an important way to break through the technical bottleneck of biodiesel recovery from wastewater. This review also analyzes the research hotspots and trends of mycelial pellets as carriers in recent years, discusses the challenges faced by this technology, and puts forward corresponding solutions.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Phenol biodegradation by immobilized Rhodococcus qingshengii isolated from coking effluent on Na-alginate and magnetic chitosan-alginate nanocomposite

Phenol is a hazardous organic solvent to living organisms, even in its small amounts. In order to bioremediation of phenol from aqueous solution, a novel bacterial strain was isolated from coking wastewater, identified as Rhodococcus qingshengii based on 16S rRNA sequence analysis and named as strain Sahand110. The phenol-biodegrading capabilities of the free and immobilized cells of Sahand110 on the beads of Na-alginate (NA) and magnetic chitosan-alginate (MCA) nanocomposite were evaluated under different initial phenol concentrations (200, 400, 600, 800 and 1000 mg/L). Results illustrated that Sahand110 was able to grow and complete degrade phenol up to 600 mg/L, as the sole carbon and energy source. Immobilized cells of Sahand110 on NA and MCA were more competent than its free cells in degradation of high phenol concentrations, 100% of 1000 mg/L phenol within 96 h, indicating the improved tolerance and performance of the immobilized cells against phenol toxicity. Therefore, the immobilized Sahand110 on the studied beads, especially MCA bead regarding its suitable properties, has significant potential to enhanced bioremediation of phenol-rich wastewaters.

A unique, inexpensive, and abundantly available adsorbent: composite of synthesized silver nanoparticles (AgNPs) and banana leaves powder (BLP)

The purpose of this study is to investigate the development of a new and inexpensive adsorbent by immobilization synthesized silver nanoparticles (AgNPs) onto banana leaves powder (BLP), and the prepared composite (BLP)/(AgNPs) was used as an adsorbent for Zn(II), Pb(II), and Fe(III) ion removal from aqueous solutions under the influence of various reaction conditions. (BLP)/(AgNPs) demonstrated remarkable sensitivity toward Zn (II), Pb (II), and Fe (III) ions; metal ions eliminations increased with increasing contact time, agitation speed, adsorbent dose, and temperature, yielding adequate selectivity and ideal removal efficiency of 79%, 88%, and 91% for Zn (II), Pb (II), and Fe (III) ions, respectively, at pH = 5 for Zn(II) and pH = 6 for Pb(II), and Fe(III). The equilibrium contact time for elimination of Zn (II), Pb (II), and Fe (III) ions was reaches at 40 min. Langmuir, Freundlich, and Temkin equations were used to test the obtained experimental data. Langmuir isotherm model was found to be more accurate in representing the data of Zn(II), Pb(II), and Fe(III) ions adsorption onto (BLP)/(AgNPs), with a regression coefficient (R² = 0.999) and maximum adsorption capacities of 190, 244, and 228 mg/g for Zn(II), Pb(II), and Fe(III) ions, respectively. The thermodynamic parameters proved that adsorption of metal ions is spontaneous, feasible, and endothermic, whereas Kinetic studies revealed that the process was best described by a pseudo second order kinetics.

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By reduction reaction, silver nanoparticles were impregnated in banana leaves homogeneous powder and used as an adsorbent.

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The fabricated composites are used as adsorbent for the removal of Zn (II), Pb (II), and Fe (III) ions from aqueous solutions.

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The new adsorbent exhibited high adsorption capacity with three metal ions and followed the order Pb (II)> Fe (III) >Zn (II) ions.

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The metal ions vanished from the solution within approximately 40 min.

Self-immobilized biochar fungal pellet combined with bacterial strain H29 enhanced the removal performance of cadmium and nitrate

A newly isolated strain Phoma sp. ZJ6, which could form fungal pellet (FP) by self-immobilization, was identified. A novel longan seed biochar embedded in FP (BFP) combined with strain H29 (BFP-H29) effectively improved the Cd(II) removal efficiency and simultaneously removed nitrate. The adsorption process of BFP was well fitted with the pseudo-second-order kinetics model and Langmuir isotherm model, which demonstrated that the adsorption process was favorable and mainly dominated by chemisorption. Compared with single FP, biochar, and strain H29, BFP-H29 significantly enhanced the Cd(II) removal and the removal ratio reached 90.47%. Meanwhile, the simultaneous removal efficiency of the BFP-H29 for nitrate could reach 93.80%. Characterization analysis demonstrated that the primary removal mechanisms of BFP-H29 were precipitation and surface complexation. BFP-H29 had excellent performance in simultaneous removal of Cd(II) and nitrate, indicating its potential as a promising composite in the removal of cadmium and nitrate in wastewater.

Ultra-selective ion sieve for thorium recovery from rare earth elements using oxygen-rich microporous carbon adsorption

The ultra-selective extraction of thorium ions (Th(IV)) from lanthanides is of significance to both solve the radioactive pollution issue in rare earth (RE) production and sustainably provide thorium fuel for the liquid fluoride thorium reactors (LFTR). However, it remains a great challenge. Here, we reported an oxygen-rich microporous carbon for ultra-selective extraction of Th(IV) from rare earth elements (REEs) in a wide pH range. This selectivity was derived from the synergy of the oxygen-rich nature, microporous structure of the carbons, the chemical valence, and the ionic size of Th(IV) species. This oxygen-rich microporous carbon presented an ultra-high distribution coefficient (K_d) of 1.15 × 10⁸ mL g^-1 for Th(IV) at pH 4.9 in the presence of 15 REEs and revealed outstanding performance for Th(IV) extraction from three simulated RE solutions with high ionic strength of lanthanides. Meanwhile, an exceptional adsorption capacity of 624.98 mg g^-1 was obtained in the single Th(IV) solution. Both values were superior to those of reported adsorbents. More importantly, the new adsorbent developed here could be prepared from cigarette butts. These features ensured the oxygen-rich carbon as a promising and cost-effective adsorbent for high-purity thorium extraction from REEs.

Polysaccharides as Support for Microbial Biomass-Based Adsorbents with Applications in Removal of Heavy Metals and Dyes

The use of biosorbents for the decontamination of industrial effluent (e.g., wastewater treatment) by retaining non-biodegradable pollutants (antibiotics, dyes, and heavy metals) has been investigated in order to develop inexpensive and effective techniques. The exacerbated water pollution crisis is a huge threat to the global economy, especially in association with the rapid development of industry; thus, the sustainable reuse of different treated water resources has become a worldwide necessity. This review investigates the use of different natural (living and non-living) microbial biomass types containing polysaccharides, proteins, and lipids (natural polymers) as biosorbents in free and immobilized forms. Microbial biomass immobilization performed by using polymeric support (i.e., polysaccharides) would ensure the production of efficient biosorbents, with good mechanical resistance and easy separation ability, utilized in different effluents' depollution. Biomass-based biosorbents, due to their outstanding biosorption abilities and good efficiency for effluent treatment (concentrated or diluted solutions of residuals/contaminants), need to be used in industrial environmental applications, to improve environmental sustainability of the economic activities. This review presents the most recent advances related the main polymers such as polysaccharides and microbial cells used for biosorbents production; a detailed analysis of the biosorption capability of algal, bacterial and fungal biomass; as well as a series of specific applications for retaining metal ions and organic dyes. Even if biosorption offers many advantages, the complexity of operation increased by the presence of multiple pollutants in real wastewater combined with insufficient knowledge on desorption and regeneration capacity of biosorbents (mostly used in laboratory scale) requires more large-scale biosorption experiments in order to adequately choose a type of biomass but also a polymeric support for an efficient treatment process.

Nanotechnology in Wastewater Management: A New Paradigm Towards Wastewater Treatment

Clean and safe water is a fundamental human need for multi-faceted development of society and a thriving economy. Brisk rises in populations, expanding industrialization, urbanization and extensive agriculture practices have resulted in the generation of wastewater which have not only made the water dirty or polluted, but also deadly. Millions of people die every year due to diseases communicated through consumption of water contaminated by deleterious pathogens. Although various methods for wastewater treatment have been explored in the last few decades but their use is restrained by many limitations including use of chemicals, formation of disinfection by-products (DBPs), time consumption and expensiveness. Nanotechnology, manipulation of matter at a molecular or an atomic level to craft new structures, devices and systems having superior electronic, optical, magnetic, conductive and mechanical properties, is emerging as a promising technology, which has demonstrated remarkable feats in various fields including wastewater treatment. Nanomaterials encompass a high surface to volume ratio, a high sensitivity and reactivity, a high adsorption capacity, and ease of functionalization which makes them suitable for application in wastewater treatment. In this article we have reviewed the techniques being developed for wastewater treatment using nanotechnology based on adsorption and biosorption, nanofiltration, photocatalysis, disinfection and sensing technology. Furthermore, this review also highlights the fate of the nanomaterials in wastewater treatment as well as risks associated with their use.

Exemplifying an archetypal thorium-EPS complexation by novel thoriotolerant Providencia thoriotolerans AM3

It is the acquisition of unique traits that adds to the enigma of microbial capabilities to carry out extraordinary processes. One such ecosystem is the soil exposed to radionuclides, in the vicinity of atomic power stations. With the aim to study thorium (Th) tolerance in the indigenous bacteria of such soil, the bacteria were isolated and screened for maximum thorium tolerance. Out of all, only one strain AM3, found to tolerate extraordinary levels of Th (1500 mg L⁻¹), was identified to be belonging to genus Providencia and showed maximum genetic similarity with the type strain P. vermicola OP1T. This is the first report suggesting any bacteria to tolerate such high Th and we propose to term such microbes as ‘thoriotolerant’. The medium composition for cultivating AM3 was optimized using response surface methodology (RSM) which also led to an improvement in its Th-tolerance capabilities by 23%. AM3 was found to be a good producer of EPS and hence one component study was also employed for its optimization. Moreover, the EPS produced by the strain showed interaction with Th, which was deduced by Fourier Transform Infrared (FTIR) spectroscopy.

Tartaric Acid-Modified Holarrhena antidysenterica and Citrullus colocynthis Biowaste for Efficient Eradication of Crystal Violet Dye from Water

Two novel adsorbents Holarrhena antidysenterica (HA) and Citrullus colocynthis (CC) were collected from native Pakistan and treated with tartaric acid. The adsorbents were characterized by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy, and their adsorptive behavior was studied against model cationic dye crystal violet (CV). Role of biosorbent dose, time of contact, temperature studies, agitation rates, and solution pH was investigated. Optimum conditions obtained for the removal of CV dye for H. antidysenterica-tartaric acid modified (HA-TA) were as follows: 0.8 g adsorbent dose, 35 minutes contact time, 5.0 pH, 40°C temperature, and 150 rpm agitation rates as compared to H. antidysenterica that gave 1.4 g adsorbent dose, 40 minutes time of contact, 6.0 pH, 50°C temperature, and 150 rpm agitation speed. C. colocynthis-tartaric acid modified (CC-TA) removed CV dye at 0.6 g adsorbent dose, 30 minutes contact interval, 4.0 pH, 40°C temperature, and 125 rpm agitation speed in contrast to C. colocynthis which gave 0.8 g adsorbent dose, 40 minutes time of contact, 6.0 pH, 50°C temperature, and 125 rpm agitation speed, respectively. Isothermal studies for both raw and modified biosorbents were compliant with the Langmuir model indicating monolayer, chemisorption. The maximum Langmuir capacities were up to 128.20 mg/g, 136.98 mg/g, 144.92 mg/g, and 166.66 mg/g for HA, CC, HA-TA, and CC-TA. Pseudo-second-order kinetic model well fitted the dye removal data. The rate-determining steps involved both surface and intraparticle diffusion mechanisms. Adsorption of dye molecules on active surfaces was governed by electrostatic attractions and chelating abilities. Thermodynamics research revealed the spontaneous and exothermic nature of the reaction. The adsorbents serve promising candidates for the effective removal of hazardous dyes from aqueous solutions.

Potentiality of living Bacillus pumilus SWU7-1 in biosorption of strontium radionuclide

Bacillus pumilus SWU7-1 was isolated from strontium ion (Sr(II))-uncontaminated soil, its biosorption potential was evaluated, and the effect of γ-ray radiation treatment on its biosorption was discussed. Domesticated under Sr(II) stress promoted the biosorption ability of B. pumilus to Sr(II), and the biosorption efficiency increased from 46.09% to 94.69%. At a lower initial concentration, the living bacteria had the ability to resist the biosorption of Sr(II). The optimal initial concentration range was 54-130 mg/L. The biosorption profile was better matched by Langmuir than Freundlich model, showing that the biosorption process of Sr(II) by the experimental strain was closer to the surface adsorption. According to Langmuir model, the maximum biosorption capacity of B. pumilus on Sr (II) was 299.4 mg/g. During the bacterial growth in the biosorption process, the changes in biosorption capacity and efficiency can be divided into two phases, and a pseudo-second-order model is followed in each phase. There was no significant difference in the biosorption efficiency of bacteria with different culture time after γ-ray radiation, and all of them were above 90%, which showed that B. pumilus had significant radiation resistance under experimental conditions. This study emphasized the potential application of B. pumilus in the treatment of radioactive Sr(II) pollution by biosorption.

Adsorptive Removal of Se(IV) by Citrus Peels: Effect of Adsorbent Entrapment in Calcium Alginate Beads

Selenium (Se) contamination in natural waters impacted by anthropogenic activities is becoming a prevalent and widespread problem. Investigation of novel, low-cost, and sustainable food-waste-sourced adsorbents for Se removal has largely been unexplored. Here, we report on the Se(IV) biosorption from a liquid solution using three waste-derived/low-cost biosorbents, namely citrus peels (bare), Ca-alginate gel beads, and Ca-alginate-citrus peels composite beads (Ca-alginate@citrus). The entrapment of citrus peels by Ca-alginate not only provided a structural framework for the citrus peel particles but also preserved the high-efficiency Se(IV) removal property of the citrus peels. From the modeling results, it was established that Se(IV) biosorption followed the fixed-film diffusion model, along with pseudo-second-order kinetics. Investigation of pH impacts along with initial dosing of sorbent/sorbate demonstrated that all of the three biosorbents exhibited optimum biosorption of Se(IV) at pH 6-8, 50-75 mg·L^-1 of Se(IV), and 1-5 mg·L^-1 of biosorbent. Overall, the maximum Se(IV) biosorption capacities were measured to be 116.2, 72.1, and 111.9 mg·g^-1 for citrus peels, Ca-alginate, and Ca-alginate@citrus, respectively, with citrus peels (bare and immobilized) showing among the highest reported values in the literature for Se(IV) adsorption. This work provides a platform for the future development of an efficient filtration system using Ca-alginate@citrus as an inexpensive, novel, and sustainable biosorbent to treat Se(IV) contaminated water.

Megamerger of biosorbents and catalytic technologies for the removal of heavy metals from wastewater: Preparation, final disposal, mechanism and influencing factors

Heavy metal pollution, because of its high toxicity, non-biodegradability and biological enrichment, has been identified as a global aquatic ecosystems threat in recent decades. Due to the high efficiency, low cost, satisfactory recyclability, easy storage and separation, biosorbents have exhibited a promising prospect for heavy metals treatment in aqueous phase. This article comprehensively summarized different types of biosorbents derived from available low-cost raw materials such as agricultural and forestry wastes. The raw materials obtained are treated with conventional pretreatment or novel methods, which can greatly enhance the adsorption performance of the biosorbents. The suitable immobilization methods can not only further enhance the adsorption performance of the biosorbents, but also facilitate the process of separating the biosorbents from the wastewater. In addition, once biosorbents are put into large-scale use, the final disposal problems cannot be avoided. Therefore, it is necessary to review the currently accepted final disposal methods of biosorbents. Moreover, through the analysis of the adsorption and desorption mechanisms of biosorbents, it is not only beneficial to find the better methods to improve the adsorption performance of the biosorbents, but also better to explain the influencing factors of adsorption effect for biosorbents. Especially, different from many researches focused on biosorbents, this work highlighted the combination of biosorbents with catalytic technologies, which provided new ideas for the follow-up research direction of biosorbents. Finally, the purpose of this paper is to inject new impetus into the future development of biosorbents.

Self-assembly biochar colloids mycelial pellet for heavy metal removal from aqueous solution

To effectively improve the heavy metal removal efficiency and stability of biomass adsorbents, a novel biochar colloids-mycelial pellets (BC-MP) composite was prepared via a biological assembly method. BC-MP was successfully produced with increased surface area and multisorption sites by physical adsorption, electrostatic interaction and hydrogen-bond formation between BC and extracellular polymers on MP. To investigate the performance and mechanisms of heavy metal adsorption by BC-MP, batch experiments were conducted with cadmium (Cd (II)) as the model pollutant. Results showed that BC-MP had higher removal efficiency (57.66%) compared to BC (5.45%) and MP (38.45%), respectively, due to the synergistic effect. The maximum adsorption capacity of Cd (II) on BC-MP was 102.04 mg/g based on Langmuir isotherm model. Adsorption kinetics analysis indicated that chemical sorption was the key factor controlling the adsorption of Cd (II) onto BC-MP. Multiple characterization tests revealed that the main mechanisms of the adsorption process were surface complexation, cation exchange and precipitation. The BC-MP composite showed excellent heavy metal removal efficiency with long-term adsorption stability, suggesting its potential as a promising biosorbent for heavy metal removal from industrial wastewater.

Enhanced removal of trichlorfon and Cd(II) from aqueous solution by magnetically separable chitosan beads immobilized Aspergillus sydowii

Simultaneous removal of heavy metals and organics from wastewater has always been an environmental problem with great concern. In this study, a novel ecofriendly bioborbent, magnetic chitosan beads immobilized Aspergillus sydowii (MCBAs) were synthesized and used to simultaneously remove trichlorfon (TCF) and Cd(II) from aqueous solution. MCBAs showed an increased special surface area (55.38 m²·g^-1) through immobilizing A. sydowii and its saturation magnetization reached 14.62 emu·g^-1. The equilibrium removal capacities of TCF and Cd(II) were 135.43 mg·g^-1 and 56.40 mg·g^-1 in the co-system with 200 mg·L^-1 TCF and 50 mg·L^-1 Cd(II), respectively. The removal capacities of TCF and Cd(II) were strongly depended on the immobilized A. sydowii spore concentration, initial concentrations of TCF and Cd(II), and MCBAs dose. TCF biodegradation intermediates were identified by gas chromatography-mass spectrometry system. Fourier transform infrared spectra displayed that -OH and -NH groups on MCBAs mainly participated in the Cd(II) sequestration and the CO stretching vibration was possibly related to the degradation intermediates of TCF. MCBAs exhibited excellent recyclability upto four cycles. Therefore, MCBAs are suitable and effective for the simultaneous removal of TCF and Cd(II) from wastewater.

Phytoremediation of Heavy Metal Pollution: A Bibliometric and Scientometric Analysis from 1989 to 2018

This paper aims to evaluate the knowledge landscape of the phytoremediation of heavy metals (HMs) by constructing a series of scientific maps and exploring the research hotspots and trends of this field. This study presents a review of 6873 documents published about phytoremediation of HMs in the international context from the Web of Science Core Collection (WoSCC) (1989–2018). Two different processing software applications were used, CiteSpace and Bibliometrix. This research field is characterized by high interdisciplinarity and a rapid increase in the subject categories of engineering applications. The basic supporting categories mainly included “Environmental Sciences & Ecology”, “Plant Sciences”, and “Agriculture”. In addition, there has been a trend in recent years to focus on categories such as “Engineering, Multidisciplinary”, “Engineering, Chemical”, and “Green & Sustainable Science & Technology”. “Soil”, “hyperaccumulator”, “enrichment mechanism/process”, and “enhance technology” were found to be the main research hotspots. “Wastewater”, “field crops”, “genetically engineered microbes/plants”, and “agromining” may be the main research trends. Bibliometric and scientometric analysis are useful methods to qualitatively and quantitatively measure research hotspots and trends in phytoremediation of HM, and can be widely used to help new researchers to review the available research in a certain research field.