Removal Of Selenite Research Articles

Treatment of Se-Impacted Wastewater Using a Three-Dimensional Packed Bed Electrochemical Reactor

Selenium is an essential element for flora and fauna in trace amounts. It plays a crucial role in bolstering photosynthesis and facilitating thyroid hormone metabolism. However, excessive consumption of selenium can result in health concerns such as reproductive complications and cancer. Selenium usually coexists with minerals such as copper and coal in the natural environment. The associated activities, such as copper mining and coal combustion, have greatly accelerated the mobilization of selenium. The selenium released through coal combustion is mostly captured in the flue gas desulfurization (FGD) wastewater as inorganic selenite and selenate.Our lab previously validated the viability of direct electrochemical reduction (SeDER) to remove dissolved selenite from a simplified FGD water matrix using planar gold and graphite cathodes, where more than 94% of the aqueous selenite can be converted to elemental Se(0) deposited on the cathode surface. Graphite is eventually selected for its low material cost, decent removal performance, and minimum secondary pollution as compared to gold and other non-noble metal cathodes. This direct electrochemical deposition process provides many benefits that existing biological and indirect electrochemical methods lack, such as zero chemical addition and low to zero solid generation. However, this method is only suitable for wastewater with elevated temperatures necessary to generate conductive Se(0) for continuous reduction. The inclusion of a heating process adds complexity to the design, impeding the scalability of the SeDER system. Furthermore, the application of SeDER is constrained to Se-impacted wastewater with an elevated temperature.In this study, we propose a novel reactor design utilizing electrochemical reduction to treat Se-impacted wastewater at ambient temperature. The electrodes we used are made of graphite for the reasoning stated above. The reactor consists of a pair of planar graphite anode and cathode, and the inner chamber is filled with cylindrical graphite particle electrodes (PEs) separated by a nylon spacer to create an anodic chamber and a cathodic chamber. The PEs act as an extension of the planar electrodes, which offers numerous reaction sites and minimizes the travel distance for selenite ions to reach the electrode surface. In our 120-mL batch test with 0.1-mM selenite in 100-mM phosphate buffer, the exact system without filler removed 0% selenite at room temperature, while the filled 3D system removed on average 50% of the selenite in 3 hours. Using the same 3D system, we then investigated performance enhancement with a recirculating operation. The total working volume is fixed at 200 mL, while the flow rate and the applied voltage vary. The flow rate is set at the values with hydraulic retention time (HRT) fixed at 15 min, 30 min, and 60 min. The system-applied voltage is set at -1.9V (just enough for selenite reduction), -2.1V, and -2.3V. We found that the shortest HRT combined with -2.1V system applied voltage yielded the highest selenite removal performance in all tests, with an average of 47% removal in 3 hours. We hypothesized that the shorter HRT provides a faster flow rate that refreshes the PE’s surface from insulative Se(0) deposition, which provides sustainable reaction sites for the incoming selenite. At -2.1V, the potential is negative enough to allow selenite reduction while fewer parasitic reactions (e.g., hydrogen evolution reaction) occur compared to that under -2.3V.With the selected system voltage and flow rate, we eventually explored competing ion behavior and switched from a simplified water matrix to simulated Se-impacted wastewater. We found that of all the commonly found competing ions (i.e., sulfate, nitrate, and chloride), chloride significantly impacts selenite removal, with performance dropping to 10% removal in 3 hours. Nitrate slightly decreased the selenite removal, with an average Se removal performance of 23%. Sulfate, on the other hand, resulted in an increase in selenite removal after addition. We hypothesize that a high sulfate concentration in simulated wastewater could help alleviate the repulsing force from the cathode surface for the selenite ions. The double layer of the PEs could also be compressed by the high ionic strength, which decreases the capacitance and promotes selenite reduction. To confirm this hypothesis, we conducted an electrochemical impedance study to analyze the effect of competing ions on reaction kinetics and capacitance. We also performed surface analysis for the wasted planar electrodes and PEs to investigate the change in morphology and observed possible chemical residue. These characterizations will help us develop a regeneration protocol in long-term operation and help us scale up our prototype to manage actual Se-impacted wastewater.

Reduction of selenite to selenium nanoparticles by highly selenite-tolerant bacteria isolated from seleniferous soil

The microbial reduction of selenite to elemental selenium nanoparticles (SeNPs) is thought to be an effective detoxification process of selenite for many bacteria. In this study, Metasolibacillus sp. ES129 and Oceanobacillus sp. ES111 with high selenite reduction efficiency or tolerance were selected for systematic and comparative studies on their performance in selenite removal and valuable SeNPs recovery. The kinetic monitoring of selenite reduction showed that the highest transformation efficiency of selenite to SeNPs was achieved at a concentration of 4.24 mM for ES129 and 4.88 mM for ES111. Ultramicroscopic analysis suggested that the SeNPs produced by ES111 and ES129 had been formed in cytoplasm and subsequently released to extracellular space through cell lysis process. Furthermore, the transcriptome analysis indicated that the expression of genes involved in bacillithiol biosynthesis, selenocompound metabolism and proline metabolism were significantly up-regulated during selenite reduction, suggesting that the transformation of selenite to Se0 may involve multiple pathways. Besides, the up-regulation of genes associated with nucleotide excision repair and antioxidation-related enzymes may enhance the tolerance of bacteria to selenite. Generally, the exploration of selenite reduction and tolerance mechanisms of the highly selenite-tolerant bacteria is of great significance for the effective utilization of microorganisms for environmental remediation.

Investigating the sorption behavior of selenite on commercial partially oxidized magnetite nanopowder under aerobic conditions: Characterization and mechanisms

Selenium, which belongs to essential elements, has a narrow margin between necessity and toxicity. Anthropogenic activities may lead to its elevated concentrations in aquatic ecosystems, particularly in the undesirable form of toxic selenite, due to its high environmental mobility. Hence, it is imperative to devise effective technologies to limit its potential migration through the environment. Therefore, the development and evaluation of new adsorbents for its effective removal from selenium-contaminated waters are crucial for both human health and environmental stability in affected areas. Specifically, magnetite-based nanomaterials showed promise as sorbents due to their capacity to immobile contaminants through reductive transformation or adsorption, but there is a lack of comprehensive understanding regarding the sorption mechanisms and the factors influencing the efficiency of this process. A deeper understanding of these factors is crucial for developing sustainable and efficient water treatment strategies. This study focuses on magnetite nanopowder’s sorptive properties, examining critical factors such as pH, ionic strength, and competing anions that affect selenite removal. Sorption kinetics revealed an initial rapid selenite removal followed by a slower, time-dependent phase, suggesting a complex sorption mechanism. Chemisorption was considered the primary sorptive interaction, with diffusion playing a minor role, and was best described by the pseudo-second order kinetic model. Notably, pH significantly affected sorption efficiency and the suggested sorptive mechanism. Acidic conditions favored selenite removal due to formation of inner-sphere complexes, while alkaline conditions reduced efficiency due to repulsive interactions. Equilibrium sorption data were best fitted by the Langmuir model, with maximum sorption at pH 3, indicating that acidic conditions favor selenite removal. X-ray photoelectron spectroscopy (XPS) analysis ruled out the formation of reduced selenium compounds on the magnetite nanopowder surfaces. Additionally, Mössbauer spectrometry revealed that the nanopowder is not homogeneous and contains both magnetite and maghemite phases. Ionic strength and co-occurring ions showed minimal chloride impact but significant phosphate competitiveness due to its affinity for iron oxides. In conclusion, this study sheds light on the complex selenite sorptive interactions with magnetite nanopowder, emphasizing the dominance of chemisorption, especially in acidic solutions.

Design of Z-scheme UIO-66-NH2/BiOBr heterojunctions for efficient visible-light-driven selenite removal from water: Performance and mechanism studies

Excess existence of the selenite (Se(IV)) is hazardous to water resources. Therefore, a need still exists for the removal of Se(IV) from the wastewater in the renewable, environmentally friendly, and low-cost way. This paper presents a novel way to design a Z-type heterojunction of UIO-66-NH2/BiOBr using co-precipitation technology for efficiently removal of Se(IV) from wastewater using the adsorption-visible photocatalytic synergy. The UIO-66-NH2 presents an enhanced adsorption of Se(IV) due to the expose of abundant linker defects, as the active sites. The Z-type heterojunction (UB-2) showed 96.4% removal of Se(IV) at an initial concentration of 100 mg/L under visible light conditions due to its higher charge transfer capacity and electron-hole separation ability. The photocatalytic removal rate of UB-2 toward Se(IV) was 4.12 times and 9.93 times higher than that of UIO-66-NH2 and BiOBr, respectively. UB-2 could be reused and showed a good removal capacity in real-world water samples. The used UB-2 was superior to the nano-selenium in the scavenging of superoxide radical and DPPH, revealing a potential of biological antioxidant. This work will be beneficial for the efficient decontamination of Se(IV)-containing wastewater.

Removal of aqueous selenite anions from wastewater by electrodeposition and recycling used for catalyst of effective water splitting

Transforming toxic selenium in industrial wastewater into selenium resources is a significant challenge to realize the upgrading of valuable element resources and the removal of pollutants. Here, we chose copper, cobalt, and nickel foam as the electrode materials and used electrodeposition to capture selenite from selenium-containing wastewater. The effects of operating voltage, initial concentration, stirring rate and time on the removal efficiency of selenium were investigated. Among them, the removal efficiency of copper foam for 100 mg L−1 selenite could reach 91.2 % at −1.5 V operating voltage. The composition, morphology and structure of the products after electrodeposition were characterized by XPS, FESEM and TEM. The OER and HER properties of the electrodeposited products Cu2Se, CoSe2 and NiSe were evaluated by density functional theory calculations. It was proved that selenium could improve the electron transfer rate, and CoSe2 also had better HER performance than NiSe. The products formed after electrodeposition could be combined for overall water splitting to achieve efficient hydrogen production. This study proved the mechanism and resource utilization process of selenite removal through electrodeposition.

Insight into the influence of environmental factors on selenite removal from desulfurization wastewater by NZVI@AC: An experimental and theoretical study

Nano zero-valent iron (NZVI) technology has shown good potential for the treatment of selenium in wastewater. In this study, NZVI was loaded on activated carbon (AC) by carbothermal reduction method to synthesize high-efficiency adsorbent (NZVI@AC). The agglomeration of NZVI was suppressed and its reactivity was improved. The optimum preparation temperature of NZVI@AC (600 °C) was determined by comparing its purity. Moreover, the synergistic effect between the active component (NZVI) and the support (AC) was investigated on the basis of the density functional theory method. The smaller HOMO-LUMO gap (0.87 eV) and charge distribution of NZVI@AC indicated favorable electron transfer and enhanced chemical reactivity. The adsorption and reduction to Se(0)/Se(-II) were elucidated as the underlying mechanisms for the removal of selenite by comparative analysis of the morphological transformation of iron and selenium species. Furthermore, the selenite removal performance of NZVI@AC was investigated on account of the impact of dissolved oxygen and pH values, and the interaction mechanism of these factors was revealed. The decrease of solution pH and dissolved oxygen concentration are effective ways to improve the removal efficiency of selenite.

Modelling selenite and chemical oxygen demand removal in an inverse fluidized bed bioreactor using genetic algorithm optimized artificial neural network

AbstractBACKGROUNDA genetic algorithm (GA) optimized artificial neural network (ANN) model was developed to simulate selenite removal efficiency (SRe) and chemical oxygen demand (COD) removal efficiency (CRe) in a single‐stage inverse fluidized bed reactor (IFBR) operated under different hydraulic retention time (HRT) (12–48 h), and inlet selenite concentration (12.7–635 mg L−1). Multi‐objective optimization for SRe and CRe with the ANN model was adopted to estimate the pareto optimal solutions in the bioreactor system.RESULTSGA optimized ANN topology suggested five neurons in the hidden layer, and the optimal data partitioning between training, test, and validation subsets (in 70:15:15 ratio) using cross‐validation. The average fitness for SRe and CRe of the resulting ANN model over training (R2 = 0.885), test (R2 = 0.967) and validation (R2 = 0.972) subsets were reasonably good. Sensitivity analysis suggested an increase in SRe and CRe with HRT, while an increase in inlet selenite concentration had a negative effect on SRe. Local interpretable model‐agnostic explanations and SHapley Additive exPlanations for the developed model suggested a positive coefficient of the predictors on CRe. Pareto optimal solution for SRe (92.87%–95.26%), and CRe (91.33%–99.35%) were suggested for HRT and inlet selenite concentration varying between 35.67 h and 36 h, and 0.1 g L−1 and 0.884 g L−1, respectively.CONCLUSIONSThe GA optimized ANN model could be exploited for the prediction of contaminant removal efficiencies in the bioreactor system with a fair degree of complexity (i.e., IFBR). Multiple objective pareto optimal solutions can identify the best operating conditions relevant for wastewater treatment. © 2023 Society of Chemical Industry (SCI).

Study of iron-based metal–organic framework for selenite removal from water

Study of iron-based metal–organic framework for selenite removal from water

Removal and recycling of aqueous selenite anions using cobalt-based metal–organic-framework coated on multi-walled carbon nanotubes composite membrane

The utilization of selenium as a novel functional material is rapidly expanding, and the retrieval of selenium from waste containing selenium is gaining recognition in the industry. This study prepared a novel composite membrane coated with the cobalt-based metal–organic framework coated on multi-walled carbon nanotubes (Co-MOF@MWCNTs). The MWCNTs served as the skeleton to support the active components of Co-MOF, which enabled efficient removal and resource utilization of liquid selenite (SeO32−). The morphology, structure, and composition of the prepared membrane were characterized using field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), etc.. Applying a permeate flux of 67.08 L m−2 h−1, the SeO32− removal efficiency of the composite membrane reached up to 92.2%. The composite membrane containing CoSeO4 can be used as an electrocatalytic oxygen evolution catalyst. Density functional theory calculations and electrochemical analysis showed that the conversion from O* to OOH* was a rate-determining step. Under 1.0 M KOH conditions, the lowest overpotential for Co-MOF@MWCNTs-40 at 10 mA cm−2 was 360 mV. In this study, the process of selenium resource utilization and the mechanism of SeO32− removal by Co-MOF@MWCNTs are revealed. It demonstrates that membrane-based sequestration of SeO32− can provide a viable approach for SeO32− removal and utilization in wastewater.

Elucidating the Role of Capping Agents in Facet-Dependent Adsorption Performance of Hematite Nanostructures.

Organic capping agents are a ubiquitous and crucial part of preparing reproducible and homogeneous batches of nanomaterials, particularly nanocrystals with well-defined facets. Despite studies reporting surface ligands (e.g., capping agents) having a non-negligible role in catalytic behavior, their impact is less understood in contaminant adsorption, an important consideration given their potential to obfuscate facet-dependent trends in performance. To ascribe observed behaviors to the facet or the ligand, this report evaluates the impact of poly(N-vinyl-2-pyrrolidone) (PVP), a commonly utilized capping agent, on the adsorption performance of nanohematite particles of varying prevailing facet in the removal of selenite (Se(IV)) as a model system. The PVP capping agent reduces the available surface area for contaminant binding, thus resulting in a reduction in overall Se(IV) adsorbed. However, accounting for the effects of surface area, {012}-faceted nanohematite demonstrates a significantly higher sorption capacity for Se(IV) compared with that of {001}-faceted nanohematite. Notably, chemical treatment is minimally effective in removing strongly bound PVP, indicating that complete removal of surface ligands remains challenging.

Attachment of Fe3O4 nanoparticles on UiO-66: A stable composite for efficient sorption and reduction of selenite from water

In the present work, Fe3O4 nanoparticles were attached to the surface of UiO-66, a zirconium-based metal–organic framework material and the composite material formed was used to remove selenite (Se(IV)) in water. The Fe3O4/UiO-66 composite were assembled by a facile two-stage strategy. Benefiting from the ultra-high specific surface area of UiO-66, the Fe3O4/UiO-66 also had a large specific surface area, which made it easier to expose the active sites of Fe3O4 on the surface of UiO-66. The XPS and Mössbauer spectroscopy analysis indicated that there was charge transfer between Fe3O4 and UiO-66 in the Fe3O4/UiO-66, which made the Fe3O4 on the surface of UiO-66 had enhanced reductive activity. The mechanism of Fe3O4/UiO-66 to removed Se(IV) from the solution was further investigated by Zeta potential, FT-IR, SEM, TEM, and XPS spectra. The results indicated that the Fe3O4 nanoparticles on the surface of UiO-66 not only interacted with selenite through electrostatic action and inner-sphere complex but could also reduce a large amount of selenite to the insoluble Se0. The combination of these three actions finally strengthened the removal of selenite. This study cloud promote the practical application of MOF-based composites in removing heavy metal ions.

Effects of sodium selenite on the growth, biochemical composition and selenium biotransformation of the filamentous microalga Tribonema minus

This study aimed to investigate the physiological and biochemical responses of filamentous microalga Tribonema minus to different Na2SeO3 concentrations and its selenium absorption and metabolism to evaluate the potential in treating selenium-containing wastewater. The results showed that low Na2SeO3 concentrations promoted growth by increasing chlorophyll content and antioxidant capacity, whereas high concentrations caused oxidative damage. Although Na2SeO3 exposure reduced lipid accumulation compared with the control, it significantly increased carbohydrate, soluble sugar, and protein contents, with the highest carbohydrate productivity of 117.97 mg/L/d at 0.5 mg/L Na2SeO3. Furthermore, this alga effectively absorbed Na2SeO3 in the growth medium and converted most of it into volatile selenium and a small part into organic selenium (predominantly as selenocysteine), showing strong selenite removal efficacy. This is the first report on the potential of T. minus to produce valuable biomass while removing selenite, providing new insights into the economic feasibility of bioremediation of selenium-containing wastewater.

Construction of defective zirconium-based metal–organic frameworks for enhanced removal of toxic selenite: performance and mechanism studies

The development of effective adsorbents for the adsorption and removal of toxic selenite (SeO32−) from wastewater is urgently required but challenging. Herein, formic acid (FA), a monocarboxylic acid, was used as a template to construct serial defective Zr-Fumarate (Fum) -FA based on a green and facile preparation method. Physicochemical characterization shows that the defect degree of Zr-Fum-FA can be flexibly controlled by regulating the amount of FA to be added. Owing to rich defect units, the diffusion and mass transfer of guest SeO32− into the channel can be boosted. Particularly, Zr-Fum-FA-6 with the most defects exhibits superior adsorption capacity (519.6 mg g−1) and rapid adsorption equilibrium (∼200 min). The adsorption isotherms and kinetics can be well described by the Langmuir and pseudo-second-order kinetic models. Moreover, this adsorbent possesses excellent resistance towards co-existing ions, high chemical stability and good applicability in a broad pH range of 3–10. Thus, our study provides a promising adsorbent for SeO32−, and more importantly, it proposes a strategy for rationally tailoring the adsorption behavior of adsorbents via defect construction.

Microbial Enhancement of Selenium Removal in Chemically Modified Zeolite Columns

Selenium (Se) is an essential micro-nutrient for living organisms, but elevated concentrations in water can adversely affect health. In this research, we investigate the removal of selenium oxyanions (selenate and selenite) in aqueous systems by integration of adsorption on modified zeolites and microbial reduction. Dynamic sorption-reduction experiments were conducted using two sets of zeolite columns for the removal of selenite and selenate oxyanions, respectively. In each case, one column was fully packed with natural, unmodified zeolites, while the other column was composed of 80% natural and 20% iron-coated zeolites, by mass. The initial selenium concentration, selenite (SeIV) or selenate (SeVI), was 790 μg/L, the pH was 7.5, and the flow rate was 3 mL/min. Initially, as expected, the higher selenate removal (34%) was observed with coated zeolite, twice as high compared to the results with unmodified zeolite. Maximum selenite removal was 89% in the column with modified zeolite. Within approximately 14 days, as the biofilm developed inside the columns, selenium reduction in all four columns reached approximately 99%. Biofilm microbial community composition, assessed by 16S rRNA sequencing, is consistent with the presence of mainly selenium-reducing bacteria (Veillonella, Bacteroides, and Escherichia). Selenium oxyanions were reduced to elemental selenium, visible within the bioreactors as red-color aggregates.

Development of Manganese-Coated Graphite Electrode in a Dual-Chambered Fuel Cell for Selenite Removal and Bio-Electricity Generation from Wastewater Effluent by Bacillus cereus

A manganese oxide-coated cylindrical graphite cathode with a zinc anode was developed to treat wastewater containing selenite in a dual-chambered microbial fuel cell. COD and selenite removal in the anodic chamber by Bacillus cereus with energy generation were evaluated in batch mode. A manganese dioxide-coated graphite cathode was tested for its surface morphology and chemical composition using scanning electron microscopy and dispersive energy analysis of X-rays. Compared to the non-coated graphite electrode, up to 69% enhancement was observed in the manganese dioxide-coated electrode voltage generation with 150 ppm selenite concentration. The fuel cell achieved a maximum power density of 1.29 W/m2 with 91% selenite reduction and up to 74% COD (initial COD of 120 mg/L) removal for an initial selenite concentration from 100 to 150 ppm. The current study demonstrated the possibility of a modified cathode in enhancing energy generation and the use of microbial fuel cell technology to treat wastewater containing selenite.

Selenite reduction and biogenesis of selenium-nanoparticles by different size groups of aerobic granular sludge under aerobic conditions

Microbial transformations play a vital role in Se cycle in the environment and decrease the solubility and toxicity of Se oxyanions by converting to elemental selenium (Se0) nanostructures. Aerobic granular sludge (AGS) has attracted interest due to efficient reduction of selenite to biogenic Se0 (Bio-Se0) and retention in bioreactors. Here, selenite removal, biogenesis of Bio-Se0 and entrapment of Bio-Se0 by different size groups of aerobic granules were investigated to optimize biological treatment process for Se-laden wastewaters. Furthermore, a bacterial strain showing high selenite tolerance and reduction was isolated and characterized. Removal of selenite and conversion to Bio-Se0 were achieved by all the size groups of granules ranging from 0.12 mm to 2 mm and above. However, selenite reduction and Bio-Se0 formation were rapid and more efficient with large aerobic granules (≥0.5 mm). The formed Bio-Se0 was majorly associated with the large granules, due to better entrapment capabilities. In contrast, the Bio-Se0 formed by the small granules (≤0.2 mm) was distributed both in the granules and aqueous phase because of ineffective entrapment. Scanning electron microscope and energy dispersive X-ray (SEM-EDX) analysis confirmed formation of Se0 spheres and association with the granules. Efficient selenite reduction and entrapment of Bio-Se0 was related to prevalent anoxic/anaerobic zones in the large granules. A bacterial strain showing efficient SeO32− reduction of up to 15 mM SeO32− under aerobic conditions was identified as Microbacterium azadirachtae. SEM-EDX analysis confirmed the formation and entrapment of Se0 nanospheres (size: 100 ± 5 nm) in the extracellular matrix. The cells immobilized in alginate beads showed effective SeO32− reduction and Bio-Se0 entrapment. Efficient reduction and immobilization of bio-transformed metalloids by large AGS and AGS-borne bacteria implicates prospective use in bioremediation of metal(loid) oxyanions and bio-recovery.

Aerobic reduction of selenite and tellurite to elemental selenium and tellurium nanostructures by Alteromonas sp. under saline conditions

Selenium (Se) and tellurium (Te) wastewaters are typically characterized with higher salinities. Limited studies have determined microbial reduction of Se/Te oxyanions under saline conditions. This study reports bacterial reduction of Se(IV)/Te(IV) oxyanions at different salinities by a bacterial strain isolated from selenite-reducing halophilic aerobic granular sludge. Among several isolates, ORB-2 was consistent and efficient in reducing selenite and tellurite under saline conditions. This strain showed higher tolerance and grew rapidly in the presence of 10 mM selenite (790 mg L−1 Se(IV)) and 7.5 mM tellurite (957 mg L−1 Te(IV)). Growth was accompanied by Se(IV)/Te(IV) removal and conversion to cell-associated red/black elemental forms. Selenite (0.25–2 mM; 20–158 mg L−1 Se(IV)) removal efficiencies ranged between 82 and 96% with maximum removal by 48 h. For tellurite (0.25–2 mM; 32–254 mg L−1 Te(IV)), the removal efficiencies were 75–92% in 72 h. Growth of ORB-2 and concomitant removal of selenite or tellurite was observed in the presence of 2–8% NaCl. Biogenesis of Se(0) and Te(0) nanostructures was confirmed by micro-Raman spectroscopy. Extracted Se(0) and Te(0) nanostructures had a hydrodynamic diameter of 180 and 111 nm, respectively. Based on 16S rRNA gene sequencing, ORB-2 was identified as Alteromonas sp. Efficient conversion and association of biogenic Se(0)/Te(0) nanostructures with the cells under saline conditions shows promising use in bioremediation and scarce metal(loid) recovery.

Biomineralization of indium to indium selenide by anaerobic granular sludge in the presence of selenium oxyanions for sustainable recovery

This study examined simultaneous removal of indium (In(III)) and selenium oxyanions (Se(IV) and Se(VI)) using anaerobic granular sludge in batch and sequencing batch experiments. The indium removal efficiency was very high (>95%) throughout the experimental period, whereas the selenite removal values (78.9–98.2%) were considerably higher than the values obtained for selenate removal (15.5–70.0%) in the absence of In(III). The presence of In(III), however, increased the selenite and selenate removal efficiency to values up to 96–98%. The removal mechanism involved adsorption onto granular sludge followed by biomineralization to indium selenide. The presence of indium selenide in granular sludge treating indium and either of the selenium oxyanions was confirmed by SEM-EDX, XRD and XPS analysis. The granular sludge biomass exposed to only indium, mineralized it to form indium hydroxide. The microbial community analysis showed dominance of methanogenic microorganism in the granular sludge exposed to different combinations of indium and selenium. This study demonstrated the potential of anaerobic granular sludge biomass for production of indium selenide from co-mineralization of indium in the presence of selenium oxyanions Se(IV) and Se(VI) which provides an alternative novel strategy for its recovery from waste streams.

Indium removal by Aspergillus niger fungal pellets in the presence of selenite and tellurite

The feasibility of simultaneous removal of indium, selenite and tellurite using biological reduction by Aspergillus niger fungal pellets is explored. Initially, batch experiments were conducted to study the capability of A. niger pellets to remove indium, selenium and tellurium in different combinations. The indium removal efficiency ranged between 52.3 and 65.6 % at 10 mg/L, with a maximum removal (~65 %) in incubations with only indium or indium with tellurite. The tellurium removal efficiency was maximum (76.7 %) in experiments with indium, but dropped drastically to 47.2 and 33.7 %, respectively, when selenite and indium were incubated together. The selenite removal efficiencies of the A. niger pellets were more consistent (50.2–59.5 %) for different experimental combinations and were not affected by either indium or tellurium. Further characterization of fungal biomass showed accumulation of mainly elemental Se and Te nanoparticles within the pellets. In addition, XRD analysis showed the formation of indium selenide and indium telluride during their simultaneous removal. The EPS production by A. niger increased in the presence of these elements along with changes in the polysaccharide and protein content of the EPS. The fluorescence EEM spectra revealed that the EPS produced by A. niger during pollutant removal was mostly composed of soluble microbial products and humic acid like substances. This study demonstrated recovery of elemental chalcogen and indium chalcogenide nanoparticles can be achieved using fungal pelleted systems.

Predictive modelling and optimization of an airlift bioreactor for selenite removal from wastewater using artificial neural networks and particle swarm optimization

Selenite (Se4+) is the most toxic of all the oxyanion forms of selenium. In this study, a feed forward back propagation (BP) based artificial neural network (ANN) model was developed for a fungal pelleted airlift bioreactor (ALR) system treating selenite-laden wastewater. The performance of the bioreactor, i.e., selenite removal efficiency (REselenite) (%) was predicted through two input parameters, namely, the influent selenite concentration (ICselenite) (10 mg/L – 60 mg/L) and hydraulic retention time (HRT) (24 h – 72 h). After training and testing with 96 sets of data points using the Levenberg-Marquardt algorithm, a multi-layer perceptron model (2-10-1) was established. High values of the correlation coefficient (0.96 ≤ R ≤ 0.98), along with low root mean square error (1.72 ≤ RMSE ≤ 2.81) and mean absolute percentage error (1.67 ≤ MAPE ≤ 2.67), clearly demonstrate the accuracy of the ANN model (> 96%) when compared to the experimental data. To ensure an efficient and economically feasible operation of the ALR, the process parameters were optimized using the particle swarm optimization (PSO) algorithm coupled with the neural model. The REselenite was maximized while minimizing the HRT for a preferably higher range of ICselenite. Thus, the most favourable optimum conditions were suggested as: ICselenite – 50.45 mg/L and HRT – 24 h, resulting in REselenite of 69.4%. Overall, it can be inferred that ANN models can successfully substitute knowledge-based models to predict the REselenite in an ALR, and the process parameters can be effectively optimized using PSO.