Biosorption and bioaccumulation behavior of uranium on Bacillus sp. dwc-2: Investigation by Box-Behenken design method

Insights into the Impact of Physicochemical and Microbiological Parameters on the Safety Performance of Deep Geological Repositories

Currently, the production of radioactive waste from nuclear industries is increasing, leading to the development of reliable containment strategies. The deep geological repository (DGR) concept has emerged as a suitable storage solution, involving the underground emplacement of nuclear waste within stable geological formations. Bentonite clay, known for its exceptional properties, serves as a critical artificial barrier in the DGR system. Recent studies have suggested the stability of bentonite within DGR relevant conditions, indicating its potential to enhance the long-term safety performance of the repository. On the other hand, due to its high resistance to corrosion, copper is one of the most studied reference materials for canisters. This review provides a comprehensive perspective on the influence of nuclear waste conditions on the characteristics and properties of DGR engineered barriers. This paper outlines how evolving physico-chemical parameters (e.g., temperature, radiation) in a nuclear repository may impact these barriers over the lifespan of a repository and emphasizes the significance of understanding the impact of microbial processes, especially in the event of radionuclide leakage (e.g., U, Se) or canister corrosion. Therefore, this review aims to address the long-term safety of future DGRs, which is critical given the complexity of such future systems.

The biochemical behavior and mechanism of uranium(Ⅵ) bioreduction induced by natural Bacillus thuringiensis

For a broader understanding of uranium migration affected by microorganisms in natural anaerobic environment, the bioreduction of uranium(Ⅵ) (U(Ⅵ)) was revealed in Bacillus thuringiensis, a dominant bacterium strain with potential of uranium-tolerant isolated from uranium contaminated soil. The reduction behavior was systematically investigated by the quantitative analysis of U(Ⅳ) in bacteria, and mechanism was inferred from the pathway of electron transmission. Under anaerobic conditions, appropriate biomass and sodium lactate as electron donor, reduction behavior of U(Ⅵ) induced by B. thuringiensis was restricted by the activity of lactate dehydrogenase, which was directly affected by the initial pH, temperature and initial U(Ⅵ) concentration of bioreduction system. Bioreduction of U(Ⅵ) was driven by the generation of nicotinamide adenine dinucleotide (NADH) from enzymatic reaction of sodium lactate with various dehydrogenase. The transmission of the electrons from bacteria to U(Ⅵ) was mainly supported by the intracellular NADH dehydrogenase-ubiquinone system, this process could maintain the biological activity of cells.

Biosorption of U(VI) and mechanisms by live and dead cells of Sphingopyxis sp. YF1

Heavy metal pollution seriously threatens the environment and human health. The biosorption of heavy metals has attracted worldwide attention due to its cost-effectiveness and environmental friendliness. It is significant to develop biosorbents with excellent adsorption performance. Sphingopyxis is widely used in the removal of various organic pollutants, but its potential application in heavy metal adsorption has been largely overlooked. This study investigates the biosorption of U(VI) onto live and dead cells of a Sphingopyxis strain YF1. The effects of pH, contact time and initial ion concentration on U(VI) adsorption investigated, and kinetic and isothermal models were used to fit the adsorption results. The results show that under pH 3-6, the adsorption of U(VI) by YF1 live cells increased with the increase of the pH. Both the pseudo-first order and pseudo-second order models can satisfactorily interpret the adsorption by live and dead cells. Three isothermal adsorption models (Langmuir, Freundlich, and Sips) were used to fit the adsorption process. The adsorption of uranium by live and dead cells was best fitted by the Sips model. The maximal adsorption capacities of U(VI) by live and dead cells were 140.7 mg g-1 and 205.7 mg g-1, respectively. The mechanisms of U(VI) adsorption by Sphingopyxis sp. YF1 were revealed. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) show that U(VI) was deposited on the surface of the bacterial cells. Fourier-transform infrared spectroscopy (FTIR) shows that amine, hydroxyl, alkyl, amide I, amide II, phosphate, carboxylates and carboxylic acids were the major functional groups that are involved in U(VI) adsorption by live and dead cells. X-ray photoelectron spectroscopy (XPS) suggests that the main functional groups of live cells involved in adsorption were O = C-O, C-OH/C-O-C and N-C = O. This study indicates Sphingopyxis sp. YF1 is a high-efficiency U(VI)-adsorbing strain, promising to remove U(VI) from aquatic environment.

Kinetic and isotherm of competitive adsorption cadmium and lead onto Saccharomyces cerevisiae autoclaved cells

Heavy metal pollution has been regarded as a significant public health hazard during the industrialization, which also have exhibited various types of toxicological manifestations. Moreover, due to the high cost and toxic by-products, some conventional remediation methods were limited to heavy metals pollution control. In this work, autoclaved Saccharomyces cerevisiae was used as a biosorbent for the removal of Cd2+ and Pb2+ from single and binary ions aqueous solution system. The kinetics and isotherm of Cd2+ and Pb2+ were studied in different ion systems. The results showed that the competitive adsorption ability of S. cerevisiae to Pb2+ was stronger than that to Cd2+ in binary ions solution. To all the single ion solution of Cd2+ or Pb2+ and binary ions solution of Cd2+-Pb2+, there always existed that the adsorption of metal ions on S. cerevisiae fitted well with pseudo-second-order kinetic model and Langmuir isotherms model. The adsorption quantity qt in different solutions followed the sequence as qt (Cd2+-Pb2+) > qt (Pb2+-single) > qt (Pb2+-binary) > qt (Cd2+-single) > qt (Cd2+-binary). The autoclaved S. cerevisiae used in this research was one kind of rapid and favourable biosorbent for Pb2+ and Cd2+. In Pb2+ and Cd2+-containing solutions, sites competition and jointed toxicity of Pb2+ and Cd2+ on S. cerevisiae cells were the key to the total adsorption effect, and further researches were necessary in the next work. Thus, the current research presented that the autoclaved S. cerevisiae could be applied as an effective biosorbent for heavy metal adsorption from water environment and the design of eco-friendly technologies for the treatment of waste liquor.

A strategy for bioremediation of nuclear contaminants in the environment

Radionuclides released from nuclear contamination harm the environment and human health. Nuclear pollution spread over large areas and the costs associated with decontamination is high. Traditional remediation methods include both chemical and physical, however, these are expensive and unsuitable for large-scale restoration. Bioremediation is the use of plants or microorganisms to remove pollutants from the environment having a lower cost and can be upscaled to eliminate contamination from soil, water and air. It is a cheap, efficient, ecologically, and friendly restoration technology. Here we review the sources of radionuclides, bioremediation methods, mechanisms of plant resistance to radionuclides and the effects on the efficiency of biological adsorption. Uptake of radionuclides by plants can be facilitated by the addition of appropriate chemical accelerators and agronomic management, such as citric acid and intercropping. Future research should accelerate the use of genetic engineering and breeding techniques to screen high-enrichment plants. In addition, field experiments should be carried out to ensure that this technology can be applied to the remediation of nuclear contaminated sites as soon as possible.

The dynamic behavior and mechanism of uranium (VI) biomineralization in Enterobacter sp. X57

The important role of microbes in the biomineralization and migration behavior of uranium in the field of environmental chemistry has been well emphasized in previous work. However, limited work on mineralization processes of indigenous microorganism has prevented us from a deeper understanding of the process and mechanisms of uranium biomineralization. In this work, the dynamic process and mechanism of uranium biomineralization in Enterobacter sp. X57, a novel uranium-tolerant microorganism separated from uranium contaminated soil, were systematically investigated. Enterobacter sp. X57 can induce intracellular mineralization of U (VI) to Uramphite (NH₄UO₂PO₄·3H₂O) under neutral conditions by alkaline phosphatase. In this biomineralization process, soluble U (VI) first bonded with the amino and phosphate groups on the plasma membrane, providing initial nucleation site for the formation of U (VI) biominerals. Then the impairment of cell barrier function and the enhancement of alkaline phosphatase metabolism occurred with the accumulation of uranium in cells, creating a possible pathway for soluble U (VI) to diffuse into the cell and be further mineralized into U (VI)-phosphate minerals. All the results revealed that the intracellular biomineralization of uranium by Enterobacter sp. X57 was a combined result of biosorption, intracellular accumulation and phosphatase metabolism. These findings may contribute to a better understanding of uranium biomineralization behavior and mechanism of microorganisms, as well as possible in-situ bioremediation strategies for uranium by indigenous microorganisms.

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.

Application of response surface method in the separation of radioactive material: a review

Response Surface Method (RSM) is one of the most popular and powerful tools for experimental design and optimization. This paper first reviewed the research progress of RSM in the separation and recovery of various radioactive materials, and verified the application of RSM in adsorption isotherm analysis and thermodynamic calculation. The main advantage of RSM in radioactive material separation is the reduction in the number of experiments required, resulting in considerably less radioactive material consumption, secondary waste generation, workload and radiation dose, which is valuable for the research of radioactive material separation.

Isolation and Identification of Uranium Tolerant Phosphate-Solubilizing Bacillus spp. and Their Synergistic Strategies to U(VI) Immobilization

The remediation of uranium (U) through phosphate-solubilizing bacteria (PSB) is an emerging technique as well as an interesting phenomenon for transforming mobile U into stable minerals in the environment. While studies are well needed for in-depth understanding of the mechanism of U(VI) immobilization by PSB. In this study, two PSB were isolated from a U-tailing repository site. These bacterial strains (ZJ-1 and ZJ-3) were identified as Bacillus spp. by the sequence analysis of 16S ribosomal RNA (rRNA) genes. Incubation of PSB in liquid medium showed that the isolate ZJ-3 could solubilize more than 230 mg L^-1 P from glycerol-3-phosphate and simultaneously removed over 70% of 50 mg L^-1 U(VI) within 1 h. During this process, the rapid appearance of yellow precipitates was observed. The microscopic and spectroscopic analysis demonstrated that the precipitates were associated with U-phosphate compound in the form of saleeite-like substances. Besides, scanning electron microscopy coupled with energy-dispersive X-ray (SEM-EDS) and Fourier transform infrared spectroscopy (FTIR) analysis of the precipitates confirmed that the extracellular polymeric substances (EPS) might also play a key role in U sequestration. Furthermore, SEM and FTIR analysis revealed that part of U(VI) was adsorbed on the bacterial surface through cellular phosphate, hydroxy, carboxyl, and amide groups. This study provides new insights into the synergistic strategies enhancing U immobilization rates by Bacillus spp. that uses glycerol-3-phosphate as the phosphorus source, the process of which contributes to harmful pollutant biodegradation.

Shifts in bentonite bacterial community and mineralogy in response to uranium and glycerol-2-phosphate exposure

The multi-barrier deep geological repository system is currently considered as one of the safest option for the disposal of high-level radioactive wastes. Indigenous microorganisms of bentonites may affect the structure and stability of these clays through Fe-containing minerals biotransformation and radionuclides mobilization. The present work aimed to investigate the behavior of bentonite and its bacterial community in the case of a uranium leakage from the waste containers. Hence, bentonite microcosms were amended with uranyl nitrate (U) and glycerol-2-phosphate (G2P) and incubated aerobically for 6 months. Next generation 16S rRNA gene sequencing revealed that the bacterial populations of all treated microcosms were dominated by Actinobacteria and Proteobacteria, accounting for >50% of the community. Additionally, G2P and nitrate had a remarkable effect on the bacterial diversity of bentonites by the enrichment of bacteria involved in the nitrogen and carbon biogeochemical cycles (e.g. Azotobacter). A significant presence of sulfate-reducing bacteria such as Desulfonauticus and Desulfomicrobium were detected in the U-treated microcosms. The actinobacteria Amycolatopsis was enriched in G2P‑uranium amended bentonites. High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy analyses showed the capacity of Amycolatopsis and a bentonite consortium formed by Bradyrhizobium-Rhizobium and Pseudomonas to precipitate U as U phosphate mineral phases, probably due to the phosphatase activity. The different amendments did not affect the mineralogy of the bentonite pointing to a high structural stability. These results would help to predict the impact of microbial processes on the biogeochemical cycles of elements (N and U) within the bentonite barrier under repository relevant conditions and to determine the changes in the microbial community induced by a uranium release.

Effect of Staphylococcus epidermidis on U(VI) sequestration by Al-goethite

Effect of Staphylococcus epidermidis (S. epidermidis) on U(VI) sequestration by Al-goethite were conducted under different geologic conditions. The batch experiments showed that S. epidermidis significantly enhanced the adsorption rates of U(VI) at pH < 9.0 due to the additional metal binding sites. The maximum adsorption capacities of U(VI) on Al-goethite and Al-goethite +S. epidermidis at pH 4.0 and 310 K were calculated from Langmuir equation to be 13.16 and 47.86 mg/g, respectively. The decreased adsorption of U(VI) on Al-goethite+ S. epidermidis at high carbonate and pH conditions were primarily driven by the electrostatic repulsion between negatively charged U(VI)-carbonate complexes and the negatively charged adsorbents. According to XPS analysis, the adsorbed U(VI) can be reduced to U(IV) by S. epidermidis, whereas inhibited reduction of U(VI) on Al-goethite + S. epidermidis at high pH could be attributed to the complexation of structural Fe(III) with the oxygen-containing functional groups of S. epidermidis. FT-IR analysis further demonstrated that the bonding of structural Fe(III) with functional groups (e.g., carboxyl and phosphate groups) of S. epidermidis. These results herein are important to understand the fate and transport of U(VI) on the mineral-bacteria ternary systems in the near-surface environment.

Adsorption of cesium ion by marine actinobacterium Nocardiopsis sp. 13H and their extracellular polymeric substances (EPS) role in bioremediation

This paper evaluates the cesium adsorption of marine actinobacterium Nocardiposis sp. 13H strain isolated from nuclear power plant sites in India. It could remove 88.6 ± 0.72% of Cs⁺ from test solution containing 10 mM CsCl₂. The biosorption of Cs⁺ with different environmental factors such as pH, temperature, and time interval is also determined. Scanning electron microscopy coupled with energy dispersive spectroscopy (EDS) confirmed the Cs⁺ adsorption by Nocardiopsis sp. 13H. Most of the bound cesium was found to be associated extracellular polymeric substances (EPS) suggesting its interaction with the surface active groups. The main component of the EPS was carbohydrate followed by protein and nucleic acid. Further, Fourier transform infrared (FTIR) spectroscopy suggested the carboxyl, hydroxyl, and amide groups on the strain cell surface were likely to be involved in Cs⁺ adsorption. Results from this study show Nocardiopsis sp. 13H microorganism could be useful in exploring the biosorption of radioisotope pollution and developing efficient and eco-friendly biosorbent for environmental cleanup.

Characteristics of uranium biosorption from aqueous solutions on fungus Pleurotus ostreatus

Uranium(VI) biosorption from aqueous solutions was investigated in batch studies by using fungus Pleurotus ostreatus biomass. The optimal biosorption conditions were examined by investigating the reaction time, biomass dosage, pH, temperature, and uranium initial concentration. The interaction between fungus biomass and uranium was confirmed using Fourier transformed infrared (FT-IR), scanning electronic microscopy energy dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) analysis. Results exhibited that the maximum biosorption capacity of uranium on P. ostreatus was 19.95 ± 1.17 mg/g at pH 4.0. Carboxylic, amine, as well as hydroxyl groups were involved in uranium biosorption according to FT-IR analysis. The pseudo-second-order model properly evaluated the U(VI) biosorption on fungus P. ostreatus biomass. The Langmuir equation provided better fitting in comparison with Freundlich isotherm models. The obtained thermodynamic parameters suggested that biosorption is feasible, endothermic, and spontaneous. SEM-EDX and XPS were additionally conducted to comprehend the biosorption process that could be described as a complex process involving several mechanisms of physical adsorption, chemisorptions, and ion exchange. Results obtained from this work indicated that fungus P. ostreatus biomass can be used as potential biosorbent to eliminate uranium or other radionuclides from aqueous solutions.