Magnesium polypeptide combined with microbially induced calcite precipitation for remediation of lead contamination in phosphate mining wasteland soil.

Soil Pb contamination is inevitable, as a result of phosphate mining. It is essential to explore more effective Pb remediation approaches in phosphate mining wasteland soil to ensure their viability for a gradual return of soil quality for cultivation. In this study, a Pb-resistant urease-producing bacterium, Serratia marcescens W1Z1, was screened for remediation using microbially induced carbonate precipitation (MICP). Magnesium polypeptide (MP) was prepared from soybean meal residue, and the combined remediation of Pb contamination with MP and MICP in phosphate mining wasteland soil was studied. Remediation of Pb using a combination of MP with MICP strain W1Z1 (WM treatment) was the most effective, with the least exchangeable Pb at 30.37% and the most carbonate-bound Pb at 40.82%, compared to the other treatments, with a pH increase of 8.38. According to the community analysis, MP moderated the damage to microbial abundance and diversity caused by MICP. Total nitrogen (TN) was positively correlated with Firmicutes, pH, and carbonate-bound Pb. Serratia inoculated with strain W1Z1 were positively correlated with bacteria belonging to the Firmicutes phylum and negatively correlated with bacteria belonging to Proteobacteria. The available phosphate (AP) in the phosphate mining wasteland soil could encapsulate the precipitated Pb by ion exchange with carbonate, making it more stable. Combined MP-MICP remediation of Pb contamination in phosphate mining wasteland soil was effective and improved the soil microenvironment.

Sodium citrate increases the aggregation capacity of calcium ions during microbial mineralization to accelerate the formation of calcium carbonate.

The microbially induced carbonate precipitation (MICP) technique is widely used in soil heavy metal pollution control. Microbial mineralization involves extended mineralization times and slow crystallization rates. Thus, it is important to discover a method to accelerate mineralization. In this study, we selected six nucleating agents to screen and investigated the mineralization mechanism using polarized light microscopy, scanning electron microscopy, X-ray diffraction and Fourier-transform infrared spectroscopy. The results showed that sodium citrate removed 90.1% Pb better than traditional MICP and generated the highest amount of precipitation. Interestingly, due to the addition of sodium citrate (NaCit), the rate of crystallization increased and vaterite was stabilized. Moreover, we constructed a possible model to explain that NaCit increases the aggregation capacity of calcium ions during microbial mineralization to accelerate the formation of calcium carbonate (CaCO3). Thus, sodium citrate can increase the rate of MICP bioremediation, which is important for improving MICP efficiency.

A newly-constructed bifunctional bacterial consortium for removing butyl xanthate and cadmium simultaneously from mineral processing wastewater: Experimental evaluation, degradation and biomineralization.

Due to the technological limitations associated with beneficiation technology, large amounts of flotation reagents and heavy metals remain in mineral processing wastewater. Unfortunately, however, no treatment methods are available to mitigate the resulting pollution by them. In this study, a bacterial consortium SDMC (simultaneously degrade butyl xanthate and biomineralize cadmium) was constructed in an effort to simultaneously degrade butyl xanthate (BX) and biomineralize cadmium (Cd) by screening and domesticating two different bacterial species including Hypomicrobium and Sporosarcina. SDMC is efficient in removing the combined pollution due to BX and Cd with a 100% degradation rate for BX and 99% biomineralization rate for Cd within 4 h. Besides, SDMC can tolerate high concentrations of Fe(III) (0-40 mg/L). It has an excellent ability to utilize Fe(III) for enhanced removal of the combined pollutants. SDMC can effectively remove pollutants with a pH range of 6-9. Further, we discussed pathways for potential degradation and biomineralization: Cd(BX)2-Cd2+, BX-; BX--CS2, butyl perxanthate (BPX); Cd2+-(Ca0.67,Cd0.33)CO3. The removal of the combined pollutants primarily entails decomposition, degradation, and biomineralization, C-O bond cleavage, and microbially induced carbonate precipitation (MICP). SDMC is a simple, efficient, and eco-friendly bifunctional bacterial consortium for effective treatment of BX-Cd combined pollution in mineral processing wastewater.

A Low-Tech Bioreactor System for the Enrichment and Production of Ureolytic Microbes.

Ureolysis-driven microbially induced carbonate precipitation (MICP) has recently received attention for its potential biotechnological applications. However, information on the enrichment and production of ureolytic microbes by using bioreactor systems is limited. Here, we report a low-tech down-flow hanging sponge (DHS) bioreactor system for the enrichment and production of ureolytic microbes. Using this bioreactor system and a yeast extract-based medium containing 0.17 M urea, ureolytic microbes with high potential urease activity (> 10 µmol urea hydrolyzed per min per ml of enrichment culture) were repeatedly enriched under non-sterile conditions. In addition, the ureolytic enrichment obtained in this study showed in vitro calcium carbonate precipitation. Fluorescence in situ hybridization analysis showed the existence of bacteria of the phylum Firmicutes in the bioreactor system. Our data demonstrate that this DHS bioreactor system is a useful system for the enrichment and production of ureolytic microbes for MICP applications.

Application of microbially induced calcium carbonate precipitation (MICP) process in concrete self-healing and environmental restoration to facilitate carbon neutrality: a critical review.

Soil contamination, land desertification and concrete cracking can have significant adverse impacts on sustainable human economic and societal development. Cost-effective and environmentally friendly approaches are recommended to resolve these issues. Microbially induced carbonate precipitation (MICP) is an innovative, attractive and cost-effective in situ biotechnology with high potential for remediation of polluted or desertified soils/lands and cracked concrete and has attracted widespread attention in recent years. Accordingly, the principles of MICP technology and its applications in the remediation of heavy metal-contaminated and desertified soils and self-healing of concrete were reviewed in this study. The production of carbonate mineral precipitates during the MICP process can effectively reduce the mobility of heavy metals in soils, improve the cohesion of dispersed sands and realize self-healing of cracks in concrete. Moreover, CO2 can be fixed during MICP, which can facilitate carbon neutrality and contribute to global warming mitigation. Overall, MICP technology exhibits great promise in environmental restoration and construction engineering applications, despite some challenges remaining in its large-scale implementation, such as the substantial impacts of fluctuating environmental factors on microbial activity and MICP efficacy. Several methods, such as the use of natural materials or wastes as nutrient and calcium sources and isolation of bacterial strains with strong resistance to harsh environmental conditions, are employed to improve the remediation performance of MICP. However, more studies on the efficiency enhancement, mechanism exploration and field-scale applications of MICP are needed.

Effect of sand minerals on microbially induced carbonate precipitation by denitrification.

Soil improvement techniques utilizing the metabolic functions of microorganisms, including microbially induced carbonate precipitation (MICP), have been extensively researched over the past few decades as part of bio-inspired geotechnical engineering research. Given that metabolic reactions in microorganisms produce carbonate minerals, an enhanced understanding of microbial interaction with soils could improve the effectiveness of MICP as a soil improvement technique. Therefore, this study investigated the effects of sands on MICP by denitrification to employ MICP for geotechnical soil improvement. Under the coexistence of natural sand and artificial silica sand, nitrate-reducing bacteria were cultured in a mixed liquid medium with nitrate, acetate, and calcium ions at 37 °C. Nitrate reduction occurred only in the presence of natural sand. However, the lack of chemical weathering of the composed minerals likely prevented the progress of bacterial growth and nitrate reduction in artificial silica sands. For natural sand, artificial chemical weathering by acid wash and ferrihydrite coating of the sand improved bacterial growth and accelerated nitrate reduction. The calcium carbonate formation induced by denitrification was also influenced by the state of the minerals in the soil and the nitrate reduction rate. The observed MICP enhancement is due to the involvement of coexisting secondary minerals like ferrihydrite with large specific surface areas and surface charges, which may improve the reaction efficiency by serving as adsorbents for bacteria and electron donors and acceptors in the solid phases, thereby promoting the precipitation and crystallization of calcium carbonate on the surfaces. This crystal formation in the minerals provides valuable insights for improving sand solidification via MICP. Considering the interactions between the target soil and microorganisms is essential to improving MICP processes for ground improvement.

Immobilization of Cd2+ and Pb2+ by biomineralization of the carbonate mineralized bacterial consortium JZ1.

Microbially induced carbonate precipitation (MICP) has been proven to effectively immobilize Cd2+ and Pb2+ using a single bacterium. However, there is an urgent need for studies of Cd2+ and Pb2+ immobilized by a bacterial consortium. In this study, a stable consortium designated JZ1 was isolated from soil that was contaminated with cadmium and lead, and the dominant genus Sporosarcina (99.1%) was found to have carbonate mineralization function. The results showed that 91.52% and 99.38% of Cd2+ and Pb2+ were mineralized by the consortium JZ1 with 5 g/L CaCl2 at an initial concentration of 5 mg/L Cd2+ and 150 mg/L Pb2+, respectively. The bioprecipitates were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Moreover, the kinetic studies indicated that the urea hydrolysis reaction fit well with the Michaelis-Menten equation, and the kinetic parameters Km and Vmax were estimated to be 38.69 mM and 58.98 mM/h, respectively. When the concentration of urea increased from 0.1 to 0.3 M, the mineralization rate increased by 1.58-fold. This study can provide a novel microbial resource for the biomineralization of Cd and Pb in soil and water environments.

Naturally Derived Cements Learned from the Wisdom of Ancestors: A Literature Review Based on the Experiences of Ancient China, India and Rome.

For over a thousand years, many ancient cements have remained durable despite long-term exposure to atmospheric or humid agents. This review paper summarizes technologies of worldwide ancient architectures which have shown remarkable durability that has preserved them over thousands of years of constant erosion. We aim to identify the influence of organic and inorganic additions in altering cement properties and take these lost and forgotten technologies to the production frontline. The types of additions were usually decided based on the local environment and purpose of the structure. The ancient Romans built magnificent structures by making hydraulic cement using volcanic ash. The ancient Chinese introduced sticky rice and other local materials to improve the properties of pure lime cement. A variety of organic and inorganic additions used in traditional lime cement not only changes its properties but also improves its durability for centuries. The benefits they bring to cement may also be useful in enzyme-induced carbonate precipitation (EICP) and microbially induced carbonate precipitation (MICP) fields. For instance, sticky rice has been confirmed to play a crucial role in regulating calcite crystal growth and providing interior hydrophobic conditions, which contribute to improving the strength and durability of EICP- and MICP-treated samples in a sustainable way.

Passivation of heavy metals in copper-nickel tailings by in-situ bio-mineralization: A pilot trial and mechanistic analysis.

Metal tailings contain a variety of toxic heavy metals and have potential environmental risks owing to long-term open piling. In the present study, a strain of ureolytic bacteria with bio-mineralization ability, Lysinibacillus fusiformis strain Lf, was isolated from copper-nickel mine tailings in Xinjiang and applied to a pilot trial of tailings solidification under field conditions. The results of the pilot trial (0.5 m3 in scale) showed that strain Lf effectively solidified the tailings. The compressive strength of the solidified tailings increased by 121 ± 9 % and the permeability coefficient decreased by 68 ± 3 %. Compared to the control, the leaching reduction of the solidified tailings of Cu and Ni was >98 %, and that of As was 92.5 ± 1.7 %. Two mechanisms of tailings solidification and heavy metal passivation were proposed based on the findings of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy (EDS) mapping. Biogenic calcite filled the interstices of the tailings particles and cemented the adjacent particles. This improved the mechanical properties and reduced permeability. Moreover, heavy metal colloids were incorporated into large-sized calcite crystals, and heavy metal ions were sequestered within the calcite lattice. This method of using indigenous ureolytic bacteria to solidify tailings was successful in this work and may be replicated to remediate other tailings.

Synergistic solidification of lead-contaminated soil by magnesium oxide and microorganisms.

Although microbially induced carbonate precipitation (MICP) technology effectively promotes the remediation of heavy metal contaminated soils in low concentrations, the high concentration of heavy metals has a toxic effect on microorganisms, which leads to the decline of carbonate yield and makes the soil strength and environmental safety after remediation no up to the standard. This study describes the synergistic curing effect of MgO and microorganisms on soil contaminated with high concentrations of heavy metals. The experimental results with MgO showed 2-6 times increase in unconfined compressive strength (UCS) compared to bio-cemented samples without MgO. Toxicity characteristic leaching procedure experiments indicated that Pb-contaminated soil at 10,000 mg/kg with quantitative MgO for synergistic solidification could meet the international solid waste disposal standards, which leachable Pb2+ are less than 5 mg/L. In addition, the microscopic results showed that the introduction of MgO promoted the formation of magnesium calcite and dolomite, improved the solidification efficiency of heavy metal contaminants, and demonstrated the presence of Pb2+ in carbonate minerals. This study suggests that MgO and microorganisms have broad application prospects for synergistic solidification of Pb2+ soil.

Manganese Pollution and Its Remediation: A Review of Biological Removal and Promising Combination Strategies.

Manganese (Mn), as a cofactor of multiple enzymes, exhibits great significance to the human body, plants and animals. It is also a critical raw material and alloying element. However, extensive employment for industrial purposes leads to its excessive emission into the environment and turns into a significant threat to the ecosystem and public health. This review firstly introduces the essentiality, toxicity and regulation of Mn. Several traditional physicochemical methods and their problems are briefly discussed as well. Biological remediation, especially microorganism-mediated strategies, is a potential alternative for remediating Mn-polluted environments in a cost-efficient and eco-friendly manner. Among them, microbially induced carbonate precipitation (MICP), biosorption, bioaccumulation, bio-oxidation are discussed in detail, including their mechanisms, pivotal influencing factors along with strengths and limitations. In order to promote bioremediation efficiency, the combination of different techniques is preferable, and their research progress is also summarized. Finally, we propose the future directions of Mn bioremediation by microbes. Conclusively, this review provides a scientific basis for the microbial remediation performance for Mn pollution and guides the development of a comprehensive competent strategy towards practical Mn remediation.

Inhibition of cadmium releasing from sulfide tailings into the environment by carbonate-mineralized bacteria.

Microbially induced carbonate precipitation (MICP) could be a potential green solution to resolve the issue of heavy metal releasing from the sulfide tailings. However, detailed mechanism of heavy metal-biomineralization in sulfide tailings and impact of procedure parameters on in-situ applications remain unexplored. We systematically investigated the biomineralization process in the column tests for a better understanding of the mechanism and effects on the inhibition of cadmium (Cd) releasing from sulfide tailings. Results revealed that uniform and efficient mineralization in the tailings column occurred under bacterial concentration of 1 × 108 cfu mL-1, bacterial retention time of 3 h, concentration of mineralization solution of 0.25 mol L-1, and flow rate of 1.5 mL min-1. The leachable Cd concentration decreased 80.7% after 7 mineralization cycles. From a suit of characterizations, bacteria can adhere on the tailings and acted as the nucleation sites to induce the mineralization of Ca and Cd (to (Ca0.67, Cd0.33)CO3 and calcite phase); eventually, tailings particles were coated with the growth of mineralized carbonates, resulting in a reduction of exposure for tailings (especially sulfur). And thus, Cd release was inhibited. Results from this study will provide a fundamental basis for future in-situ applications of MICP to mitigate heavy metal pollutions.

Experimental Study on Sand Stabilization Using Bio-Cementation with Wastepaper Fiber Integration.

Recently, green materials and technologies have received considerable attention in geotechnical engineering. One of such techniques is microbially-induced carbonate precipitation (MICP). In the MICP process, CaCO3 is achieved bio-chemically within the soil, thus enhancing the strength and stiffness. The purpose of this study is to introduce the wastepaper fiber (WPF) onto the MICP (i) to study the mechanical properties of MICP-treated sand with varying WPF content (0-8%) and (ii) to assess the freeze-thaw (FT) durability of the treated samples. Findings revealed that the ductility of the treated samples increases with the increase in WPF addition, while the highest UCS is found with a small fiber addition. The results of CaCO3 content suggest that the WPF addition enhances the immobilization of the bacteria cells, thus yielding the precipitation content. However, shear wave velocity analysis indicates that a higher addition of WPF results in rapid deterioration of the samples when subjected to freeze-thaw cycles. Microscale analysis illuminates that fiber clusters replace the solid bonding at particle contacts, leading to reduced resistance to freeze-thaw damage. Overall, the study demonstrates that as a waste material, WPF could be sustainably reused in the bio-cementation.

Impact of C/N ratio on the fate of simultaneous Ca2+ precipitation, F- removal, and denitrification in quartz sand biofilm reactor.

The coexistence of F-, Ca2+, nitrates, and other pollutants in water body has aroused widespread concern. In this research, a novel quartz sand biofilm reactor was established, aiming to study the key factors of different carbon to nitrogen (C/N) ratios (5:1, 4:1, and 3:1), initial Ca2+ concentration (180 mg L-1, 144 mg L-1, and 108 mg L-1), and hydraulic retention time (HRT) (4 h, 6 h, and 8 h) on simultaneous Ca2+ precipitation, F- removal, and denitrification. Results showed that the removal efficiencies of Ca2+, F-, and nitrate were 55.04%, 82.64%, and 97.69% under the low C/N ratio of 3:1, initial Ca2+ concentration of 180 mg L-1, and HRT of 8 h. 3-D Excitation-Emission Fluorescence Spectroscopy (3-D EEM) demonstrates that extracellular polymeric substances (EPS) was generated during the growth metabolism. Scanning Electron Microscopy (SEM) and X-ray diffractometer images showed that Ca2+, F- removed in the form of CaCO3, Ca5(PO4)3F and CaF2 under Acinetobacter sp. H12 induction. Moreover, high-throughput sequencing results display that the biomineralized bacteria Acinetobacter sp. H12 exerted great influence in the bioreactor. This research will underpin the practical use of multiple pollutants such as F- and Ca2+ wastewater under the different C/N ratios.

A novel constructed carbonate-mineralized functional bacterial consortium for high-efficiency cadmium biomineralization.

A stable, urease-producing consortium (UPC) was constructed for high-efficiency cadmium (Cd) ion mineralization via a short-term and efficient acclimation process (five acclimation transfers). 16S rRNA gene high-throughput sequencing and quantitative polymerase chain reaction (qPCR) analyses of the urease subunit C (ureC) gene suggested that the three functional genera, all belonging to the phylum Firmicutes, rapidly increased during the process and finally composed the UPC (70.22-75.41 % of Sporosarcina, 13.83-20.66 % of norank_f_Bacillaceae, and 5.91-13.69 % of unclassified_f_Bacillaceae). The UPC exhibited good adaptability to a wide range of environmental conditions (a pH range of 4.0-11.0, temperature range of 10-45 °C, and Cd concentration range of 0-200 mg L-1). After 8 h of incubation, 92.87 % of Cd at an initial concentration of 100 mg L-1 was mineralized by UPC, exhibiting a great improvement as compared to the first acclimated consortium (C-1). Furthermore, although the acclimated consortium had been successively transferred 21 times, the Cd biomineralization efficiency remained stable, and this was consistent with the observed stable microbial community structure. X-ray diffraction (XRD) spectra revealed that Cd was mineralized in a (Ca0.67, Cd0.33)CO3 phase. This research obtained a promising microbial resource for the biomineralization of Cd or other hazardous heavy metal contaminants.

Simultaneous removal of As(III) and Cu(II) from real bottom ash leachates by manganese-oxidizing aerobic granular sludge: Performance and mechanisms.

Manganese-oxidizing aerobic granular sludge (Mn-AGS) is a novel extension of AGS technology to treat arsenic (As) in organic wastewater. In this study, Mn-AGS was first applied to treat real wastewater (bottom ash leachates) containing high levels of As(III) and Cu(II) in a sequencing batch reactor (SBR) for 91 days. Influent and effluent As(III), As(V), Cu(II), as well as pH and chemical oxygen demand (COD) were monitored daily, and sludge was collected regularly for morphological observation, chemical characterization, and microbial analysis. The results indicated that As(III) and Cu(II) could be efficiently removed from wastewater (∼83% and ∼100%, respectively), but the performance was sensitive to pH variation, especially for As(III). The removed As and Cu were mostly bound to carbonates (60.2 ±â€¯2.0% and 70.0 ±â€¯0.6%, respectively) and Fe/Mn oxides (28.2 ±â€¯1.6% and 14.6 ±â€¯0.5%, respectively) in the final sludge. Influent As(III) was partially oxidized into As(V), and high fractions of As(V) were obtained in the Fe/Mn oxide-bound phase. Unexpectedly, microbial analysis revealed that community richness was only slightly changed when the influent was acidized (pH 4.0) but greatly reduced after the influent pH back to 6.0. It could be explained by that acid-fast bacteria rapidly grew after pH recovery and eliminated non-acid-fast bacteria. This work further supported the practical application of Mn-AGS to treat As(III)-containing organic wastewaters.

Suppression of coal dust by microbially induced carbonate precipitation usingStaphylococcus succinus.

Coal dust from open-cast mines is a significant air pollutant; thus, dust particles and toxins contained in the dust are a severe threat to human health and ecosystems. Microbially induced carbonate precipitation (MICP) is a low-cost and environmentally friendly way to suppress coal dust. With high urease activity and tolerance to coal dust, a bacterial strain, Staphylococcus succinus J3, was isolated from soil in a mine area. Thus, in dust suppression experiments, we used coal dust dominated by fine granule particles (100-250 µm) from an open-cast mine. Consequently, four factors were identified: initial bacterial biomass, calcium concentration, urea concentration, and spraying frequency; we investigated their effects on MICP as a dust suppression technique using one-factor-at-a-time experiments. Maximum threshold broken wind speed (45.5 m s-1) and pressure (912 kPa) were obtained under the following condition: OD600 = 0.7, 40 mmol calcium, 6% (w/w) urea in the bonding solution which was sprayed five times in 35 days. Pearson correlation analysis described that urea concentration and spraying frequency both significantly positive correlations with the threshold broken wind speed and pressure via Pearson analysis. When the coal dust suppression process was complete, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy showed that a solidified layer of calcareous precipitate had formed on the surface of the dust. These results indicate that Staphylococcus succinus J3 has considerable potential for use in MICP as a coal dust suppression technique.