[Research advances of microbial transformation of CO2 in geological sequestration].

Carbon capture, utilization and storage is the vital technology for China to achieve the goals of carbon peaking and carbon neutrality. Microbial activities in situ are an indispensable part in the process of geological CO2 sequestration. Some microorganisms can convert CO2 into methane and organics as the resource for utilization or into carbonate to achieve long-term sequestration. These activities contribute to the stable storage of CO2 and even negative carbon emission. This paper focuses on the processes of bio-methanation, bio-liquefaction, and bio-precipitation that may be involved in CO2 sequestration in deep stratum and discusses the research progress in the bio-transformation pathways. Bio-methanation and bio-liquefaction can convert CO2 into methane or high-value organic compounds to realize resource reuse. The two technologies can be used alone or coupled to expand the application range of CO2 biotransformation. Bio-mineralization can convert CO2 into calcite by microorganism-induced carbonate precipitation, being a technology of great potential in fixing CO2 and limiting CO2 escape. At present, this field is still in the infancy stage, and there is an urgent need to establish and improve the theoretical and technical systems of CO2 in-situ biotransformation from transformation principle, influencing factors, conversion efficiency, economy, environmental protection, and technological conditions. Moreover, it can be combined with CCUS to establish a technical system integrating capture, transport, displace, storage, transfer, and exploit, so as to promote the value-added application of CCUS and the achievement of carbon peaking and carbon neutrality.

Microbial induced carbonate precipitation for remediation of heavy metals, ions and radioactive elements: A comprehensive exploration of prospective applications in water and soil treatment.

Improper disposal practices have caused environmental disruptions, possessing by heavy metal ions and radioactive elements in water and soil, where the innovative and sustainable remediation strategies are significantly imperative in last few decades. Microbially induced carbonate precipitation (MICP) has emerged as a pioneering technology for remediating contaminated soil and water. Generally, MICP employs urease-producing microorganisms to decompose urea (NH2CONH2) into ammonium (NH4+and carbon dioxide (CO2), thereby increasing pH levels and inducing carbonate precipitation (CO32-), and effectively removing remove contaminants. Nonetheless, the intricate mechanism underlying heavy metal mineralization poses a significant challenge, constraining its application in contaminants engineering, particularly in the context of prolonged heavy metal leaching over time and its efficacy in adverse environmental conditions. This review provides a comprehensive idea of recent development of MICP and its application in environmental engineering, examining metabolic pathways, mineral precipitation mechanisms, and environmental factors as well as providing future perspectives for commercial utilization. The use of ureolytic bacteria in MICP demonstrates cost-efficiency, environmental compatibility, and successful pollutant abatement over tradition bioremediation techniques, and bio-synthesis of nanoparticles. limitations such as large-scale application, elevated Ca2+levels in groundwater, and gradual contaminant release need to be overcome. The possible future research directions for MICP technology, emphasizing its potential in conventional remediation, CO2 sequestration, bio-material synthesis, and its role in reducing environmental impact for long-term economic benefits.

Rapidly derived equimolar Ca: P phasic bioactive glass infused flexible gelatin multi-functional scaffolds - A promising tissue engineering.

The study aims to design and fabricate an ultra-easier multi-functional biomedical polymeric scaffold loaded with unique equimolar Ca:P phasic bioactive glass material (BG). Gelatin (G) - 45S5 bioactive glass (BG) scaffolds were synthesized via a simple laboratory refrigerator with higher biocompatibility and cytocompatibility. The results proved that BG has enhanced bio-mineralization of the scaffolds and results support that the G: BG (1:2) ratio is the more appropriate composition. Brunauer-Emmett-Teller (BET) study confirms the higher surface area for pure Gelatin and G: BG (1:2). Scanning Electron Microscopic images display the precipitation of hydroxycarbonate apatite layer over the scaffolds on immersing it in simulated body fluid. Alkaline phosphate activity proved that G: BG (1:2) scaffold could induce mitogenesis in MG-63 osteoblast cells, thus helping in hard tissue regeneration. Sirius red collagen deposition showed that higher content bioactive glass incorporated Gelatin polymeric scaffold G: BG (1:2) could induce rapid collagen secretion of NIH 3T3 fibroblast cell line that could help in soft tissue regeneration and earlier wound healing. The scaffolds were also tested for cell viability using NIH 3T3 fibroblast cell lines and MG 63 osteoblastic cell lines through methyl thiazolyl tetrazolium (MTT) assay. Thus, the study shows a scaffold of appropriate composition G: BG (1:2) can be a multifunctional material to regenerate hard and soft tissues.

Microbial bio-film calcite mediated removal of heavy metals from industrial wastewater of Kasur, Pakistan.

Heavy metals in the industrial wastewater are an area of great concern as act as source of bioaccumulation in edible plants and posing a major health risk to humans like cancers. This study was planned by exploiting the bio-film producing microbes that have the potential to remediate heavy metals by calcite mediated removal from industrial wastewater. Samples (n = 10) from a marble factory wastewater were collected. Samples were serially diluted and were spread on nutrient agar media supplemented with 2% urea and 0.28 g calcium chloride. All the isolates were observed for colony morphology, gram staining, and spore staining, for biochemical profile and for their efficacy in producing calcium carbonate crystals. All isolates showed cell densities at varying metal (chromium) concentrations ranging from 100 to 500 µg/mL. Determination of biofilm formation is performed by recording Optical density (OD = 600 nm). Normalized biofilm (570/600 nm) was formed. Different concentrations of chromium were used to measure their reduction ability and also by using tannery water. In tannery wastewater, significant reduction was recorded (p = 0.05) by AS4 bacterial isolate as compared to rest of the isolates and treatments. It showed remarkable chromium VI reduction ability.

TRPV4 regulates osteoblast differentiation and mitochondrial function that are relevant for channelopathy.

Different ion channels present in the osteoblast regulate the cellular functions including bio-mineralization, a process that is a highly stochastic event. Cellular events and molecular signaling involved in such process is poorly understood. Here we demonstrate that TRPV4, a mechanosensitive ion channel is endogenously present in an osteoblast cell line (MC3T3-E1) and in primary osteoblasts. Pharmacological activation of TRPV4 enhanced intracellular Ca2+-level, expression of osteoblast-specific genes and caused increased bio-mineralization. TRPV4 activation also affects mitochondrial Ca2+-levels and mitochondrial metabolisms. We further demonstrate that different point mutants of TRPV4 induce different mitochondrial morphology and have different levels of mitochondrial translocation, collectively suggesting that TRPV4-mutation-induced bone disorders and other channelopathies are mostly due to mitochondrial abnormalities. These findings may have broad biomedical implications.

Artemisinin Loaded Cerium-Doped Nanopowders Improved In Vitro the Biomineralization in Human Periodontal Ligament Cells.

BACKGROUND: A promising strategy to enhance bone regeneration is the use of bioactive materials doped with metallic ions with therapeutic effects and their combination with active substances and/or drugs. The aim of the present study was to investigate the osteogenic capacity of human periodontal ligament cells (hPDLCs) in culture with artemisinin (ART)-loaded Ce-doped calcium silicate nanopowders (NPs); Methods: Mesoporous silica, calcium-doped and calcium/cerium-doped silicate NPs were synthesized via a surfactant-assisted cooperative self-assembly process. Human periodontal ligament cells (hPDLCs) were isolated and tested for their osteogenic differentiation in the presence of ART-loaded and unloaded NPs through alkaline phosphatase (ALP) activity and Alizarine red S staining, while their antioxidant capacity was also evaluated; Results: ART promoted further the osteogenic differentiation of hPDLCs in the presence of Ce-doped NPs. Higher amounts of Ce in the ART-loaded NPs inversely affected the mineral deposition process by the hPDLCs. ART and Ce in the NPs have a synergistic role controlling the redox status and reducing ROS production from the hPDLCs; Conclusions: By monitoring the Ce amount and ART concentration, mesoporous NPs with optimum properties can be developed towards bone tissue regeneration demonstrating also potential application in periodontal tissue regeneration strategies.

ROS-activatable biomimetic interface mediates in-situ bioenergetic remodeling of osteogenic cells for osteoporotic bone repair.

Bioenergy (ATP) is essentially required for supporting the osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs). However, factors such as high ROS levels and decreased glucose metabolism severely limit the bioenergy production in osteoporotic MSCs. We have prepared CaCO3-Quercetin- chromium (CaCO3-Qu-Cr) nanoparticles via ion coordination and packaged them into ROS-responsive gelatin/chitosan coating on titanium surface (Ti/Gel/CaCO3-Qu-Cr), aiming to improve the ATP production and cell mineralization by ameliorating ROS levels via Qu-mediated antioxidative effect and the promotional effect of Qu-Cr combination on glucose metabolism. Characterization results confirmed that Ti/Gel/CaCO3-Qu-Cr could be degraded in an ROS-responsive manner to release CaCO3-Qu-Cr nanoparticles continuously and eliminate excessive ROS in both the MSCs and microenvironment. Meanwhile, Ti/Gel/CaCO3-Qu-Cr significantly increased the glucose uptake and metabolism in osteoporotic MSCs and boosted their ATP and citrate production. This study laid the foundation for the development of functional titanium-based implants for the improvement of osteoporotic osseointegration.

Bioremediation of stainless steel pickling sludge through microbially induced carbonate precipitation.

In this study, microbial induce carbonate precipitation (MICP) was introduced to immobilize chromium (Cr) in stainless steel pickling sludge (SSPS). Two methods were utilized to conduct the MICP process - Bacteria lysis liquor (BLL)-based MICP and bacteria-based MICP. BLL was obtained by breaking the cell walls with ultrasonic treatment. The urea hydrolyzation test illustrated that the BLL was better than bacteria solution. Both the treatments of bacteria lysis liquor-based MICP and bacteria-based MICP process can effectively entrap the Cr into mineral lattices, that reduce the potential environmental risk of SSPS. With 30 g/L urea and 7 days' treatment, BLL-based MICP presented better immobilization performance than bacteria-based MICP by lowering the bacteria concentration (OD600) from 0.8 to 0.7. The excellent biosorption of BLL contributed to Cr removal. Nevertheless, the addition of calcium (Ca) significantly enhanced the immobilization performance of bacteria-based MICP process rather than BLL-based MICP process. pH-dependent leaching tests illustrated the leaching of Cr followed an amphoteric pattern, while the leaching of Ni and Ca followed the cation pattern. Geochemical modeling revealed that the leaching of Cr from bio-mineralized products was solubility-controlled by Cr(OH)3 and Cr2O3.

Surface engineering of 3D-printed scaffolds with minerals and a pro-angiogenic factor for vascularized bone regeneration.

Scaffolds functionalized with biomolecules have been developed for bone regeneration but inducing the regeneration of complex structured bone with neovessels remains a challenge. For this study, we developed three-dimensional printed scaffolds with bioactive surfaces coated with minerals and platelet-derived growth factor. The minerals were homogeneously deposited on the surface of the scaffold using 0.01 M NaHCO3 with epigallocatechin gallate in simulated body fluid solution (M2). The M2 scaffold demonstrated enhanced mineral coating amount per scaffold with a greater compressive modulus than the others which used different concentration of NaHCO3. Then, we immobilized PDGF on the mineralized scaffold (M2/P), which enhanced the osteogenic differentiation of human adipose derived stem cells in vitro and promoted the secretion of pro-angiogenic factors. Cells cultured in M2/P showed remarkable ratio of osteocalcin- and osteopontin-positive nuclei, and M2/P-derived medium induced endothelial cells to form tubule structures. Finally, the implanted M2/P scaffolds onto mouse calvarial defects had regenerated bone in 80.8 ± 9.8% of the defect area with the arterioles were formed, after 8 weeks. In summary, our scaffold, which composed of minerals and pro-angiogenic growth factor, could be used therapeutically to improve the regeneration of bone with a highly vascularized structure. STATEMENT OF SIGNIFICANCE: Surface engineered scaffolds have been developed for bone regeneration but inducing the volumetric regeneration of bone with neovessels remains a challenge. In here, we developed 3D printed scaffolds with bioactive surfaces coated with bio-minerals and platelet-derived growth factors. We proved that the 0.01 M NaHCO3 with polyphenol in simulated body fluid solution enhanced the deposition of bio-minerals and even distribution on the surface of scaffold. The in vitro studies demonstrated that the attached cells on the bioactive surface showed the enhanced osteogenic differentiation and secretion of pro-angiogenic factors. Finally, the scaffold with bioactive surface not only improved the regenerated volume of bone tissues but also increased neovessel formation after in vivo implantation onto mouse calvarial defect.

Characterization of bio-adsorptive removal performance of strontium through ureolysis-mediated bio-mineralization.

The adsorptive removal performance of strontium (Sr) through bio-mineralization metabolism under various parameters was evaluated in this study. The primary mechanism of bio-mineralization used in this study was the urea hydrolysis process through bacterial enzymatic catalysis. Bacillus sp, which was isolated from river sediment, was used as a ureolytic bacteria. Various environmental conditions were set as different initial concentrations of Sr (10, 50, 100, 200, and 500 mg/L), and various ratios of Mg/Ca (4, 2, 1, 0.5, and 0.25). The concentrations of Sr2+, Ca2+, and Mg2+ in the solution of the batch experiment were measured to identify the bio-mineralization performance and the removal rate of Sr. In addition, the main Sr removal mechanism of ureolytic bacteria was identified. As a result, for Sr removal of bacteria, the bio-mineralization mechanism was more predominant than the adsorption of Sr. The rapid growth and high nucleation site production were observed when the initial concentration of Sr2+ increased and the Mg/Ca ratio was lowered, resulting in high biomineralization performance and Sr removal rate. The main phases of carbonate minerals formed in the presence of Sr, Ca, and Mg were SrCO3 and SrCa(CO3)2. Mg2+ could retard the bacterial growth and participate in the formation of carbonate minerals, when a large amount of Mg2+ was present. Furthermore, the desorption rate of Sr2+ from bacterial pastes containing the carbonate minerals increased as the concentration of HCl increased, although the carbonate minerals were in a stable state.

Role of Na-Montmorillonite on Microbially Induced Calcium Carbonate Precipitation.

The use of additives has generated significant attention due to their extensive application in the microbially induced calcium carbonate precipitation (MICP) process. This study aims to discuss the effects of Na-montmorillonite (Na-MMT) on CaCO3 crystallization and sandy soil consolidation through the MICP process. Compared with the traditional MICP method, a larger amount of CaCO3 precipitate was obtained. Moreover, the reaction of Ca2+ ions was accelerated, and bacteria were absorbed by a small amount of Na-MMT. Meanwhile, an increase in the total cementing solution (TCS) was not conducive to the previous reaction. This problem was solved by conducting the reaction with Na-MMT. The polymorphs and morphologies of the CaCO3 precipitates were tested by using X-ray diffraction and scanning electron microscopy. Further, when Na-MMT was used, the morphology of CaCO3 changed from an individual precipitate to agglomerations of the precipitate. Compared to the experiments without Na-MMT in the MICP process, the addition of Na-MMT significantly reduced the hydraulic conductivity (HC) of sandy soil consolidated.

Bio-mineralization induced by Bacillus mucilaginosus in crack mouth and pore solution of cement-based materials.

Cement-based Materials have been widely used in the world, and bacteria have a capacity to induce mineral precipitation and can be applied to heal crack and resist efflorescence of cement-based materials. In this paper, Bacillus mucilaginosus was used for inducing mineralization by fixing CO2 from the air. The calcium-containing substances in cement-based materials that participating in the bio-mineralization were analyzed. Among them, the reaction between C3S and CO2 in the air can be ignored, and the mineralized products of Ca(OH)2 were mainly calcite, while the mineralized products of C-S-H were mainly aragonite. The results of XRD and SEM indicated that products obtained by reaction between C3S paste and CO2 were calcite, so the calcium-containing substances participating in bio-mineralization was mainly Ca(OH)2. The effect of bacteria cells on the formation of carbonate ions was analyzed. The pH value and the concentration of ions indicated that the absorption of CO2 was accelerated when the bacteria were involved, and more carbonate ions were supplied to bio-mineralization. The experiments of Zeta potential and conductivity showed that bacteria cells had an adsorption effect on Ca2+ because of its negatively charged surface. The analysis of nucleation kinetics indicated that calcium carbonate nucleated on the surface of bacteria cells, and its followed heterogeneous model, the rate of nucleation was 3.36 × 10-4 s-1-3.38 × 10-3 s-1. Analysis of every mineralization step showed that the enzyme-catalyzed reaction rate was the minimum when microorganisms existed, and it was the control step.

Cathodic selenium recovery in bioelectrochemical system: Regulatory influence on anodic electrogenic activity.

Metal(loid)s are used in various industrial activities and widely spread across the environmental settings in various forms and concentrations. Extended releases of metal(loid)s above the regulatory levels cause environmental and health hazards disturbing the ecological balance. Innovative processes for treating the metal(loid)-contaminated sites and recovery of metal(loid)s from disposed waste streams employing biotechnological routes provide a sustainable way forward. Conventional metal recovery technologies demand high energy and/or resource inputs, which are either uneconomic or unsustainable. Microbial electrochemical systems are promising for removal and recovery of metal(loid)s from metal(loid)-laden wastewaters. In this communication, a bioelectrochemical system (BES) was designed and operated with selenium (Se) oxyanion at varied concentrations as terminal electron acceptor (TEA) for reduction of selenite (Se4+) to elemental selenium (Se0) in the abiotic cathode chamber. The influence of varied concentrations of Se4+ towards Se0 recovery at the cathode was also evaluated for its regulatory role on the electrometabolism of anode-respiring bacteria. This study observed 26.4% Se0 recovery (cathode; selenite removal efficiency: 73.6%) along with organic substrate degradation of 74% (anode). With increase in the initial selenite concentration, there was a proportional increase in the dehydrogenase activity. Bioelectrochemical characterization depicted increased anodic electrogenic performance with the influence of varied Se4+ concentrations as TEA and resulted in a maximum power density of 0.034 W/m2. The selenite reduction (cathode) was evaluated through spectroscopic, compositional and structural analysis. X-ray diffraction and Raman spectroscopy showed the amorphous nature, while Energy Dispersive X-ray spectroscopy confirmed precipitates of the deposited Se0 recovered from the cathode chamber. Scanning electron microscopic images clearly depicted the Se0 depositions (spherical shaped; sized approximately 200 nm in diameter) on the electrode and cathode chamber. This study showed the potential of BES in converting soluble Se4+ to insoluble Se0 at the abiotic cathode for metal recovery.

Visualizing mineralization processes and fossil anatomy using synchronous synchrotron X-ray fluorescence and X-ray diffraction mapping.

Fossils, including those that occasionally preserve decay-prone soft tissues, are mostly made of minerals. Accessing their chemical composition provides unique insight into their past biology and/or the mechanisms by which they preserve, leading to a series of developments in chemical and elemental imaging. However, the mineral composition of fossils, particularly where soft tissues are preserved, is often only inferred indirectly from elemental data, while X-ray diffraction that specifically provides phase identification received little attention. Here, we show the use of synchrotron radiation to generate not only X-ray fluorescence elemental maps of a fossil, but also mineralogical maps in transmission geometry using a two-dimensional area detector placed behind the fossil. This innovative approach was applied to millimetre-thick cross-sections prepared through three-dimensionally preserved fossils, as well as to compressed fossils. It identifies and maps mineral phases and their distribution at the microscale over centimetre-sized areas, benefitting from the elemental information collected synchronously, and further informs on texture (preferential orientation), crystallite size and local strain. Probing such crystallographic information is instrumental in defining mineralization sequences, reconstructing the fossilization environment and constraining preservation biases. Similarly, this approach could potentially provide new knowledge on other (bio)mineralization processes in environmental sciences. We also illustrate that mineralogical contrasts between fossil tissues and/or the encasing sedimentary matrix can be used to visualize hidden anatomies in fossils.

Facilitated bio-mineralization of N,N-dimethylformamide in anoxic denitrification system: Long-term performance and biological mechanism.

Due to highly recalcitrant and toxicological nature of N,N-dimethylformamide (DMF), efficient removal of DMF is challenging for biological wastewater treatment. In this study, an anoxic denitrification system was developed and continuously operated for 220 days in order to verify the enhanced DMF biodegradation mechanism. As high as 41.05 mM DMF could be thoroughly removed in the anoxic denitrification reactor at hydraulic residence time (HRT) of 24 h, while the total organic carbon (TOC) and nitrate removal efficiencies were as high as 95.7 ± 2.5% and 98.4 ± 1.1%, respectively. Microbial community analyses indicated that the species related to DMF hydrolysis (Paracoccus, Brevundimonas and Chryseobacterium) and denitrification (Paracoccus, Arenimonas, Hyphomicrobium, Aquamicrobium and Bosea) were effectively enriched in the anoxic denitrification system. Transcriptional analysis coupled with enzymatic activity assay indicated that both hydrolysis and mineralization of DMF were largely enhanced in the anoxic denitrification system. Moreover, the occurrence of microbial denitrification distinctly facilitated carbon source utilization to produce electron and energy, which was rather beneficial for better reactor performance. This study demonstrated that the anoxic denitrification system would be a potential alternative for efficient treatment of wastewater polluted by recalcitrant pollutants such as DMF.

Role of matrix vesicles and crystal ghosts in bio-mineralization.

Matrix vesicles (MVs) are extracellular membrane-bound vesicles of about ~ 50-200 nm in diameter that play a role in the bio-mineralization process of hard tissue formation. The present review is based on the empirical phenomenon of primary mineralization process via matrix vesicle-mediated mechanism with special reference to crystal ghosts as well as the mechanism on the organic-inorganic relationship between matrix vesicles and crystal ghosts, and the transformation that these structures undergo during bio-mineralization.

Arsenic mobilization affected by extracellular polymeric substances (EPS) of the dissimilatory iron reducing bacteria isolated from high arsenic groundwater.

The factors that control arsenic (As) mobilization by dissimilatory iron reduction (DIR) are complicated. The association between As mobilization and extracellular polymeric substance (EPS) of dissimilatory iron reducing bacteria (DIRB) remained unclear. In this study, three DIRB were isolated from high arsenic groundwater to understand the effects of EPS on As mobilization. In the laboratory settings, strain Klebsiella oxytoca IR-ZA released As into aqueous phase from As-bearing ferrihydrite, while strain Shewanella putrefaciens IAR-S1 and S. xiamenensis IR-S2 re-sequestrated As by forming secondary minerals during ferrihydrite reduction. Characterization of EPS contents with Fourier Transform Infrared Spectroscopy and high-performance liquid chromatography suggested that mannan and succinic acid were the main different EPS contents of the DIRB. The biomineralization processes were tightly regulated by EPS compositions. Mannan secreted by IAR-S1 and IR-S2 promoted while succinic acid secreted by IR-ZA suppressed the biomineralization and As immobilization. Energy-dispersive X-ray Spectroscopy mapping indicated that As in the secondary minerals was wrapped with EPS. X-ray diffraction and room temperature Mössbauer spectroscopy showed these secondary minerals were vivianite and magnetite, respectively. The amount of As mobilized into aqueous phase was strongly affected by available anions (H2PO4- and HCO3-). Our results indicated that the EPS of DIRB significantly influenced As mobilization.

Determination of iron(II) and iron(III) via static quenching of the fluorescence of tryptophan-protected copper nanoclusters.

"Tryptophan-coated blue fluorescent copper nanocluster (CuNC@Trp) was prepared by a strategy where Trp acts as both the reducing and capping agent. The fluorescence of the CuNC, with excitation/emission peaks at 340/405 nm, is selectively quenched by iron(II) and iron(III) ions. Studying the mechanism of this interaction revealed that Fe2+ and Fe3+ ions can make a ground state complex with the protecting ligand which can result in quenching of the cluster emission. Structural and optical properties of the modified CuNC were investigated by ESI-MS, DLS, TEM, UV-vis and photoluminescence. The effects of pH value and temperature, time of interaction, and cluster volume were optimized. Under optimized conditions, the probe response is linear in concentration range of 10-1000 µM for Fe(II) and Fe(III) with the relative standard deviations of 0.13 and 0.14% (n = 5) respectively. The respective limits of detection are 3.0 and 2.2 µM. The method was successfully used for determination of trace amount of both ions in spiked water, blood and iron supplement tablets. The results were in good agreement with those obtained by the ICP-AES method." Graphical abstractThe scheme represents the synthesis of CuNC@Trp at basic conditions and at elevated temperature. The emission of the cluster decreases due to static quenching of fluorescence by iron ions.

Removal of lead from acidic wastewater by bio-mineralized bacteria with pH self-regulation.

Microorganisms with the function of bio-mineralization were isolated from a soil. They were identified as urease-producing bacteria and phosphate-solubilizing bacteria. These two kinds of bacteria belong to the eosinophilic bacteria, which regulated the pH of solution and removed Pb2+ the best at the initial solution pH of 4. The Pb2+ removal mechanism was further explored using various techniques including zeta potential measurement, three-dimensional fluorescence, FTIR, XRD, and TEM-EDS. The results showed that extracellular adsorption, intracellular accumulation and bio-mineralization occurred at the same time and converted to each other. The extracellular adsorption of urease-producing bacteria was through electrostatic adsorption and gradually decomposed urea to produce PbCO3 minerals. The extracellular adsorption of phosphate-solubilizing bacteria was controlled by extracellular polymeric substances (EPS) and rapidly formation of Pb3(PO4)2 stable minerals. In addition, the stabilities of Lead minerals of the two strains were compared. The results showed that the precipitates of phosphate-solubilizing bacteria were more stable. While phosphate-solubilizing bacteria have some advantages, both strains can play important roles in bio-mineralization of HMs in acidic wastewater.

Bio-mineralized self-healing recycled aggregate concrete for sustainable infrastructure.

Various carriers have been investigated by researchers to introduce bacteria inside the concrete however, factors such as local availability, cost and long-term protection of bacterial cells have barred the application of this contemporary technology in the construction industry. In the present study, bacteria were immobilized via recycled coarse aggregate (RCA) and virgin fine aggregate (FA) besides direct induction to preserve natural resources and emulate sustainability. The application of RCA in substitution of virgin coarse aggregate is dropping anthropogenic emissions, minimizing energy consumption and managing construction waste effectively. Vegetative cells of Bacillus subtilis bacterium were incorporated in RCA through vacuum impregnation to boost crack healing efficiency. Crack healing efficiency was studied by quantifying the crack healing widths and percentage of strength regained after pre-cracking at 3,7 and 28 days. Similarly, mechanical properties were gauged via compressive and split tensile strengths at specified intervals while healing precipitate was characterized using analytical means. Results of experimental work revealed that specimens having RCA and 50% virgin FA as bacteria immobilizers exhibited the most efficient crack healing remedy by healing crack widths up to 1.1 mm and recovering 85% of compressive strength. Specimens containing RCA exclusively displayed a maximum of 0.7 mm crack healing widths and 76% strength recovery while direct incorporation of bacteria lagged behind with 0.6 mm crack healing width having 69% strength recovery. Likewise, synergetic formulation and direct induction depicted increase in compressive strength of 4% and 6% respectively while exclusive RCA formulation decreased the compressive strength up to 3% Moreover, field-emission scanning electron microscopy (FE-SEM), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and X-ray fluorescent (XRF) characterized the crack healing precipitate as bio-mineralized calcite crystals.