CaCl2 Medium Research Articles

Characterization and applicability of novel alkali–tolerant carbonatogenic bacteria as environment-friendly bioconsolidants for management of concrete structures and soil erosion

Cracking and erosion are critical factors that reduce the mechanical properties and stability of concrete structures and soil, respectively. They are recognized worldwide as severe disasters causing the collapse of many structures including stone heritage and dams, and landslides. Therefore, it is essential to propose effective and environment-friendly management methods to prevent them. Carbonatogenesis has recently received considerable attention as a reliable biological process for remediating cracks in calcareous structures, stabilizing loose soils, and sequestering CO2 in the environment. Isolating and characterizing carbonatogenic bacteria with excellent performance is crucial for applying this process to the field of environmental and civil engineering. The aim of this study was to isolate new CaCO3–precipitating bacteria and investigate various properties for their use as bioconsolidants. Furthermore, the possibility of restoring damaged structures and stabilizing loose sandy soil using isolated strain was investigated. Strain LC13 with urease and CaCO3–precipitating activity was isolated from limestone cave soil in Korea and identified as Arthrobacter sulfureus by phenotypic characterization and 16S rRNA gene analysis. Although cell growth was observed after an adaptation period at pH 11, strain LC13 grew well at pH 7–11, indicating alkali tolerance. The optimal conditions for CaCO3 precipitation were 1.0% yeast extract, 2.5% urea, 0.35% NaHCO3, and 400 mM CaCl2, with an initial pH of 6.5 at 30 °C. Under optimized conditions, maximal CaCO3 (22.92 ± 0.14 g/l) precipitated after 3 days, which was 10.8–fold higher than the value in a urea–CaCl2 medium. CaCO3 precipitation by strain LC13 was associated with an increased pH due to ureolysis and protein deamination. Using an optimized medium as a cementation solution, strain LC13 completely remediated 340–760 μm wide cracks over 3 days, and also restored the spalling of concrete surfaces. Furthermore, the sand treated with LC13 solidified with a surface strength of 14.9 kPa. Instrumental analysis confirmed that the crystals precipitated were a mixture of CaCO3 polymorphs composed of rhombohedral calcite and spherical vaterite. These results suggest that A. sulfureus LC13 may be useful for implementing sustainable biorestoration and environmental management technologies such as the in situ remediation of structural cracks and in situ prevention of soil erosion.

A Review on the Performance Evaluation of Autonomous Self-Healing Bacterial Concrete: Mechanisms, Strength, Durability, and Microstructural Properties

The development of cracks, owing to a relatively lower tensile strength of concrete, diverse loading, and environmental factors driving the deterioration of structures, is an inescapable key concern for engineers. Reparation and maintenance operations are thus extremely important to prevent cracks from spreading and mitigating the lifetime of structures. However, ease of access to the cracked zone may be challenging, and it also needs funds and manual power. Hence, autonomous sealing of cracks employing microorganisms into the concrete sans manual intervention is a promising solution to the dilemma of the sustainable improvement of concrete. ‘Ureolytic bacteria’, key organism species in rumen-producing ‘urease’ enzymes such as Bacillus pasteurii or subtilis—when induced—are capable of producing calcium carbonate precipitations into the concrete. As their cell wall is anionic, CaCO3 accumulation on their surface is extensive, and the whole cell, therefore, becomes crystalline and ultimately plugs pores and cracks. This natural induction technique is an environmentally friendly method that researchers are studying intensively. This manuscript reviews the application process of bacterial healing to manufacture autonomous self-healing bacterial concrete. Additionally, it provides a brief review of diverse attributes of this novel concrete which demonstrate the variations with the auto-addition of different bacteria, along with an evaluation of crack healing as a result of the addition of these bacteria directly into concrete or after encapsulation in a protective shell. Comparative assessment techniques for autonomous, bio-based self-healing are also discussed, accompanied by progress, potential, modes of application of this technique, and its resultant benefits in the context of strength and durability. Imperatives for quantitative sustainability assessment and industrial adoption are identified, along with the sealing of artificially cracked cement mortar with sand as a filling material in given spaces, as well as urea and CaCl2 medium treatment with Bacillus pasteurii and Sporosarcina bacteria. The assessment of the impact on the compressive strength and rigidity of cement mortar cubes after the addition of bacteria into the mix is also considered. Scanning electron microscope (SEM) images on the function of bacteria in mineral precipitation that is microbiologically induced are also reviewed. Lastly, future research scope and present gaps are recognised and discussed.

Minimising oxygen contamination through a liquid copper-aided group IV metal production process

This paper demonstrates for the first time the fabrication of Zr-Cu alloy ingots from a Hf- free ZrO2 precursor in a molten CaCl2 medium to recover nuclear-grade Zr. The reduction of ZrO2 in the presence of CaO was accelerated by the formation of Ca metal in the intermediate stage of the process. Tests conducted with various amounts of ZrO2 indicate that the ZrO2 was reduced to the metallic form at low potentials applied at the cathode, and the main part of the zirconium was converted to a CuZr alloy with a different composition. The maximum oxygen content values in the CuZr alloy and Zr samples upon using liquid Cu were less than 300 and 891 ppm, respectively. However, Al contamination was observed in the CuZr during the electroreduction process. In order to solve the Al contamination problem, the fabrication process of CuZr was performed using the metallothermic reduction process, and the produced CuZr was used for electrorefining. The CuZr alloy was further purified by a molten salt electrorefining process to recover pure nuclear-grade Zr in a LiF-Ba2ZrF8-based molten salt, the latter of which was fabricated from a waste pickling acid of a Zr clad tube. After the electrorefining process, the recovered Zr metal was fabricated into nuclear-grade Zr buttons through arc melting following a salt distillation process. The results suggest that the removal of oxygen from the reduction product is a key reason for the use of a liquid CaCu reduction agent.

Microbially Induced Calcite Precipitation Employing Environmental Isolates.

In this study, five microbes were employed to precipitate calcite in cohesionless soils. Four microbes were selected from calcite-precipitating microbes isolated from calcareous sand and limestone cave soils, with Sporosarcina pasteurii ATCC 11859 (standard strain) used as a control. Urease activities of the four microbes were higher than that of S. pasteurii. The microbes and urea–CaCl2 medium were injected at least four times into cohesionless soils of two different relative densities (60% and 80%), and the amount of calcite precipitation was measured. It was found that the relative density of cohesionless soils significantly affects the amount of calcite precipitation and that there is a weak correlation between urease activity and calcite precipitation.

BIO CONCRETE AND BACTERIA BASED SELF HEALING CONCRETE

Concrete is cheap and easily available construction material in the world. So advancement in the concrete is to improve its compressive strength and durability of structures by using micro organisms carrying process of MICP. This project discusses the filling of voids in fresh concrete and plugging of artificially cracked cement mortar using Bacillus Sphaericus and Proteus Vulgarious bacteria combined with sand as a filling material in artificially made cuts in cement mortar which was cured in urea and CaCl2 medium. The effect on the compressive strength, flexural strength due to the mixing of bacteria along with effect of water absorption and sorptivity on concrete cubes is also discussed in this project. The main aim of the project is to evaluate the strength in comparison with conventional and bio concrete cubes. The evaluated results suggest that there is significant increase in the strength of concrete

Corrosion of high density graphite anodes during direct electrochemical de-oxidation of solid oxides in molten CaCl2 medium

Graphite anode used in the direct electrochemical de-oxidation of solid oxides in molten calcium chloride medium (FFC Cambridge process) degrades by formation of carbon oxides and erosion. The problem was studied by using graphite as anode in the electrochemical de-oxidation of powder compacted and sintered Nb2O5 pellet electrodes in molten CaCl2 at 1173K and at a constant voltage of 3.1V. The degradation of the graphite anodes, recovered from the electro-de-oxidation cells at predetermined intervals of time (2, 9, 22, 26, 35, 44 and 56h) during the long-duration electrolysis, was determined by mass loss measurements and the morphological changes by SEM imaging. The graphite rods were found corroded differently along the lengths, with the maximum corrosion being at the melt-immersed surface of the electrode close to the melt–gas interface. The prominent carbon consuming reaction C+2O2−→CO2+4e− apart, the impregnation of salt into the defects of the graphite anode and convection currents existing in the melt appeared to enhance the corrosion and hence the mass loss of graphite towards the later stages of electrolysis.

A study of the reaction pathways during electrochemical reduction of dense Nb2O5 pellets in molten CaCl2 medium

Electrochemical behaviour of powder compacted and sintered Nb2O5 pellet electrodes (~4mm thick, open porosity ~10%) in molten CaCl2 medium at 1173K was studied using cyclic voltammetry and polarisation measurements. Similar dense Nb2O5 pellets were subsequently electrolysed by using them as cathodes against graphite counter electrode in the molten CaCl2 electrolyte medium with an aim to gain insight into the electro-reduction mechanism. The chemical changes that are taking place in the cathode and also in the electrolyte melt at different stages of electrolysis were analysed. The electro-reduction experiments were carried out at an applied voltage of 3.1V and terminated after 2, 9, 22, 26 and 35h of electrolysis and the visibly distinct layers present in the partially reduced samples were analysed. The analysis showed presence of CaxNbyOz compounds, sub-oxides of Nb like NbO2, NbO, etc. and metallic Nb in the samples. A pellet, which was electrolysed for 44h was found to be reduced completely to Nb metal. The CaO, Ca and CaCO3 produced and released to the melt during the cathodic polarisation was found to be associated with the electrochemical changes that are taking place on the electrode and this was ascertained by determination of the ‘total solubilised basicity (TSB)’ and ‘total insolubilised basicity (TIB)’ of the melt as a function of time during electrolysis. Based on the results, a three-stage mechanism comprising (i) cathodic insertion of Ca2+ into the oxide pellet, (ii) reduction of the oxide electrode via formation and decomposition of ternary intermediates and (iii) chemical reduction of the cathode with electro-generated calcium metal has been proposed for electro-reduction of dense Nb2O5 pellets.

Mircobial Sediment Solidification

In recent years, the reservoir sediments have been a disturbance to Taiwan government, and are getting worse due to the climate change. Consequently, it becomes an urgent issue for the authority to dredge and dispose reservoir sludge effectively. Material researchers in civil engineering and environmental engineering, cooperating with microbiologists and geochemists, have recently attempted the solidification of sludge granules into sandstone-like materials employing microorganisms. The aim of this study is to investigate the approach to solidify sludge or soil particle rapidly to attain strength through the growth of bacteria and apply the technique in practical. In this research, we used Bacillus pasteurii in the solidification of reservoir sludge. The sludge used in the experiment has a moisture content of 40%. The change of bacteria broth culture concentration (0%, 25%, 50%, 75%, and 100%) and CaCl2 ratio in the culturing Urea-CaCl2 medium (10%, 30% and 70%) were used as the experimental variables. The culture broth was mixed directly with reservoir sludge to form a cubic specimen (50 mm x 50 mm x 50 mm), which was then used in compressive strength, XRD and SEM test. The test results showed that being cultured in 70%-CaCl2 medium, the specimen blended with 100% bacteria broth had the highest compressive strength. Compared with the blank samples (0% bacteria broth), the compressive strength was enhanced by approximately 13.48%. Also, it was suggested that the solidification by bacteria can indeed enhance the compressive strength of the cube. The sludge solidified with bacteria cultured in 70%-CaCl2 medium has the highest compressive strength. The result also showed that the higher the content of CaCl2 used in the culturing medium is, the more CaCO3 deposit is induced by the bacteria.

Mineral trioxide aggregate solution inhibits osteoclast differentiation through the maintenance of osteoprotegerin expression in osteoblasts

Mineral trioxide aggregate (MTA) is a therapeutic, endodontic repair material that is reported to exhibit calcified tissue-conductive activity. The aim of this study was to investigate whether MTA may prevent osteoclast differentiation in vitro. MTA solution, but not other commonly used retrofilling materials, such as Dycal, Super-EBA, or intermediate restorative material (IRM) solution, dose-dependently inhibited osteoclastogenesis in cocultures of mouse bone marrow cells (BMCs) with primary osteoblast cells (POBs) induced by 1α,25-dihydroxyvitamin D(3) [1α,25(OH)(2) D(3) ]. Exogenous CaCl(2) medium supplementation did not inhibit osteoclastogenesis in cocultures. Furthermore, MTA solution did not affect receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis, suggesting that POBs are targets of MTA. MTA solution suppressed the 1α,25(OH)(2) D(3) -induced reduction of osteoprotegerin (OPG) mRNA and protein production without changing RANKL expression in POBs. Consistent with this result, MTA solution did not inhibit osteoclastogenesis in cocultures of BMCs and POBs from OPG-deficient mice. Therefore, the maintenance of OPG expression in POBs appears to be critical for the inhibitory effect of MTA solution on osteoclast differentiation.

Zinc desorption kinetics as influenced by pH and phosphorus in soils

The rate of zinc (Zn) desorption from soil surfaces into soil solution is a dynamic factor that regulates its continuous supply to growing plants. To ascertain the pattern of Zn desorption as a function of phosphorus (P) application rate and pH, kinetics of Zn desorption from three surface soils representative of three major benchmark soil series were investigated using four equations. Zinc desorption decreased continuously with increase in pH from 4.25 to 8.00 in Oxisol. By contrast, Alfisol and Vertisol exhibited maximum Zn desorption at pH 5.50. Thereafter, Zn desorption decreased abruptly at pH 6.75 and finally steady state condition was obtained in both sodium chloride (NaCl) and calcium chloride (CaCl2) medium. The Elovich equation described Zn desorption kinetics much better at pH 4.25 and 5.50 followed by Parabolic diffusion equation at pH 6.75 and 8.00 for all the soils in NaCl medium. Whereas in the CaCl2 medium, the Elovich equation was superior in fitting the Zn desorption data irrespective of P level, pH, and soil. The Elovich constant (β) indicated that P affects Zn desorption inversely up to pH values 6.75.

Characterisation of surface properties of ceramic membranes by streaming and membrane potentials

The charge of ceramic UF membranes is studied in NaCl and CaCl2 media from streaming potential and membrane potential measurements. The amphoteric behaviour of these materials is observed with both methods. The apparent transport numbers of cations in the membrane are determined from cell potential measurements. Streaming potential measurements and the study of the transport properties lead to similar isoelectric points of the membrane. It also appears that the presence of Ca2+ cations leads to a more positive net charge of the membrane at pH lower than the isoelectric point and a less negative charge for the higher pH.

Glutamate release evoked by glutamate receptor agonists in cultured chick retina cells: Modulation by arachidonic acid

We studied the effect of ionotropic glutamate receptor agonists on the release of endogenous glutamate or of [3H]D-aspartate from reaggregate cultures (retinospheroids) or from monolayer cultures of chick retinal cells, respectively. Kainate increased the fluorescence ratio of the Na+ indicator SBFI and stimulated a dose-dependent release of glutamate in low (0.1 mM) Ca2+ medium, as measured using a fluorometric assay. Under the same experimental conditions, the release evoked by N-methyl-D-aspartate (NMDA; 400 microM) was about half of that evoked by the same kainate concentration; alpha-amino-3-hydroxy-5-methyl-4-isoxasolepropionic acid (AMPA; 400 microM) did not trigger a significant response. In the presence of 1 mM CaCl2, all of the agonists increased the [Ca2+]i, as determined with the fluorescence dye Indo-1, but the glutamate release evoked by NMDA and kainate was significantly lower than that measured in 0.1 mM CaCl2 medium. Inhibition by Ca2+ of the kainate-stimulated release of glutamate was partially reversed by the phospholipase A2 inhibitor oleiloxyethyl phosphorylcholine (OPC), suggesting that the effect was mediated by the release of arachidonic acid, which inhibits the glutamate carrier. Accordingly, kainate, NMDA, and AMPA stimulated a Ca(2+)-dependent release of [3H]arachidonic acid, and the direct addition of the exogenous fatty acid to the medium decreased the release of glutamate evoked by kainate in low (0.1 mM) CaCl2 medium. In monolayer cultures, we showed that NMDA, kainate, and AMPA also stimulated the release of [3H]D-aspartate, but in this case release in the presence of 1 mM CaCl2 was significantly higher than that evoked in media with no added Ca2+. The ranking order of efficacy for stimulation of Ca(2+)-dependent release of [3H]D-aspartate was NMDA > > kainate > AMPA.

Preparation and Characterization of New Molybdenum Nitride or Oxynitride Phases

ABSTRACTSeveral methods of synthesizing molybdenum nitride or oxynitride fine powders are presented.We have prepared a γ-Mo2N type oxynitride phase by reacting ammonia with MoO3. The surface area and morphology of the oxynitride powders depend on the synthesis conditions. Characterization of the solids by elemental analysis, X-ray and neutron diffraction, and thermogravimetric analysis shows dramatic modification of the stoichiometry of conventional Mo2N nitride. Aging at room temperature under air results in decreasing the material surface area. The initial surface area can be recovered be fine tuning of experimental conditions. MoCl5 and Ca3N2 are reacted in a molten CaCl2 medium leading to a new Mo2N structure type.The reaction between molybdenum sulfide and NH3 produces two different phases depending on the reaction conditions. They are structurally related to δ-MoN.

Polyacrylamide adsorption onto kaolinite in the presence of sodium dodecylbenzenesulfonate in saline medium

Adsorption of partially hydrolyzed polyacrylamides onto kaolinite in strongly saline medium is higher than in pure water. Polymer uptake is inversely proportional to the degree of hydrolysis. In CaCl2 medium, the uptake is more significant than in NaCl medium. In the presence of sodium dodecylbenzenesulfonate (NaDBS), polymer adsorption is reduced in NaCl medium but remains unaffected in CaCl2 medium, since calcium concentration is sufficient in this case to induce surfactant precipitation.