Microbial carbonate precipitation is known as an efficient process for the remediation of heavy metals from contaminated soils. In the present study, a urease positive bacterial isolate, identified ...as Bacillus cereus NS4 through 16S rDNA sequencing, was utilized on a large scale to remove nickel from industrial soil contaminated by the battery industry. The soil was highly contaminated with an initial total nickel concentration of approximately 900 mg kg−1. The soluble-exchangeable fraction was reduced to 38 mg kg−1 after treatment. The primary objective of metal stabilization was achieved by reducing the bioavailability through immobilizing the nickel in the urease-driven carbonate precipitation. The nickel removal in the soils contributed to the transformation of nickel from mobile species into stable biominerals identified as calcite, vaterite, aragonite and nickelous carbonate when analyzed under XRD. It was proven that during precipitation of calcite, Ni2+ with an ion radius close to Ca2+ was incorporated into the CaCO3 crystal. The biominerals were also characterized by using SEM-EDS to observe the crystal shape and Raman-FTIR spectroscopy to predict responsible bonding during bioremediation with respect to Ni immobilization. The electronic structure and chemical-state information of the detected elements during MICP bioremediation process was studied by XPS. This is the first study in which microbial carbonate precipitation was used for the large-scale remediation of metal-contaminated industrial soil.
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•Microbial carbonate precipitation for large-scale remediation of metal-contaminated soil.•Soluble-exchangeable Ni fraction was reduced to 38 mg kg−1 after treatment from 898 mg kg−1.•Ni transformation from mobile species into stable biominerals, mainly calcite and NiCO3.•Characterization of biominerals by SEM-EDS, Raman-FTIR spectroscopy and XRD.
Microbial carbonate precipitation for nickel remediation was studied. Soluble-exchangeable Ni fraction from contaminated industrial soil was reduced from initial 898 mg kg−1 to 38 mg kg−1.
A new efficient framework coupling the two dimensional (2D) discrete dislocation dynamics (DDD) and the extended finite element method (XFEM) is developed for modeling the dynamic evolution of ...multiple dislocations in crystalline materials with abundant interfaces/surfaces. By a specially introduced stress calculation scheme with cut-off radius and virtual elements, the present algorithm can capture interaction between neighboring dislocations accurately although no time-consuming dislocation-core enrichment is employed. Since it is not sensitive to the FE mesh size and large XFEM time step can be used, its efficiency is evidently improved compared with other DDD frameworks. Due to the merits of XFEM itself, the present DDD-XFEM scheme can treat intractable surface/interface problems conveniently, with no additional image stress calculation as in the DDD-FEM superposition framework and special plastic-strain distribution near the surfaces/interfaces as in the discrete-continuous method (DCM) needed. For these, it can be used to model plastic behaviors of crystals with abundant interfaces/surfaces (i.e. grain/phase boundaries and crack/void surfaces). To show the ability of present DDD-XFEM scheme, it is used to simulate the mechanical responses of polycrystalline aluminum with assumed rigid and penetrable grain boundaries. A three-stage model for dislocation penetrating through grain boundary (DPTGB) is suggested. The results show that the present DDD-XFEM scheme can capture the formation of dislocation pile-ups and thus the Hall-Petch effect successfully. The DPTGB can decrease the flow stress and hardening rate evidently; moreover, it can weaken the grain size effect and may enhance the cyclic stress relaxation of polycrystals greatly.
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•A more efficient and accurate XFEM-DDD framework for simulating the micro-plasticity of materials is developed.•The newly developed XFEM-DDD framework can well deal with various complex discontinuities in materials.•The present XFEM-DDD framework can simulate efficiently the problems on much longer/larger temporal/spatial scale.•A three-stage model for dislocation penetrating through GB (DPTGB) is suggested.•The grain size effect on strength and the cyclic stress relaxation are captured efficiently by the present scheme.
In polycrystalline materials, microvoid size is usually of the same order of magnitude as grain size. However, in most previous studies, matrix around microvoid is generally assumed to be isotropic ...and homogeneous, ignoring local heterogeneous polycrystalline microstructure. In this paper, microvoid growth under finite deformation in a face centered cubic (FCC) polycrystal is studied, focusing on the effect of local heterogeneous polycrystalline microstructure. Crystal plasticity finite element simulation (CPFEM) of polycrystalline representative volume element (RVE) is performed, with special attention to three important factors influencing the microvoid growth, i.e., external macroscopic stress triaxiality, internal crystallographic orientation of grains and ratio of microvoid size to grain size. The results indicate that the crystallographic orientation of grains has significant influences on the microvoid growth, especially when the stress triaxiality is not high. The local heterogeneous polycrystalline microstructure in polycrystals is found to retard the microvoid growth, suggesting that the traditional microvoid growth models based on the assumption of homogeneous isotropic matrix can significantly overestimate the microvoid growth. Besides, the size ratio of microvoid to the voided grain can heavily influence the microvoid growth, showing a strong size effect due to the first order heterogeneous deformation effect around the microvoid in heterogeneous polycrystals. Due to random grain-orientation distributions in polycrystals, the microvoid growth rate exhibits randomness and dispersion. To assess this dispersion under different stress triaxialities, a statistical microvoid growth model is proposed, which well envelops all the dispersed CPFEM results.
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•The microvoid growth in heterogeneous polycrystalline environment is random and dispersed.•The dispersion of microvoid growth is closely related to the stress triaxiality.•Heterogeneous polycrystalline matrix tends to retard the microvoid growth.•Size-dependent void growth can be induced by the first order heterogeneous deformation effect.•A statistical void growth model involving dispersed grain-orientation effect was proposed.
► We model the stress–strain responses of a Ni-based superalloy by 3D DDD. ► The three-stage response of this material may relate to the precipitate shearing. ► The major hardening mechanism is the ...interfacial polarised dislocation network. ► The size effects on stress–strain responses are different in different stages. ► The influence of precipitate shape, arrangement and coherency stress are investigated.
Discrete dislocation dynamics (DDD) has been used to model the deformation of nickel-based single crystal superalloys with a high volume fraction of precipitates at high temperature. A representative volume cell (RVC), comprising of both the precipitate and the matrix phase, was employed in the simulation where a periodic boundary condition was applied. The dislocation Frank–Read sources were randomly assigned with an initial density on the 12 octahedral slip systems in the matrix channel. Precipitate shearing by superdislocations was modelled using a back force model, and the coherency stress was considered by applying an initial internal stress field. Strain-controlled loading was applied to the RVC in the 0
0
1 direction. In addition to dislocation structure and density evolution, global stress–strain responses were also modelled considering the influence of precipitate shearing, precipitate morphology, internal microstructure scale (channel width and precipitate size) and coherency stress. A three-stage stress–strain response observed in the experiments was modelled when precipitate shearing by superdislocations was considered. The polarised dislocation structure deposited on the precipitate/matrix interface was found to be the dominant strain hardening mechanism. Internal microstructure size, precipitate shape and arrangement can significantly affect the deformation of the single crystal superalloy by changing the constraint effect and dislocation mobility. The coherency stress field has a negligible influence on the stress–strain response, at least for cuboidal precipitates considered in the simulation. Preliminary work was also carried out to simulate the cyclic deformation in a single crystal Ni-based superalloy using the DDD model, although no cyclic hardening or softening was captured due to the lack of precipitate shearing and dislocation cross slip for the applied strain considered.
•Phytoplankton functional groups concept was applied in the river-connected lake.•Succession of group P/MP/D (RⅠ) → P/MP/J (RⅡ) → MP (FⅠ) → MP/P/Y (FⅡ) was observed.•Water level was the key factor ...for the phytoplankton biomass and functional groups.•Organic matter and nitrogen fertilizer input were the main factors for algal blooms.
Identifying the drivers that impact phytoplankton biomass and dynamics of functional groups (FGs) is crucial to the management of lake aquatic systems. To explore the interactive effects of hydrological characteristics, physicochemical parameters and phytoplankton FGs in the largest river-connected lake, a case study was carried out at Dongting Lake, China. We analyzed the changes in the hydrological characteristics of the lake as well as in the phytoplankton biomass throughout the year to explore the driving factors that influence phytoplankton FGs. Four periods were defined in our study based on water level (WL) fluctuations including the rising periods (RⅠ and RⅡ) and the falling periods (FⅠ and FⅡ). The phytoplankton biomass in Dongting Lake was the highest in RⅡ, followed by RⅠ, FⅠ, and FⅡ. And the trend of FGs dominance through the four periods were P/MP/D (RⅠ) → P/MP/J (RⅡ) → MP (FⅠ) → MP/P/Y (FⅡ). Changes in phytoplankton biomass and FGs were the result of a combination of hydrological characteristics and physicochemical parameters. Throughout the water period, the hydrological characteristics did not directly influence phytoplankton, instead exerting a more indirect effect on phytoplankton biomass and FGs by affecting the water’s physicochemical parameters, e.g., permanganate index (CODMn), nitrogen nutrients, dissolved oxygen (DO), water temperature (WT), and conductivity (Cond). CODMn might be a significant predictor of phytoplankton biomass and FGs in all water periods, explaining 36.6% of the variability, followed by Cond, WT, ammonia nitrogen (NH4+-N), and DO explaining 17.6%, 12.3%, 11.3%, and 7.2%, respectively. However, according to each water phase analysis, the WL was the key factor for phytoplankton growth in RⅡ. Nitrogen nutrients, WT and Cond had more pronounced effects on phytoplankton in RⅠ, FⅠ and FⅡ, respectively., Based on the findings of our study, we suggest that increased control of organic matter input into the lake and nitrogen fertilizer use at nearby agricultural surface sources are effective actions that are needed to prevent and control algal blooms in Dongting Lake.
A two-dimensional discrete-continuous scheme (DCS), which couples the motions of dislocations and diffusion of vacancies, is developed. There are three modules in this scheme. The glide and climb of ...dislocations are performed by the discrete dislocation dynamics (DDD) module, by which the evolution of dislocations is captured and the plastic strain due to dislocation motions is obtained. The diffusion of vacancies is performed by the finite difference method (FDM) module, by which the vacancy concentration field and the inelastic strain due to vacancy diffusion are obtained. The plastic strain by the DDD and the inelastic strain by the FDM, as the eigen-strains, are transferred to the finite element method (FEM) module, by which the stress field is obtained and then transferred back to the DDD module and FDM module to drive dislocation motions and vacancy diffusion. By this vacancy diffusion coupled discrete dislocation dynamics scheme, the compression creep of single crystalline and bi-crystalline aluminum micro-pillars at elevated temperature is modeled. Some interesting creep behaviors are computationally captured. The compression creep of single crystalline and bi-crystalline micro-pillars is size dependent: the creep strain of micro-pillars at higher compressive stress increases with increasing micro-pillar diameter, which is in good agreement with experimental results reported in the literature. This is believed to result from higher dislocation density in those micro-pillars with larger diameter.
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Artificial floating islands (AFIs) are a variation of wetland treatment systems for water quality improvement. This paper provides a review concerning AFIs in terms of their development, ...classification, and applications in the removal of nutrients, heavy metals, and chemical oxygen demand on waterways. The role of microorganisms, aquatic plants, and aquatic animals in AFIs for water decontamination and purification was also discussed. Additionally, some key factors influencing the AFIs’ performances were discussed and comparisons between AFIs and constructed wetlands were reviewed. Finally, further perspectives of artificial floating islands were identified to possibly improve their performances. The understanding of the mechanisms in AFIs that drive removal of various contaminants to improve water quality is crucial, and is also highlighted in this paper.
Microbially induced carbonate precipitation (MICP) is one of techniques for consolidation of cementitious materials; however, limited biodiversity and inadequate information on its application ...suggests further extensive research in this area. In this study, bacteria with ability to precipitate carbonate, preferably CaCO3, were isolated from Yixing Shanjuan Cave, China after analyzing bacterial diversity using Illumina MiSeq sequencing the V3-V4 region of 16S rRNA gene. A total of 58,712 effective 16S rRNA gene sequences were obtained, classified into 31 bacterial phyla. One of the highest urease-producing bacterium, Acinetobacter sp. SC4, was then used in consolidation of cracks created in masonry cement mortars. The bio-consolidation led to significant improvement in compressive strength and reduction in water absorption of mortars. It formed calcite observed under scanning electron microscopy, which were in agreement with X-ray diffraction and thermogravimetric analysis. The presented work is the first extensive study on Acinetobacter sp. induced carbonate precipitation in MICP related research.
•Bacterial diversity of a karst cave by Illumina MiSeq sequencing V3-V4 region of the 16S rRNA gene.•A total of 58,712 effective 16S rRNA gene sequences, classified into 31 bacterial phyla.•Acinetobacter sp. SC4 was used in consolidation of cracks created in masonry cement mortars.•Bio-consolidation resulted in significant improvement in compressive strength of mortars.•First report on Acinetobacter sp. induced carbonate precipitation in biocementation research.
The dislocation-induced shielding effect on the crack-tip depends on not only the number of dislocations but also the distance of dislocations from the crack-tip. The former is closely related to the ...nucleation of dislocation but the latter to the grain size and the obstruction of grain boundaries (GBs) to dislocations. In this paper, a discrete dislocation dynamic framework was further developed with a crack-tip dislocation emission scheme especially introduced, and then a series of discrete dislocation dynamic simulations were performed to study the shielding effect of dislocations on the crack-tip in poly-crystals. The different roles of the dislocation nucleation from the Frank-Read sources (DNFR) and dislocation emission from the crack-tip (DECT) in the shielding effect were studied, which indicates the DECT mechanism plays more important role compared with the DNFR one for the cases considered here. The shielding effect of dislocation is dominated by the grain size as well as the energy barrier for dislocation transmission across GB. With the increase of grain size, the shielding effect of dislocations on the crack-tip increases significantly, showing strong grain size effect. Moreover, with the increase of the GB energy barrier for dislocation transmission, the shielding effect of dislocations on the crack-tip first increases and then reaches its peak and finally decreases, showing an interesting mountain-shaped dependence on the GB energy barrier. This mountain-shaped dependence is gradually flattened with the increases of grain size. These interesting results enrich our understanding of the dislocations-induced shielding effect on the crack-tip in the poly-crystals.
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•Crack tip stress field of a polycrystalline material has been modelled under cyclic loads using DDD.•Both dislocation climb and grain boundary penetration are considered in the model.•Strain ...ratchetting is found near the crack tip, to which dislocation climb is found to be mainly responsible.•Multiple slip systems are found close to the crack tip.
The near-tip deformation of a transgrannular crack under cyclic loading conditions has been modelled using discrete dislocation dynamics (DDD) with both dislocation climb and dislocation-grain boundary (GB) penetration considered. A representative cell was built to model the constitutive behaviour of the material, from which the DDD model parameters were fitted against the experimental data. The near-tip constitutive behaviour was simulated for a transgranular crack in a polycrystalline nickel-based superalloy. A phenomenon of cyclic creep or strain ratchetting was reproduced, similar to that obtained using viscoplastic and crystal-plastic models in continuum mechanics. Ratchetting has been found to be associated with dislocation accumulation, dislocation climb and dislocation-GB penetration, among which dislocation climb seems to be the dominant mechanism for the cases considered at elevated temperature. Ratchetting behaviour seems to have a distinctive discrete characteristic in that more pronounced ratchetting occurred within slip bands than elsewhere. Multiple slip systems were activated in grains surrounding the crack tip, as opposed to single active slip system in grains away from the crack tip. The present DDD results show that, the near-tip ratchetting strain ahead of the crack tip seems to be a physical phenomenon, which may be of particular significance for developing a physical-based model of crack growth.
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