Immobilization Of Heavy Metals Research Articles

Impacts of atmospheric deposition on the heavy metal mobilization and bioavailability in soils amended by lime

Atmospheric deposition is an important source of heavy metal in agricultural soils, but there is limited research on the mobility of these metals in soil and their impact on soil amendment. Here, we performed a dust incubation experiment in soils in the laboratory and a factorial transplant experiment at three field sites with a gradient of atmospheric deposition to examine the impacts of atmospherically deposited heavy metals (Cu, Cd, and Pb) on the mobility and bioavailability in soils with and without lime applications. Results showed that the atmospherically deposited heavy metals showed high mobility and were primarily presented in the soluble ionic fractions in the wet part and acid-exchangeable and reducible fractions in the dry part of atmospheric deposition. Atmospheric dust addition caused the 2p3/2 and 2p1/2 electrons of Cu atoms in uncontaminated soils to transition the 3d vacant states, resulting in similar copper absorption peaks as atmospheric particles by the observation of X-ray absorption near-edge spectroscopy (XANES). In the field, atmospheric deposition can only increase the mobile fractions in the surface soils, but not in the deeper layers. However, the deposition can increase the soluble and diffusive gradients in thin films (DGT)-measured bioavailable fractions in profile along with the soil depth. Lime applications cannot significantly reduce the mobile fractions of heavy metals in the surface soils exposed to atmospheric deposition, but significantly reduce the heavy metal concentrations in soil solutions and the DGT-measured bioavailable concentrations, particularly in the deeper layer (6–10 cm). The major implication is that atmospherically deposited heavy metals can significantly increase their bioavailable concentrations in the plough horizon of soil and constrain the effects of soil amendments on heavy metal immobilization, thereby increasing the risks of crop uptake.

Magnetic biochar enhanced copper immobilization in agricultural lands: Insights from adsorption precipitation and redox

Biochar has exceeded expectations for heavy metal immobilization and has been prepared from widely available sources and inexpensive materials. In this research, coconut shell biochar (CSB), bamboo biochar (BC), magnetic coconut shell charcoal (MCSB), and magnetic bamboo biochar (MBC) were manufactured via co-pyrolysis, and their adsorption properties were tested. The pseudo-secondary (R2 = 0.980–0.985) adsorption kinetic fittings for the four biochas were superior to the pseudo-primary kinetics (R2 = 0.969–0.982). Unmodified biochar adsorption isotherms were more consistent with the Freundlich model, while magnetic biochar fitted Langmuir models better. The maximum adsorption capacity of MCSB for Cu(Ⅱ) reached 371.50 mg g−1. The adsorption mechanisms quantitatively analysis of the biochar indicated that chemical precipitation and ion exchange contributed to the adsorption, in which the magnetic biochar metal-π complexation also enhanced the adsorption. The pot experiment revealed that MCSB (2.0 %DW) significantly enhanced the biomass of lettuce, and facilitated the immobilization of DTPA-Cu (p < 0.05). SEM-EDS, XPS, and FTIR were utilized for morphological characterization and functional group identification, and the increased active adsorption sites (-OH, –COOH, CO, and Fe–O) of MCSB enhanced chemisorption and π-π EDA complexation with Cu(Ⅱ). EEM-PARAFAC and RDA analysis further elucidated that magnetic biochar immobilized copper and reduced biotoxicity (efficiency: 76.12%) by adjusting soil pH, phosphate, and SOM release (negative correlation). The presence of iron oxides (FeOx) promoted in situ adsorption of metallic copper and offered new insights into soil remediation.

The change of coordination environments induced by vacancy defects in hematite leads to a contrasting difference between cation Pb(II) and oxyanion As(V) immobilization

Hematite is an iron oxide commonly found in terrestrial environments and plays an essential role in controlling the migration of heavy metal(loid)s in groundwater and sediments. Although defects were shown to exist both in naturally occurring and laboratory-synthesized hematite, their influences on the immobilization of heavy metal(loid)s remain poorly understood. In this study, hematite samples with tunable vacancy defect concentrations were synthesized to evaluate their adsorption capacities for the cation Pb(II) and for the oxyanion As(V). The defects in hematite were characterized using XRD, TEM-EDS mapping, position annihilation lifetime spectroscopy, and XAS. The surface charge characteristics in defective hematite were investigated using zeta potential measurements. We found that Fe vacancies were the primary defect type in the hematite structure. Batch experiments confirmed that Fe vacancies in hematite promoted As(V) adsorption, while they decreased Pb(II) adsorption. The reason for the opposite effects of Fe vacancies on Pb(II) and As(V) immobilization was investigated using DFT calculations and EXAFS analysis. The results revealed that Fe vacancies altered As–Fe coordination from a monodentate to a bidentate complex and increased the length of the Pb–Fe bond on the hematite surface, thereby leading to an increase in As(V) bonding strength, while decreasing Pb(II) adsorption affinity. In addition, the zeta potential analysis demonstrated that the presence of Fe vacancies led to an increase in the isoelectric point (IEP) of hematite samples, which therefore decreased the attraction for the cation Pb(II) and increased the attraction for the oxyanion As(V). The combination of these two effects caused by defects contributed to the contrasting difference between cation Pb(II) and oxyanion As(V) immobilization by defective hematite. Our study therefore provides new insights into the migration and fate of toxic heavy metal(loid)s controlled by iron minerals.

Modulatory Role of Biochar Properties and Environmental Risk of Heavy Metals by Co-Pyrolysis of Fenton Sludge and Biochemical Sludge.

Recent studies have reported that Fenton sludge and biochemical sludge contain high concentrations of toxic substances and heavy metals (HMs), whereas improper treatment can pose serious threats to environmental safety. Pyrolysis is considered an efficient technology to replace conventional sludge treatment. This study investigated the pyrolysis and kinetic processes of Fenton sludge and biochemical sludge, revealed the physicochemical properties of sludge biochar, and highlighted the role of co-pyrolysis in sludge immobilization of HMs and environmental risks. Results showed that Fenton sludge and biochemical sludge underwent three stages of weight loss during individual pyrolysis and co-pyrolysis, especially co-pyrolysis, which increased the rate of sludge pyrolysis and reduced the decomposition temperature. The kinetic reaction indicated that the activation energies of Fenton sludge, biochemical sludge, and mixed sludge were 11.59 kJ/mol, 8.50 kJ/mol, and 7.11 kJ/mol, respectively. Notably, co-pyrolysis reduced the activation energy of reactions and changed the specific surface area and functional group properties of the biochar produced from sludge. Meanwhile, co-pyrolysis effectively immobilized Cu, Pb, and Zn, increased the proportion of metals in oxidizable and residual states, and mitigated the environmental risks of HMs in sludge. This study provided new insights into the co-pyrolysis properties of sludge biochar and the risk assessment of HMs.

Interactive Suitability of Rice Stubble Biochar and Arbuscular Mycorrhizal Fungi for Improving Wastewater-Polluted Soil Health and Reducing Heavy Metals in Peas

Arable soils irrigated with wastewater (SIWs) cause ecological and human health issues due to the presence of heavy metals (HMs). Burning rice stubble (RS) poses severe environmental and human health hazards. Converting RS into rice stubble compost (RSC) and rice stubble biochar (RSB) can overcome these issues. Here, we considered the role of RS, RSC, and RSB as individual soil amendments and combined each of them with arbuscular mycorrhiza fungi (AMF) to observe their effectiveness for HM immobilization in SIW, their uptake in pea plants, and improvements in the physicochemical properties of soil. The results revealed that adding RSB and AMF reduced the bioavailable concentrations of Pb, Cd, Ni, Cu, Co, and Zn in SIW by 35%, 50%, 43%, 43%, 52%, and 22%, respectively. Moreover, RSB+AMF treatment also reduced Pb, Cd, Ni, Cu, Co, and Zn concentrations in grain by 93%, 76%, 83%, 72%, 71%, and 57%, respectively, compared to the control. Improvements in shoot dry weight (DW) (66%), root DW (48%), and grain yield (56%) per pot were also the highest with RSB+AMF. RSB+AMF treatment enhanced soil health and other soil attributes by improving the activity of urease, catalase, peroxidase, phosphatase, β-glucosidase, and fluorescein diacetate by 78%, 156%, 62%, 123%, 235%, and 96%, respectively. Interestingly, RSB+AMF also led to the strongest AMF–plant symbiosis, as assessed by improved AMF root colonization (162%), mycorrhizal intensity (100%), mycorrhizal frequency (104%), and arbuscular abundance (143%). To conclude, converting RS into RSB can control air pollution caused by RS burning. Moreover, adding RSB with AMF to SIW can reduce HM uptake in plants, improve soil health, and thus minimize ecological and human health issues.

Comparing struvite, K-struvite and hydroxyapatite for the remediation of lead and cadmium contaminated soil

Heavy metal pollution leads to severe soil contamination and raises environmental concerns. Phosphorus-bearing minerals have been identified as effective and environmentally friendly agents for remediating contaminated soil. However, using recycled phosphorus for metal remediation remains limited. In this study, we investigated the potential use of recovered magnesium ammonium phosphate (MAP), potassium magnesium phosphate hydrate (KMP), and hydroxyapatite (HAP) to immobilize lead (Pb) and cadmium (Cd) in contaminated soil. The effectiveness of MAP, KMP, and HAP in modifying the chemical composition of Pb and Cd in the soil and reducing their mobility was demonstrated by the results. When added at dosages of 5:1 and 10:1, the extractable fraction of Pb decreased to 0.43–13.43 % of the control group. Similarly, the extractable fraction of Cd decreased to 49.18–76.44 % of the control group at the same dosages. Moreover, the application of these products resulted in an increase in soil pH value, urease activity, and bacterial Shannon index, thereby enhancing soil properties. The immobilization effects were more significant in Pb-contaminated soil compared to Cd-contaminated soil, and MAP and KMP exhibited a stronger passivation effect on Pb in comparison to HAP. For soil fertility improvement, a molar ratio of 10:1 was recommended, whereas a ratio of 5:1 effectively passivated Pb in contaminated soil. These findings provide evidence for the feasibility of utilizing MAP, KMP, and HAP in the immobilization of heavy metals in polluted soil.

Study on the physical encapsulation mechanism of heavy metals in fly ash carbonation solidification based on synthetic pellets

The physical encapsulation mechanism prevents the leaching of heavy metals by forming calcium carbonate-encapsulated fly ash through the reaction of carbon dioxide and calcium oxide. However, current research in this area primarily involves qualitative analysis, focusing on various methods to enhance the fixation effect of heavy metals. There is a lack of quantitative description regarding how physical encapsulation solidifies heavy metals, and the solidification mechanism of heavy metals is challenging to verify through macroscopic experiments. In this paper, a method for synthesizing small fly ash particles into pellets is proposed to quantitatively study the mechanism of physically encapsulating heavy metals. The data from the carbonation reaction and leaching reaction are fitted using the shrinking core model. The depth of carbonation increases with the lengthening of carbonation time, and the physical encapsulation strengthens the immobilization of heavy metals. The leaching of heavy metals after carbonation can be categorized into three stages based on the shrinking core model: external diffusion, internal diffusion, and chemical reaction control. Synthetic pellets enhance all three stages, especially the external diffusion, which is not detectable with fly ash powder. The fitting results of the experimental data for the carbonation reaction of the enlarged synthetic pellets and the shrinking core model are both above 0.9. This indicates that the primary barrier to leaching of heavy metals is the physical encapsulation formed by the carbonation reaction following the shrinking core model. The physical encapsulation serves as the primary mechanism for the solidification of heavy metals during the carbonation process.

Synergetic Effect of Digestate Dissolved Organic Matter and Phosphogypsum Properties on Heavy Metals Immobilization in Soils

The main idea was to justify the natural, technological, and ecological aspects of digestate-based composite for heavy metals (HMs) binding in soil due to organic matter content and mineral additives’ biosorption properties. The study aimed to determine the potential of a composite made from digestate and phosphogypsum for remediation of HMs polluted soils and the role of dissolved organic matter (DOM) in binding HMs. Methods used included a literature review to identify the mechanisms for HM binding to digestate DOM, a laboratory setup for producing a digestate-based composite with digestate (from manure or sewage sludge) mixed with phosphogypsum, and an analysis of digestate fluorescence properties. Results show that a composite based on digestate from manure as feedstock had a higher fluorescence complexity index than a composite with sewage sludge digestate (2.2 and 1.71, respectively). However, the DOM stability in the sewage sludge digestate composite was higher than reported in the literature, probably due to the mineral composition of phosphogypsum, which resulted in a high HMs sorption capacity and its positive effect on soil microbial activity. Based on the theoretical substantiation of DOM content and its binding properties, manure was the most effective feedstock type out of the two tested if digestate was used for HM remediation. Using a digestate-based composite with phosphogypsum can potentially reduce the ecological risk levels imposed by HM-contaminated soils from considerably too low.

Biomineralization mechanism and remediation of Cu, Pb and Zn by indigenous ureolytic bacteria B. intermedia TSBOI

Microbially induced carbonate precipitation (MICP) is an effective and eco-friendly technology for remediating heavy metal-contaminated sites. In this study, we investigated the response discrepancies and proposed the dominant removal mechanism of the ureolytic bacteria Brucella intermedia TSBOI for different heavy metal species (Cu, Pb and Zn) under concentration gradients (0.1, 0.2, 0.4, 0.8, and 1.6 mmol/L), and explored the remediation of soil heavy metal pollution by B. intermedia TSBOI under laboratory conditions. The results showed that the heavy metal concentration significantly affected the bacterial cell concentration, urease activity, cell morphology, surface functional groups, and removal efficiency of B. intermedia TSBOI. The presence of Ca2+ negatively affected the biomass and urease activity to some extent but had a non-negligible positive effect of removing heavy metals and was more conducive to the formation and precipitation of biomineralization products. The ability of B. intermedia TSBOI to produce urease intracellularly and secrete it in large quantities to act extracellularly is key to the sustained immobilization of heavy metals and the outstanding performance of B. intermedia TSBOI bacterial solution. The results of heavy metal-contaminated soil remediation showed that B. intermedia TSBOI effectively increased the proportion of carbonate-bound states of Cu, Pb and Zn in the soil and reduced the bioavailability of heavy metals within 30 days. B. intermedia TSBOI could adapt fully to the soil environment and became a dominant genus.

Clay mineral as catalysis for controlling the nitrogen containing pollutants during sewage sludge pyrolysis

Pyrolysis technology is considered one of the most promising processes for the environmentally friendly disposal of sewage sludge (SS), as it can neutralize pathogens, reduce hazardous substances, and promote the immobilization of heavy metals. However, nitrogen-containing gases produced in SS pyrolysis can be converted to nitrogen oxides, causing serious environmental pollution. In this study, we investigated the evolution of the nitrogen (N) element in rapid pyrolysis of SS and explored the effect of clay minerals (attapulgite, montmorillonite, and kaolin) in regulating N conversion. The results showed that the higher temperature (800 °C) could promote the conversion of pyrroles/pyridines and NOx precursors in char to N2 (the conversion rate was 32.76 %), and clay minerals catalyzed the cleavage of N-containing macromolecules in the bio-oil, reducing the N content in bio-oil from 28.70 % to 6.23 %, and was conducted to realize the denitrification of bio-oil. Notably, the attapulgite (ATP) on N migration was more effective and could reduce the yield of NOx precursors from 23.80 % to 10.55 % by capturing NH4* and inhibiting the secondary reaction, while catalyzing the removal of N2 from pyridine/pyrrole (N2 production increased to 34.38 %). MgO and CaO in the clays played a major role in facilitating the conversion of char-N to N2, and clay structures loading on the biochar surface promoted the catalysis of N-containing volatiles to N2 by metal oxides. This study provides a viable and harmless approach to SS minimization.

Effect of different calcium salts on phosphorus availability and immobilization of heavy metals in municipal sludge derived biochar

Transforming municipal sludge (MS) into biochar via co-pyrolysis with calcium salts enhances phosphorus (P) recovery and reduces the risk of heavy metal contamination. In this study, the performance and mechanism of bioavailable P conversion and heavy metal stabilization were systematically compared under co-pyrolysis of MS with CaCO3, CaO, and CaCl2 at mass ratios of 2.5–10 % at 700 °C. The results showed that CaCl2 had the best ability to convert P from non-apatite inorganic P to apatite P, followed by CaO and then CaCO3. CaO and CaCO3 addition induced more Ca5(PO4)3OH formation, while CaCl2 induced more Ca2PO4Cl and Ca5(PO4)3Cl formation. The degree of stabilization of heavy metals (e.g., Cd, Cr, Cu, Ni, Pd, and Zn) was significantly improved after co-pyrolysis of MS with these salts, thus reducing the potential environmental risk. In particular, because of the dual action mechanism of chloride ions and calcium ions, co-pyrolysis with CaCl2 exhibited the lowest risk of heavy metal contamination compared with CaCO3 and CaO. These findings suggest that addition of 2.5 % CaCl2 can optimize the production of bioavailable P and the stabilization of heavy metals in biochar. This treatment is recommended for the safe utilization of P resources derived via MS pyrolysis.

The competitive and selective adsorption of heavy metals by struvite in the Pb(II)-Cd(II)-Zn(II) composite system and its environmental significance

The prevalence of struvite and other phosphate minerals in eutrophic environments has a significant effect on the transport and transformation of environmental heavy metals, but their competitive immobilization characteristics and mechanisms for heavy metals remain unclear. Three different sources of struvite (BS, CSHS, and CSS) were obtained respectively by biosynthesis and chemical synthesis with or without humic acid to investigate their competitive immobilization characteristics and mechanism of heavy metals in the Pb(II)-Cd(II)-Zn(II) composite system. The results showed that the immobilization of heavy metals by struvite is physico-chemical adsorption and the affinity (in descending order) is Pb(II) >> Cd(II)/Zn(II). Cd(II) promotes the immobilization of Pb(II)/Zn(II) by BS. The order of the selective strength by struvite for Pb(II) is BS >> CSS ≈ CSHS. The study indicates that the difference between struvite holding heavy metal ions is related to the material composition and heavy metal types, and BS shows best selective immobilization for Pb(II) in the Pb(II)-Cd(II)-Zn(II) composite system. This study provides a theoretical basis for understanding the environmental geochemical role and eco-environmental effects of struvite.

Experimental study on solidification/stabilization of leachate sludge by sulfoaluminate cement and MSWI by-products.

Leachate sludge is generated from the biochemical treatment sludge tank for disposing the leachate from landfill municipal solid waste (MSW). It has the characteristics of high water content and high organic matter content. Sulfoaluminate cement (SAC) is used as the main curing agent, and municipal solid waste incineration (MSWI) by-products are used as auxiliary curing agents to solidify/stabilize the leachate sludge. The influences of SAC content and MSWI by-products content on the strength and solidification mechanism of the leachate sludge are investigated by unconfined compressive strength (UCS) test and micro-observation tests. Moreover, the leaching concentration of heavy metals of the solidified samples is analyzed by leaching toxicity test. The results show that the UCS of the solidified samples increases with an increase in cement content. When the cement content is larger than 20%, the UCS of the solidified samples satisfies the strength requirement of landfill. The enhancing effect of bottom ash on the cement-solidified samples is slight. The fly ash is a good auxiliary curing agent for improving the UCS of cement-solidified samples, and the optimal dosage of fly ash is 5% and 15% for the solidified samples with 10 ~ 30% and 40 ~ 50% cement content, respectively. Ten percent fly ash can replace 10% cement to achieve better solidification effect for the solidified samples. The leaching concentration of heavy metals in the solidified sample with 30%/40% cement and 15% fly ash/bottom ash can satisfy the strength and leaching toxicity requirements of landfill. The immobilization of heavy metal of the cement and MSWI by-products solidified samples is mainly achieved through physical adsorption, physical encapsulation, ion exchange, and chemical precipitation.

Cassava (Manihot esculenta) Yield, Nutrition, and Heavy Metal Bioaccumulation Responses to Circular Economy-Based Innovations in a Mining-Degraded Landscape

Mining operations in Ghana's Forest-Savannah Transition Zone have caused widespread land degradation, jeopardizing ecosystems, food security, and agroecological sustainability. In response, we conducted an experiment to evaluate the effects of biochar and poultry litter amendments on cassava (Manihot esculenta) growth, nutritional quality, and heavy metal accumulation at an illegal mining-degraded site in the Amansie Central District of Ashanti, Ghana. The experiment included five treatments: biochar (10 ton/ha), poultry manure (10 ton/ha), a biochar-poultry manure mix (1:1 ratio, 10 ton/ha each), and two control groups (degraded and forest sites). The combined biochar and poultry manure treatment yielded the highest cassava stover biomass (22.9 ton/ha) during the first year. Nutritional characteristics of cassava such as %carbohydrate, %protein and %total ash tubers were influenced by treatment amendments. Additionally, biochar and poultry manure reduced the accumulation of Arsenic (As) by 168.9% and Lead (Pb) by 149.8% in cassava compared with galamsey soil control. This study showcases a circular economy-based approach that employs locally available resources to restore mining-degraded landscapes and enhance regenerative agricultural practices, reducing waste, bioaccumulation of heavy metals and improving carbon sequestration. Promoting the use of biochar and poultry manure amendments for ecological restoration in mining-degraded areas can contribute to sustainable land use, food security, and livelihoods. Policymakers should consider these strategies to align with global and national development goals while improving food systems and ecosystem services. Future research should explore the long-term impacts of cassava cultivation on amended mining sites and assess the potential of these amendments for agroecological enhancement and heavy metal immobilization.

Recycling of waste glass and incinerated sewage sludge ash in glass-ceramics

Disposal of waste glass and incinerated sewage sludge ash (ISSA) in landfills is a waste of resources and poses significant environmental risks. This work aims to recycle waste glass and ISSA together to form value-added glass-ceramics. The physical and mechanical properties, leaching behaviour, and microstructure of the glass-ceramics produced with different proportions of waste glass powder (WGP) and ISSA were investigated. Thermodynamic calculations were performed to predict the formation of crystalline phases and the phase transformation involved. The results showed the potential of WGP and ISSA as raw materials in glass-ceramics production. WGP effectively densified the microstructure of the glass-ceramics by forming a viscous phase. As WGP content increased, the total porosity of glass-ceramics decreased whereas the density increased, accompanied by the formed anorthite transforming into wollastonite. The incorporation of WGP densified and refined the pore structure of the glass-ceramics, thereby improving the mechanical properties and reducing the water absorption. The glass-ceramics produced with a 50:50 blend of WGP and ISSA exhibited the highest compressive strength of 43.7 MPa and the lowest water absorption of 0.3 %. All fabricated glass-ceramics exhibited innocuous heavy metal leaching. The co-sintering of ISSA and WGP can produce additive-free glass-ceramics, characterized by reduced energy consumption and notable heavy metal immobilization capacity. These materials hold promise for utilization in construction as building materials.

Simultaneous Immobilization of Heavy Metals in MKPC-Based Mortar-Experimental Assessment.

Heavy metal contamination, associated with the increase in industrial production and the development of the population in general, poses a significant risk in terms of the contamination of soil, water, and, consequently, industrial plants and human health. The presence of ecotoxic heavy metals (HMs) thus significantly limits the sustainable development of society and contributes to the deterioration of the quality of the environment as a whole. For this reason, the stabilization and immobilization of heavy metals is a very topical issue. This paper deals with the possibility of the simultaneous immobilization of heavy metals (Ba2+, Pb2+, and Zn2+) in mortar based on magnesium potassium phosphate cement (MKPC). The structural, mechanical, and hygric parameters of mortars artificially contaminated with heavy metals in the form of salt solutions were investigated together with the formed hydration products. In the leachates of the prepared samples, the content of HMs was measured and the immobilization ratio of each HM was determined. The immobilization rate of all the investigated HMs was >98.7%, which gave information about the effectiveness of the MKPC-based matrix for HM stabilization. Furthermore, the content of HMs in the leachates was below the prescribed limits for non-hazardous waste that can be safely treated without any environmental risks. Although the presence of heavy metals led to a reduction in the strength of the prepared mortar (46.5% and 57.3% in compressive and flexural strength, respectively), its mechanical resistance remained high enough for many construction applications. Moreover, the low values of the parameters characterizing the water transport (water absorption coefficient Aw = 4.26 × 10-3 kg·m-2·s-1/2 and sorptivity S = 4.0 × 10-6 m·s-1/2) clearly demonstrate the limited possibility of the leaching of heavy metals from the MKPC matrix structure.

Insights into the interaction between mineral formation and heavy metals immobilization, mediated by Virgibacillus exopolymeric substances

Heavy metal pollution poses significant risks to both the environment and human health due to their toxicity, long residence times, and their ability to bioaccumulate and bio magnify across the food chain. To address this issue, microbial biomineralization has emerged as a promising approach to the bio-removal of heavy metals through immobilization. This process is facilitated by extracellular polymeric substances (EPS), which also play a crucial role in mediating mineral formation. In this study, the interactions between several selected heavy metals (Cd2+, Cu2+, Ni2+, Zn2+), EPS, and mineral formation were investigated using two mineral-forming Virgibacillus strains isolated from the Qatari sabkhas, which are known to be suitable sites for the formation of biominerals. An additional non-mineral-forming Virgibacillus strain isolated from the Dukhan oil waste dumpsite was also investigated. Cd2+ and Zn2+ were to inhibit mineral formation, likely due to competition with Ca2+ and Mg2+ ions during biomineralization. However, exposure to Ni2+ or Cu2+ resulted in changes in the FTIR spectra of the EPS, suggesting the presence of specific functional group bindings within the EPS matrix. The EPS produced by each strain was also directly associated with their efficiency (%) at removing heavy metals. Notably, the EPS from Virgibacillus halodenitrificans Z4D1, the non-mineral-forming strain, exhibited the highest heavy metal removal efficiency of 31.7 % for Zn2+. These findings reveal that EPS do not only affect the biomineralization process but also that the functional groups in EPS have a direct effect on the immobilization of several heavy metals. Conditions that are not suitable for mineral formation may instead be appropriate for the removal of specific heavy metals.

Influence of Enriched Urease Producing Bacteria from Leachate and Restaurant Wastewater on Heavy Metal Removal

The escalation of heavy metal pollution in natural ecosystems due to industrialization presents a critical environmental concern, endangering the well-being of living organisms. Microbially Induced Carbonate Precipitation (MICP) technology, an emerging innovation, has gained attention from the scientific community for its potential in biocementation and bioremediation applications. However, a substantial gap in understanding exists regarding the utilization of ureolytic microbial strains from waste sources capable of effectively immobilizing high concentrations of heavy metals. This study endeavors to explore the latent potential of indigenous ureolytic bacteria derived from leachate and restaurant wastewater, possessing bioremediation capabilities for heavy metal immobilization. The investigation includes microbial screening, physiological characterization of ureolytic bacteria, assessment of their tolerance levels, and evaluation of heavy metal removal efficacy through Atomic Absorption Spectrophotometry (AAS) analysis. Notably, the results reveal that ureolytic bacteria from restaurant wastewater are more tolerant to Cd2+ concentrations compared to their leachate counterparts, manifesting optimum conductivity, pH, and optical density (OD). More so, AAS analysis demonstrates the restaurant wastewater-derived sample's remarkable proficiency in Cd2+ removal, achieving a substantial 95% removal rate, significantly outperforming the leachate wastewater sample's removal rate of 53%.

A comprehensive study of artificial neural network for sensitivity analysis and hazardous elements sorption predictions via bone char for wastewater treatment

Using bone char for contaminated wastewater treatment and soil remediation is an intriguing approach to environmental management and an environmentally friendly way of recycling waste. The bone char remediation strategy for heavy metal-polluted wastewater was primarily affected by bone char characteristics, factors of solution, and heavy metal (HM) chemistry. Therefore, the optimal parameters of HM sorption by bone char depend on the research being performed. Regarding enhancing HM immobilization by bone char, a generic strategy for determining optimal parameters and predicting outcomes is crucial. The primary objective of this research was to employ artificial neural network (ANN) technology to determine the optimal parameters via sensitivity analysis and to predict objective function through simulation. Sensitivity analysis found that for multi-metals sorption (Cd, Ni, and Zn), the order of significance for pyrolysis parameters was reaction temperature > heating rate > residence time. The primary variables for single metal sorption were solution pH, HM concentration, and pyrolysis temperature. Regarding binary sorption, the incubation parameters were evaluated in the following order: HM concentrations > solution pH > bone char mass > incubation duration. This approach can be used for further experiment design and improve the immobilization of HM by bone char for water remediation.

Sustainable Alkali-Activated Mortars for the Immobilization of Heavy Metals from Copper Mine Tailings

Sustainable Alkali-Activated Mortars for the Immobilization of Heavy Metals from Copper Mine Tailings