Heavy metal adsorption with biogenic manganese oxides generated by Pseudomonas putida strain MnB1

Reviewing arsenic biomineralization: An upcoming strategy for mining wastewater treatment

Human activities are the main cause of arsenic contamination in the environment and water resources, being the mining industry an important source of arsenic contamination because this element is released into the environment in solid, liquid, and gaseous wastes. Currently, several physical and chemical processes could be used for the removal of arsenic in water, but these alternatives depend on the concentration of arsenic. At low concentrations (nanograms or micrograms per liter) arsenic can be removed by membrane technologies. When arsenic is at high concentrations (milligrams or grams per liter), treatment options are reduced to inefficient processes of high economic cost and poor chemical stability of the precipitate, returning consequently arsenic into the environment. Biomineralization is a biological process where microorganisms induce the formation of minerals. This bioprocess has gained interest in recent years for the removal of contaminants from liquid effluents. This review details the harmful effects of arsenic on the health and exposes the relevance of arsenic contamination related to mining activity, whose effluents contain high concentration of arsenic. It also describes and analyzes advances in arsenic treatment strategies through biomineralization using microorganisms, such as sulfate-reducing bacteria, iron- and manganese-oxidizing microorganisms, and ureolytic microorganisms, detailing aspects of effectiveness, applicability, chemical stability of biominerals and future perspectives in their industrial application. To our knowledge, there are no previous reports compiling, analyzing, and explaining in detail the biomineralization of arsenic as a single element. The importance of this review is to deliver in a summarized and systematized way the main aspects and perspectives on the application of microorganisms to remove toxic elements, such as arsenic, from effluents.

Removal of Heavy Metals by Pseudomonas sp. - Model Fitting and Interpretation

Industrial and urban modernization processes generate significant amounts of heavy metal wastewater, which brings great harm to human production and health. The biotechnology developed in recent years has gained increasing attention in the field of wastewater treatment due to its repeatable regeneration and lack of secondary pollutants. Pseudomonas, being among the several bacterial biosorbents, possesses notable benefits in the removal of heavy metals. These advantages encompass its extensive adsorption capacity, broad adaptability, capacity for biotransformation, potential for genetic engineering transformation, cost-effectiveness, and environmentally sustainable nature. The process of bacterial adsorption is a complex phenomenon involving several physical and chemical processes, including adsorption, ion exchange, and surface and contact phenomena. A comprehensive investigation of parameters is necessary in order to develop a mathematical model that effectively measures metal ion recovery and process performance. The aim of this study was to explore the latest advancements in high-tolerance Pseudomonas isolated from natural environments and evaluate its potential as a biological adsorbent. The study investigated the adsorption process of this bacterium, examining key factors such as strain type, contact time, initial metal concentration, and pH that influenced its effectiveness. By utilizing dynamic mathematical models, the research summarized the biosorption process, including adsorption kinetics, equilibrium, and thermodynamics. The findings indicated that Pseudomonas can effectively purify water contaminated with heavy metals and future research will aim to enhance its adsorption performance and expand its application scope for broader environmental purification purposes.

A method for studying the influence of Mn oxyhydroxides on the trace element content of aquatic bryophytes

The main objective of this study was to develop and test a method of separating externally deposited Mn oxyhydroxides and co-precipitated elements from samples of aquatic moss (the moss Fontinalis antipyretica). The method, which uses 0.1 M hydroxylamine to dissolve the oxyhydroxides, was tested with samples collected in rivers with slightly acidic, well‑oxygenated waters, where high rates of Mn precipitation occur. The method was effective (it extracted up to 84 % of the Mn) and selective (Fe oxyhydroxides were not extracted). The elements Ba, Cd, Zn and Ni were associated with the Mn oxyhydroxides, while Al, As, Cr, Cu, Fe, Hg and Pb were not. Deposition of Mn therefore increased the concentration of some elements in the moss samples. However, as Mn precipitation depends on Eh and pH, which are independent of the concentrations of the elements in water, the relationship between water and moss element concentrations is not clear (i.e. the data are noisy). This is a problem in biomonitoring studies, which assume a close relationship between element concentrations in moss and water. The value of the proposed extraction method is that it can be used to correct the effect of Mn deposition. We present an example of this correction applied to the Cd concentrations in the test data. We found that the noise introduced by the Mn, including age-related effects (observed by comparing concentrations in 0-2.5 and 2.2-5.0 cm sections from the shoot apex), can be reduced. Additionally, the correction revealed recent increases in Cd concentrations in one site that were not observed in the uncorrected data. Another finding of interest was the low content of total Mn and different extractability (of most elements) observed in moss samples collected in alkaline waters. Finally, we discuss how future studies designed for different environmental scenarios can benefit from application of the proposed method.

Formation of Biogenic Manganese Oxide Nodules on Hyphae of a New Fungal Isolate of Periconia That Immobilizes Aqueous Copper

Mn(II)-oxidizing microorganisms are considered to play significant roles in the natural geochemical cycles of Mn and other heavy metals because the insoluble biogenic Mn oxides (BMOs) that are produced by these microorganisms adsorb other dissolved heavy metals and immobilize them as precipitates. In the present study, a new Mn(II)-oxidizing fungal strain belonging to the ascomycete genus Periconia, a well-studied plant-associating fungal genus with Mn(II)-oxidizing activity that has not yet been exami-ned in detail, was isolated from natural groundwater outflow sediment. This isolate, named strain TS-2, was confirmed to oxidize dissolved Mn(II) and produce insoluble BMOs that formed characteristic, separately-located nodules on their hyphae while leaving major areas of the hyphae free from encrustation. These BMO nodules also adsorbed and immobilized dissolved Cu(II), a model analyte of heavy metals, as evidenced by elemental mapping ana-lyses of fungal hyphae-BMO assemblages using a scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX). Analyses of functional genes within the whole genome of strain TS-2 further revealed the presence of multiple genes predicted to encode laccases/multicopper oxidases that were potentially responsible for Mn(II) oxidation by this strain. The formation of BMO nodules may have functioned to prevent the complete encrustation of fungal hyphae, thereby enabling the control of heavy metal concentrations in their local microenvironments while maintaining hyphal functionality. The present results will expand our knowledge of the physiological and morphological traits of Mn(II)-oxidizing Periconia, which may affect the natural cycle of heavy metals through their immobilization.

Startup performance and microbial composition of a pilot-scale rapid sand filter for the treatment of manganese-containing mine water

The inexpensive removal of soluble manganese [Mn(II)] from mine water that contains large quantities of Mn(II) should be prioritized given that large quantities of alkaline reagents are typically used in the chemical treatment of Mn-rich water from abandoned mines. Rapid sand filter (RSF) systems are widely used as a cost-effective technology in drinking water treatment processes to remove iron and Mn from groundwater. Here, we applied a pilot-scale RSF to treat mine water with a neutral pH and containing approximately 22 mg/L of Mn(II). Following a lag phase from its startup (day 1-day 26), Mn removal rates increased to approximately 40% for around 1 month (day 27-day 55) without the use of alkaline reagents but did not increase during further operation. Quantitative elemental analysis revealed Mn oxides on the sand filters during the Mn removal period. The bacterial communities on the RSFs, recorded on day 42 and day 85, were characterized and compared using 16S rRNA gene amplicon sequencing. Although the well-known Mn-oxidizing bacteria (MOB) were not listed among the ten most dominant operational taxonomic units (OTUs) on the sand filters (relative abundances: >0.68%), a significant increase in the OTUs related to well-known alphaproteobacterial MOB, such as Pedomicrobium spp., were observed during the period.

Efficient utilization of biogenic manganese oxides in bioaugmentation columns for remediation of thallium(I) contaminated groundwater

Little attention has been paid to the in situ-generated biogenic manganese oxides (BMnOx) for practical implementation in continuous groundwater remediation systems. The enrichment effects of manganese oxidizing bacteria (MOB) in bioaugmentation columns and the in situ-generated BMnOx for continuous thallium(I) (Tl(I)) removal from groundwater were investigated. Results indicated that Pseudomonas Putida MnB1 (strain MnB1) attached on the groundwater sediments (GS) can achieve a maximum of 97.37 % Mn(II) oxidation and generate 29.6 mg/L BMnOx, which was superior than that of traditional quartz sand (QS). The in situ-generated BMnOx in MOB_GS column effectively removed 10-100 μg/L Tl(I) under the interference of high concentrations of Fe(II) and Mn(II) in groundwater. Distinctive microbial enrichment effects occurred in the bioaugmentation columns under the competition of indigenous microbes in groundwater. The release of Mn(II) from the BMnOx inhibited with the decrease in Tl(I) removal efficiency. XAFS analysis revealed Tl(I) was effectively adsorbed by BMnOx and Mn-O octahedra with Tl-O tetrahedral coordination existed in BMnOx. This study provides an in-depth understanding of the in situ-generated BMnOx for the Tl(I) removal and contributes to the application of BMnOx in groundwater remediation.

BPA degradation using biogenic manganese oxides produced by an engineered Escherichia coli with a non-blue laccase from Bacillus sp. GZB

Bisphenol A (BPA), an endocrine disruptor that is often found in a variety of environmental matrixes, poses a serious health risk. One of the most effective methods for completely degrading BPA is biological oxidation. This study used a non-blue laccase to develop an engineer Escherichia coli strain for the synthesis of biogenic manganese oxides (BMO). The recombinant strain LACREC3 was utilized for the efficient production of BMO. The LACREC3 strain developed the erratic clumps of BMO after prolonged growth with Mn²⁺, as shown by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDS) tests. After 12 days of incubation under liquid culture conditions, a total of 51.97 ± 0.56% Mn-oxides were detected. The Brunauer-Emmett-Teller (BET) surface areas, X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) experiments were further used to characterize the purified BMO. Data revealed that Mn(IV)-oxides predominated in the structure of BMO, which was amorphous and weakly crystalline. The BPA oxidation assay confirmed the high oxidation efficiency of BMO particle. BMO degraded 96.16 ± 0.31% of BPA in total over the course of 60 min. The gas chromatography and mass spectroscopy (GC-MS) identified BPA-intermediates showed that BPA might break down into less hazardous substances that were tested by Photobacterium Phosphoreum in an acute toxicity experiment. Thus, employing BMO generated by a non-blue laccase, this study introduces a new biological technique of metal-oxidation and organic-pollutant degradation.

Biologically-induced synthetic manganese carbonate precipitate (BISMCP) for potential applications in heavy metal removal

Heavy metal pollution of water is a burning issue of today's world. Among several strategies involved for heavy metal remediation purpose, biomineralization has shown great potential. Of late, research has been focused on developing effective mineral adsorbents with reduced time and cost consumption. In this present paper, the Biologically-Induced Synthetic Manganese Carbonate Precipitate (BISMCP) was produced based on the biologically-induced mineralization method, employing Sporosarcina pasteurii in aqueous solutions containing urea and MnCl2. The prepared adsorbent was characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), SEM-energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and BET surface area analyzer. EDX analysis showed the elements in the crystal BISMCP were Mn, C, and O. XRD result of BISMCP determined the crystal structure, which is close to rhodochrosite (MnCO3). Spectral peaks of FTIR at 1641.79 cm-1 confirmed the appearance of C[bond, double bond]O binding, with strong stretching of CO32- in Amide I. From the six kinds of BISMCP produced, sample MCP-6 has the higher specific surface area by BET analysis at 109.01 m2/g, with pore size at 8.76 nm and higher pore volume at 0.178 cm3/g. These specifications will be suitable as an adsorbent for heavy metal removal by adsorption process. This study presents a preliminary analysis of the possibility of BISMCP for heavy metals adsorption using ICP multi-element standard solution XIII (As, Cr, Cd, Cu, Ni, and Zn). BISMCP formed from 0.1 MnCl2 and 30 ml of bacteria volume (MCP-6) produced a better adsorbent material than others concentrations, with the adsorption efficiency of total As at 98.9%, Cr at 97.0%, Cu at 94.7%, Cd at 88.3%, Zn at 48.6%, and Ni at 29.5%. Future work could be examined its efficiency adsorbing individual heavy metals.

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.

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.

Mechanistic and recent updates in nano-bioremediation for developing green technology to alleviate agricultural contaminants

The rise in environmental pollutant levels in recent years is mostly attributable to anthropogenic activities such as industrial, agricultural and other activities. Additionally, these activities may produce excessive levels of dangerous toxicants such as heavy metals, organic pollutants including pesticide and herbicide chemicals, and sewage discharges from residential and commercial sources. With a focus on environmentally friendly, sustainable technology, new technologies such as combined process of nanotechnology and bioremediation are urgently needed to accelerate the cost-effective remediation process to alleviate toxic contaminants than the conventional remediation methods. Numerous studies have shown that nanoparticles possess special qualities including improved catalysis and adsorption as well as increased reactivity. Currently, microorganisms and their extracts are being used as promising, environmentally friendly catalysts for engineered nanomaterial. In the long term, this combination of both technologies called nano-bioremediation may significantly alter the field of environmental remediation since it is more intelligent, safe, environmentally friendly, economical and green. This review provides an overview of soil and water remediation techniques as well as the use of nano-bioremediation, which is made from various living organisms. Additionally, current developments related to the mechanism, model and kinetic studies for remediation of agricultural contaminants have been discussed.

Static magnetic field enhances Cladosporium sp. XM01 growth and fungal Mn(II) oxidation

Fungal Mn oxidation is a crucial pathway in the biogeochemical cycling of toxic substances. However, few studies have aimed to promote the process of fungal Mn oxidation or systematically establish the mechanism of action. The effects of static magnetic field (SMF) treatment on the growth and Mn(II) oxidation capability of an Mn-oxidizing fungus, Cladosporium sp. XM01, were investigated. Results showed that 20.1 mT SMF treatment promoted the growth of strain XM01, and increased the Mn(II) removal rate by accelerating the adsorption and oxidation of Mn(II). In addition, the results of RNA sequencing suggested that SMF mainly stimulated energy metabolism and protein synthesis, accelerating the growth of strain XM01. Notably, KEGG pathway enrichment analysis found that SMF treatment significantly up-regulated the pathway of oxidative phosphorylation system, which is capable of stimulating the generation of superoxide (O₂^•-). Moreover, exposure to 20.1 mT SMF significantly promoted the activities of antioxidant enzymes including SOD and CAT. These results indicate that SMF treatment stimulates the generation of O₂^•- by strain XM01, and therefore, accelerates Mn(II) oxidation. This is a novel study using external SMF treatment to enhance fungal Mn(II) oxidation.

Insights into the synergistic removal mechanisms of thallium(I) by biogenic manganese oxides in a wide pH range

The behavior and mechanism of thallium (Tl) adsorption by biogenic manganese oxides (BMnOx) are poorly understood. In this study, BMnOx was applied for Tl(I) removal from aqueous solution, and the adsorption interactions were systematically revealed for the first time. BMnOx was successfully prepared with high productivity by effectively oxidizing Mn(II) with a manganese oxide bacterium in an optimal Mn(II) concentration range of 4.0-28 mg/L. Compared with other adsorbents, the prepared BMnOx achieved high Tl(I) adsorption capacity over a wide pH range from 3.0 to 9.0 and high humic acid (HA) concentration (40 mg/L) interference. The experimental results were well depicted by pseudo-second-order kinetics and the Langmuir isotherm model, indicating that chemisorption played the dominant role during the adsorption process. The adsorption mechanisms were verified as synergetic interactions of oxidation-precipitation, electrostatic attraction, ion exchange and surface complexation. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) results suggested that 19.46% of the highly toxic Tl(I) was transformed into the much less toxic product Tl₂O₃ after adsorption onto BMnOx. This study provides theoretical guidance for high-concentration Tl(I) decontamination from groundwater by biogenic manganese oxides.

Synthesis, optimization, and characterization of biogenic manganese oxide (BioMnOx) by bacterial isolates from mangrove soils with sorbents property towards different toxic metals

Manganese oxidizing bacteria, Bacillus mycoides and Bacillus subtilis were isolated from mangrove soils and optimized for the removal of Mn(II) with simultaneous production of biogenic manganese oxide (BioMnOx). The removal rate of Mn(II) was 90% in 48 h for B. mycoides and 72 h for B. subtilis under the optimized conditions at pH 7, temperature 37 °C, 120 rpm, with 1% inoculum containing 10 mM MnCl₂. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy dispersive X-Ray analysis (EDAX), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to characterize the synthesized biogenic manganese oxide. BioMnOx by Bacillus mycoides and Bacillus subtilis were identified as Bixbyite (Mn₂O₃) and Hausmannite (Mn₃O₄), respectively, with nano-sized monocrystalline nature. BioMnOx of Bacillus subtilis strain was more efficient in the removal of metals Zn and Co than BioMnOx of Bacillus mycoides except for mercury. The removal property of synthesized BioMnOx could be applied to treat multi-metal containing wastewater.

An efficient manganese-oxidizing fungus Cladosporium halotolerans strain XM01: Mn(II) oxidization and Cd adsorption behavior

The applications of biogenic Mn oxides (BMOs) formed by Mn-oxidizing fungus in decontaminating heavy metals have attracted increasing attention. In this study, an efficient Mn-oxidizing fungus was isolated from soil and identified as Cladosporium halotolerans strain XM01. The Mn(II) adsorption and oxidation activities of this strain were investigated, showing significantly high removal and oxidation rates of soluble Mn(II) of 99.9% and 88.2%, respectively. Dynamic analysis of the Mn(II) removal process demonstrated the oxidation process of Mn(II) to Mn(III) was the rate-limiting step in the Mn(II) metabolic process. The XRD and SAED characterization showed that more layers were orderly accumulated along the c-axis with the formation of fungal BMOs, which might lead to the decrease in its specific surface area. The adsorption of Cd(II) by the formed BMOs was investigated and compared with two typical abiotic Mn oxides, indicating that the adsorption capacity decreased with the following order: immature BMO, mature BMO, δ-MnO₂, acid birnessite, while the fixation capacity decreased in the order of acid birnessite, mature BMO, δ-MnO₂, immature BMO. The inverse correlation between the capacity of Cd(II) adsorption and fixation of immature and mature BMOs was probably attributed to the increase in the layer stacking of BMOs. This result indicates an interesting phenomenon of high reservation of Cd(II) resulting from sequential transformation from strong adsorption to strong fixation with the formation of BMOs. This study offers considerable insights into fungal Mn oxidation mechanisms and provides theoretical guidance for fungal BMOs in heavy metals bioremediation.

Experimental study on treatment of heavy metal-contaminated soil by manganese-oxidizing bacteria

There are many studies on the treatment of heavy metals by manganese-oxidizing bacteria and the reaction is good; the problem of compound pollution of heavy metals in soil has been difficult to solve. In this study, the application of manganese-oxidizing bacteria in soil was studied. The tolerance of manganese-oxidizing strains (Pseudomonas taiwanensis) to environmental conditions and the treatment effect of heavy metals As, Pb, and Cd in aqueous solution were investigated, and the effect of iron-manganese ratio on the treatment effect was discussed. The results showed that the suitable pH conditions for the growth of P. taiwanensis were 5-9, and the salt tolerance was 6% (by sodium chloride). The tolerant concentrations for heavy metals As(V) and Mn(II) were 500 mg L^-1 and 120 mg L^-1, respectively. The strains were enriched by nutrient broth medium. After the logarithmic phase, the bacterial suspension was mixed with ATCC#279 medium at a ratio of 1:10, and a certain amount (10 mg L^-1) of Mn(II) was added. The results of As, Pb, and Cd removal in the composite polluted water phase were 22.09%, 30.75%, and 35.33%, respectively. The molar ratio of manganese and iron affected the removal efficiency of single arsenic, the highest efficiency is 68%, and the ratio of iron to manganese is 1:5. However, when the soil was treated by the same method, the results showed that not all metals were passivated, such as Cu. At the same time, for As, Pb, and Cd, the treatment effects in soil were worse than those in water, perhaps more consideration should be given to environmental conditions, such as soil moisture and temperature, when manganese-oxidizing bacteria are used to treat soil.

Removal of Mn(II) by a nitrifying bacterium Acinetobacter sp. AL-6: efficiency and mechanisms

A nitrifying bacterium Acinetobacter sp. AL-6 showed a high efficiency of 99.05% for Mn(II) removal within 144 h when the Mn(II) concentration was 200 mg L^-1; meanwhile, 64.23% of NH₄⁺-N was removed. With the Mn(II) concentration increased from 25 to 300 mg L^-1, bacterial growth and Mn(II) removal were stimulated. However, due to the electron acceptor competition between Mn(II) oxidation and nitrification reactions, the increase in NH₄⁺-N concentration would inhibit Mn(II) removal. By measuring Mn metabolic form and locating oxidative active factors, it was proved that extracellular oxidation effect played a dominant role in the removal process of Mn(II). The self-regulation of pH during strain metabolism further promoted the occurrence of biological Mn oxidation. Characterization results showed that the Mn oxidation products were tightly attached to the surface of the bacteria in the form of flakes. The product crystal composition (mainly MnO₂ and Mn₂O₃), Mn-O functional group, and element level fluctuations confirmed the biological oxidation information. The changes of -OH, N-H, and -CH₂ groups and the appearance of new functional groups (such as C-H and C-O) provided more possibilities for Mn ion adsorption and bonding.

An Efficient Strategy for Enhancing the Adsorption Capabilities of Biochar via Sequential KMnO4-Promoted Oxidative Pyrolysis and H2O2 Oxidation

In this study, sequential KMnO4-promoted oxidative pyrolysis and H2O2 oxidation were employed to upgrade the adsorption capacities of durian shell biochar for methylene blue (MB) and tetracycline (TC) in an aqueous solution. It was found that the KMnO4/H2O2 co-modification was greatly influenced by pyrolysis temperature and the optimal temperature was 300 °C. Moreover, a low concentration of H2O2 enabled the improvement of the adsorption capabilities greatly with the catalysis of pre-impregnated manganese oxides, addressing the shortcoming of single H2O2 modification. The co-modified biochar exhibited high adsorption capabilities for MB and TC, remarkably surpassed KMnO4- and H2O2- modified biochars as well as pristine biochar. The increase of adsorption capabilities could be mainly contributed to the incorporation of MnOx and carboxyl by KMnO4-promoted oxidative decomposition and Mn-catalyzed H2O2 oxidation. This would provide a novel and efficient method for preparing highly adsorptive biochar using sequential KMnO4-promoted oxidative pyrolysis and H2O2 oxidation.

Biogenic manganese oxides combined with 1-hydroxybenzotriazol and an Mn(II)-oxidizing enzyme from Pleosporales sp. Mn1 oxidize 3,4-dimethoxytoluene to yield 3,4-dimethoxybenzaldehyde

Using soil samples, we screened for microbes that produce biogenic manganese oxides (BMOs) and isolated Mn(II)-oxidizing fungus, namely Pleosporales sp. Mn1 (Mn1). We purified the Mn(II)-oxidizing enzyme from intracellular extracts of Mn1. The enzyme oxidized Mn(II) most effectively at pH 7.0 and 45 °C. The N-terminal amino acid sequence of the purified enzyme possessed homology with multicopper oxidases in fungi. The properties of the enzyme and the effects of the pH and inhibitors on the Mn(II)-oxidization activity suggested that the enzyme is a member of the multicopper oxidase family. The X-ray diffraction pattern of the BMOs produced by Mn1 showed a strong correlation with that of a typical poorly crystalized vernadite (δ-MnO₂). Since BMOs are some of the most reactive materials in the environment, we investigated a potential new application of BMOs as oxidation catalysts. We confirmed that BMOs oxidized aromatic methyl groups when combined with the purified enzyme and a mediator, 1-hydroxybenzotriazole (HBT). BMO oxidation of 3,4-dimethoxytoluene achieved a better yield than that of abiotic MnO₂ and white-rot fungus laccase under acidic and neutral pH conditions. Under neutral pH, the BMOs oxidized 3,4-dimethoxytoluene to yield 200-fold more 3,4-dimethoxybenzaldehyde than that of abiotic MnO₂. This is the first report to reveal that BMOs combined with a Mn(II)-oxidizing enzyme and mediator can oxidize aromatic hydrocarbons to yield corresponding aldehydes.

Green-synthesized nanocatalysts and nanomaterials for water treatment: Current challenges and future perspectives

Numerous hazardous environmental pollutants in water bodies, both organic and inorganic, have become a critical global issue. As greener and bio-synthesized versions of nanoparticles exhibit significant promise for wastewater treatment, this review discusses trends and future prospects exploiting the sustainable applications of green-synthesized nanocatalysts and nanomaterials for the removal of contaminants and metal ions from aqueous solutions. Recent trends and challenges about these nanocatalysts and nanomaterials and their potential applications in wastewater treatment and water purification are highlighted including toxicity and biosafety issues. This review delineates the pros and cons and critical issues pertaining to the deployment of these nanomaterials endowed with their superior surface area, mechanical properties, significant chemical reactivity, and cost-effectiveness with low energy consumption, for removal of hazardous materials and contaminants from water; comprehensive coverage of these materials for industrial wastewater remediation, and their recovery is underscored by recent advancements in nanofabrication, encompassing intelligent and smart nanomaterials.

Microbiomes in a manganese oxide producing ecosystem in the Ytterby mine, Sweden: impact on metal mobility

Microbe-mediated precipitation of Mn-oxides enriched in rare earth elements (REE) and other trace elements was discovered in tunnels leading to the main shaft of the Ytterby mine, Sweden. Defining the spatial distribution of microorganisms and elements in this ecosystem provide a better understanding of specific niches and parameters driving the emergence of these communities and associated mineral precipitates. Along with elemental analyses, high-throughput sequencing of the following four subsystems were conducted: (i) water seeping from a rock fracture into the tunnel, (ii) Mn-oxides and associated biofilm; referred to as the Ytterby Black Substance (YBS) biofilm (iii) biofilm forming bubbles on the Mn-oxides; referred to as the bubble biofilm and (iv) fracture water that has passed through the biofilms. Each subsystem hosts a specific collection of microorganisms. Differentially abundant bacteria in the YBS biofilm were identified within the Rhizobiales (e.g. Pedomicrobium), PLTA13 Gammaproteobacteria, Pirellulaceae, Hyphomonadaceae, Blastocatellia and Nitrospira. These taxa, likely driving the Mn-oxide production, were not detected in the fracture water. This biofilm binds Mn, REE and other trace elements in an efficient, dynamic process, as indicated by substantial depletion of these metals from the fracture water as it passes through the Mn deposit zone. Microbe-mediated oxidation of Mn(II) and formation of Mn(III/IV)-oxides can thus have considerable local environmental impact by removing metals from aquatic environments.

A manganese-oxidizing bacterial consortium and its biogenic Mn oxides for dye decolorization and heavy metal adsorption

Manganese (Mn) contamination is a common environmental problem in the world and manganese oxidizing bacteria (MOB) play important roles in bioremediation of heavy metal and organic pollution. In this study, a novel MOB consortium AS containing core microbes of Sphingobacterium and Bacillus was acclimated from Mn-contaminated rivulet sediments. The MOB consortium AS presented good Mn(II) removal performance under 500-10,000 mg/L Mn(II), with Mn(II) removal capacities ranging from 481 to 3478 mg/L. In coexistence systems of Mn(II) and Fe(II), Ni(II), Cu(II), and Zn(II), the MOB consortium AS removed 98%, 91%, 99%, and 76% of Mn(II), respectively. Additionally, the MOB consortium AS could utilize multiple carbon sources (e.g., Chitosan, β-Cyclodextrin, and Phenanthrene) to remove Mn(II), with Mn(II) removal efficiencies ranging from 11% to 97%. Meanwhile, XRD, XPS, FTIR, SEM, and EDS analyses reflected that biogenic Mn oxides (bio-MnOx-C) contained C, O, Mn (Mn(II) and Mn(IV)) and embodied in rhodochrosite and birnessite. The bio-MnOx-C exhibited second-order kinetic reaction for removal of dye, with corresponding decolorization capacities of 22.0 mg/g for methylene blue and 23.8 mg/g for crystal violet. In addition, bio-MnOx-C showed adsorption capacities of 159.0 mg/g for Cu(II), 130.7 mg/g for Zn(II), and 123.3 mg/g for Pb(II). Overall, this study illustrates consortium AS and bio-MnOx-C have great potentials in remediation of pollution caused by heavy metals and organic pollutants.

Mineral Materials Coated with and Consisting of MnOx-Characteristics and Application of Filter Media for Groundwater Treatment: A Review

For groundwater treatment, the technologies involving oxidation on MnOx filter bed are beneficial, common, and effectively used. The presence of MnOx is the mutual feature of filter media, both MnOx-coated mineral materials like quartz sand and gravel, chalcedonite, diatomite, glauconite, zeolite, or anthracite along with consisting of MnOx manganese ores. This review is based on the analysis of research and review papers, commercial data sheets, and standards. The paper aimed to provide new suggestions and useful information for further investigation of MnOx filter media for groundwater treatment. The presented compilations are based on the characteristics of coatings, methods, and conditions of its obtaining and type of filter media. The relationship between the properties of MnOx amendments and the obtained purification effects as well as the commonly used commercial products, their features, and applications have been discussed. The paper concludes by mentioning about improving catalytic/adsorption properties of non-reactive siliceous media opposed to ion-exchange minerals and about possible significance of birnessite type manganese oxide for water treatment. Research needs related to the assessment of the use MnOx filter media to heavy metals removal from groundwater in field operations and to standardize methodology of testing MnOx filter media for water treatment were identified.

Manganese(II) Oxidizing Bacteria as Whole-Cell Catalyst for β-Keto Ester Oxidation

Manganese oxidizing bacteria can produce biogenic manganese oxides (BMO) on their cell surface and have been applied in the fields of agriculture, bioremediation, and drinking water treatment to remove toxic contaminants based on their remarkable chemical reactivity. Herein, we report for the first time the synthetic application of the manganese oxidizing bacteria, Pseudomonas putida MnB1 as a whole-cell biocatalyst for the effective oxidation of β-keto ester with excellent yield. Differing from known chemical protocols toward this transformation that generally necessitate the use of organic solvents, stoichiometric oxygenating agents and complex chemical catalysts, our strategy can accomplish it simply under aqueous and mild conditions with higher efficiency than that provided by chemical manganese oxides. Moreover, the live MnB1 bacteria are capable of continuous catalysis for this C-O bond forming reaction for several cycles and remain proliferating, highlighting the favorable merits of this novel protocol for sustainable chemistry and green synthesis.

Discovery of a novel native bacterium of Providencia sp. with high biosorption and oxidation ability of manganese for bioleaching of heavy metal contaminated soils

Heavy metal removal from contaminated soils is a long-term challenging problem important for global economics, environment, and human health. Marine and freshwater-originated Mn(II)-oxidizing bacteria are considered as the promising bioremediation agents for environmental applications. However, practical application of soil-originated Mn(II)-oxidizing bacteria remains to be developed for contaminated soil remediation. In this work, the Mn(II) biosorption/oxidation mechanism of a new soil-originated bacterium and its bioleaching efficiency of heavy metals from soils was studied in detail. First, we found, isolated and identified a new highly Mn(II)-tolerant bacterial strain Providencia sp. LLDRA6 from heavy metal-contaminated soils. Next, strain LLDRA6 demonstrated its high Mn(II) biosorption capacity in aqueous solution. Then, Mn(II) adsorption by LLDRA6 was largely proven to be a synergistic effect of (i) Mn(II) precipitation on the cell surface, (ii) oxidation of Mn(II) into BioMnO_x on the cell surface, and (iii) intracellular accumulation of insoluble MnCO₃. Finally, combination bioleaching by the bacterium of Providencia sp. LLDRA6 and its formed BioMnO_x was proposed to develop a potential environment-friendly and cost-effective technique to remediate severely heavy metal-contaminated soils. The bioleaching tests demonstrated that the combination of Providencia sp. LLDRA6 and BioMnO_x exhibited an excellent removal efficiency for heavy metals of Pb (81.72%), Cr (88.29%), Cd (90.34%), Cu (91.25%), Mn (56.13%), and Zn (59.83%) from contaminated soils, resulting in an increase of removal efficiency in the range of 1.68-26.4% compared to Providencia sp. LLDRA6 alone. Moreover, the bacterial leachate facilitated the residual fraction of metals to transform into the easily migratory fractions in soils. These findings have demonstrated that strain LLDRA6 has high adsorption ability to remove heavy metals from contaminated soils, thus providing a promising bio-adsorbent for environmental bioremediation.

Simultaneous removal of As(III) and Cu(II) from real bottom ash leachates by manganese-oxidizing aerobic granular sludge: Performance and mechanisms

Manganese-oxidizing aerobic granular sludge (Mn-AGS) is a novel extension of AGS technology to treat arsenic (As) in organic wastewater. In this study, Mn-AGS was first applied to treat real wastewater (bottom ash leachates) containing high levels of As(III) and Cu(II) in a sequencing batch reactor (SBR) for 91 days. Influent and effluent As(III), As(V), Cu(II), as well as pH and chemical oxygen demand (COD) were monitored daily, and sludge was collected regularly for morphological observation, chemical characterization, and microbial analysis. The results indicated that As(III) and Cu(II) could be efficiently removed from wastewater (∼83% and ∼100%, respectively), but the performance was sensitive to pH variation, especially for As(III). The removed As and Cu were mostly bound to carbonates (60.2 ± 2.0% and 70.0 ± 0.6%, respectively) and Fe/Mn oxides (28.2 ± 1.6% and 14.6 ± 0.5%, respectively) in the final sludge. Influent As(III) was partially oxidized into As(V), and high fractions of As(V) were obtained in the Fe/Mn oxide-bound phase. Unexpectedly, microbial analysis revealed that community richness was only slightly changed when the influent was acidized (pH 4.0) but greatly reduced after the influent pH back to 6.0. It could be explained by that acid-fast bacteria rapidly grew after pH recovery and eliminated non-acid-fast bacteria. This work further supported the practical application of Mn-AGS to treat As(III)-containing organic wastewaters.

Coupling the phenolic oxidation capacities of a bacterial consortium and in situ-generated manganese oxides in a moving bed biofilm reactor (MBBR)

Phenolic wastewater containing phenol and 4-chlorophenol pose a risk to the environment and to human health. Treating them using chemical-biological coupling method is challenging. In this study, manganese oxidizing bacteria (MnOB) were enriched in moving bed biofilm reactor (MBBR) using synthetic phenol wastewater (800 mg L^-1) to facilitate in situ production of biogenic manganese oxides (BioMnOx) after 90 days of operation. Then, 4-chlorophenol (4-CP) was added to the MBBR to simulate mixed phenolic wastewater. Comparing the MBBR (R1) without feeding Mn(II) and the MBBR with BioMnOx (R2) production, R2 exhibited robust phenol and 4-CP removal performance. 16S rRNA gene sequencing was employed to determine the microbial community. Subsequently, a batch experiment demonstrated that partly purified BioMnOx does not exhibits a capacity for phenol removal, but can efficiently remove 4-CP. Interestingly, 5-chloro-2-hydroxymuconic semialdehyde was found in the products of 4-CP degradation, which was the unique product of 4-CP degradation by catechol 2,3-dioxygenase (C23O). In both reactors, only catechol 1,2-dioxygenase (C12O) activity from microbes can be detected, indicating that the existence of BioMnOx provide an alternative pathway in addition to microbe driven 4-CP degradation. Overall, MBBR based MnOB enrichment under high phenol concentration was achieved, and 4-CP/phenol removal can be accelerated by in situ-formed BioMnOx. Considering the C23O-like activity of BioMnOx, our results suggest a new coupling strategy that involves nanomaterials and a microbial consortium.

Removal of Manganese(II) from Acid Mine Wastewater: A Review of the Challenges and Opportunities with Special Emphasis on Mn-Oxidizing Bacteria and Microalgae

Many global mining activities release large amounts of acidic mine drainage with high levels of manganese (Mn) having potentially detrimental effects on the environment. This review provides a comprehensive assessment of the main implications and challenges of Mn(II) removal from mine drainage. We first present the sources of contamination from mineral processing, as well as the adverse effects of Mn on mining ecosystems. Then the comparison of several techniques to remove Mn(II) from wastewater, as well as an assessment of the challenges associated with precipitation, adsorption, and oxidation/filtration are provided. We also critically analyze remediation options with special emphasis on Mn-oxidizing bacteria (MnOB) and microalgae. Recent literature demonstrates that MnOB can efficiently oxidize dissolved Mn(II) to Mn(III, IV) through enzymatic catalysis. Microalgae can also accelerate Mn(II) oxidation through indirect oxidation by increasing solution pH and dissolved oxygen production during its growth. Microbial oxidation and the removal of Mn(II) have been effective in treating artificial wastewater and groundwater under neutral conditions with adequate oxygen. Compared to physicochemical techniques, the bioremediation of manganese mine drainage without the addition of chemical reagents is relatively inexpensive. However, wastewater from manganese mines is acidic and has low-levels of dissolved oxygen, which inhibit the oxidizing ability of MnOB. We propose an alternative treatment for manganese mine drainage that focuses on the synergistic interactions of Mn in wastewater with co-immobilized MnOB/microalgae.

Characterization of the Cd(II) and nitrate removal by bacterium Acinetobacter sp. SZ28 under different electron donor conditions

In this study, zero-valent iron (ZVI), nanoscale zero-valent iron (nZVI), Fe(II), and Mn(II) were investigated for their effects on mixotrophic denitrification coupled with cadmium (Cd(II)) adsorption process by Acinetobacter sp. SZ28. The removal rates of nitrate were 0.228 mg L^-1 h^-1 (ZVI), 0.133 mg L^-1 h^-1 (nZVI), 0.309 mg L^-1 h^-1 (Fe(II)) and 0.234 mg L^-1 h^-1 (Mn(II)), respectively. The Cd(II) removal efficiencies were 97.23% (ZVI), 95.79% (nZVI), 80.63% (Fe(II)), and 84.58% (Mn(II)), respectively. Meteorological chromatography analysis indicated that the characteristics of gas composition were different under different electron donor conditions. Moreover, characterization of bacterial metabolites produced by strain SZ28 under different conditions was analyzed. Sequence amplification identified the presence of the nitrate reductase gene (napA) and Mn(II)-oxide gene (cumA) in strain SZ28. The results of XRD and SEM indicated that ZVI, nZVI, Fe(II), and Mn(II) were oxidized into corresponding oxides. XPS spectra indicated that the Cd(II) was adsorbed onto biogenic precipitation.

Coprecipitation of Co2+, Ni2+ and Zn2+ with Mn(III/IV) Oxides Formed in Metal-Rich Mine Waters

Manganese oxides are widespread in soils and natural waters, and their capacity to adsorb different trace metals such as Co, Ni, or Zn is well known. In this study, we aimed to compare the extent of trace metal coprecipitation in different Mn oxides formed during Mn(II) oxidation in highly concentrated, metal-rich mine waters. For this purpose, mine water samples collected from the deepest part of several acidic pit lakes in Spain (pH 2.7–4.2), with very high concentration of manganese (358–892 mg/L Mn) and trace metals (e.g., 795–10,394 µg/L Ni, 678–11,081 µg/L Co, 259–624 mg/L Zn), were neutralized to pH 8.0 in the laboratory and later used for Mn(II) oxidation experiments. These waters were subsequently allowed to oxidize at room temperature and pH = 8.5–9.0 over several weeks until Mn(II) was totally oxidized and a dense layer of manganese precipitates had been formed. These solids were characterized by different techniques for investigating the mineral phases formed and the amount of coprecipitated trace metals. All Mn oxides were fine-grained and poorly crystalline. Evidence from X-Ray Diffraction (XRD) and Scanning Electron Microscopy coupled to Energy Dispersive X-Ray Spectroscopy (SEM–EDX) suggests the formation of different manganese oxides with varying oxidation state ranging from Mn(III) (e.g., manganite) and Mn(III/IV) (e.g., birnessite, todorokite) to Mn(IV) (e.g., asbolane). Whole-precipitate analyses by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), and/or Atomic Absorption Spectrometry (AAS), provided important concentrations of trace metals in birnessite (e.g., up to 1424 ppm Co, 814 ppm Ni, and 2713 ppm Zn), while Co and Ni concentrations at weight percent units were detected in asbolane by SEM-EDX. This trace metal retention capacity is lower than that observed in natural Mn oxides (e.g., birnessite) formed in the water column in a circum-neutral pit lake (pH 7.0–8.0), or in desautelsite obtained in previous neutralization experiments (pH 9.0–10.0). However, given the very high amount of Mn sorbent material formed in the solutions (2.8–4.6 g/L Mn oxide), the formation of these Mn(III/IV) oxides invariably led to the virtually total removal of Co, Ni, and Zn from the aqueous phase. We evaluate these data in the context of mine water pollution treatment and recovery of critical metals.

A novel manganese oxidizing bacterium-Aeromonas hydrophila strain DS02: Mn(II) oxidization and biogenic Mn oxides generation

The extensive applications of biogenic manganese oxides (BioMnOx) generated by manganese oxidizing bacteria (MOB) have attracted considerable attentions. In this study, we report on a novel MOB that has been isolated from sediments and identified as Aeromonas hydrophila strain DS02. The Mn(II) oxidation activity of strain DS02 under Mn(II) stress and the application of the associated BioMnOx products were investigated. Nearly 90.0% (495 mg L^-1) of the soluble Mn(II) were removed and 45.6% (240 mg L^-1) was converted to Mn(III/IV). Fitting the XPS data showed that Mn(IV)-oxide is the major component (82.0%) of the flake-shaped BioMnOx, corresponding to an average Mn oxidation number of 3.71. When the BioMnOx were coupled with the PMS activation, a 99.5% catalytic degradation of 2,4-dimethylaniline was observed after 80 min, revealing a high degradation efficiency.

Non-competitive and competitive adsorption of Cd2+, Ni2+, and Cu2+ by biogenic vaterite

Ubiquitous bio-minerals exert significant effects on the migration and transformation of metal ions in the environment, however, research into the adsorption of heavy metals by biogenic vaterite (BV) has rarely been reported. The aim of our research was to evaluate the removal effects of Cd²⁺, Ni²⁺, and Cu²⁺ in single and multi-metal ion aqueous solutions using BV induced by Bacillus subtilis. The results demonstrate that the adsorption data of BV for metal ions are more accurately fitted to the Langmuir model compared with the Freundlich model. The max adsorption capacity (mg/g) order of BV was Ni (270.27) > Cu (178.57) > Cd (172.41) in a single-metal system, and Cu (175.44) > Ni (94.34) > Cd (30.30) in a multi-metal system (pH = 5.0, 2.5 g/L). A competitive effect exists amongst heavy metals in multi-metal ion systems, and Cu²⁺ adsorption is less affected by other two ions. Furthermore, BV can maintain favourable adsorption characteristics even in a very strong acidic environment (pH = 3.0), and its adsorptive capability becomes more favourable at higher temperatures. Kinetic analysis shows that the adsorption process can be better described by a pseudo-second-order model. XRD, FTIR, and SEM-EDS results reveal that metal ion adsorption on BV mostly happened through physical means, and the favourable adsorption characteristics of BV might be attributable to its larger specific surface area, aggregated spherical polyporous and organic-inorganic structure.

Synthesis and applications of biogenic nanomaterials in drinking and wastewater treatment

The continuous increase in water pollution by various organic & inorganic contaminants has become a major issue of concern worldwide. Furthermore, the anthropogenic activities for the manufacturing of various products have boosted this problem manifold. To overcome this serious issue, nanotechnology has initiated to explore various proficient strategies to treat waste water in a more precise and accurate way with the support of various nanomaterials. In recent times, nanosized materials have proved their applicability to provide clean and affordable water treatment technologies. The exclusive features such as high surface area and mechanical properties, greater chemical reactivity, lower cost and energy, efficient regeneration for reuse allow the nanomaterials perfect for water remediation. But the conventional routes of synthesis of nanomaterials encompass the involvement of hazardous and volatile chemicals; therefore the use of nanomaterials further creates the secondary pollution. This issue has intrigued the scientists to develop biogenic pathways and procedures which are environmentally safer and inexpensive. It has led to the new trends that involve developing bio-inspired nano-scale adsorbents and catalysts for the removal and degradation of a wide range of water pollutants. Carbohydrates, proteins, polymers, flavonoids, alkaloids and several antioxidants obtained from plants, bacteria, fungi, and algae have proven their effectiveness as capping and stabilizing agents during manufacture of nanomaterials. Application of biogenic nanomaterials for waste water treatment is relatively newer but rapidly escalating area of research. In the present review, promises and challenges for the synthesis of various biogenic nanomaterials and their potential applications in waste water treatment and/or water purification have been discussed.

Adsorption performance and mechanisms of Pb(II), Cd(II), and Mn(II) removal by a β-cyclodextrin derivative

In this study, the novel adsorbent PVA-TA-βCD was synthesized via thermal cross-linking between polyvinyl alcohol and β-cyclodextrin. The characterization methods SEM-EDS, FTIR, and XPS were adopted to characterize the adsorbent. The effect of pH, contact time, initial concentrations, and temperature during the adsorption of Pb(II), Cd(II), and Mn(II) onto the PVA-TA-βCD was also investigated. In a single-component system, the data fitted well to pseudo-second-order, and film diffusion and intra-particle diffusion both played important roles in the adsorption process. As for isotherm study, it showed a heterogeneous adsorption capacity of 199.11, 116.52, and 90.28 mg g^-1 for the Pb(II), Cd(II), and Mn(II), respectively. Competition between the ions existed in a multi-component system; however, owing to the stronger affinity of the PVA-TA-βCD for Pb(II) relative to Cd(II) and Mn(II), the Pb(II) adsorption onto the PVA-TA-βCD was less affected by the addition of the other metals, which could be effectively explained by the hard and soft acid and base theory (HSAB). Furthermore, PVA-TA-βCD showed good reusability throughout regeneration experiments.

Colorimetric detection of Ba2+, Cd2+ and Pb2+ based on a multifunctionalized Au NP sensor

A colorimetric method for the detection of three kinds of ions in water with one kind of detection reagent was developed.

Optimization of Pb(II) ions adsorption on nanohydroxyapatite adsorbents by applying Taguchi method

This paper presents an optimization approach for the removal of lead ions (Pb⁺²) by nano-hydroxyapatite powder form adsorbents that were produced from bovine bone by mechanical activation method. The Taguchi method was implemented for designing the experiments by considering four controllable factors including (1) ball milling time (A), (2) the initial concentration of lead ions (B), (3) initial pH of the solution (C); and (4) the adsorbent dosage (D), each factor at four different levels. According to the ANOVA analysis results, the removal efficiency of the lead ions was predominantly influenced by the adsorbent dosage (38.2%) and the initial lead ions concentration (23.64%), whereas the effect of initial pH of the solution was ignorable and the ball milling time had a mild contribution of 14.79%. The total optimum adsorptive lead ions removal of 100% was achieved by optimization process at operating conditions of C_o = 180 mg L^{- 1}, ball milling time = 2 h, pH = 3, and adsorbent dosage = 0.15 g. The Langmuir isotherm model fitted to the equilibrium results with good accuracy and a maximum sorption capacity of 200 mg g^-1 was predicted by the model for the hydroxyapatite adsorbent ball milled for 2 h.

Synergistic effects of biogenic manganese oxide and Mn(II)-oxidizing bacterium Pseudomonas putida strain MnB1 on the degradation of 17 α-ethinylestradiol

While biogenic manganese oxide (BMO) generated via the oxidation of Mn(II) by the Mn-oxidizing bacteria (MOB) have received attention, the relative roles of biological activity by MOB themselves were not clearly investigated. In this study, the synergistic effects of BMO and MOB Pseudomonas putida strain MnB1 on the degradation of 17α-ethinylestradiol (EE2) was investigated. Experiments with BMO in the presence of P. putida MnB1 showed 15-fold higher removal than that with BMO alone, suggesting that EE2 degradation was mediated by the biological activity of MOB as well as abiotic reaction by BMO. Trapping experiments with pyrophosphate (PP) proved that Mn(III) intermediate formed during the biological process from Mn (II) to Mn (IV) contribute much to the EE2 removal. Also, sharp decreases in EE2 removal were observed when microbial activity was inactivated by heat treatment or sodium azide. From this study, the EE2 removal mechanisms by BMO in the presence P. putida MnB1 are described as follows: (1) abiotic oxidation of EE2 by BMO occurs. (2) P. putida MnB1 indirectly oxidizes EE2 by transferring electrons from the Mn (III) intermediate. (3) P. putida MnB1 continuously re-oxidizes the Mn(II) released from the oxidative degradation of EE2 by BMO, generating new Mn(III)-intermediates or BMO.

The role of biogenic Fe-Mn oxides formed in situ for arsenic oxidation and adsorption in aquatic ecosystems

As(III&V), Mn(II), and Fe(II) may occur simultaneously in some groundwater and surface water. Studying their redox reactions and interactions is essential to unravel the biogeochemical cycles of these metal ions in aquatic ecosystems and to find effective methods to remove them simultaneously in drinking water treatment. Here, the formation of biogenic Fe-Mn oxides (BFMO, defined as a mixture of biogenic Mn oxide (BMO) and Fe oxide) as well as its oxidation and adsorption of As in a Fe(II)-Mn(II)-As(III&V)-Mn-oxidizing microbe (Pseudomonas sp. QJX-1) system were investigated. Batch experiments and structure characterization revealed that the BFMO was formed via a sequential precipitation of Fe oxide and BMO. The first formed Fe oxide was identified as FeOOH (lepidocrocite) and the latter formed BMO was identified as MnO2 (similar to hexagonal birnessite). In the BFMO mixture, the BMO part was mainly responsible for As(III) oxidation, and the Fe oxide part dominated As adsorption. Remarkably, the BMO could oxidize Fe(II) to form FeOOH, which may improve As adsorption. The optimum Mn(II)/Fe(II) ratio for As removal was approximately 1:3 (mol/mol). Taken together, in Fe(II)-Mn(II)-As(III&V)-Mn-oxidizing microbe ecosystems, the in situ formation of BFMO could eliminate or decrease Fe(II), Mn(II), and As(III&V) species simultaneously. Therefore, based on this study, new approaches may be developed for As removal from water containing high concentrations of Fe(II) and Mn(II).