Search Results (547)

Extracellular electron transfer is crucial in the microbial reduction of hexavalent chromium [Cr(VI)], and N-acylated-_L-homoserine lactones (AHLs) could accelerate this process. In this study, fulvic acid (FA) was used as an electron shuttle to enhance the microbial reduction process via stimulating extracellular electron transfer efficiency. Compared with 9,10-anthraquinone-2-sulfonic acid (AQS), FA had a stronger positive effect on Cr(VI) reduction by S. putrefaciens, showing the ability of stimulating S. putrefaciens to release AHLs. The concentrations of C6-HSL, C8-HSL and 3OC10-HSL increased by 11.79 ng/L, 19.82 ng/L and 3.01 ng/L after the addition of 2% FA. The bioinformation analysis indicated that AHLs could regulate the synthesis of electron shuttles by S. putrefaciens, such as riboflavin. And the addition of exogenous C6-HSL, C8-HSL, C10-HSL, C12-HSL and 3OC10-HSL increased the Cr(VI) reduction rates by 1.73%, 2.39%, 4.18%, 1.45% and 2.70%, because they could promote the release of riboflavin. It revealed a new pathway by which FA promoted microbial Cr(VI) reduction. This study also provides a novel approach for enhancing the microbial Cr(VI) reduction and a deeper understanding of the communication mechanism among microorganisms. Full article

Microbial reduction in hexavalent chromium (Cr(VI)) is a well characterized bioremediation strategy, yet the mechanistic diversity among bacterial taxa necessitates detailed investigations into strain-specific pathways. Here, we report the isolation and characterization of Bacillus safensis BSF-4, a halophilic bacterium derived from saline-alkali soil, which demonstrates efficient Cr(VI) reduction capacity. Physiological assays showed that BSF-4 achieved 89.15% reduction of 20 mg/L Cr(VI) within 72 h, with Cr(III) identified as the primary extracellular end product. Resting cell assays and subcellular fractionation analyses confirmed that Cr(VI) reduction predominantly occurs in the extracellular milieu. X-ray photoelectron spectroscopy (XPS) further revealed soluble Cr(III) complexed with extracellular polymeric substances (EPS). Transcriptomic profiling indicated upregulation of membrane-associated transport systems (facilitating Cr(VI) exclusion) and quorum sensing (QS) pathways (mediating adaptive stress responses). These findings highlight a dual mechanism: (1) extracellular enzymatic reduction mediated by EPS-bound redox proteins, and (2) intracellular detoxification via QS-regulated defense pathways. Collectively, Bacillus safensis BSF-4 exhibits robust Cr(VI) reduction capacity under saline conditions, positioning it as a promising candidate for bioremediation of Cr(VI)-contaminated saline soils and aquatic ecosystems. Full article

The rational design of functional and sustainable polymers is central to addressing global environmental challenges. In this context, unmodified lignin derived from Sarkanda grass (Tripidium bengalense), an abundant agro-industrial lignocellulosic byproduct, was systematically investigated as a natural polymeric adsorbent for the remediation of aqueous media contaminated with heavy metals. The study evaluates lignin’s behavior toward nine metal(loid) ions: arsenic, cadmium, chromium, cobalt, copper, iron, nickel, lead, and zinc. Adsorption performance was systematically investigated under static batch conditions, optimizing key parameters, with equilibrium and kinetic data modeled using established isotherms and rate equations. Surface characterization and seed germination bioassays provided supporting evidence. Unmodified Sarkanda grass lignin demonstrated effective adsorption, exhibiting a clear preference for Cu(II) followed by other divalent cations, with lower capacities for As(III) and Cr(VI). Adsorption kinetics consistently followed a pseudo-second-order model, indicating chemisorption as the dominant mechanism. Thermodynamic studies revealed spontaneous and endothermic processes. Bioassays confirmed significant reduction in aqueous toxicity and strong metal sequestration. This work positions unmodified Sarkanda grass lignin as a bio-based, low-cost polymer platform for emerging water treatment technologies, contributing to circular bioeconomy goals and highlighting the potential of natural polymers in sustainable materials design. Full article

Porous carbon-loaded MnO was prepared via a combination of the sol–gel method and the chemical blow molding method using polyvinylpyrrolidone (PVP) and manganese nitrate as starting materials. SEM, EDX, TEM, FTIR, XRD, XPS, nitrogen adsorption–desorption, and elemental analysis were used to assess its physical and chemical characteristics. Furthermore, the adsorption property of porous carbon-loaded MnO for hexavalent chromium (Cr(VI)) in polluted water was investigated in detail. The results demonstrated that large numbers of MnO nanoparticles were evenly mounted on the surfaces of carbon walls, with a uniform distribution of C, N, and O elements. The BET surface area was 46.728 m²/g, and the pore sizes of porous carbon ranged from 2 nm to 10 nm. Additionally, abundant surface functional groups were found in porous carbon-loaded MnO, a result consistent with XPS data and applicable to the adsorption of heavy metals from aqueous solutions containing Cr(VI). The Freundlich model fitted the adsorption isotherm well, and the pseudo−second−order model precisely matched the adsorption kinetics. According to the study results, the adsorption was multilayer, and the adsorption process involved an endothermic reaction. These results indicate that this is a feasible way to synthesize a high−efficiency adsorbent for the removal of harmful heavy−metal ions from wastewater. Full article

This study analyzed the heavy metal tolerance and chromium reduction and the potential of plant growth to promote Rhizobium sp. OS-1. By genetic makeup, the Rhizobium strain is nitrogen-fixing and phosphate-solubilizing in metal-contaminated agricultural soil. Among the Rhizobium group, bacterial strain OS-1 showed a significant tolerance to heavy metals, particularly chromium (900 µg/mL), zinc (700 µg/mL), and copper. In the initial investigation, the bacteria strains were morphologically short-rod, Gram-negative, appeared as light pink colonies on media plates, and were biochemically positive for catalase reaction and the ability to ferment glucose, sucrose, and mannitol. Further, bacterial genomic DNA was isolated and amplified with the 16SrRNA gene and sequencing; the obtained 16S rRNA sequence achieved accession no. HE663761.1 from the NCBI GenBank, and it was confirmed that the strain belongs to the Rhizobium genus by phylogenetic analysis. The strain’s performance was best for high hexavalent chromium [Cr(VI)] reduction at 7–8 pH and a temperature of 30 °C, resulting in a total decrease in 96 h. Additionally, the adsorption isotherm Freundlich and Langmuir models fit best for this study, revealing a large biosorption capacity, with Cr(VI) having the highest affinity. Further bacterial chromium reduction was confirmed by an enzymatic test of nitro reductase and chromate reductase activity in bacterial extract. Further, from the metal biosorption study, an Artificial Neural Network (ANN) model was built to assess the metal reduction capability, considering the variables of pH, temperature, incubation duration, and initial metal concentration. The model attained an excellent expected accuracy (R² > 0.90). With these features, this bacterial strain is excellent for bioremediation and use for industrial purposes and agricultural sustainability in metal-contaminated agricultural fields. Full article

Hexavalent chromium (Cr(VI)), a common contaminant in industrial wastewater, poses severe health risks due to its carcinogenic and mutagenic properties. Consequently, the development of efficient and environmentally friendly methods to reduce Cr(VI) to the less toxic trivalent chromium (Cr(III)) is of great importance. In this study, we present a cost-effective photocatalytic approach using graphitic carbon nitride (g-C₃N₄) modified with 1,3,5-trihydroxybenzene via one-step thermal condensation. The modified photo-catalyst exhibited improved surface area, porosity, visible-light absorption, and a narrowed band gap, all of which contributed to enhanced charge separation. As a result, nearly complete reduction in Cr(VI) was achieved within 90 min under visible-light irradiation. Further optimization of catalyst dosage and EDTA concentration gave even higher reduction efficiency. This work offers a promising strategy for the design of high-performance photocatalysts for environmental remediation. Full article

Chromium slag sites pose severe environmental risks due to hexavalent chromium (Cr(VI)) contamination, characterized by high mobility and toxicity. This study focused on chromium-contaminated soil from a historical chromium slag site in North China, where long-term accumulation of chromate production residues has led to serious Cr(VI) pollution, with Cr(VI) accounting for 13–22% of total chromium and far exceeding national soil risk control standards. To elucidate Cr(VI) transformation mechanisms and elemental linkages, a combined approach of macro-scale condition experiments and micro-scale analysis was employed. Results showed that acidic conditions (pH < 7) significantly enhanced Cr(VI) reduction efficiency by promoting the conversion of CrO₄²⁻ to HCrO₄⁻/Cr₂O₇²⁻. Among reducing agents, FeSO₄ exhibited the strongest effect (reduction efficiency >30%), followed by citric acid and fulvic acid. Temperature variations (−20 °C to 30 °C) had minimal impact on Cr(VI) transformation in the 45-day experiment, while soil moisture (20–25%) indirectly facilitated Cr(VI) reduction by enhancing the reduction of agent diffusion and microbial activity, though its effect was weaker than chemical interventions. Soil grain-size composition influenced Cr(VI) distribution unevenly: larger particles (>0.2 mm) in BC-35 and BC-36-4 acted as main Cr(VI) reservoirs due to accumulated Fe-Mn oxides, whereas BC-36-3 showed increased Cr(VI) in smaller particles (<0.074 mm). μ-XRF and correlation analysis revealed strong positive correlations between Cr and Ca, Fe, Mn, Ni (Pearson coefficient > 0.7, p < 0.01), attributed to adsorption–reduction coupling on iron-manganese oxide surfaces. In contrast, Cr showed weak correlations with Mg, Al, Si, and K. This study clarifies the complex factors governing Cr(VI) behavior in chromium slag soils, providing a scientific basis for remediation strategies such as pH adjustment (4–6) combined with FeSO₄ addition to enhance Cr(VI) reduction efficiency. Full article

The dichromate ion (Cr₂O₇²⁻), a highly toxic chromium VI species, is widely used in industrial processes, generating serious environmental problems when released into water bodies. This investigation proposes the use of a functionalized polymer as an adsorbent material for its removal in the aqueous phase. Poly(butyl methacrylate) (PBMA) was synthesized and modified by impregnation with resorcinarenes derived from long-chain aliphatic aldehydes. To improve the affinity for the dichromate, the resorcinarenes were functionalized with sulfomethyl groups by treatment with Na₂SO₃. The resulting matrices were characterized using IR-ATR, ¹H-NMR, and ¹³C-NMR, and their adsorbent performance was evaluated via UV-Vis spectroscopy in batch extraction assays. The results showed that the functionalized polymer exhibited a higher adsorption capacity than the base polymer, reaching up to 81.1% removal at pH 5.0 in one hour. These results highlight the potential of PBMA as an effective support and raise a promising research perspective for functionalized resorcinarenes in the development of new materials for the treatment of contaminated water. Full article

This study introduces an advanced strategy for improving microbial fuel cell (MFC) performance in hexavalent chromium (Cr(VI)) wastewater treatment. A high-performance nano-iron sulfide (nano-FeS) hybridized biocathode was developed by regulating glucose concentration and applying an external voltage. The combination of a glucose concentration of 1000 mg/L and a 0.2 V applied voltage greatly promoted the in situ biosynthesis of nano-FeS, resulting in smaller particle sizes and increased quantities within the biocathode, leading to enhanced electrochemical performance. The MFC with the hybridized biocathode exhibited the highest power density (43.45 ± 1.69 mW/m²) and Cr(VI) removal rate (3.99 ± 0.09 mg/L·h), outperforming the control by 29% and 71%, respectively. The improvements were attributed to the following processes. (1) Nano-FeS provided additional active sites that enhanced electron transfer and electrocatalytic activity, reducing cathode passivation; (2) it protected microorganisms by reducing Cr(VI) toxicity, promoting redox-active substance enrichment and antioxidant enzyme secretion, which maintained microbial activity; (3) the biocathode selectively enriched electroactive and Cr(VI)-reducing bacteria (such as Brucella), fostering a stable and symbiotic microbial community. This study highlights the promising potential of regulating carbon source and external voltage to boost nano-FeS biosynthesis, offering a sustainable and efficient strategy for MFC-based Cr(VI) wastewater treatment with practical implications. Full article

Municipal solid waste (MSW) and refuse-derived fuel (RDF) incineration generate over 20 million tons of residues annually in the EU. These include bottom ash (IBA), fly ash (FA), and air pollution control residues (APCr), which pose significant environmental challenges due to their leaching potential and hazardous properties. While these residues contain valuable metals and reactive mineral phases suitable for carbonation or alkaline activation, chemical, techno-economic, and policy barriers have hindered the implementation of sustainable, full-scale management solutions. Accelerated carbonation technology (ACT) offers a promising approach to simultaneously sequester CO₂ and enhance residue stability. This review provides a comprehensive assessment of waste incineration residue carbonation, covering 227 documents ranging from laboratory studies to field applications. The analysis examines reactor designs and process layouts, with a detailed classification based on material characteristics, operating conditions, investigated parameters, and the resulting pollutant stabilization, CO₂ uptake, or product performance. In conclusion, carbonation-based approaches must be seamlessly integrated into broader waste management strategies, including metal recovery and material repurposing. Carbonation should be recognized not only as a CO₂ sequestration process, but also as a binding and stabilization strategy. The most critical barrier remains chemical: the persistent leaching of sulfates, chromium(VI), and antimony(V). We highlight what we refer to as the antimony problem, as this element can become mobilized by up to three orders of magnitude in leachate concentrations. The most pressing research gap hindering industrial deployment is the need to design stabilization approaches specifically tailored to critical anionic species, particularly Sb(V), Cr(VI), and SO₄²⁻. Full article

This study investigates the hydrothermal synthesis of calcium silicate hydrate (C-S-H) from photovoltaic (PV) waste glass and carbide sludge as a strategy for resource recovery and sustainable chromium removal from wastewater. Waste-derived precursors were co-ground, blended at controlled Ca/Si molar ratios (0.8, 1.0, 1.2), and hydrothermally treated at 180 °C for 96 h to yield C-S-H with tunable morphology and crystallinity. Comprehensive characterization using XRD, FT-IR, SEM-EDX, and UV-Vis spectroscopy revealed that a Ca/Si ratio of 1.0 produced a well-ordered tobermorite/xonotlite structure with a high surface area and fibrous network, which is optimal for adsorption. Batch adsorption experiments showed that this material achieved rapid and efficient Cr(III) removal, exceeding 90% uptake within 9 h through a combination of surface complexation, ion exchange (Ca²⁺/Na⁺ ↔ Cr³⁺), and precipitation of CaCrO₄ phases. Morphological and structural evolution during adsorption was confirmed by SEM, FT-IR, and XRD, while EDX mapping established the progressive incorporation of Cr into the C-S-H matrix. These findings highlight the viability of upcycling industrial waste into advanced C-S-H sorbents for heavy metal remediation. Further work is recommended to address sorbent regeneration, long-term stability, and application to other contaminants, providing a foundation for circular approaches in advanced wastewater treatment. Full article

Chabazite, a tectosilicate mineral, belongs to the zeolite group and has been widely used for the adsorptive removal of a number of cationic contaminants from the aqueous phase. However, a negatively charged chabazite surface can be altered by chemical modification in order to change its adsorption abilities towards anions. This study reports the potential for the removal of hexavalent chromium ions from aqueous solutions by modified chabazite. In this regard, natural chabazite was modified by the immobilization of HDTMA-Br to achieve double-layer coverage on its surface, defined as the double external cation exchange capacity. Next, a batch adsorption system was applied to study the adsorption of inorganic Cr(VI) anions from aqueous solutions. The process equilibrium was described by 11 theoretical isotherm equations, while 6 adsorption kinetics were represented by four models. Among those tested, the most appropriate model for the description of the studied process kinetics was the pseudo-second order irreversible model. The obtained results suggest that Cr(VI) adsorption takes place according to a complex mechanism comprising both Langmuir-type sorption with the maximum adsorption capacity of modified chabazite, approx. 9.3–9.9 mg g⁻¹, and the trapping of Cr(VI) inside the capillaries of the amorphous sorbent, making it a viable option for water treatment applications. Full article

Chromium (III) ions are essential for biological functions, whereas chromium (VI) ions (Cr (VI)) pose toxicity risks to both humans and animals. Therefore, it is crucial to remove these ions from industrial sources. In this work, to remove hazardous Cr (VI) from wastewater or convert it to Cr (III), catechol-modified alkali lignin (CAL) was prepared using catechol, acetone, and alkali lignin, which is a byproduct in the paper-pulping process. The sample was characterized using a combination of techniques, including scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Various factors influencing the adsorption behavior of CAL were investigated. The adsorption behavior aligns with the pseudo-second-order kinetic model and adheres to the Langmuir isotherm model. CAL simultaneously achieves Cr (VI) adsorption (498.4 mg/g) and reduction (54.6% to Cr (III)), surpassing single-function lignin adsorbents by integrating catechol’s redox capacity with lignin’s structural stability, which is another way to efficiently utilize Cr (VI) solutions. The mechanism of adsorption and reduction is discussed, which is influenced by its functional groups. In brief, this method paves a new path for the utilization of alkali lignin and provides novel opportunities for the removal of Cr (VI) contamination. Full article

Significant heavy metals contamination is often caused by rapid industrialization, which is devastating to both public health and the environment. Conventional processes of metal removal also result in the accumulation of secondary waste. This work proposes the use of a novel fungal biomass (microwave heat dried) from Arthrinium malaysianum for the biosorption of toxic chromium. We have meticulously explored and investigated the interactions of hexavalent chromium with dried biomass using several cutting-edge techniques like FTIR for studying the involvement of functional groups on the biomass surface, XRD for the surface architecture changes after metal binding, XPS to unravel the reduction of hexavalent chromium into its non-toxic form, and FESEM-EDX for the visualization of the ultra-structure of fungal cell surface. The Langmuir isotherm demonstrates that the maximum removal capacity Q_max of Cr(VI) is 102.310 mgg⁻¹, at a pH of 3.5 with 100% removal of Cr(VI). There were substantial changes in the surface architecture during adsorption, confirmed by FESEM and AFM studies. FTIR and XPS data analysis indicated that carbonyl, hydroxyl, phosphate, and amine groups were responsible for the conversion of Cr(VI) (toxic) to Cr(III) (non-toxic). The IR spectra of biomass treated with Cr showed a decreased C-O stretching intensity and slight shriveling of the -OH band, and the bands in the FTIR spectra at 1642 cm⁻¹ to 1635 cm⁻¹ and at 1549 cm⁻¹ to 1547 cm⁻¹ shifted and appeared quite distinct. XRD revealed that the chromium-treated biomass had greater crystalline features and also the appearance of a wide peak where 2θ = 20°, approximately, indicating an amorphous nature at 576.0 eV and in highly loaded chromium (500 mg/L) biomass, with the Cr2p level displaying a slight shift, eventually terminating in a (576.0 eV) Cr₂O₃ to Cr(III) peak. Since the FTIR and XPS data obtained revealed that Cr(VI) reduces to Cr(III), this fungal biomass can also be used for generating metallic nanoparticles during biosorption. Thus, we suggest that the above-mentioned fungal biomass could be a very useful biomaterial for future translational research. We are in the process of fabricating beads with powdered biomass for further studies. Full article

Hexavalent chromium [Cr(VI)] is a hazardous environmental contaminant, and palladium nanoparticles (PdNPs) have shown promise as catalysts for its reduction. This study explores the primary factor influencing the catalytic performance of PdNPs in Cr(VI) reduction by investigating the crystal structure and composition of PdNPs in fungal-based catalysts. Five Pd-loaded catalysts were synthesized by treating fungal biomass with different chemical reagents, resulting in varying Pd(0) contents. The nanoparticle morphology, chemical states, and functional group interactions during Pd adsorption and reduction were investigated using multiple analytical techniques. The results showed that fungal hyphae remained structurally intact throughout the treatment process. PdNPs smaller than 2 nm were observed, with both Pd(0) and PdO present. The proportion of Pd(0) ranged from 6.4% to 37.2%, depending on the chemical reagent used. In addition, functional groups such as phosphate, amine, hydroxyl, and carboxyl were found to play key roles in palladium binding, underscoring the importance of surface chemistry in the adsorption and reduction process. A strong positive correlation was observed between the Pd(0) content and catalytic activity. Notably, the NCPdSF sample (palladium-loaded biomass treated with sodium formate) exhibited the highest Pd(0) content of 59.2% and achieved the most effective Cr(VI) reduction. These results suggest that Pd(0) content is a key determinant of catalytic efficiency in Cr(VI) reduction and that optimizing chemical treatments to enhance Pd(0) levels can substantially improve catalyst performance. Full article