Removal of Strontium Ions by Immobilized Saccharomyces Cerevisiae in Magnetic Chitosan Microspheres

Biodegradation of phenolic pollutants and bioaugmentation strategies: A review of current knowledge and future perspectives

The widespread use of phenolic compounds renders their occurrence in various environmental matrices, posing ecological risks especially the endocrine disruption effects. Biodegradation-based techniques are efficient and cost-effective in degrading phenolic pollutants with less production of secondary pollution. This review focuses on phenol, 4-nonylphenol, 4-nitrophenol, bisphenol A and tetrabromobisphenol A as the representatives, and summarizes the current knowledge and future perspectives of their biodegradation and the enhancement strategy of bioaugmentation. Biodegradation and isolation of degrading microorganisms were mainly investigated under oxic conditions, where phenolic pollutants are typically hydroxylated to 4-hydroxybenzoate or hydroquinone prior to ring opening. Bioaugmentation efficiencies of phenolic pollutants significantly vary under different application conditions (e.g., increased degradation by 10-95% in soil and sediment). To optimize degradation of phenolic pollutants in different matrices, the factors that influence biodegradation capacity of microorganisms and performance of bioaugmentation are discussed. The use of immobilization strategy, indigenous degrading bacteria, and highly competent exogenous bacteria are proposed to facilitate the bioaugmentation process. Further studies are suggested to illustrate 1) biodegradation of phenolic pollutants under anoxic conditions, 2) application of microbial consortia with synergistic effects for phenolic pollutant degradation, and 3) assessment on the uncertain ecological risks associated with bioaugmentation, resulting from changes in degradation pathway of phenolic pollutants and alterations in structure and function of indigenous microbial community.

Intensification of strontium (II) ion biosorption on Sargassum sp via response surface methodology

A batch system was employed to investigate the biosorption of strontium (II) on Sargassum sp. The biosorption of strontium on Sargassum sp was studied with response surface methodology to determine the combined effect of temperature, initial metal ion concentration, biomass treatment, biosorbent dosage and pH. Under optimal conditions, the algae's biosorption capacity for strontium (initial pH 7.2, initial strontium concentration 300 mg/l for Mg-treated biomass and biosorbent dosage 0.1 g in 100 mL metal solution) was measured at 103.95 mg/g. In our analysis, equilibrium data were fitted to Langmuir and Freundlich isotherms. Results show that the best fit is provided by the Freundlich model. Biosorption dynamics analysis of the experimental data indicated that strontium (II) was absorbed into algal biomass in accordance with the pseudo-second-order kinetics model well.

Synthesis, Characterization and Investigation of Cross-Linked Chitosan/(MnFe2O4) Nanocomposite Adsorption Potential to Extract U(VI) and Th(IV)

A cross-linked chitosan/(MnFe2O4) CCsMFO nanocomposite was prepared using co-precipitation methods and used as a nanomaterial to extract U(VI) and Th(IV) from an aqueous solution based on adsorption phenomena. The contact time of experiments shows a rapid extraction process within 30 min by the CCsMFO nanocomposite. The solution pH acts a critical role in determining qm value, where pH 3.0 was the best pH value to extract both ions. The pseudo-second-order equilibrium model illustrated the kinetics equilibrium modal extraction process. Adsorption isotherm of U(VI) at pH 3.0 by CCsMFO nanocomposite is an endothermic process. In contrast, the adsorption isotherm of Th(IV) at pH 3.0 by CCsMFO nanocomposite is an exothermic process. The reusability of CCsMFO nanocomposite was tested using basic eluents as suitable conditions for the chemical stability of CCsMFO nanocomposite; the reusability results show promising results for the removal of U(VI) adsorbed onto CCsMFO nanocomposite with 77.27%, after 12 h by Na2CO3 as eluent. At the same time, the reusability results show good reusability for removal of U(VI) adsorbed onto CCsMFO nanocomposite with 21.82%, after 8 h by EDTA as eluent.

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.

Origin of the exceptional selectivity of NaA zeolite for the radioactive isotope 90Sr2+

A NaA zeolite shows exceptionally high selectivity for radioactive 90Sr2+. Structural Rietveld refinements reveal that all Sr2+ ions are located at the center of the s6rs of lta cages.

Adsorptive removal of Sr(II) from aqueous solution by polyvinyl alcohol/graphene oxide aerogel

In this study, a new adsorbent, polyvinyl alcohol (PVA) and graphene oxide (GO), was prepared, characterized and used for the removal of Sr²⁺ from aqueous solution. In PVA/GO composite, the inter-lamellar spacing of adjacent GO layers was dramatically enlarged due to the intercalation of PVA molecules, such a unique architecture significantly mitigated the aggregation of GO layers, which facilitated the accessible exposure of active sites and the mass transfer of strontium ions (Sr²⁺), thus enhancing the adsorption capacity toward Sr²⁺. The adsorption of Sr²⁺ by PVA/GO composite conformed to the pseudo second-order kinetic model (R² = 0.9994), the Langmuir model (R² = 0.9042), and the Freundlich model (R² = 0.9598). The complexation interaction between Sr²⁺ and oxygen atoms/π-electron domain of PVA/GO composite was primarily responsible for the adsorption mechanism, based on the characterization results of X-ray photoelectron spectroscopy (XPS), scanning electron microscope equipped with energy dispersion spectroscopy (SEM-EDS) and powder X-ray diffraction (PXRD).

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 Sr(II) from water with highly-elastic carboxymethyl chitosan gel

A carboxymethyl chitosan (O-CMC) gel was prepared by crosslinking and functionalizing with ethylenediaminetetraacetic acid (EDTA) using a one-pot reaction under mild conditions. Structural characterizations have revealed that the prepared O-CMC/EDTA gel has 3D porous structure with abundant carboxyl groups distributed in the pores. The prepared O-CMC/EDTA gel was used to adsorb Sr(II) ions in water while X-ray photoelectron spectroscopy (XPS) was used to explore the adsorption mechanism. In order to analyze the adsorption process, we performed the adsorption kinetics and isotherms. The results show that the maximum adsorption capacity of O-CMC/EDTA for Sr (II) ions is about 105.81 mg/g at pH = 7. Notably, it exhibited fairly high compression elasticity due to multiple hydrogen bonds in the network. The showed no deformation after 30 continuous compression cycles. The ratio of O-CMC:EDTA significantly influences the adsorption property by affecting the crosslinking degree as well as the number of active sites. The high adsorption capacity, elasticity, and reusability have demonstrated that the prepared material is an effective and promising adsorbent for Sr(II) removal.

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.

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.

Adsorptive removal of strontium ions from aqueous solution by graphene oxide

Graphene oxide (GO) was prepared, characterized, and applied for adsorption of Sr(II) in aqueous solution. The adsorption capacity was calculated to be 137.80 mg/g according to the Langmuir model. The observation by scanning electron microscope with energy dispersive X-ray detector (SEM-EDX), high-resolution transmission electron microscope (HRTEM), and X-ray diffraction (XRD) revealed the crystal structure of Sr compound on the surface of graphene sheets. The analyses by the Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated the involvement of O-C=O, C-O, and C-O-C groups during the adsorption. The X-ray absorption fine structure (XAFS) analysis provided the detail information of GO-Sr composites, and the fitting results were given by Sr(HCOO)₂ and SrCO₃ model, and the coordination numbers (CN) and interatomic distances (R) of Sr-O shell and Sr-C shell were calculated. The adsorption mechanism of Sr(II) was attributed to complexation between Sr and the acidic oxygen-containing groups, which lead to the agglomeration of graphene oxide. Two types of crystals were proposed. Type 1 was formed by coordination between Sr(II) and O-C=O groups, and type 2 was formed by coordination between Sr(II) and C-O/C-O-C groups.

Removal of Co, Sr and Cs ions from simulated radioactive wastewater by forward osmosis

The removal of Co, Sr and Cs ions form simulated radioactive wastewater using forward osmosis (FO) process was investigated. The effect of various factors on nuclide transport was examined, including membrane orientation, NaCl concentration, flow velocity, and the main factors were identified by correlation analysis. The mechanisms of nuclides transfer through membrane were explored. The results indicated that the active layer facing draw solution (AL-DS) had higher nuclide flux than AL-FS. At AL-FS mode, the highest flux of Co, Sr and Cs were only 1.54, 10.22 and 15.63 mg m^-2 h^-1 respectively by cellulose triacetate with embedded polyester screen support (CTA-ES) membrane. At AL-DS mode, the flux of Co and Cs increased when NaCl concentration and flow velocity increased. Convection, diffusion and electrostatic interactions were found to influence the nuclide transport all together. The Pearson correlation and partial correlation analysis identified that the diffusion coefficient of nuclides and reverse NaCl flux were the most important factors affecting nuclide flux through cellulose triacetate membrane. The water flux, NaCl concentration, flow velocity and partition coefficient were not the main affecting factors for nuclide flux.

Characterization and Adsorption Behavior of Strontium from Aqueous Solutions onto Chitosan-Fuller's Earth Beads

Fuller's earth spherical beads using chitosan as a binder were prepared for the removal of strontium ions from aqueous solution. The adsorbents were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed the porous nature of the beads. The Brunauer⁻Emmett⁻Teller (BET) surface area of the beads was found to be 48.5 m²/g. The adsorption capacities of the beads were evaluated under both batch and dynamic conditions. The adsorption capacity was found to be ~29 mg/g of adsorbent at 298 K when the equilibrium concentration of strontium in the solution was 925 mg/L at pH 6.5. The X-ray photoelectron spectroscopy (XPS) data suggest that strontium uptake by the beads occurs mainly through an ion-exchange process. Kinetic data indicate that the sorption of strontium onto the beads follows anomalous diffusion. Thermodynamic data suggest that the ion-exchange of Sr²⁺ on the bead surface was feasible, spontaneous and endothermic in nature.

Algal sorbent derived from Sargassum horneri for adsorption of cesium and strontium ions: equilibrium, kinetics, and mass transfer

An algal sorbent derived from Sargassum horneri was prepared and used to adsorb cesium and strontium ions from aqueous solution. The phenomenological mathematical models associated to the predicted equilibrium isotherms were developed to determine the rate-limiting steps of the adsorption process. The maximum adsorption capacity of cesium ion and strontium ion was calculated to be 0.358 and 1.72 mmol g-1, respectively. The adsorption kinetics followed to the pseudo-second-order equation. It was found that adsorption of cesium or strontium ions onto the active sites of the biosorbent was the rate-limiting step. In addition, the external mass transfer and the internal mass transfer cannot be neglected for the adsorption of strontium ion based on the error analysis. The functional groups relevant to the adsorption were carboxyl and sulfate groups.

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.

Radiation, radionuclides and bacteria: An in-perspective review

There has been a significant surge in consumption of radionuclides for various academic and commercial purposes. Correspondingly, there has been a considerable amount of generation of radioactive waste. Bacteria and archaea, being earliest inhabitants on earth serve as model microorganisms on earth. These microbes have consistently proven their mettle by surviving extreme environments, even extreme ionizing radiations. Their ability to accept and undergo stable genetic mutations have led to development of recombinant mutants that are been exploited for remediation of various pollutants such as; heavy metals, hydrocarbons and even radioactive waste (radwaste). Thus, microbes have repeatedly presented themselves to be prime candidates suitable for remediation of radwaste. It is interesting to study the behind-the-scenes interactions these microbes possess when observed in presence of radionuclides. The emphasis is on the indigenous bacteria isolated from radionuclide containing environments as well as the five fundamental interaction mechanisms that have been studied extensively, namely; bioaccumulation, biotransformation, biosorption, biosolubilisation and bioprecipitation. Application of microbes exhibiting such mechanisms in remediation of radioactive waste depends largely on the individual capability of the species. Challenges pertaining to its potential bioremediation activity is also been briefly discussed. This review provides an insight into the various mechanisms bacteria uses to tolerate, survive and carry out processes that could potentially lead the eco-friendly approach for removal of radionuclides.

Biosorption of strontium ions from aqueous solution using modified eggshell materials

Green composites emphasize renewable starting materials for better economy using biomass materials. Therefore, low-cost composite biosorbent was prepared by modification of eggshell material using heteropoly acid for removal of strontium ions from aqueous solution. The resulted composite was characterized and evaluated for the sorption process using the batch technique. Low concentration of strontium ions was used to evaluate the sorption sensitivity of the prepared composite. The obtained experimental results illustrated that the modification process of eggshell material enhanced the percent uptake from 49.9 to 95.7%. From kinetic studies, the sorption of strontium ions follows the pseudo-second-order kinetic model. The isotherm studies indicated that Langmuir is more applicable than Freundlich isotherm. Moreover, Dubinin–Radushkevich isotherm was studied. Thermodynamic studies revealed that the sorption process is spontaneous and has endothermic nature. Strontium ions can be desorbed from the modified eggshell using HNO3, desorption percent was found to be 96.4%; the results revealed the reusability of the modified eggshell for further sorption.