Porous Alginate Beads Research Articles

Extracellular Electron Exchange Capabilities of Desulfovibrio ferrophilus and Desulfopila corrodens.

Microbial extracellular electron transfer plays an important role in diverse biogeochemical cycles, metal corrosion, bioelectrochemical technologies, and anaerobic digestion. Evaluation of electron uptake from pure Fe(0) and stainless steel indicated that, in contrast to previous speculation in the literature, Desulfovibrio ferrophilus and Desulfopila corrodens are not able to directly extract electrons from solid-phase electron-donating surfaces. D. ferrophilus grew with Fe(III) as the electron acceptor, but Dp. corrodens did not. D. ferrophilus reduced Fe(III) oxide occluded within porous alginate beads, suggesting that it released a soluble electron shuttle to promote Fe(III) oxide reduction. Conductive atomic force microscopy revealed that the D. ferrophilus pili are electrically conductive and the expression of a gene encoding an aromatics-rich putative pilin was upregulated during growth on Fe(III) oxide. The expression of genes for multi-heme c-type cytochromes was not upregulated during growth with Fe(III) as the electron acceptor, and genes for a porin-cytochrome conduit across the outer membrane were not apparent in the genome. The results suggest that D. ferrophilus has adopted a novel combination of strategies to enable extracellular electron transport, which may be of biogeochemical and technological significance.

Uranium removal from complex mining waters by alginate beads doped with cells of Stenotrophomonas sp. Br8: Novel perspectives for metal bioremediation

Uranium-containing effluents generated by nuclear energy industry must be efficiently remediated before release to the environment. Currently, numerous microbial-based strategies are being developed for this purpose. In particular, the bacterial strain Stenotrophomonas sp. Br8, isolated from U mill tailings porewaters, has been already shown to efficiently precipitate U(VI) as stable U phosphates mediated by phosphatase activity. However, the upscaling of this strategy should overcome some constraints regarding cell exposure to harsh environmental conditions. In the present study, the immobilization of Br8 biomass in an inorganic matrix was optimized to provide protection to the cells as well as to make the process more convenient for real-scale utilization. The use of biocompatible, highly porous alginate beads for Br8 cells immobilization resulted the best alternative when investigating by a multidisciplinary approach (High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM), Environmental Scanning Electron Microscopy (ESEM), Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance, etc.) several consolidated entrapment methods. This biomaterial was applied to complex real U mining porewaters (containing 47 mg/L U) in presence of an organic phosphate source (glycerol-2-phosphate) to produce reactive free orthophosphates through Br8 phosphatase activity. Uranium immobilization rates around 98 % were observed after one cycle of 72 h. In terms of U removal ability as a function of biomass, Br8-doped alginate beads were determined to remove up to 1199.5 mg U/g dry biomass over two treatment cycles. Additionally, optimized conditions for storing Br8-doped beads and for a correct application were assessed. Results for U accumulation kinetics and HAADF-STEM/ESEM analyses revealed that U removal by the immobilized cells is a biphasic process combining a first passive U sorption onto bead and/or cell surfaces and a second slow active biomineralization. This work provides new practical insights into the biological and physico-chemical parameters governing a high-efficient U bioremediation process based on the phosphatase activity of immobilized bacterial cells when applied to complex mining waters under laboratory conditions.

Aqueous two-phase emulsions-templated tailorable porous alginate beads for 3D cell culture

A facile method was developed to produce porous alginate beads (PABs) with a controllable interconnected porous structure with aqueous two phase (ATPS) emulsions as template for 3D cell culture. ATPS emulsions, containing two biocompatible immiscible aqueous phases of cell/dextran (Dex) mixture and alginate (Alg)/polyethylene glycol (PEG) mixture and stabilized by mPEG-BSA particles, were introduced to form PABs. The pore size of PABs could be controlled by changing the emulsification frequency and the volume ratio between the ATPS emulsions and PEG-Alg solution. Moreover, cells could be directly encapsulated in the interconnected pores due to the excellent biocompatibility of ATPS. HeLa and human liver cancer cells encapsulated in the PABs present stronger cell activity (>95 %), proliferation, and enhanced functions compared with the cells encapsulated in general alginate beads (GABs). It is believed that the PABs is a promising microcarriers for 3D cell culture in vitro.

Selective adsorption of Pd (II) by ion-imprinted porous alginate beads: Experimental and density functional theory study

In this study, a novel thiourea grafted porous sodium alginate-based adsorbent was synthesized by combining ion-imprinting and direct templating method. Due to ion-imprinting, the prepared adsorbent has demonstrated outstanding selectivity towards Pd (II) from bi-metallic solution at different pH values. Langmuir and both pseudo-first and pseudo-second kinetic equations were used to describe the adsorption isotherm and kinetics, respectively. FT-IR, XPS, and SEM-EDX analyses suggested that selective adsorption of Pd (II) was dominated by electrostatic interactions at pH 1.0 and chelation on imprinted sorption sites at pH 3.0. Density functional theory (DFT) calculation further explained the effect of ion-imprinting and provided two binding configurations, which is consistent with characterization analyses. The pregnant adsorbent can be regenerated and reused by thiourea solution in dilute hydrochloric acid. Therefore, the synthesized adsorbent would be useful as a selective adsorbent for the enrichment of Pd (II) from effluents.

Investigating the influences of quorum quenching and nutrient conditions on activated sludge flocs at a short-time scale

Quorum sensing signals regulate various functions within activated sludge processes such as formation of microbial aggregates. Disturbance of this signaling system, known as quorum quenching (QQ), provides opportunities for eliminating some problems related to biological wastewater treatment (e.g., biofouling and excess sludge production). However, it is poorly understood how and to what extent QQ systems can affect the microbial aggregation processes and the following floc formation. In particular, an in-depth structural characterization at the scale of microbial aggregate while considering nutrient conditions in the reactor is still largely disregarded. Here, we evaluated the QQ effects at the short-term time scale (i.e., after 4 h for the exogenous period and 19 h for exogenous/endogenous period), by combining advanced techniques for microbial characterization (flow cytometry, CARD-FISH, and confocal laser scanning microscopy) and conventional physical-chemical assessments. The results indicated that by implementing QQ agents (immobilized Acylase I enzyme in porous alginate beads) the abundance of single cells and suspended microbial aggregates in the supernatant did not show significant changes during the exogenous period. Conversely, at the end of the exogenous/endogenous period a significant increase of single prokaryotic cells, small and large microbial aggregates favored the growth of grazers, including free-living nanoflagellates and ciliates. Flocs became looser and thinner than those in the control reactor, thus affecting the sludge settling behavior. Inability of microbial community in degradation of soluble protein during the endogenous period confirmed that the QQ agents are likely to inhibit the secretion of protease enzyme within microbial communities of activated sludge.

Mechanistic study of selective adsorption of Hg2+ ion by porous alginate beads

Porous alginate beads prepared by template-assisted emulsion polymerization were investigated as selective adsorbents for Hg2+ ions from tri-metallic solutions containing the same molar concentration of Hg2+, Cd2+ and Pb2+. We observed experimentally that mechanisms of selective adsorption of Hg2+ ion by the porous alginate beads are complicated and highly dependent on solution pH. Interactions between metal cations and the porous adsorbent at different pH values were further characterized by IR and XPS analyses. Results indicated that metal uptake at low solution pH is regulated predominantly by cation exchange, making the adsorbent extremely selective to Hg2+. Nonetheless, metal binding by electrostatic attraction and complexation become important with the increase of solution pH. To validate the sorption mechanisms, density functional theory (DFT) was employed to study the binding properties of metal cations with the porous alginate adsorbent. Our computational results are completely consistent with our experimental findings, providing the theoretical basis and explanations for selective adsorption of Hg2+ by porous alginate beads.

Zinc oxide templating of porous alginate beads for the recovery of gold ions

In this study, a novel porous alginate adsorbent was prepared by zinc oxide templating to selectively adsorb Au (III) ions from multi-metallic solutions under acidic condition. Due to the porous structure of the prepared sorbent, high uptake capacity and fast adsorption kinetics of Au (ІІІ) were achieved, which renders the prepared adsorbent great potential for practical applications in fixed-bed columns for large-scale applications. The adsorption of Au (III) by the prepared adsorbent led to the reduction of Au (III) to metallic gold. Adsorption and reduction of Au (III) in the process are mediated by the ionic and covalent interaction between Au (III) ions and the protonated functional groups on the modified alginate.

Immobilization of hydrous iron oxides in porous alginate beads for arsenic removal from water

For removal of arsenic in the aqueous phase, hydrous iron oxides (HIOs) were immobilized in alginate beads with enhanced porosity (designated as HIO-P-alginate beads).