Microscopic deposition-property relationships in microbial-induced consolidation of coal dusts.

In recent years, the preparation of new microbial dust suppressants based on microbial induced carbonate precipitation (MICP) technology through enriched urease-producing microbial communities has become a new topic in the field of coal dust control. The deposition of CaCO3 was the key to suppress coal dust. However, deposition characteristics in the field is not sufficient and the relationship between deposition characteristics and erosion resistance is not clear, which hinders the development of engineering application of new microbial dust suppressant. Therefore, based on X-CT technology, this paper observed and quantified micro-deposition of bio-consolidated coal dust with different calcium sources. Furthermore, a conceptual framework for deposition was proposed and its correlation with erosion resistance was revealed. The results showed that CaCO3 induced by calcium chloride and calcium lactate was aggregate deposited. Aggregate deposited CaCO3 was small in volume, showed the distribution of aggregation in the central area and loose outside, and mosaiced pores. CaCO3 induced by calcium nitrate was surface deposition due to attached biomass. Surface deposition was mostly large volume CaCO3 expanding from the inside out, which could cover coal dust to a high degree and completely cemented pores. In addition, the threshold detachment velocity of coal dust cemented by surface deposition was increased by 17.6-19.1% compared to aggregate deposition. This depended on the abundance and strength of CaCO3 bonding between coal dust particles under different deposition. The two-factor model based on porosity and CaCO3 coverage can well express relationship between erosion resistance and depositional characteristics. Those results will help the engineering application of MICP technology in coal dust suppression.

Heavy metals remediation through bio-solidification: Potential application in environmental geotechnics.

Heavy metals are pervasive pollutants found in water, soil, and solid wastes. Bio-solidification offers an environmentally friendly approach to immobilize heavy metal ions using two types of bacteria: urease-producing bacteria (UPB) and phosphatase-producing bacteria (PPB). UPB, exemplified by Sporosarcina pasteurii, secretes urease to hydrolyze urea and generate CO32- ions, while PPB, like Bacillus subtilis, produces alkaline phosphatase to hydrolyze organophosphate monoester (ROP) and produce PO43- ions. These ions react with heavy metal ions, effectively reducing their concentration by forming insoluble carbonate or phosphate precipitates. The success of bio-solidification is influenced by various factors, including substrate concentration, temperature, pH, and bacterial density. Optimal operational conditions can significantly enhance the remediation performance of heavy metals. UPB and PPB hold great potential for remediating heavy metal pollution in diverse contaminated areas such as tailings ponds, electroplating sewage, and garbage incineration plants. In conclusion, harnessing the power of these microbial methods can provide effective solutions for remediating heavy metal-induced pollution across a range of environmental conditions.

A cleaner biocementation method of soil via microbially induced struvite precipitation: A experimental and numerical analysis.

Microbial-induced struvite precipitation (MISP) is a new biocementation method for soil improvement and hydraulic permeability reduction. Compared with traditional microbial-induced carbonate precipitation (MICP), MISP can significantly reduce the production of harmful ammonium ions during biochemical reactions and convert ammonium ions into struvite with promising mechanical strength. In this study, a series of experiments were conducted to compare the performance of the MICP and the MISP processes on sandy soils. Results showed that the average content of calcium carbonate in MISP cemented sand columns after 3 times of injection is similar to that in MICP cemented sand columns after 9 times of injection. The hydraulic permeability of MISP cemented sand columns after 3 times of injection is an order of magnitude lower than that of MICP cemented sand columns after 9 times of injection. To further investigate the physicochemical interactions during MISP and MICP processes, a one-dimensional finite element code considering the chemical reactions and the solute transportation was proposed. Results show that most of the MISP were formed in the early 3 h of the 6 h injection cycle, whereas most of the MICP were formed in the last 5 h of the injection cycle. The simulated total mass of the MISP precipitation, 11.3 g, was close to the experimental result of 9.6 g. The spatial distribution of MISP is more uneven as compared to MICP, as a result of the much faster reaction rate of struvite than calcium carbonate. The findings suggested that MISP could partially replace MICP in the applications of leakage mitigation and reinforcement of sandy soils.

Phosphate microbial mineralization consolidation of waste incineration fly ash and removal of lead ions.

This paper proposes a green environment-friendly Bacillus subtilis to mineralize and consolidate waste incineration fly ash and heavy metal cations, and there is no harmful by-product in the mineralization process. Different phosphate products can be prepared, and are more stable than the microbially-induced carbonate precipitation (MICP) in nature. Typical heavy metal oxides were mainly PbO, ZnO, CdO, NiO, CuO and Cr2O3 in the chemical composition of waste incineration fly ash. Microstructure and chemical composition of waste incineration fly ash before and after treatment were characterized by powder X-ray diffraction (XRD) analysis and scanning electron microscopy. Scanning electron microscopy (SEM) images showed that the morphology of the Bacillus subtilis was mainly a rod-like structure. The optimal hydrolysis dosage of the organic phosphate monoester sodium salt was 0.2mol in the bacterial solution (1L, 20 g/L). The optimum required mass of the bacterial powder was 15 g/kg in treatment process of the waste incineration fly ash. The initial concentration of lead ions was 40.28 mg/L in waste incineration fly ash solution. After the optimum dosage treatment, the removal efficiency of lead ions was 78.15%, 79.64%, 77.70% and 80.14% when curing time was 1, 2, 4 and 6d, respectively. The waste incineration fly ash had a Shore hardness of 22 after the optimum amount of bacterial liquid treatment. Results of wind erosion test showed that the wind erosion rate of waste incineration fly ash was 2.6, 0, 0, 0, 0 and 0 g/h when blank group, deionized water, 100, 200, 300 and 400 mL of bacterial solutions treated, respectively. The bio-mineralization method provides an approach for the safe disposal of heavy metals in the contaminated areas of tailings, electroplating sewage, waste incineration plants, and so on.

Flocculation-bio-treatment of heavy metals-vacuum preloading of the river sediments.

Heavy metals pollution in river sediments is irreversible, and it is not easy to be found to be concealed. The pollution of heavy metals for river sediments is currently a serious environmental problem. In the paper, the Bacillus subtilis was selected to remove heavy metals by bio-mineralization method in river sediments. Optimal content of Bacillus subtilis powder and organophosphate monoester was 20 g and 0.2 mol in 1 L of bacterial solution, respectively. The optimum reaction time and temperature were 36 h and 30 °C, respectively. The optimal reaction conditions were applied to zinc ions in river sediments. After heavy metals treatment, there was little effect on the water content before and after flocculation and vacuum preloading. Treatment of heavy metals had no effect on the cross-plate shear strength of river sediments after vacuum preloading. After treatment of heavy metals, the effect of purifying water quality was the group B(Polyacrylamide + Polysilicate aluminium ferric) bigger than the group A (Polyacrylamide). The removal efficiency of zinc ions (Zn2+) in the group B was 89.59% and 74.99% before and after the vacuum preloading, respectively, which was better than that in the group A.

Phosphate microbial mineralization removes nickel ions from electroplating wastewater.

Nickel ions in electroplating wastewater can be removed by the bio-mineralization method. Bacillus subtilis can produce alkaline phosphatase, which hydrolyzes organophosphate monoesters and produces phosphate ions. Fourier-transform infrared spectroscopy (FTIR) showed that the precipitated material contains phosphate ions. X-ray diffraction (XRD) showed that nickel ions in electroplating wastewater react with Bacillus subtilis and organophosphate monoesters to obtain nickel phosphate octahydrate (Ni3(PO4)2·8H2O). The removal efficiency of nickel ions could reach 76.41% with the optimum content of the organophosphate monoester (0.02 mol), Bacillus subtilis powder (2 g), pH (6), standing time (36 h), and reaction temperature (25 °C) in the medium solution (100 mL). The average particle size of Ni3(PO4)2·8H2O was 80.51 nm, which was calculated by the Scherrer formula. The Lorentz-Transmission Electron Microscope (L-TEM) further showed that Ni3(PO4)2·8H2O was composed of clusters of irregular nanoparticles, and the individual particle size was in the range of 40-90 nm. The TGA curve shows that the mass loss of crystal water was 25.45%, which was close to the theoretical total mass loss of 28.24% in bio-Ni3(PO4)2·8H2O.

Bio-cement-modified construction materials and their performances.

The microbial induced mineral precipitation can be used to modify and improve the performance of construction materials and can partially replace ordinary Portland cement. Microbially induced carbonate precipitation (MICP) mainly uses the urease secreted during the growth of urease-producing bacteria (UPB) to hydrolyze urea produce CO32- and reacts with Ca2+ to form CaCO3. Microbially induced struvite precipitation (MISP) mainly uses the urease to decompose urea to produce NH4+. In the presence of hydrogen phosphate and magnesium ions, the struvite can be precipitated. The elemental composition and chemical composition of the precipitates produced by the MICP and MISP processes are analyzed by energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffraction analysis (XRD). The morphology of the precipitates can be observed by scanning electron microscope (SEM). Compared with the initial porosity, the MICP method can reduce the initial porosity of the sand column by 2.98% within 90 min. However, the MISP is only 1.45%. The permeability coefficient of the sand column can be effectively reduced in the MICP process. The total content of cementitious materials is 27.71g and 13.16g in MICP- and MISP-cemented sand columns, respectively. The MICP technology can improve the strength of alkali-activated mortars under different pH values of the UPB solution.

Mechanical properties of bio-cementation materials in pre-precipitation mixing process.

Urease-producing bacteria (UPB) could be used to cement loose sand particles. The UPB would produce free ammonia and carbon dioxide during the process of hydrolyzing urea, and part of the free ammonia would be discharged into the air to cause certain pollution to the atmospheric environment. The carbon dioxide could react with alkaline oxide to form carbonates and improved the strength in GGBS comparing with medium containing different concentrations of urea. By adding hydrogen phosphate ions and magnesium salts, free ammonia could be converted into environmentally friendly magnesium ammonium phosphate. The mixture of biological magnesium ammonium phosphate and basic magnesium carbonate could be synthesized through the bio-mineralization process. Through the pre-precipitation mixing process, the loose sand particles could be cemented into a whole. Scanning electron microscopy (SEM) images of the sand column showed that the mixture of biological magnesium ammonium phosphate and basic magnesium carbonate could better fill in the pores of sand grains. In the pre-precipitation mixing process, the optimal standing time and dosage of the bio-cement slurry prepared by the bio-mineralization method were 6 h and 30%, respectively. The average interface bonding force between CJ2 and glass slide was 2.12 N.

Solidification effect of river bottom sediments after flocculation via different composite flocculants.

The main problem in the reduction of river bottom sediments is to solve the dewatering of the rive sediments. The reduction of river bottom sediments is usually dehydrated by natural air drying and requires more time and economic costs. Different proportions of composite flocculants and curing agents have been developed to the reduction of river bottom sediments according to the requirements of the project. Two or more flocculants were mixed with the rive sediments. Therefore, anionic polyacrylamide (PAM), polyaluminum chloride (PAC), polysilicate aluminum ferric (PSAF), and iron perchloride (IC) were selected for flocculation of river sediments. Through the sedimentation column test, the relationship between sedimentation amount and time was plotted, the turbidity value and pH value of the supernatant filtration supernatant were detected, and the flocculation effect of different flocculants was evaluated to obtain suitable groups of composite flocculants. The optimum ratio of two types of polyacrylamide with a molecular weight of 18 million and 23 million was 3:7. The turbidity of the supernatant of water could well be reduced by adding polysilicate aluminum ferric. Finally, the 6 groups of composite flocculants were determined according to the sedimentation and the turbidity value of the supernatant. The relative water content was maintained at about 60% before and after flocculation. At the same curing age, the compressive strength increased as the amount of curing agent increased after flocculation. At the same curing agent dosage, the overall solidification effect was reduced with increase of curing time after flocculation.

Performance of river sediments after flocculation-pressure filter membrane-vacuum preloading.

The main problem in the reduction of river bottom sediments is to solve the dewatering of the sludge. The commonly used natural air drying method requires a large amount of time and economic cost. In this paper, different treatments were developed for the needs of the project, and related tests were carried out on the reduction of the sludge. Firstly, two or more flocculants were compounded according to the nature of the sludge. The 6 different treatments were determined according to the sedimentation and the turbidity value of the supernatant. Secondly, the dewatering test was carried out on river sediments after flocculation-vacuum preloading. The dewatering effect of different flocculants, water quality, dissipation of pore water pressure, vane shear strength, compression coefficient, and coefficient of consolidation have been analyzed after flocculation-vacuum preloading. The polysilicate aluminium ferric (PSAF) can greatly increase the dewatering efficiency of the filter press membrane, and the final dewatering amount could reach 310 g. The effect of purifying water quality was PSAF>PAM (polyacrylamide, PAM-1(18 million): PAM-2(23 million) = 3:7)>PAC (polyaluminium chloride). The PSAF and PAC could increase the pH of the water during the vacuum preloading test. The PAM has the best the vane shear strength. Lime could improve the vacuum preloading and the vane shear strength when it was added to other flocculants. The incorporation of PSAF could accelerate the dissipation and increase the final dissipation value of pores water pressure. Compared with PAM+PAC+lime, PAM+lime, PAM+PSAF+lime, PAM+PSAF, and PAM+PAC, the overall effect and price of the PAM is optimal.

Synthesis of illite/iron nanoparticles and their application as an adsorbent of lead ions.

Illite/iron nanoparticles (I-nZVI) with different iron contents were synthesized using a liquid-phase reduction method to remove Pb(II) from aqueous solution. The adsorbents were characterized by Lorentz transmission electron microscopy (L-TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and the BET-N2 technique. The composite adsorbents and illite removed Pb(II) from aqueous solution to explore the effect of different reaction conditions, including contact time, concentration, pH, and temperature. The results of batch experiments demonstrated that the removal efficiency mainly depends on the amount of nanoscale zerovalent iron. Under different conditions, the order of the removal efficiency was 30% I-nZVI > 20% I-nZVI > 10% I-nZVI > illite. Reactions between Fe(0) and Pb(II) took place on the surface of the absorbents, and the removal of Pb(II) was based on adsorption and reductive reactions. The adsorption of lead ions by I-nZVI and pure illite conformed to the pseudo-second-order reaction kinetic model, and intraparticle diffusion may not play a remarkable role in removing Pb(II). The adsorption of Pb(II) by 30% I-nZVI, 20% I-nZVI, 10% I-nZVI, and illite was more in line with the Langmuir adsorption model. Thermodynamic studies indicated that the Pb(II) removal process is endothermic in nature, which is in agreement with the experimental results. The high removal efficiency helps to achieve the goal of remediation.

Strength, microstructure, and thermal conductivity of the insulation wallboards prepared with rice husk fiber and recycled concrete aggregates.

This paper intends to evaluate the influence of content of rice husk fiber and cementitious materials on mechanical properties and thermal conductivity of thermal insulation wallboards. Thermal insulation wallboard contained different mass of rice husk fiber was prepared when the weight of cement, fly ash, cellulose ether, naphthalene superplasticizer, and recycled concrete aggregates was equal. Scanning electron microscopy (SEM) shows the internal structure of the insulation wallboards is very dense. Compared to thermal conductivity of blank group (0.9600 W/m·°C), B2 (0.1997 W/m·°C) and C2 (0.1810 W/m·°C) measured by the DRCD-3030 intelligent thermal conductivity tester can meet certain engineering requirements. Average compressive strength, flexural strength, and thermal conductivity of wallboards decreases with content of rice husk fiber increasing when other materials mass are the same. Under the same conditions of curing time and rice husk content, average compressive and flexural strength increase with the increase of the amount of cementitious material.

Mineralization and cementing properties of bio-carbonate cement, bio-phosphate cement, and bio-carbonate/phosphate cement: a review.

Due to high pollution associated with traditional Portland cement and bio-carbonate cement, a new generation of cementitious material needs to be developed. Bio-barium phosphate, magnesium phosphate, and ferric phosphate are synthesized by bio-mineralization. Firstly, the substrate is hydrolyzed by alkaline phosphatase secreted via phosphate-mineralization microbes, obtaining phosphate ions. Micro- and nano-scale phosphate minerals are prepared by phosphate ions reacting with different types of metal cation. The setting time of bio-BaHPO4 has a greater effect on the strength of sand columns when a mixing precipitation process is innovatively adopted. The strength of the sand columns increases as bio-BaHPO4 content (10~50%) increases. The optimum content of bio-BaHPO4 is 60%. Porosity and permeability of the sand columns decrease as bio-BaHPO4 content (10~60%) increases. Ammonium and ammonia can effectively be synthesized to magnesium ammonium phosphate by adding K2HPO4·3H2O to Sporosarcina pasteurii liquid. Permeability, porosity, and compressive strength of the sand columns are close to CJ1, CJ1.5, and CJ2 cementation. However, the fixation ammonia ratio of CJ2 is bigger than CJ1 and CJ1.5 (The mixture solutions of Sporosarcina pasteurii and K2HPO4·3H2O (1, 1.5, and 2 mol/L) are named as CJ1, CJ1.5, and CJ2) cementation. The results show that the Sporosarcina pasteurii liquid containing K2HPO4·3H2O (2 mol/L) and the mixture solution of MgCl2 and urea (3 mol/L) cemented loose sand particles best. Two types of bio-cement are environmentally friendly and can partially or completely replace bio-carbonate cement.

Study on transport and transformation of contaminant through layered soil with large deformation.

Based on large-deformation consolidation theory and the advection-dispersion equation of contaminant in saturated porous media, a one-dimensional theoretical model for coupled large-deformation and solute transport through layered finite soil is presented. This model comprehensively takes the effect of soil weight, sorption, and biodegradation into account. Model validation and applications are achieved through case studies of double-layered finite soil, with the transport and transformation process of contaminant being reproduced numerically. It is found that the breakthrough time of contaminant obtained from the linear adsorption solution is greater than the case of the non-linear adsorption solution, which can provide a reference for the design of landfill liner. Simulation results also indicate that relevant factors affect the transport of contaminant in layered soil interdependently; comprehensive study is required to assess the capacity of natural clay barrier for contaminant transportation.

Nanoscale Zero-Valent Iron Decorated on Bentonite/Graphene Oxide for Removal of Copper Ions from Aqueous Solution.

The removal efficiency of Cu(II) in aqueous solution by bentonite, graphene oxide (GO), and nanoscale iron decorated on bentonite (B-nZVI) and nanoscale iron decorated on bentonite/graphene oxide (GO-B-nZVI) was investigated. The results indicated that GO-B-nZVI had the best removal efficiency in different experimental environments (with time, pH, concentration of copper ions, and temperature). For 16 hours, the removal efficiency of copper ions was 82% in GO-B-nZVI, however, it was 71% in B-nZVI, 26% in bentonite, and 18% in GO. Bentonite, GO, B-nZVI, and GO-B-nZVI showed an increased removal efficiency of copper ions with the increase of pH under a certain pH range. The removal efficiency of copper ions by GO-B-nZVI first increased and then fluctuated slightly with the increase of temperature, while B-nZVI and bentonite increased and GO decreased slightly with the increase of temperature. Lorentz-Transmission Electron Microscope (TEM) images showed the nZVI particles of GO-B-nZVI dispersed evenly with diameters ranging from 10 to 86.93 nm. Scanning electron microscope (SEM) images indicated that the nanoscale iron particles were dispersed evenly on bentonite and GO with no obvious agglomeration. The qe,cal (73.37 mg·g-1 and 83.89 mg·g-1) was closer to the experimental value qe,exp according to the pseudo-second-order kinetic model. The qm of B-nZVI and GO-B-nZVI were 130.7 mg·g-1 and 184.5 mg·g-1 according to the Langmuir model.

Synthesis of nano-hydroxyapatite via microbial method and its characterization.

Nanoparticles of hydroxyapatite were successfully synthesized by microbial method at ambient temperature and pressure, using calcium chloride and specific substrate as reactants. The compositional and morphological properties of products of the syntheses were studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The characterization data obtained showed that the phase composition, functional groups, and surface morphology of samples obtained by microbial method were mainly similar to that by chemical precipitation method. The hydroxyapatite powder was shown to be nanometer-grade in size and sphere-like in shape.