Uranium removal by novel graphene oxide-immobilized Saccharomyces cerevisiae gel beads

Enhanced uranium removal from aqueous solution by core-shell Fe0@Fe3O4: Insight into the synergistic effect of Fe0 and Fe3O4

In this study, Fe0@Fe3O4 was synthesized and used to remove U(VI) from groundwater. Different experimental conditions and cycling experiments were used to investigate the performance of Fe0@Fe3O4 in the U(VI) removal, and the XRD, TEM, XPS and XANES techniques were employed to characterize the Fe0@Fe3O4. The results showed that the U(VI) removal efficiency of Fe0@Fe3O4 was 48.5 mg/g that was higher than the sum of removal efficiency of Fe0 and Fe3O4. The uranium on the surface of Fe0@Fe3O4 mainly existed as U(IV), followed by U(VI) and U(V). The Fe0 content decreased after reaction, while the Fe3O4 content increased. Based on the results of experiments and characterization, the enhanced removal efficiency of Fe0@Fe3O4 was attributed to the synergistic effect of Fe0 and Fe3O4 in which Fe3O4 accelerated the Fe0 corrosion that promoted the progressively formation of Fe(II) that promoted the reduction of adsorbed U(VI) to U(IV) and incorporated U(VI) to U(V). The performance of Fe0@Fe3O4 at near-neutrality condition was better than at acidic and alkalic conditions. The chloride ions, sulfate ions and nitrate ions showed minor effect on the Fe0@Fe3O4 performance, while carbonate ions exhibited significant inhibition. The metal cations showed different effect on the Fe0@Fe3O4 performance. The removal efficiency of Fe0@Fe3O4 decreased with the number of cycling experiment. Ionizing radiation could regenerate the used Fe0@Fe3O4. This study provides insight into the U(VI) removal by Fe0@Fe3O4 in aqueous solution.

Screening and performance optimization of fungi for heavy metal adsorption in electrolytes

The resource recovery and reuse of precious metal-laden wastewater is widely recognized as crucial for sustainable development. Superalloy electrolytes, produced through the electrolysis of superalloy scrap, contain significant quantities of precious metal ions, thereby possessing substantial potential for recovery value. This study first explores the feasibility of utilizing fungi to treat Superalloy electrolytes. Five fungi resistant to high concentrations of heavy metals in electrolytes (mainly containing Co, Cr, Mo, Re, and Ni) were screened from the soil of a mining area to evaluate their adsorption characteristics. All five fungi were identified by ITS sequencing, and among them, Paecilomyces lilacinus showed the best adsorption performance for the five heavy metals; therefore, we conducted further research on its adsorption characteristics. The best adsorption effect of Co, Cr, Mo, Re, and Ni was 37.09, 64.41, 47.87, 41.59, and 25.38%, respectively, under the conditions of pH 5, time 1 h, dosage 26.67 g/L, temperature 25-30°C, and an initial metal concentration that was diluted fivefold in the electrolyte. The biosorption of Co, Mo, Re, and Ni was better matched by the Langmuir model than by the Freundlich model, while Cr displayed the opposite pattern, showing that the adsorption process of P. lilacinus for the five heavy metals is not a single adsorption mechanism, but may involve a multi-step adsorption process. The kinetics study showed that the quasi-second-order model fitted better than the quasi-first-order model, indicating that chemical adsorption was the main adsorption process of the five heavy metals in P. lilacinus. Fourier transform infrared spectroscopy revealed that the relevant active groups, i.e., hydroxyl (-OH), amino (-NH2), amide (- CONH2), carbonyl (-C = O), carboxyl (-COOH), and phosphate (PO43-), participated in the adsorption process. This study emphasized the potential application of P. lilacinus in the treatment of industrial wastewater with extremely complex background values.

Uranium removal in groundwater by Priestia sp. isolated from uranium-contaminated mining soil

Priestia sp. WW1 was isolated from a uranium-contaminated mining soil and identified. The uranium removal characteristics and mechanism of Priestia sp. WW1 were investigated. The results showed that the removal efficiency of uranium decreased with the increase of initial uranium concentration. When the uranium initial concentration was 5 mg/L, the uranium removal efficiency achieved 92.1%. The increase of temperature could promote the uranium removal. Carbon source could affect the removal rate of uranium, which was the fastest when the methanol was used as carbon source. The solution pH had significant effect on the uranium removal efficiency, which reached the maximum under solution pH 5.0. The experimental results and FTIR as well as XPS demonstrated that Priestia sp. WW1 could remove uranium via both adsorption and reduction. The common chloride ions, sulfate ions, Mn(II) and Cu(II) enhanced the uranium removal, while Fe(III) depressed the uranium removal. The Priestia sp. WW1 could effectively remove the uranium in the actual mining groundwater, and the increase of initial biomass could improve the removal efficiency of uranium in the actual mining groundwater. This study provided a promising bacterium for uranium remediation in the groundwater.

Environmental biotechnology and the involving biological process using graphene-based biocompatible material

Biotechnology is a promising approach to environmental remediation but requires improvement in efficiency and convenience. The improvement of biotechnology has been illustrated with the help of biocompatible materials as biocarrier for environmental remediations. Recently, graphene-based materials (GBMs) have become promising materials in environmental biotechnology. To better illustrate the principle and mechanisms of GBM application in biotechnology, the comprehension of the biological response of microorganisms and enzymes when facing the GBMs is needed. The review illustrated distinct GBM-microbe/enzyme composites by providing the GBM-microbe/enzyme interaction and the determining factors. There are diverse GBM modifications for distinct biotechnology applications. Each of these methods and applications depends on the physicochemical properties of GBMs. The applications of these composites were mainly categorized as pollutant adsorption, anaerobic digestion, microbial fuel cells, and organics degradation. Where information was available, the strategies and mechanisms of GBMs in improving application efficacies were also demonstrated. In addition, the biological response, from microbial community changes, extracellular polymeric substances changes to biological pathway alteration, may become important in the application of these composites. Furthermore, we also discuss challenges facing the environmental application of GBMs, considering their fate and toxicity in the ecosystem, and offer potential solutions. This research significantly enhances our comprehension of the fundamental principles, underlying mechanisms, and biological pathways for the in-situ utilization of GBMs.

Fabrication of phosphoric-crosslinked chitosan@g-C3N4 gel beads for uranium(VI) separation from aqueous solution

In this work, a novel g-C₃N₄ filled, phosphoric-crosslinked chitosan gel bead (P-CS@CN) was successfully prepared to adsorb U(VI) from water. The separation performance of chitosan was improved by introducing more functional groups. At pH 5 and 298 K, the adsorption efficiency and adsorption capacity could reach 98.0 % and 416.7 mg g^-1, respectively. After adsorption, the morphological structure of P-CS@CN did not change and adsorption efficiency remained above 90 % after 5 cycles. P-CS@CN exhibited an excellent applicability in water environment based on dynamic adsorption experiments. Thermodynamic analyses demonstrated the value of ΔG, manifesting the spontaneity of U(VI) adsorption process on P-CS@CN. The positive values of ΔH and ΔS showed that the U(VI) removal behavior of P-CS@CN was an endothermic reaction, indicating that the increase of temperature was great benefit to the removal. The adsorption mechanism of P-CS@CN gel bead could be summarized as the complexation reaction with the surface functional groups. This study not only developed an efficient adsorbent for the treatment of radioactive pollutants, but also provided a simple and feasible strategy for the modification of chitosan-based adsorption materials.

Sustainable removal of uranium from acidic wastewater using various mineral raw materials

Various types of plutonic and volcanic rocks and their alteration products from Greece (serpentinite, magnesite and andesite), have been used for sustainable removal of Uranium (U) from the acidic drainage of Kirki mine, as well as for the pH increase of the polluted solutions. In this light, this study aims at the further understanding and improvement of the ecofriendly reuse of sterile, natural raw materials (including those remaining through industrial processing and engineering testing of aggregate rocks), for remediation of acid mine drainage. The selected rocks constitute such residues of sterile materials were used as filters in experimental continuous flow devices in the form of batch-type columns, in order to investigate acidic remediation properties with special focus on U removal. The initial pH of the wastewater was 2.90 and increased after seven (7) days of experimental application and more specifically from the fourth day onwards. Uranium removal became quantitatively significant once pH reached the value of 5.09. The volcanic rocks appeared to be more effective for U removal than the plutonic ones because of microtextural differences. However, optimum U removal was mainly achieved by serpentinite: while the raw materials rich in Mg strongly reacted and remediated the pH of the drainage water waste. Furthermore, the increase of pH values due to the presence of mineral raw materials, provided increased oxidation potential which deactivated the toxic load of metals, particularly U. Consequently, batch-type serpentinite reaction with the tailing fluid caused a drop in U concentration from an initial value of 254 ppb to the one of 8 ppb, which corresponds to 97% of removal. Andesite presented the second best reactant for experimental remediation, especially when it was mixed with magnetically separated mineral fractions. Despite the fact that the proposed methodology is currently at a relatively low Technology Readiness Level (TRL), it carries the potential to become an extremely effective and low-cost alternative to conventional environmental restoration technologies.

Development of multifarious carrier materials and impact conditions of immobilised microbial technology for environmental remediation: A review

Microbial technology is the most sustainable and eco-friendly method of environmental remediation. Immobilised microorganisms were introduced to further advance microbial technology. In immobilisation technology, carrier materials distribute a large number of microorganisms evenly on their surface or inside and protect them from external interference to better treat the targets, thus effectively improving their bioavailability. Although many carrier materials have been developed, there have been relatively few comprehensive reviews. Therefore, this paper summarises the types of carrier materials explored in the last ten years from the perspective of structure, microbial activity, and cost. Among these, carbon materials and biofilms, as environmentally friendly functional materials, have been widely applied for immobilisation because of their abundant sources and favorable growth conditions for microorganisms. The novel covalent organic framework (COF) could also be a new immobilisation material, due to its easy preparation and high performance. Different immobilisation methods were used to determine the relationship between carriers and microorganisms. Co-immobilisation is particularly important because it can compensate for the deficiencies of a single immobilisation method. This paper emphasises that impact conditions also affect the immobilisation effect and function. In addition to temperature and pH, the media conditions during the preparation and reaction of materials also play a role. Additionally, this study mainly reviews the applications and mechanisms of immobilised microorganisms in environmental remediation. Future development of immobilisation technology should focus on the discovery of novel and environmentally friendly carrier materials, as well as the establishment of optimal immobilisation conditions for microorganisms. This review intends to provide references for the development of immobilisation technology in environmental applications and to further the improve understanding of immobilisation technology.

Characteristic Aspects of Uranium(VI) Adsorption Utilizing Nano-Silica/Chitosan from Wastewater Solution

A new nano-silica/chitosan (SiO₂/CS) sorbent was created using a wet process to eliminate uranium(VI) from its solution. Measurements using BET, XRD, EDX, SEM, and FTIR were utilized to analyze the production of SiO₂/CS. The adsorption progressions were carried out by pH, SiO₂/CS dose, temperature, sorbing time, and U(VI) concentration measurements. The optimal condition for U(VI) sorption (165 mg/g) was found to be pH 3.5, 60 mg SiO₂/CS, for 50 min of sorbing time, and 200 mg/L U(VI). Both the second-order sorption kinetics and Langmuir adsorption model were observed to be obeyed by the ability of SiO₂/CS to eradicate U(VI). Thermodynamically, the sorption strategy was a spontaneous reaction and exothermic. According to the findings, SiO₂/CS had the potential to serve as an effectual sorbent for U(VI) displacement.

A critical review of uranium contamination in groundwater: Treatment and sludge disposal

Dissolved uranium in groundwater at high concentrations is an emerging global threat to human and ecological health due to its radioactivity and chemical toxicity. Uranium can enter groundwater by geochemical reactions, natural deposition from minerals, mining, uranium ore processing, and spent fuel disposal. Although much progress has been made in uranium remediation in recent years, most published reviews on uranium treatment have focused on specific methods, particularly adsorption. This article systematically reviews the major treatment technologies, explains their mechanism and progress of uranium removal, and compares their performance under various environmental conditions. Of all treatment methods, adsorption has received much attention due to its ease of use and adaptability under various conditions. However, salinity and competition from other ions limit its application in actual field conditions. Biosorption and bioremediation are also promising methods due to their low-cost and chemical-free operation. Strong base anion exchange resins are more effective at typical groundwater pH conditions. Advanced oxidation processes like photocatalysis produce less sludge and are effective even at low uranium concentrations. Electrocoagulation shows significantly improved performance when organic ligands are added prior to treatment. The significant advantages of membrane filtration are high removal efficiency and the ability to recover uranium. While each technology has its merits and demerits, no single technology is entirely suitable under all conditions. One major area of concern with all technologies is the need to dispose of liquid and solid waste generated after treatment safely. Future research must focus on developing hybrid and state-of-the-art technologies for effective and sustainable uranium removal from groundwater. Developing holistic management strategies for uranium removal will hinge on understanding its speciation, mechanisms of fate and transport, and socio-economic conditions of the affected areas.

Fabrication and investigation of novel monochloroacetic acid fortified, tripolyphosphate-crosslinked chitosan for highly efficient adsorption of uranyl ions from radioactive effluents

Chitosan crosslinked with potassium tripolyphosphate (CTPP) and monochloroacetic-acid-modified chitosan crosslinked with potassium tripolyphosphate (MCTPP) were synthesized for removing UO₂²⁺ from acidic radioactive effluents. The influential factors, operational requirements, and interactive mechanisms of the adsorption process were systematically investigated. The mesh-structured composites adsorbed UO₂²⁺ most effectively at pH 5.0. The maximum adsorption capacities for pure chitosan, CTPP, and MCTPP were 374.93, 780.89, and 1487.72 mg/g, respectively. Batch experiments indicated that the pH and adsorbent dose strongly influenced UO₂²⁺ adsorption. MCTPP could adsorb most UO₂²⁺ within 15 min, and equilibrium was reached by ~1 h. The adsorption isotherms indicated that UO₂²⁺ adsorption by MCTPP may be an endothermic single-layer adsorption process. Moreover, common metal ions in single-metal systems only slightly affected this process. The results of instrumental characterization and natural water application suggested that the highly developed pore structure and abundant tripolyphosphate groups in synthesized composites were dominant adsorption contributors besides amino and hydroxyl groups. Successful development of the novel material for efficiently adsorbing UO₂²⁺ and identification of the adsorption mechanism will provide valuable guidance to chitosan modification and further remediation practices of radioactive effluents.

Sustainable Remedy Waste to Generate SiO2 Functionalized on Graphene Oxide for Removal of U(VI) Ions

The Hummer process is applied to generate graphene oxide from carbon stocks’ discharged Zn-C batteries waste. SiO2 is produced from rice husks through the wet process. Subsequently, SiO2 reacted with graphene oxide to form silica/graphene oxide (SiO2/GO) as a sorbent material. XRD, BET, SEM, EDX, and FTIR were employed to characterize SiO2/GO. Factors affecting U(VI) sorption on SiO2/GO, including pH, sorption time, a dosage of SiO2/GO, U(VI) ions’ concentration, and temperature, were considered. The experimental data consequences indicated that the uptake capacity of SiO2/GO towards U(VI) is 145.0 mg/g at a pH value of 4.0. The kinetic calculations match the pseudo second-order model quite well. Moreover, the sorption isotherm is consistent with the Langmuir model. The sorption procedures occur spontaneously and randomly, as well as exothermically. Moreover, SiO2/GO has essentially regenerated with a 0.8 M H2SO4 and 1:50 S:L phase ratio after 60 min of agitation time. Lastly, the sorption and elution were employed in seven cycles to check the persistent usage of SiO2/GO.

A novel freeze-dried natural microalga powder for highly efficient removal of uranium from wastewater

It is of great significance to develop convenient methods and low-cost materials to remove uranium from wastewater. Ankistrodesmus sp., an easy growing green alga, was employed for highly efficient removal of uranium from aqueous solution. The biosorption results under different experimental condition indicate that the alga possess outstanding uranium adsorption ability (q_max = 601.2 mg g^-1). Moreover, Ankistrodesmus sp. could be effectively regenerated with hydrochloric acid solution (0.1 M) and used again for uranium adsorption. Even in simulated mine water with various coexisting ions, Ankistrodesmus sp. also exhibits high removal efficiency (95.6%) towards uranium. Furthermore, the adsorption behavior of uranium by alga could be described in the Freundlich isotherms model and the adsorption process was consistent with the pseudo-second-order kinetics model. The characteristic of Fourier transform infrared spectrum, scanning electron microscopy, transmission electron microscope and X-ray photoelectron spectroscopy reveal that -NH₂, -COOH, -CONH₂ and C-O groups have participated in biosorption process. Therefore, complexation, electrostatic adsorption and ions exchange are the dominated action of uranium biosorption in the algae. All findings in this work suggest that Ankistrodesmus sp. can be a promising candidate for the effective and practical application in field of disposed uranium contamination.

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.

Removal of PAHs at high concentrations in a soil washing solution containing TX-100 via simultaneous sorption and biodegradation processes by immobilized degrading bacteria in PVA-SA hydrogel beads

Soil washing process enhanced by surfactants is a promising technique in removing organic pollutants from soil. In this work, a simultaneous sorption and biodegradation technique was used to remove 16 PAHs from a soil washing solution (SWS) obtained by rinsing a heavily contaminated soil from a coking plant with Triton X-100 (TX-100). This was done by immobilizing a pyrene-degrading bacterial strain in polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads. Removal performance of free bacteria, blank PVA-SA beads and beads with immobilized degrading bacteria at a low, medium and high initial concentration was evaluated. The recycling and removal performance of the used beads were also examined. Our findings showed that hydrogel beads with immobilized bacteria at a medium concentration can remove around 77% ∑16PAHs from SWS in 96 h. The beads can be recycled and reused to treat a new SWS; 32-55% ∑16PAHs was removed in 24 h. The bead provided protection for bacteria against the co-existing substances such as TX-100. The bacteria-immobilized beads are more efficient and sustainable than free bacteria and blank beads due to simultaneous sorption and biodegradation processes, thus providing a solid reference for possible industrial application of bacteria immobilization technique to deal with SWSs with complex composition.

Use of calcium alginate beads and Saccharomyces cerevisiae for biosorption of 241Am

Calcium alginate beads, inactivated Saccharomyces cerevisiae and inactivated S. cerevisiae immobilized in calcium alginate beads (S. cerevisiae-calcium alginate beads) are examined as potential biosorption materials as regards their capacity to remove ²⁴¹Am. In this study, initial experiments were carried out to evaluate the effects of pH (2 and 4) and ²⁴¹Am initial concentration: 75, 150, and 300 Bq mL^-1. The experiments were conducted in a batch reactor. Higher removal capacity was observed at pH 2 with the use of S. Cerevisiae, whereas pH 4 performed better for the essays with calcium alginate beads and S. Cerevisiae-calcium alginate beads. The pseudo-first-order kinetic model described the kinetics of biosorption. Calcium alginate was the adsorbent of choice to further experiments with synthetic organic liquid waste. A lower removal rate was observed in the organic waste, although calcium alginate beads have also been able to achieve high sorption capacity in less than 4 h. With the organic waste, the highest value of sorption capacity of ²⁴¹Am was 4.38 × 10^-7 mmol g^-1 with an initial ²⁴¹Am concentration of 2.31 × 10^-8 mmol L^-1.

Kinetics of a fixed bed reactor with immobilized microorganisms for the removal of organic matter and phosphorous

The biodegradation of domestic wastewater contaminants has been carried out using microorganisms immobilized in sodium alginate gel (Alg-Na). A fixed bed reactor with immobilized microorganisms was used for the treatment of domestic wastewater. A wastewater pretreatment was carried out to remove the larger particulate matter, which consisted of a reactor packed with different materials (anthracite, zeolite, and activated carbon). Later, a second reactor packed with balls with immobilized microorganisms was used to eliminate organic matter and nutrients. 2.5% w/v of Alg-Na was used as a support to immobilize the microorganisms. According to the results, a total phosphorus (TP) and chemical oxygen demand (COD) removal of 94.26% and 78.25% was obtained, respectively. In addition, the degradation rate for both organic matter and phosphorous was studied by using the kinetic model for fix bed reactor. © 2020 Water Environment Federation PRACTITIONER POINTS: Phosphorous and organic matter removal by adsorption and immobilized microorganisms. High removal efficiency of phosphorous and organic matter was found. An innovative wastewater treatment alternative is proposed. Kinetic model for fixed bed reactor is also proposed for scaling-up purposes.

Adsorption isotherm models: Classification, physical meaning, application and solving method

Adsorption is widely applied separation process, especially in environmental remediation, due to its low cost and high efficiency. Adsorption isotherm models can provide mechanism information of the adsorption process, which is important for the design of adsorption system. However, the classification, physical meaning, application and solving method of the isotherms have not been systematical analyzed and summarized. In this paper, the adsorption isotherms were classified into adsorption empirical isotherms, isotherms based on Polanyi's theory, chemical adsorption isotherms, physical adsorption isotherms, and the ion exchange model. The derivation and physical meaning of the isotherm models were discussed in detail. In addition, the application of the isotherm models were analyzed and summarized based on over 200 adsorption equilibrium data in literature. The statistical parameters for evaluating the fitness of the models were also discussed. Finally, a user interface (UI) was developed based on Excel software for solving the isotherm models, which was provided in supplemental material and can be easily used to model the adsorption equilibrium data. This paper will provide theoretical basis and guiding methodology for the selection and use of the adsorption isotherms.

Removal of radionuclides from acidic solution by activated carbon impregnated with methyl- and carboxy-benzotriazoles

The removal efficiencies of metals commonly used to model the fate and transport of aqueous uranium and radioactive its daughter products, were observed on activated carbons impregnated with different benzotriazole derivatives. Acidic solutions containing U(VI), Sr(II), Eu(III), and Ce(III) were used to determine the immobilization potential of carboxybenzotriazole (CBT) and methylbenzotriazole (MeBT), where these derivatives were sorbed to different types of granular activated carbon (GAC). This sorption behavior can be predicted by Redlich–Peterson model. Flow-through column tests showed that the immobilization of uranium and some of its daughter products, significantly improves in response to oxidized GACs saturated with carboxybenzotrzole (CBT), which reached a maximum elimination for U(VI) at 260 BV, Eu(III) at 114 BV, Ce(III) at 126 BV, and Sr(II) at 100. MeBT significantly desorbed from GAC under acidic conditions. Trace amounts of CBT were observed in some column effluents, but this did not appear to alter the effectiveness of metal removal, regardless of the model radionuclide studied. These results suggest that enhanced immobilization of selected metals on GAC, can be achieved by impregnating oxidized activated carbon with carboxylated benzotriazoles, and that metal removal efficiency on this media, is related to their valence and ionic radius in acidic environments.

Utilization of grape pomaces and brewery waste Saccharomyces cerevisiae for the production of bio-based microencapsulated pigments

This research approaches the utilization of brewery waste yeast Saccharomyces cerevisiae as a vehicle for the encapsulation and protection of phenolic compounds from Cabernet Sauvignon and Bordeaux grape pomace extracts. The main purpose of this research was to enrich the biomass of yeast to investigate its potential as a novel vehicle for further application as pigment or functional ingredient. The obtained powders presented characteristics appropriated for storage, such as low water activity (<0.289), hygroscopicity (<13.71 g/100 g) and moisture (<7.10%) and particle sizes lower than the sensory perceptible (<11.45 µm). This work proved that yeasts were loaded after spray-drying, thus, they might be considered as biocapsules. Furthermore, the bioaccessibility of encapsulated phenolic compounds from Bordeaux and Cabernet Sauvignon extracts was 34.96% and 14.25% higher compared to their respective free extracts, proving that yeasts are not only biocapsules of easy application, but also a biological material capable of protecting and delivering the compounds during gastrointestinal digestion.

Removal of Arsenic, Chromium and Uranium from Water Sources by Novel Nanostructured Materials Including Graphene-Based Modified Adsorbents: A Mini Review of Recent Developments

Groundwater is commonly used as a drinking water resource all over the world. Therefore, groundwater contamination by toxic metals is an important issue of utmost concern for public health, and several technologies are applied for their effective removal, such as coagulation, ion exchange, adsorption, and membrane applications like reverse osmosis. Adsorption is acknowledged as a simple, effective and economic technology, which has received increased interest recently, despite certain limitations regarding operational applications. The respective scientific efforts have been specifically focused on the development and implementation of novel nano-structured adsorbent materials, which may offer extensive specific surface areas, much higher than the conventional adsorbents, and hence, are expected to present higher removal efficiencies of pollutants. In this paper, the recent developments of nanomaterial applications for arsenic, chromium and uranium removal from groundwaters are critically reviewed. Particularly, the use of novel composite materials, based mainly on hybrid metallic oxide nanoparticles and on composites based on graphene oxide (GO) (i.e., graphene-based hybrids), showed promising evidences to achieve efficient removal of toxic metals from water sources, even in full scale applications.

Biosorption of uranium by immobilized Saccharomyces cerevisiae

A novel biosorbent was prepared and applied for the removal of uranium from aqueous solution. A new immobilization method was studied and used to embed living yeast cells of Saccharomyces cerevisiae (2% w/v) by sodium sulfate (0.5 mol/L) based on saturated boric acid-alginate calcium cross-linking method. The swelling ratio, hydraulic and chemical stability and bioactivity of immobilized microbial cells were examined. Their ultra-microstructure and property were observed by SEM, TEM and FTIR techniques. The influencing factors, such as contact time, initial uranium concentration, and initial pH were investigated. The adsorption capacity of biosorbent increased from 0.75 to 113.4 μmol/g when the equilibrium concentration of U was 0.9, and 43.9 μmol/L, respectively. U adsorption followed pseudo first-order kinetic model. SEM-EDS and TEM-EDS observation indicated that uranium was adsorbed both on the surface and the inner parts of the biosorbent. FTIR and the XPS results confirmed the role of oxygen in capturing uranium from aqueous solution. XPS analysis showed that the mixture of U (VI) and U (IV) existed on the surface of biosorbent, which evidenced that uranium was microbiologically reduced.

RADIOACTIVE REMEDIATION OF AQUATIC ECOSYSTEMS USING MICROALGAE

Radionuclides that have entered the environment through nuclear weapon tests, nuclear accidents or other human activities represent an ecological hazard. Many decontamination techniques are technically and financially demanding and often not environmentally beneficial. A suitable alternative is bioremediation techniques. One of them, phycoremediation utilizes the metabolic activity of microorganisms that degrade or eliminate contaminants from the environment. In our work, we focused on phycoremediation with microalgae Dunaliella salina and Chlorella vulgaris. An important parameter was the determination of the optimal pH values of the environment and subsequent monitoring of the radionuclide activity decline over time.

Copolymeric Hydrogel-Based Immobilization of Yeast Cells for Continuous Biotransformation of Fumaric Acid in a Microreactor

Although enzymatic microbioreactors have recently gained lots of attention, reports on the use of whole cells as biocatalysts in microreactors have been rather modest. In this work, an efficient microreactor with permeabilized Saccharomyces cerevisiae cells was developed and used for continuous biotransformation of fumaric into industrially relevant L-malic acid. The immobilization of yeast cells was achieved by entrapment in a porous structure of various hydrogels. Copolymers based on different ratios of sodium alginate (SA) and polyvinyl alcohol (PVA) were used for hydrogel formation, while calcium chloride and boric or phenylboronic acid were tested as crosslinking agents for SA and PVA, respectively. The influence of hydrogel composition on physico-chemical properties of hydrogels prepared in the form of thin films was evaluated. Immobilization of permeabilized S. cerevisiae cells in the selected copolymeric hydrogel resulted in up to 72% retained fumarase activity. The continuous biotransformation process using two layers of hydrogels integrated into a two-plate microreactor revealed high space time yield of 2.86 g/(L·h) while no activity loss was recorded during 7 days of continuous operation.

Removal of Cadmium from Aqueous Solutions by Saccharomyces cerevisiae-Alginate System

The aim of this study was to determine the Cd²⁺ removal capacity of a biosorbent system formed by Saccharomyces cerevisiae in calcium alginate beads. The adsorption of Cd²⁺ by a S. cerevisiae–alginate system was tested either by batch or fixed-bed column experiments. The S. cerevisiae–alginate system was characterized using dynamic light scattering (DLS, zeta potential), size, hardness, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy. Beads of the S. cerevisiae–alginate system showed a spherical–elliptical morphology, diameter of 1.62 ± 0.02 mm, 96% moisture, negative surface charge (−29.3 ± 2.57 mV), and texture stability during storage at 4 °C for 20 days. In batch conditions, the system adsorbed 4.3 µg of Cd²⁺/g of yeast–alginate beads, using a Cd²⁺ initial concentration of 5 mg/L. Adsorption capacity increased to 15.4 µg/g in a fixed-bed column system, removing 83% of total Cd²⁺. In conclusion, the yeast–alginate system is an efficient option for the removal of cadmium at low concentrations in drinking water.

Uranium biosorption by immobilized active yeast cells entrapped in calcium-alginate-PVA- GO-crosslinked gel beads

A novel biosorbent, i. e. Saccharomyces cerevisiae entrapped in graphene oxide (GO), polyvinyl alcohol (PVA) and alginate and cross-linked in CaCl2- boric acid solution, was prepared, characterized and applied for U (VI) biosorption. The performance of U sorption and cations release (Na, K, Ca and Mg ions) was investigated under different contact time, initial uranium concentration and initial pH. Uranium sorption equilibrium basically achieved after 360 min. The kinetic data of U biosorption and Ca release were best described by the pseudo first-order equation. Both Langmuir and Freundlich models could fit the U sorption isotherm data. With increase of initial uranium (3.7 ~ 472.2 μmol/L) and sodium concentration (78.8 ~ 3911.7 μmol/L), the cations release ((Na + K)/2 + (Ca + Mg)) decreased from 116.9 to 30.1 μmol/g when the corresponding U sorption increased from 0.6 to 77.3 μmol/g. Initial solution pH at 3 was favorable for U sorption when pH ranged from 3 to 7. With increase of uranium concentration, ion exchange played a less role in U removal. The maximum U sorption capacity reached 142.1 μmol/g, calculated from the Langmuir model at initial pH 5. The O-containing functional group, such as carboxyl on the gel bead played an important role in U adsorption according to FTIR and XPS analysis. XPS analysis showed the existence of U (VI) and U (IV) on the surface of gel bead. Ion exchange, complexation and uranium reduction involved in uranium adsorption by the immobilized active dry yeast gel beads.

Characterization and mechanism of copper biosorption by a highly copper-resistant fungal strain isolated from copper-polluted acidic orchard soil

In this paper, a highly copper-resistant fungal strain NT-1 was characterized by morphological, physiological, biochemical, and molecular biological techniques. Physiological response to Cu(II) stress, effects of environmental factors on Cu(II) biosorption, as well as mechanisms of Cu(II) biosorption by strain NT-1 were also investigated in this study. The results showed that NT-1 belonged to the genus Gibberella, which exhibited high tolerance to both acidic conditions and Cu(II) contamination in the environment. High concentrations of copper stress inhibited the growth of NT-1 to various degrees, leading to the decreases in mycelial biomass and colony diameter, as well as changes in morphology. Under optimal conditions (initial copper concentration: 200 mg L^-1, temperature 28 °C, pH 5.0, and inoculum dose 10%), the maximum copper removal percentage from solution through culture of strain NT-1 within 5 days reached up to 45.5%. The biosorption of Cu(II) by NT-1 conformed to quasi-second-order kinetics and Langmuir isothermal adsorption model and was confirmed to be a monolayer adsorption process dominated by surface adsorption. The binding of NT-1 to Cu(II) was mainly achieved by forming polydentate complexes with carboxylate and amide group through covalent interactions and forming Cu-nitrogen-containing heterocyclic complexes via Cu(II)-π interaction. The results of this study provide a new fungal resource and key parameters influencing growth and copper removal capacity of the strain for developing an effective bioremediation strategy for copper-contaminated acidic orchard soils.

Immobilized microbial biosorbents for heavy metals removal

Intensive industrial and urban growth has led to the release of increasing amounts of environmental pollutants. Contamination by metals, in particular, deserves special attention due to their toxicity and potential to bioaccumulate via the food chain. Conventional techniques for the removal of toxic metals, radionuclides and precious metals from wastewater all have a number of drawbacks, such as incomplete metal extraction, high cost and risk of generating hazardous by-products. Biosorption is a cost-effective and environment-friendly technology, an alternative to conventional wastewater treatment methods. Biosorption is a metabolically independent process, in which dead microbial biomass is capable of removal and concentrating metal ions from aqueous solutions. Free microbial biosorbents are of small size and low density, insufficient mechanical stability and low elasticity, which causes problems with metal ion desorption, separation of the sorbent from the medium and its regeneration. Hence, the possibilities for the implementation of continuous biosorbent processes for metal removal in flow-type reactor systems are reduced and the practical application of biosorption in industrial conditions is limited. By immobilizing microbial biomass on suitable carriers the disadvantages of free biosorbents are eliminated and more opportunities for practical use of biosorption become available. This review examines different immobilization techniques and carriers, certain basic features and possibilities of using immobilized microbial biosorbents for the removal and concentration of metals from aqueous solutions.

Biosorption of strontium ions from simulated high-level liquid waste by living Saccharomyces cerevisiae

In this study, the Saccharomyces cerevisiae (S. cerevisiae) was modified by γ-ray. The RNA-seq results reflect that the high γ-ray energies could change some gene fragments, such as deletion, recombination, and mutation. The biosorption of strontium ions (Sr²⁺) to different types of S. cerevisiae (S. cerevisiae (K-0), modified S. cerevisiae (Y-7), and non-living S. cerevisiae (H-K)) from the simulated high-level liquid waste (S-HLLW) was assessed at different experimental conditions. The sorption experimental results show that, under an appropriate condition, γ-ray radiation can enhance its biosorption capacity slightly of Sr²⁺ to S. cerevisiae. The maximum metal uptake and efficiency of Y-7 under S-HLLW were 11.656 mg g^-1 and 37.91% at 32 h (wet weight), respectively. They decreased to 9.46 mg g^-1 and 30.76% under radiation conditions. SEM-EDX and TEM analysis indicates that Sr²⁺ was adsorbed both on the cellular surface and the inner parts of the cells. Our experimental results fit well to the Langmuir and Freundlich model isotherms (r² > 0.94), and the maximum biosorption capacity values reached q_max > 24.74 mg g^-1 at 32 °C. Negative values of ΔG⁰ and positive values of ΔH⁰ were observed, indicating the spontaneous and endothermic nature of Sr²⁺ biosorption on modified S. cerevisiae. The biosorption kinetics follow a pseudo-second-order equation at 32 °C (r² > 0.94). The desorption efficiency of Sr²⁺ adsorbed onto Y-7 was 7.65 ± 0.52%, 76.51 ± 2.13%, and 65.62 ± 2.42% by deionized water, 1 M HCl, and 0.1 M EDTA-Na, respectively. However, they were lower than H-K (18.82, 83.32, and 73.32%). Our findings demonstrate that living S. cerevisiae (Y-7) is a promising sorbent material for the treatment of radioactive process streams.

Adsorptive extraction of uranium (VI) from seawater using dihydroimidazole functionalized multiwalled carbon nanotubes

The adsorptive extraction of uranium (VI) was investigated using multiwalled carbon nanotubes functionalized with dihydroimidazole (DIM-MWCNTs). Dihydroimidazole was grafted onto the surface of MWCNTs via silane coupling agent, N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole. The new adsorbent was characterized using Fourier transform infrared, scanning electron microscope and X-ray Photoelectron Spectroscopy. DIM-MWCNTs were compared with MWCNTs and amidoxime modified MWCNTs (AO-MWCNTs) for uranium adsorption under seawater conditions. The adsorption capacity of uranium onto DIM-MWCNTs was 54.9 mg g−1 at 298 K, which was about 4 times of MWCNTs and similar to that of AO-MWCNTs. Compared with AO-MWCNTs, DIM-MWCNTs were more suitable for seawater pH, and less affected by vanadium. Although DIM-MWCNTs were more affected by carbonate than AO-MWCNTs, DIM-MWCNTs maintained a higher adsorption capacity than AO-MWCNTs due to its alkali resistance. Pyridine-like nitrogen (CH=N–CH) contributed to the adsorption of uranium. The results suggested that DIM-MWCNTs were a potential effective adsorbent for the separation of uranium under seawater condition.

Efficient decontamination of naturally occurring radionuclide from aqueous carbonate solutions by ion flotation process

The present study evaluates the performance of ion flotation process for removal of uranyl tricarbonate complex, UO2(CO3)3 4−, which is the dominant species in many aqueous media particularly seawater, from aqueous solutions using cetyltrimethylammonium bromide, CTAB, as a cationic surfactant. Flotation of UO2(CO3)3 4− as a function in the solution pH is investigated in absence and in presence of carbonate. Removal percentage >99% is achieved in the pH range 8.5–11.5 in presence of 5×10−3 M carbonate. The influence of concentrations of ethanol (0.1–2% v/v) and CTAB (5×10−5–1.4×10−3 M) show that UO2(CO3)3 4− is efficiently removed at concentrations of 0.5–1.5% v/v and 4×10−4–1×10−3 M, respectively. Based on the obtained kinetic data, the flotation mechanism and the flotation rate are investigated using two different flotation models. Floatability of UO2(CO3)3 4− in presence of different cations (Ba2+, Ca2+, Mg2+ and Sr2+) and anions (NO3 −, Br−, Cl−, SO4 2− and HPO4 2−) is studied. Except for Mg2+ and NO3 −, the flotation efficiency of UO2(CO3)3 4− is significantly decreased at concentrations higher than 1×10−3 and 5×10−3 M of the studied cations and anions, respectively. Ion flotation process is efficiently applied for removal of uranium(VI), R%>98.5%, from seawater. Accordingly, ion flotation can be considered as a promising technique and thus its feasibility for removal and/or recovery of uranium(VI) from many aqueous environment.

Functionalized hydrothermal carbon derived from waste pomelo peel as solid-phase extractant for the removal of uranyl from aqueous solution

To develop a high-performance solid-phase extractant for the separation of uranyl f, pomelo peel, a kind of waste biomass, has been employed as carbon source to prepare carbonaceous matrix through low-temperature hydrothermal carbonization (200 °C, 24 h). After being oxidized by Hummers method, the prepared hydrothermal carbon matrix was functionalized with carboxyl and phenolic hydroxyl groups (1.75 mmol g^-1). The relevant characterizations and batch studies had demonstrated that the obtained carbon material possessed excellent affinity toward uranyl (436.4 mg g^-1) and the sorption process was a spontaneous, endothermic and rapid chemisorption. The selective sorption of U(VI) from the simulated nuclear effluent demonstrated that the sorbent displayed a desirable selectivity (56.14% at pH = 4.5) for the U(VI) ions over the other 11 competitive cations from the simulated industrial nuclear effluent. The proposed synthetic strategy in the present work had turned out to be effective and practical, which provides a novel approach to prepare functional materials for the recovery and separation of uranyl or other heavy metals from aqueous environment.

Biosorption of the strontium ion by irradiated Saccharomyces cerevisiae under culture conditions

As a new-emerging method for strontium disposal, biosorption has shown advantages such as high sorption capacity; low cost. In this study, we investigated the potential of Saccharomyces cerevisiae (S. cerevisiae) in strontium disposal under culture conditions and the effects of irradiation on their biosorption capabilities. We found that S. cerevisiae can survive irradiation and grow. Pre-exposure to irradiation rendered S. cerevisiae resistant to further irradiation. Surprisingly, the pre-exposure to irradiation can increase the biosorption capability of S. cerevisiae. We further investigated the factors that influenced the biosorption efficiency, which were (strongest to weakest): pH > strontium concentration > time > temperature. In our orthogonal experiment, the optimal conditions for strontium biosorption by irradiated S. cerevisiae were: pH 7, 150 mg L^-1 strontium at the temperature of 32 °C with 30 h. The equilibrium of strontium biosorption was analyzed by Langmuir and Freundlich models, from which the formal model is found to provide a better fit for the experimental results. The kinetics of strontium biosorption by living irradiated S. cerevisiae was found to be comprised of three phases: dramatically increased during 0-9 h, decreased during 12-24 h, and increased during 30-50 h. These results provide a systematic understanding of the biosorption capabilities of irradiated S. cerevisiae, which can contribute to the development of remediating nuclear waste water.