Accumulation of lead (Pb II) metal ions by Bacillus toyonensis SCE1 species, innate to industrial-area ground water and nanoparticle synthesis

Microbial Removal of Heavy Metals from Contaminated Environments Using Metal-Resistant Indigenous Strains

Contamination of soil with heavy metals has become a matter of global importance due to its impact on agriculture, environmental integrity, and therefore human health and safety. Several microbial strains isolated from soil contaminated by long-term chemical and petrochemical activities were found to manifest various levels of tolerance to Cr, Pb, and Zn, out of which Bacillus marisflavi and Trichoderma longibrachiatum exhibited above-moderate tolerance. The concentrations of target heavy metals before and after bioremediation were determined using electrochemical screen-printed electrodes (SPE) modified with different nanomaterials. The morpho-structural SEM/EDX analyses confirmed the presence of metal ions on the surface of the cell, with metal uptake being mediated by biosorption with hydroxyl, carboxyl, and amino groups as per FTIR observations. T. longibrachiatum was observed to pose a higher bioremediation potential compared to B. marisflavi, removing 87% of Cr and 67% of Zn, respectively. Conversely, B. marisflavi removed 86% of Pb from the solution, compared to 48% by T. longibrachiatum. Therefore, the fungal strain T. longibrachiatum could represent a viable option for Cr and Zn bioremediation strategies, whereas the bacterial strain B. marisflavi may be used in Pb bioremediation applications.

Tolerance and Cadmium (Cd) Immobilization by Native Bacteria Isolated in Cocoa Soils with Increased Metal Content

Twelve cadmium native bacteria previously isolated in soils of cocoa farms located in the western Colombian Andes (Santander), and tolerant to 2500 µM CdCl2 (120 mg Cd/L), were chosen in order to test their tolerance and Cd immobilization using liquid culture medium (Nutritive broth) at different concentrations of heavy metals. Furthermore, in the greenhouse experiments, the strains Exiguobacterium sp. (11-4A), Klebsiella variicola sp. (18-4B), and Enterobacter sp. (29-4B) were applied in combined treatments using CCN51 cacao genotype seeds grown in soil with different concentrations of Cd. All bacterial strains’ cell morphologies were deformed in TEM pictures, which also identified six strain interactions with biosorption and four strain capacities for bioaccumulation; FT-IR suggested that the amide, carbonyl, hydroxyl, ethyl, and phosphate groups on the bacteria biomass were the main Cd binding sites. In the pot experiments, the concentration of Cd was distributed throughout the cacao plant, but certain degrees of immobilization of Cd can occur in soil to prevent an increase in this level in roots with the presence of Klebsiella sp.

Recent progress in green and biopolymer based photocatalysts for the abatement of aquatic pollutants

Enormous research studies on the abatement of anthropogenic aquatic pollutants including organic dyes, pesticides, cosmetics, antibiotics and inorganic species by using varieties of semiconductor photocatalysts have been reported in recent decades. Besides, many of these photocatalysts suffer in real applications owing to their high production cost and low stability. In many cases, the photocatalysts themselves are being considered as secondary pollutants. To eliminate these drawbacks, the green synthesized photocatalysts and the use of biopolymers as photocatalyst supports are considered in recent years. In this context, recent developments in green synthesized metals, metal oxides, other metal compounds, and carbon based photocatalysts in water purification are critically reviewed. Furthermore, the pivotal role of biopolymers including chitin, chitosan, cellulose, natural gum, hydroxyapatite, alginate in photocatalytic removal of aquatic pollutants is comprehensively reviewed. The presence of functional groups, electron trapping ability, biocompatibility, natural occurrence, and low production cost are the major reasons for using biopolymers in photocatalysis. Finally, the summary and conclusion are presented along with existing challenges in this research area.

Metal Accumulation Using a Bacterium (K-142) Identified from Environmental Microorganisms by the Screening of Au Nanoparticles Synthesis

The use of technology that uses organisms to synthesize metal nanoparticles is necessary to maintain a sustainable society. In this study, we investigated and screened the microorganisms isolated from environmental water by quantifying the reproducibility of synthetic Au nanoparticles and the ability of large amount synthesis. The microorganism (K-142) of the Bacillus genus showed the best activity in the investigation. K-142 can also synthesize Ag, CdS and PbS nanoparticles, and the deposition efficiency of Ag, Al, Cd, Cu, and Pb was about 64.8–99.2%. According to the observation results under the microscope after fluorescent staining, K-142 could survive after being treated with 0.5 mM metal solution for 24 h. Therefore, it is expected that K-142, which is easy to cultivate, would also have a high ability to reduce and deposit metal substances. K-142 can be applied to the concentration and recovery of heavy metals in environmental water, thereby opening up channels for biological water purification.

Nacre-inspired hydroxyapatite/chitosan layered composites effectively remove lead ions in continuous-flow wastewater

Design and fabrication of novel adsorbents to remove heavy metal ions in continuous-flow wastewater remained a great challenge. Inspired by the hierarchical architecture and biomineralization process of nacre, we firstly constructed hydroxyapatite/chitosan (HA/CH) layered composites. The brick-and-mortar characteristics of HA/CH layered composites improved their flexure strengths up to 3.08 MPa so that the hierarchical architectures could not be destroyed even under high-pressure drop. HA/CH layered composites had the hierarchical microstructures analogous to plate towers, facilitating the separation of adsorbents from water. The interlaminar macropores in the layered composites contributed to the transfer of continuous-flow wastewater. The Pb(II), Cd(II) and Hg(II) ions in wastewater showed similar adsorption trends, and their adsorption amounts arrived at 295.96, 192.37 and 127.38 mg g^-1 after 6 days, respectively. Among the above heavy metal ions, the HA/CH layered composites possessed the best Pb(II) adsorption ability due to forming lead hydroxyapatite rods and CH-Pb complexes. The Pb(II) adsorption performances of HA/CH layered composites matched well with Elovich equation, pseudo-first-order and pseudo-second-order kinetics models, revealing the heterogeneous chemisorption mechanism at adsorbent/wastewater interfaces. Therefore, the nacre-like HA/CH layered composites with appropriate mechanical property and excellent adsorption capacity are a novel platform for heavy metal removal in continuous-flow wastewater.