Biocomposite based on graphene oxide immobilized Pseudomonas psychrotolerans for the recovery of Y(III) in acid mine drainage

Rare earth elements (REEs) recovery is a critical issue concerning both resource recovery and wastewater utilization. In this study, a new bio-composite was fabricated using graphene oxide immobilized Pseudomonas psychrotolerans (PP@GO), which was isolated from the soil of REEs mine. Results showed that 99.6% Y(III) was removed in 48 h and various characterization confirmed that S-S, -NH2, HPO42-, -OH and -COOH from extracellular polymeric substances (EPS) secreted by microorganisms formed complexation with Y(III). As well, the Y(III) adsorption best followed Freundlich isotherm and non-linear pseudo-second-order kinetic model having R2 of 0.985 and 0.996, respectively, demonstrating that the adsorption was governed by multilayered chemisorption. Additionally, the effectiveness of PP@GO was not limited to Y(III), where 27.9% of this substance was removed in acid mine drainage (AMD), also exhibited great adsorption for other REEs, such as Er (45.0%) and Ho (43.8%). Furthermore, the adsorption efficiency of Y(III) remained high (70.0%) after a 5th cycle, emphasizing the consistent stability of PP@GO. Finally, REEs adsorbed could be greatly desorbed by KNO3, like Sm (80.1%) and La (80.0%), which revealed that PP@GO has great potential to recover REEs in AMD. Overall, this study offers a promising strategy for the green and sustainable REEs recovery and wastewater treatment.

Contemporary updates on bioremediation applications of graphene and its composites

Graphene, a 2D single-layered carbon sp² hybrid substance set in a honeycomb network, is widespread in many carbon-based materials. Due to its extraordinary optical, electrical, thermal, mechanical, and magnetic competences as well as its significant specific surface area, it has attracted a lot of interest recently. Synthesizing graphene refers to any process for creating or extracting the material, depending on the desired purity, size, and efflorescence of the finished good. Numerous methods have been employed for graphene synthesis categorized as top-down procedures and bottom-up procedures. Graphene finds its implementations in various industries such as electronics, energy, chemical, transport, defence, and biomedical areas such as accurate biosensing. It has been widely used in water treatment as a binder for organic contaminants and heavy metals. Many researches have fixated on creating various modified graphene, graphene oxide composites, graphene nanoparticle composites and semiconductor hybrids of graphene for contaminant removal from water. In this review, we have tried to address various production methods for graphene and its composites along with their advantages and disadvantages. Furthermore, we have presented a summary on graphene's outstanding immobilization of a variety of contaminants like toxic heavy metals, organic dyes, inorganic pollutants and pharmaceutical wastes. Additionally, a development of graphene-based microbial fuel cell (MFC) has been evaluated in an effort to produce ecological wastewater treatment and bioelectricity.

Bacterial response to graphene oxide and reduced graphene oxide integrated in agar plates

There are contradictory reports in the literature regarding the anti-bacterial activity of graphene, graphene oxide (GO) and reduced graphene oxide (rGO). This controversy is mostly due to variations in key parameters of the reported experiments, like: type of substrate, form of graphene, number of layers, type of solvent and most importantly, type of bacteria. Here, we present experimental data related to bacterial response to GO and rGO integrated in solid agar-based nutrient plates-a standard set-up for bacterial growth that is widely used by microbiologists. Bacillus subtilis and Pseudomonas aeruginosa strains were used for testing bacterial growth. We observed that plate-integrated rGO showed strong anti-bacterial activity against both bacterial species. By contrast, plate-integrated GO was harmless to both bacteria. These results reinforce the notion that the response of bacteria depends critically on the type of graphene material used and can vary dramatically from one bacterial strain to another, depending on bacterial physiology.

High efficiency microbial electrosynthesis of acetate from carbon dioxide by a self-assembled electroactive biofilm

Microbial electrosynthesis (MES) is a biocathode-driven process, producing high-value chemicals from CO₂. Here, an in situ self-assembled graphene oxide (rGO)/biofilm was constructed, in MES, for high efficient acetate production. GO has been successfully reduced by electroautotrophic bacteria for the first time. An increase, of 1.5 times, in the volumetric acetate production rate, was obtained by self-assembling rGO/biofilm, as compared to the control group. In MES with rGO/biofilm, a volumetric acetate production rate of 0.17gl^-1d^-1 has been achieved, 77% of the electrons consumed, were recovered and the final acetate concentration reached 7.1gl^-1, within 40days. A three-dimensional rGO/biofilm was constructed enabling highly efficient electron transfer rates within biofilms, and between biofilm and electrode, demonstrating that the development of 3D electroactive biofilms, with higher extracellular electron transfer rates, is an effective approach to improving MES efficiency.

Bioleaching of electronic waste using bacteria isolated from the marine sponge Hymeniacidon heliophila (Porifera)

The bacteria isolated from Hymeniacidon heliophila sponge cells showed bioleaching activity. The most active strain, Hyhel-1, identified as Bacillus sp., was selected for bioleaching tests under two different temperatures, 30°C and 40°C, showing rod-shaped cells and filamentous growth, respectively. At 30°C, the bacteria secreted substances which linked to the leached copper, and at 40°C metallic nanoparticles were produced inside the cells. In addition, infrared analysis detected COOH groups and linear peptides in the tested bacteria at both temperatures. The Hyhel-1 strain in presence of electronic waste (e-waste) induced the formation of crust, which could be observed due to bacteria growing on the e-waste fragment. SEM-EDS measurements showed that the bacterial net surface was composed mostly of iron (16.1% w/w), while a higher concentration of copper was observed in the supernatant (1.7% w/w) and in the precipitated (49.8% w/w). The substances linked to copper in the supernatant were sequenced by MALDI-TOF-ms/ms and identified as macrocyclic surfactin-like peptides, similar to the basic sequence of Iturin, a lipopeptide from Bacillus subtilis. Finally, the results showed that Hyhel-1 is a bioleaching bacteria and cooper nanoparticles producer and that this bacteria could be used as a copper recovery tool from electronic waste.

Graphene/biofilm composites for enhancement of hexavalent chromium reduction and electricity production in a biocathode microbial fuel cell

In this study, a simple method of biocathode fabrication in a Cr(VI)-reducing microbial fuel cell (MFC) is demonstrated. A self-assembling graphene was decorated onto the biocathode microbially, constructing a graphene/biofilm, in situ. The maximum power density of the MFC with a graphene biocathode is 5.7 times that of the MFC with a graphite felt biocathode. Cr(VI) reduction was also enhanced, resulting in 100% removal of Cr(VI) within 48h, at 40mg/L Cr(VI), compared with only 58.3% removal of Cr(VI) in the MFC with a graphite felt biocathode. Cyclic voltammogram analyses showed that the graphene biocathode had faster electron transfer kinetics than the graphite felt version. Energy dispersive spectrometer (EDS) and X-ray photoelectron spectra (XPS) analysis revealed a possible adsorption-reduction mechanism for Cr(VI) reduction via the graphene biocathode. This study attempts to improve the efficiency of the biocathode in the Cr(VI)-reducing MFC, and provides a useful candidate method for the treatment of Cr(VI) contaminated wastewater, under neutral conditions.