Manganese-contaminated groundwater treatment by novel bacterial isolates: kinetic study and mechanism analysis using synchrotron-based techniques

Synergistic Catalytic Sites in High-Entropy Metal Hydroxide Organic Framework for Oxygen Evolution Reaction

The integration of multiple elements in a high-entropy state is crucial in the design of high-performance, durable electrocatalysts. High-entropy metal hydroxide organic frameworks (HE-MHOFs) are synthesized under mild solvothermal conditions. This novel crystalline metal-organic framework (MOF) features a random, homogeneous distribution of cations within high-entropy hydroxide layers. HE-MHOF exhibits excellent electrocatalytic performance for the oxygen evolution reaction (OER), reaching a current density of 100 mA cm-2 at ≈1.64 VRHE, and demonstrates remarkable durability, maintaining a current density of 10 mA cm-2 for over 100 h. Notably, HE-MHOF outperforms precious metal-based electrocatalysts despite containing only ≈60% OER active metals. Ab initio calculations and operando X-ray absorption spectroscopy (XAS) demonstrate that the high-entropy catalyst contains active sites that facilitate a multifaceted OER mechanism. This study highlights the benefits of high-entropy MOFs in developing noble metal-free electrocatalysts, reducing reliance on precious metals, lowering metal loading (especially for Ni, Co, and Mn), and ultimately reducing costs for sustainable water electrolysis technologies.

Biomimetic mineralization of hydrated magnesium carbonate for hydrogel reinforcement and heavy metal adsorption

With excessive Mn(Ⅱ) and Cu(Ⅱ) pollution in aquatic environments posing potential health risks to inhabitants, the emergence of carbon capture, utilization and storage (CCUS) technology has promoted the improvement of heavy metal remediation technologies. Using hydrothermal sediment as a crystal seed, rhamnolipid was used to mediate biomimetic mineralization to prepare hydrated magnesium carbonate (HMC) composites to enhance the Mn(Ⅱ)/Cu(Ⅱ) adsorption performance of alginate hydrogels. Hydrothermal sediment is beneficial for accelerating biomimetic mineralization, while rhamnolipid can induce a crystalline phase transformation from dypingite to nesquehonite. The addition of sediment significantly enhanced the compressive mechanical properties and thermal stability of the hydrogels. The adsorption performances of the nesquehonite and dypingite hydrogels were better for Mn(II) and Cu(II), respectively. An increase in the amount of sediment improved the adsorption of Cu(II) by the hydrogels appropriately, resulting in stronger selectivity for Cu(II). The adsorption of Mn(II) and Cu(II) on the hydrogel beads was thermodynamically spontaneous. The inhibitory effects of sodium dodecyl benzene sulfonate (SDBS), fulvic acid (FA) and alginate on Cu(II) adsorption were more obvious than those of bovine serum albumin (BSA). Both the complexation of functional groups on alginate and mineralization by HMC participated in the adsorption of Mn(II) and Cu(II).

Detoxification and metabolism of glyphosate by a Pseudomonas sp. via biogenic manganese oxidation

Biogenic manganese oxides (BMO) are widely distributed in groundwater and provides promise for adsorbing and oxidizing a wide range of micropollutants, however, the continuous biodegradation and bioavailability of micropollutants via cycle biogenic Mn(II) oxidation remains to be elucidated. In this study, glyphosate was degraded and to serve as the nutrient source by a Pseudomonas sp. QJX-1. The addition of glyphosate will not affect the Mn(II) oxidation function of the strain but will affect its Mn(II) oxidation process and effect. The glyphosate degradation products could further be used as the C, N and P sources for bacterium growth. Analysis of the RNA-seq data suggested that Mn(II) oxidation driven by oxidoreductases for glyphosate degradation. The long-term column experiments using biological Mn(II) cycling to realize continuous detoxification and metabolism of glyphosate, and thus revealed the synergism effects of biological and chemical conversion on toxic micropollutants and continuous metabolism in an aquatic ecosystem.

Modification of Multiwalled Carbon Nanotubes and Their Mechanism of Demanganization

Multiwalled carbon nanotubes (MWCNTs) were modified by oxidation and acidification with concentrated HNO₃ and H₂SO₄, and the modified multiwalled carbon nanotubes (M-MWCNTs) and raw MWCNTs were characterized by several analytical techniques. Then the demanganization effects of MWCNTs and M-MWCNTs were well investigated and elucidated. The experimental data demonstrated that the adsorption efficiency of Mn(II) could be greatly promoted by M-MWCNTs from about 20% to 75%, and the optimal adsorption time was 6 h and the optimal pH was 6. The results of the kinetic model studies showed that Mn(II) removal by M-MWCNTs followed the pseudo-second-order model. Isothermal studies were conducted and the results demonstrated that the experimental data fitted well with the three models. The reliability of the experimental results was well verified by PSO-BP simulation, and the present conclusion could be used as a condition for further simulation. The research results provide a potential technology for promoting the removal of manganese from wastewater; at the same time, the application of various mathematical models also provides more scientific ideas for the research of the mechanism of adsorption of heavy metals by nanomaterials.

A Review of Manganese-Oxidizing Bacteria (MnOB): Applications, Future Concerns, and Challenges

Groundwater serving as a drinking water resource usually contains manganese ions (Mn2+) that exceed drinking standards. Based on the Mn biogeochemical cycle at the hydrosphere scale, bioprocesses consisting of aeration, biofiltration, and disinfection are well known as a cost-effective and environmentally friendly ecotechnology for removing Mn2+. The design of aeration and biofiltration units, which are critical components, is significantly influenced by coexisting iron and ammonia in groundwater; however, there is no unified standard for optimizing bioprocess operation. In addition to the groundwater purification, it was also found that manganese-oxidizing bacteria (MnOB)-derived biogenic Mn oxides (bioMnOx), a by-product, have a low crystallinity and a relatively high specific surface area; the MnOB supplied with Mn2+ can be developed for contaminated water remediation. As a result, according to previous studies, this paper summarized and provided operational suggestions for the removal of Mn2+ from groundwater. This review also anticipated challenges and future concerns, as well as opportunities for bioMnOx applications. These could improve our understanding of the MnOB group and its practical applications.

Efficient Mn(II) removal mechanism by Serratia marcescens QZB-1 at high manganese concentration

Manganese (Mn(II)) pollution has recently increased and requires efficient remediation. In this study, Serratia marcescens QZB-1, isolated from acidic red soil, exhibited high tolerance against Mn(II) (up to 364 mM). Strain QZB-1 removed a total of 98.4% of 18 mM Mn(II), with an adsorption rate of 71.4% and oxidation rate of 28.6% after incubation for 48 h. The strain synthesized more protein (PN) to absorb Mn(II) when stimulated with Mn(II). The pH value of the cultural medium continuously increased during the Mn(II) removal process. The product crystal composition (mainly MnO₂ and MnCO₃), Mn-O functional group, and element-level fluctuations confirmed Mn oxidation. Overall, strain QZB-1 efficiently removed high concentration of Mn(II) mainly via adsorption and showed great potential for manganese wastewater removal.

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

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

Metallo-inhibition of Mnx, a bacterial manganese multicopper oxidase complex

The manganese oxidase complex, Mnx, from Bacillus sp. PL-12 contains a multicopper oxidase (MCO) and oxidizes dissolved Mn(II) to form insoluble manganese oxide (MnO₂) mineral. Previous kinetic and spectroscopic analyses have shown that the enzyme's mechanism proceeds through an activation step that facilitates formation of a series of binuclear Mn complexes in the oxidation states II, III, and IV on the path to MnO₂ formation. We now demonstrate that the enzyme is inhibited by first-row transition metals in the order of the Irving-Williams series. Zn(II) strongly (K_i ~ 1.5 μM) inhibits both activation and turnover steps, as well as the rate of Mn(II) binding. The combined Zn(II) and Mn(II) concentration dependence establishes that the inhibition is non-competitive. This result is supported by electron paramagnetic resonance (EPR) spectroscopy, which reveals unaltered Mnx-bound Mn(II) EPR signals, both mono- and binuclear, in the presence of Zn(II). We infer that inhibitory metals bind at a site separate from the substrate sites and block the conformation change required to activate the enzyme, a case of allosteric inhibition. The likely biological role of this inhibitory site is discussed in the context of Bacillus spore physiology. While Cu(II) inhibits Mnx strongly, in accord with the Irving-Williams series, it increases Mnx activation at low concentrations, suggesting that weakly bound Cu, in addition to the four canonical MCO-Cu, may support enzyme activity, perhaps as an electron transfer agent.