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

Mechanistic and kinetic understanding of Pb-phosphate biomineralization from humic acid-bound Pb under active growth of phosphate solubilizing Enterobacter aerogenes W6

Humic acid-bound Pb (HA-Pb), as one of the representative solid-associated Pb species, plays important roles in Pb mobility and toxicity in aqueous environments. Stable Pb-phosphate minerals formation mediated by phosphate solubilizing bacteria (PSB) is a promising approach to immobilizing Pb in contaminated waters. However, the underlying processes and kinetics of Pb-phosphate biomineralization from labile HA-Pb species remain unclear. Here, experiments were conducted using dialysis bags to separate PSB Enterobacter Aerogenes W6 cells from HA-Pb and FePO4 solids, and the time-dependent evolutions of solution conditions, PSB metabolites, Pb species, and Pb-phosphate minerals were systematically analyzed. Acid-soluble Pb species (∼25%) in HA-Pb, mainly complexing with phenolic hydroxyl groups, served as the source for Pb-phosphate mineralization. Extracellular secreted small organic acids contributed to Pb solubilization from HA-Pb, while polysaccharide macromolecules played critical roles in promoting Pb-phosphate nucleation on PSB cell surfaces. By coupling time-dependent bacterial growth, an integrated kinetic model was developed and performed well in describing the underlying processes of Pb-phosphate biomineralization, including Pb solubilization from HA-Pb (RMSE<1%), Pb adsorption onto PSB cells (RMSE<20%), and Pb-phosphate mineral precipitation (RMSE<5%). The findings provide insights into the Pb-phosphate biomineralization of solid-associated Pb and could help to predict the fate of Pb in natural and engineering systems.

The role of Lysinibacillus fusiformis S01 in cadmium removal from water and immobilization in soil

Cadmium pollution is widespread in water and soil worldwide. Microbial remediation is an effective method for removing heavy metals. This study explored the cadmium remediation mechanism and efficiency of Lysinibacillus fusiformis S01. The removal process includes extracellular adsorption, intracellular accumulation, biomineralization, extracellular polymer sequestration, and binding to cell surface functional groups. In an aqueous solution with a 20 % v/v bacterial dosage, 71.22 % of 10 mg/L Cd2 + was removed within 7 days, with a dissolution rate below 3 % after 15 days. A sequencing batch reactor (V=1 L) was done with an initial concentration of 5 mg/L Cd2+ and only 200 mL of bacterial solution, over 2-day cycles, achieving an 80 % removal rate with a stable pH of around 8.30. In artificially contaminated soil experiments, 76.96 % of exchangeable cadmium was passivated in low concentration soil (3.504 mg/kg), while the passivation rate was 66.43 % in high concentration soil (9.324 mg/kg) after 7 days, with 5 mL of bacterial solution added to every 30 g of soil at 30°C. In actual contaminated soil (8.190 mg/kg), it was reduced from 22.75 % to about 14 % after 28 days. The high-throughput sequencing of the soil experiments revealed that L. fusiformis S01 became the dominant strain (from 0.01 % to 5.10 %), increasing diversity (Shannon index from 2.94 to 3.41 and Simpson index from 0.15 to 0.08) and reducing harmful organisms. The study demonstrates the potential of L. fusiformis S01 for cadmium pollution remediation.

Effect of phosphate-mineralized bacteria on multi-metals migration behavior in vanadium tailing slags: Coexistence of immobilization and mobilization

Biomineralization techniques have been utilized to remediate heavy metals (HMs) contaminated environments. However, the effect of microbial-induced phosphate precipitation (MIPP) on HMs behavior in vanadium tailing slags has not been revealed. This study is the first to report the influence of MIPP on multiple HMs including Cd, Cu, Pb and Zn in the slags with and without soil mixing. The results showed that MIPP exhibited excellent ability for Cd immobilization, Cd immobilization rate reached 43.41 % under the optimal parameters within 7 days. Cd immobilization performance was significantly improved and sustained after the slags were covered with soil, resulting from better colonization of phosphate mineralizing bacteria in slag-soil mixtures. Surprisingly, DTPA-Cu, Zn and Pb contents in slags were all increased to varying degrees after MIPP treatment. Leaching solution mineralization tests further suggested that MIPP significantly reduced the concentration of Cd2+, Pb2+, Ca2+, Mg2+ and Al3+, but barely changed Cu2+ and Zn2+ concentrations. Characterization analysis confirmed that formation of phosphates including Cd(PO4)2 and dissolution of minerals including PbZnSiO2 were the reason for HMs immobilization and mobilization in vanadium tailing slags. This study provides new insights for understanding biomineralization technology and using MIPP to remediate HMs contaminated mine waste.

Comparison of Phosphogypsum-Steel Slag-Based cement and Portland cement for stabilization of heavy metals in oil-based drillings cuttings

This research compared Portland cement and Phosphogypsum-Steel Slag-Based (PSSB) cement in terms of their capabilities to stabilize heavy metals (specifically lead and nickel) in Oil-Based Drill Cuttings (OBDC). In the experimental section, the qualitative analysis of heavy metal constituents in OBDC was captured by X-ray Photoelectron Spectroscopy (XPS). Additionally, an acetic acid leaching test was implemented for the heavy metal leaching concentration to evaluate the ceramsite stabilization effect on OBDC. In the simulation phase, cement models, heavy metal ion models, and stabilization models were constructed to explore the stabilization mechanism of heavy metals. Results demonstrated that PSSB cement exhibits superior stabilization effects on OBDC compared to Portland cement. Flame Atomic Absorption Spectrophotometry (FAAS) tests showed that PSSB cement reduced Ni and Pb leaching by 21.87 % and 47.32 %, respectively, compared to Portland cement. In PSSB cement, the diffusion coefficients for Ni and Pb ions were observed to decrease by 42.92 % and 79.63 %, respectively, as revealed through Mean Square Displacement (MSD) analysis. The cohesive energy of PSSB cement was 76.73 % lower than that of Portland cement, and its interaction energies for stabilizing Ni and Pb ions were 59.43 % and 76.22 % lower, respectively, demonstrating greater stability and efficiency in metal stabilization. PSSB cement exhibited lower heavy metal concentration and better structural stability than Portland cement.

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.

Enhanced Cd(II) biomineralization induced by microalgae after cultivating modification in high-phosphorus culture

In this study, high-phosphorus beared microalgae was prepared by cultivating modification in high-phosphorus culture, and used for the enhanced Cd(II) biomineralization in soil. Batch experiment results showed that Chlorella sorokiniana FK was modified successfully in highly phosphate culture. Both intracellular P (Poly-P, 29.7 mg/kg) and surface P (phosphoryl based functional groups, 3.7 mol/kg) were greatly enhanced, and the Cd(II) removal capacity surged to 45.98 mg/g at equilibrium in the Langmuir simulation. The EXAFS analysis indicated that Cd tended to form a more stable bidentate complex (RPO₄)₂Cd when bounding with phosphate groups on the surface of the high-phosphorus microalgae. Moreover, high-phosphorus beared microalgae not only had higher immobilization amount of Cd(II), but also promoted immobilized Cd from adsorbed state to mineralized state. After high-phosphate cultured, increased density of P-related groups provided more adsorption sites, while the decomposition of intracellular Poly-P released phosphate ions into cell surface microenvironment, which combined and promoted the formation of Cd₃(PO₄)₂/Cd(H₂PO₄)₂ on cell surface. Cd-contaminated soil remediation experiments applying high-surface-phosphate beared microalgae further showed that more Cd stabilized as a residue fraction within 49 days. This study proposes that the high-phosphate culture strategy is a good way to improve the immobilization of heavy metals in soil induced by microorganisms.

Transformation and leaching behavior of Pb in hazardous waste incineration fly ash after thermal treatment with addition of Fe2O3

This study investigated the leaching behavior of Pb in hazardous waste incineration fly ash (HWIFA) after adding Fe₂O₃ thermal treatment and revealed the leaching mechanism of Pb from the perspective of phase transformation. The static leaching results showed that at 600 °C-1300 °C, with the addition of Fe₂O₃ increased, the Pb leaching toxicity continued to decrease. The dynamic results indicated that as the thermal treatment temperature was higher than 1100 °C, the addition of Fe₂O₃ can effectively inhibit the dynamic leaching of Pb in HWIFA. Meanwhile, the inhibition effect was not very closely related to the amount of Fe₂O₃. The addition of Fe₂O₃ can react with PbO to form PbFe₁₂O₁₉, which has a better stability. The appearance of PbFe₁₂O₁₉ was the main reason for adding Fe₂O₃ to enhanced the immobilization of Pb. However, the amount of Fe₂O₃ should be carefully controlled to avoid an excessive reducible fraction of Pb in the thermal treated HWIFA, which will affect the long-term stability of Pb.

Synchronous removal of ammonia nitrogen, phosphate, and calcium by heterotrophic nitrifying strain Pseudomonas sp. Y1 based on microbial induced calcium precipitation

Pseudomonas sp. Y1, a strain with superior synchronous removal ability of ammonia nitrogen (NH₄⁺-N), phosphate (PO₄^3--P), and calcium (Ca²⁺) was isolated, with the removal efficiencies of 92.04, 99.98, and 83.40 %, respectively. Meanwhile, the chemical oxygen demand (COD) was degraded by 90.33 %. Through kinetic analysis, the optimal cultivated conditions for heterotrophic nitrification-aerobic denitrification (HNAD) and biomineralization were determined. The growth curves experimental results of different nitrogen sources indicated that strain Y1 could remove NH₄⁺-N through HNAD. The results of excitation-emission matrix (EEM) proved that the appearance of extracellular polymeric substances (EPS) promoted the precipitation of phosphate minerals. Finally, the characterization results of the bioprecipitates showed that the HNAD process produced the alkalinity required for microbial induced calcium precipitation (MICP), resulting in the removal of PO₄^3- via adsorption and co-precipitation. This study provides a theoretical basis for the application of microorganisms to achieve synchronous nutrient removal and phosphorus recovery in wastewater.

Emerging disposal technologies of harmful phytoextraction biomass (HPB) containing heavy metals: A review

Phytoextraction is an effective approach for remediation of heavy metal (HM) contaminated soil. After the enhancement of phytoextraction efficiency has been systematically investigated and illustrated, the harmless disposal and value-added use of harmful phytoextraction biomass (HPB) become the major issue to be addressed. Therefore, in recent years, a large number of studies have focused on the disposal technologies for HPB, such as composting, enzyme hydrolysis, hydrothermal conversion, phyto-mining, and pyrolysis. The present review introduces their operation process, reaction parameters, economic/ecological advantages, and especially the migration and transformation behavior of HMs/biomass. Since plenty of plants possess comparable extraction abilities for HMs but with discrepancy constitution of biomass, the phytoextraction process should be combined with the disposal of HPB after harvested in the future, and thus a grading handling strategy for HPB is also presented. Hence, this review is significative for disposing of HPB and popularizing phytoextraction technologies.

Remediation of soil cadmium pollution by biomineralization using microbial-induced precipitation: a review

In recent years, with industrial pollution and the application of agricultural fertilizers with high cadmium (Cd) content, soil Cd pollution has become increasingly serious. A large amount of Cd is discharged into the environment, greatly endangering the stability of the ecological environment and human health. The use of microorganisms to induce Cd precipitation and mineralization is an important bioremediation method. Itis highly efficient, has a low cost, enables environmental protection, and convenient to operate. This article summarizes the pollution status, pollution source, biological toxicity and existing forms of Cd, as well as the biomineralization mechanism of microbial induced Cd(II) precipitation, mainly including microbial-induced carbonate precipitation, microbial-induced phosphate precipitation and microbial-induced sulfide precipitation. Factors affecting the bioremediation of Cd, such as pH, coexisting ions, and temperature, are introduced. Finally, the key points and difficulties of future microbe-induced Cd(II) biomineralization research are highlighted, providing a scientific basis and theoretical guidance for the application of microbe-induced Cd(II) immobilization in soil.

Continuous and efficient immobilization of heavy metals by phosphate-mineralized bacterial consortium

Traditional sewage treatment technology cannot remove heavy metals, which needs to be improved urgently. Lysinibacillus with the function of bio-mineralization was screened and loaded on granular sludge to form a phosphate-mineralized bacterial consortium, which demonstrated the ability of self-regulating pH and automatic solid-liquid separation. Heavy metals could be fixed on the bacterial consortium to produce stable and harmless phosphate minerals. The highest removal efficiency of Pb(Ⅱ), Cd(Ⅱ), and Ni(Ⅱ) were 97.9%, 70%, and 40%, respectively. Organic matter and other metal ions in actual polluted water had little effect on the Pb(Ⅱ) removal efficiency. Mechanism analysis was conducted through 3D-EEM, XRD, SEM-EDS, XPS, FTIR, and high-throughput sequencing analyses. The bacterial consortium was a multi-species coexistence system, but Lysinibacillus played a major role in removing Pb(Ⅱ). C-O and O-H bonds of tyrosine and phosphorous organics were broken by enzyme catalysis and the metal-oxygen bond (Pb-O) was formed. Mineral crystals in the reactor accumulated, transforming from the initial phase non-crystalline structure to the metaphase Pb₃(PO₄)₂ and eventually to the Pb₅(PO₄)₃OH. This research obtained a promising technique for immobilizing Pb(Ⅱ) or other hazardous metals continuously and efficiently.

Municipal solid waste incineration fly ash to produce eco-friendly binders for sustainable building construction

Municipal solid waste incinerator (MSWI) fly ash is a residue of municipal solid waste incineration whose recycling is currently a worldwide problem. Therefore, considerable efforts are being made to establish effective recovery techniques so MSWI can be used as a substitute for natural resources in construction, as in masonry blocks, roads and so on, or in the manufacture of new materials. MSWI fly ashes contain elements such as Ca, Si and Al, which make it possible for them to be used as raw material to manufacture cements. This paper presents the results obtained from the physicochemical characterization of two MSWI fly ashes from two Spanish cities. The research aims to explore the feasibility of using MSWI fly ash as raw material for sintering belite cements. The results show that MSWI fly ashes have a suitable composition. However, appropriate pre-treatment will be required to eliminate chloride and possible traces of heavy metals and to improve pozzolanic activity. Furthermore, the addition of vitreous silica in the proper proportions is required. The phases generated after calcination of the blend at 800 °C are not those corresponding to pure belite cements. Nevertheless, the possibility of using these ashes as supplementary cementitious material in the manufacture of eco-cements should be contemplated.

Bacterial-induced mineralization (BIM) for soil solidification and heavy metal stabilization: A critical review

Solidification and stabilization (S/S) treatment via cement is common and effective for improving soil strength and stabilizing heavy metals in contaminated soils, but has certain drawbacks, such as high fossil energy consumption, big carbon footprint, poor chemical compatibility, and ambiguous long-term stability. This paper innovatively proposes bacterial-induced mineralization (BIM) as an eco-friendly and efficient S/S method. In the BIM-S/S treatment, life activities of bacteria produce minerals to cement the soil particles and fix the heavy metals. This review firstly summarizes the basic theories of BIM technology followed by the evaluation on remediation effects and long-term stability in terms of soil solidification and heavy metal stabilization. Then the factors in BIM-S/S application are reviewed. Emphasis is put on the comparison of the BIM-S/S effect with that of cement-based-S/S technology. It is concluded that BIM-S/S technology is promising with outstanding performance in sustainability. On the other hand, current limitations and deficiencies with this technology are identified finally, hereby the directions for future research are pointed to make a major advancement in the BIM-S/S technology.

Advances in application of cotton-based adsorbents for heavy metals trapping, surface modifications and future perspectives

Cotton-based adsorbents (CBAs) are promising materials for combating the problem of heavy metal pollution of environmental waters. This is ascribed to the low cost, abundance, biodegradability and efficiency of CBAs. Herein we review the adsorption of heavy metals (HMs) onto CBAs. We found that several surface modifications were employed to improve the efficiency of the CBAs. These modifications were effected via thermal, physical and chemical means to obtain activated carbons, biochars, ionic liquids, aerogels, hydrogels, chitosans and nanoparticle-derived CBAs. The CBAs exhibited maximum HMs uptake as low as 0.002 mg/g to as high as 505.6 mg/g. Although, the cotton-derived activated carbons and biochars exhibited enhanced HM uptake from that of the unmodified CBAs, they were less efficient than CBAs modified by other methods. Recent chemical, ionic liquid, chitosan and nano-derived CBAs were the most efficient, with high uptake and fast kinetic removal. However, the nanoparticle-based adsorbents are preferred to the chemically modified forms, due to the possibility of secondary pollution and the noxious effect of the latter to the environment. Findings showed that chemical treatment produced CBAs most efficient for As(V), Pb(II) and Fe(III), while ionic liquid CBA was more efficient for Cu(II) and Ni(II). Nano-based treatment was suitable for the uptake of Co(II), Zn(II), Pb(II) and Cd(II), while the chitosan based adsorbent was viable for Hg(II). Isotherm and kinetic evaluation of CBAs mostly conformed to the Langmuir and pseudo-second order models, respectively. Spontaneous adsorption of HMs onto CBAs was deduced from thermodynamic analysis, with endothermic and exothermic characteristics. Over 88% desorption of HMs was obtained from the CBAs studied with good average reusability from 3 to 20 cycles. We also discussed the directions for future research.