Efficient reduction of reactive black 5 and Cr(Ⅵ) by a newly isolated bacterium of Ochrobactrum anthropi

Unveiling the biointerfaces characteristics and removal pathways of Cr(Ⅵ) in Bacillus cereus FNXJ1-2-3 for the Cr(Ⅵ)-to-Cr(0) conversion

Although less toxic than hexavalent chromium, Cr (Ⅲ) species still pose a threat to human health. The Cr (Ⅵ) should be converted to Cr (0) instead of Cr (Ⅲ), which is still involved in biological detoxification filed. Herein, for the first time, it was found that Cr(Ⅵ) can be reduced into Cr(0) by Bacillus cereus FNXJ1-2-3, a way to completely harmless treatment of Cr(Ⅵ). The bacterial strain exhibited excellent performance in the reduction, sorption, and accumulation of Cr(Ⅵ) and Cr (Ⅲ). XPS etching characterization inferred that the transformation of Cr(Ⅵ) into Cr(0) followed a reduction pathway of Cr(Ⅵ)→Cr (Ⅲ)→metallic Cr(0), in which at least two secretory chromium reductases (ECrⅥ→Ⅲ and ECrⅢ→0) worked. Under the optimum condition, the yield ratio of Cr(0)/Cr (Ⅲ) reached 33.90%. In addition, the interfacial interactions, ion channels, chromium reductases, and external electron donors also contributed to the Cr(Ⅵ)/Cr(0) transformation. Findings of this study indicate that Bacillus cereus FNXJ1-2-3 is a promising bioremediation agent for Cr(Ⅵ) pollution control.

One-step synthesis of ferrous disulfide and iron nitride modified hydrochar for enhanced adsorption and reduction of hexavalent chromium in Bacillus LD513 by promoting electron transfer and microbial metabolism

Microbial immobilization technology is effective in improving bioremediation efficiency and heavy metal pollution. Herein, Bacillus LD513 with hexavalent chromium (Cr(VI)) tolerance was isolated and immobilized on a novel ferrous disulfide (FeS2)/iron nitride (FeN) modified hydrochar (Fe3-SNHC) prepared from waste straws. The prepared Fe3-SNHC-based LD513 (FeLD) significantly improves Cr(VI) adsorption and reduction by 31.4 % and 15.7 %, respectively, compared to LD513 alone. Furthermore, the FeLD composite system demonstrates efficient Cr(VI) removal efficiency and good environmental adaptability under different culture conditions. Microbial metabolism and electrochemical analysis indicate that Fe3-SNHC is an ideal carrier for protecting LD513 activity, promoting extracellular polymer secretion, and reducing oxidative stress. Additionally, the carrier serves as an electron shuttle that accelerates electron transfer and promotes Cr(VI) reduction. Overall, FeLD is an environmentally friendly biocomposite that shows good promise for reducing Cr(VI) contamination in wastewater treatment.

Temperature mediated the balance between stochastic and deterministic processes and reoccurrence of microbial community during treating aniline wastewater

Seasonal temperature changes significantly affect microbial community diversity, composition, and performance in wastewater treatment plants. However, the community assembly mechanisms under seasonal temperature variations remain unclear. Here, we carried out temperature cycling experiments (30 °C, 35 °C, 37 °C, 40 °C, 42 °C, 45 °C, 40 °C, and 30 °C) to investigate how temperature impacts microbial performance and co-occurrence network and how assembly processes determine the structure and function of microbial communities during treating aniline wastewater. During the 195-day operation, the system achieved an efficient and stable aniline removal of 99%. Interestingly, α-diversity and network complexity were negatively correlated with temperature but could be recovered when the temperature was returned to 30 °C. The results showed that functional redundancy was probably responsible for the excellent microbial performance during the whole process. Null model analyses presented that deterministic process dominated the community when the temperature was 30 °C, and stochasticity dominated the assembly process when the temperature was over 30 °C. Overall, the balance between stochastic and deterministic processes in the treatment of aniline wastewater mediated the reoccurrence of microbial community and co-occurrence network at different temperatures. This study provides new insights into microbial community reoccurrence under seasonal temperature changes and a theoretical basis for regulating microbial communities in wastewater treatment plants.

Biodegradation of di-n-octyl phthalate by Gordonia sp. Lff and its application in soil

A previous isolated Gordonia sp. (Lff) was used to degrade di-n-octyl phthalate (DOP) contamination in both aqueous solution and soil. The influence of temperature, pH, inoculum size, salt content and initial concentration of DOP on DOP degradation by Lff were analysed. The response of soil bacterial community to DOP and Lff was also analysed by Illumina MiSeq sequence method. Results showed that the optimal temperature, pH, inoculum size and salt content were 35^oC, 8.0, 5% and <5%, respectively. Under the optimal condition, more than 91.25% of DOP with different initial concentrations (100-2000 mg/L) could be degraded by Lff. Kinetics analysis indicated that biodegradation of DOP by Lff could be described by first-order kinetics (R² > 0.917) with the half-life (t_1/2) changing irregularly between 0.58 and 0.83 d. In addition, Lff enhanced the removal of DOP in soil and alleviated the toxicity of DOP on soil microorganisms. Furthermore, its influence on soil bacterial community is not obvious. These results suggested that Lff was effective in remediating DOP contamination in different environments.

Efficient removal of azo dyes by Enterococcus faecalis R1107 and its application in simulated textile effluent treatment

This study aimed to exploit the potential of Enterococcus faecalis R1107 in the bioremediation of azo dyes. The maximal decolorization of Congo Red (CR), Reactive Black 5 (RB5), and Direct Black 38 (DB38) were 90.17%, 96.82%, and 81.95%, respectively, with the bacterial treatment for 48 h. 65.57% of CR and 72.64% of RB5 could be decolorized by E. faecalis R1107 within 48 h when the concentration of azo dyes increased up to 1000 mg/L. FTIR analysis confirmed that E. faecalis R1107 could effectively break down the chemical structures of three azo dyes. E. faecalis R1107 alleviated the phytotoxicity of azo dyes and improved seed germination, which contributed to the increase in the lengths of roots, stems, and leaves of Vigna radiata seedlings. Transcriptomic analysis suggested that the gene regulatory networks in E. faecalis R1107 synergistically improved the degradation and detoxification of RB5, including the major metabolic pathways, the secondary metabolism, the transport system, the amino acid metabolic pathways, and the signal transduction systems. Simulated textile effluent (STE) was used to mimic real textile effluent to evaluate the bioremediation potential of E. faecalis R1107, and 72.79% STE can be decolorized after E. faecalis R1107 treatment for 48 h. In summary, our study demonstrated that E. faecalis R1107 might be well suitable for potential applications in the bioremediation of textile effluent.

The performance and mechanism of simultaneous removal of calcium and heavy metals by Ochrobactrum sp. GMC12 with the chia seed (Salvia hispanica) gum as a synergist

A bacterium Ochrobactrum sp. GMC12, capable of biomineralization and denitrification, was employed to investigate the performance and mechanism of heavy metals removal. A chia seeds (Salvia hispanica) gum was proposed as a synergist for the first time. The results showed that strain GMC12 reduced Ca²⁺, Cd²⁺, Zn²⁺, and nitrate by 83.38, 98.89, 98.95, and 100% (2.09, 0.29, 0.55, and 0.79 mg L^-1 h^-1), respectively, over 96 h continuous determination experiments. The concentration gradient test revealed that strain GMC12 would effectively remove Cd²⁺ and Zn²⁺ by 99.80 and 99.91% (0.67 and 1.35 mg L^-1 h^-1), respectively, under the synergistic effect of gum (1.0%, w/v). The SEM-EDS and XRD manifested that Ca²⁺, HMs ions, and anionic groups coated on the bacteria surface to form CaCO₃, Ca₅(PO₄)₃OH, CdCO₃, Cd₅(PO₄)₃OH, ZnCO₃, and Zn₂(PO₄)OH. The fluorescence spectrometry and fourier transform infrared (FTIR) spectra illustrated that extracellular polymeric substance (EPS) was the key product for the nucleation site of bacteria, and the gum promoted the accumulation of bio-precipitates and accelerated the removal of HMs. In this research, Ochrobactrum sp. GMC12 exhibited great potential in wastewater treatment and chia seeds gum would go deep into material preparation and wastewater treatment due to its non-toxic nature, high viscosity, and advantageous morphology.

Zein adsorbents with micro/nanofibrous membrane structure for removal of oils, organic dyes, and heavy metal ions in aqueous solution

Developing multi-functional media for effectively removing different contaminants coexisted in wastewater system is highly desired. Herein, zein, a natural protein possessing abundant functional groups in molecule, is chosen to be fabricated into micro/nanofibrous membranes as adsorbents and separation media. Zein fibers with novel groove ribbon structures, which possess better structural characteristics, are designed for obtaining good adsorption performance. The adsorption performances of zein fiber membranes are evaluated. The results show that zein fiber membranes have the adsorption capacities up to 94 g/g for motor oil, 168 mg/g for Congo red, and 189 mg/g for Pb²⁺ ion for 1000 mg/L initial solution concentration, showing considerable competitiveness as compared with the reported adsorbents. The zein membrane with groove ribbon fiber morphology exhibits optimal adsorption capability and can be attractive multi-functional separation media.

Investigations of Cr(VI) removal by millet bran biochar modified with inorganic compounds: Momentous role of additional lactate

In this study, millet bran biochars modified with inorganic compounds (H₃PO₄: P-BC, NaOH: Na-BC and K₂CO₃: K-BC) were prepared and applied for Cr(VI) removal to evaluate the effects of modification on biochars' physicochemical properties. The results showed that Cr(VI) reduction capacity complied with the order of Na-BC > BC > P-BC > K-BC, and reductive groups such as -OH and -NH₂ played considerable roles in electrons donating. Based on this, lactate was added for further investigation of electrons transferring. The results displayed that Cr(VI) removal of all biochars was enhanced tremendously and modified biochars exhibited better Cr(VI) reduction. This may be due to the bridging effect of lactate, which could not only chelate with Cr(VI) via -COOH (or -OH) but also form hydrogen bonds with oxygen or nitrogen containing groups on biochars through the other groups, thus facilitating electrons transferring between biochars and Cr(VI). This work provided an insight into evaluation of the influence of inorganic compounds modification on both electrons donating capability of biochars and electrons transferring potential of biochars combined with lactate in Cr(VI) removal.

Influences of modified biochar on metal bioavailability, metal uptake by wheat seedlings (Triticum aestivum L.) and the soil bacterial community

A 6 weeks pot culture experiment was carried out to investigate the stabilization effects of a modified biochar (BCM) on metals in contaminated soil and the uptake of these metals by wheat seedlings. The results showed that the application of BCM significantly increased the soil fertility, the biomass of wheat seedling roots increased by more than 50%, and soil dehydrogenase (DHA) and catalase (CAT) activities increased by 369.23% and 12.61%, respectively. In addition, with the application of BCM, the diethylenetriaminepentaacetic acid extractable (DTPA-extractable) Cd, Pb, Cu and Zn in soil were reduced from 2.34 to 0.38 mg/kg, from 49.27 to 25.65 mg/kg, from 3.55 mg/kg to below the detection limit and from 4.05 to 3.55 mg/kg, respectively. Correspondingly, the uptake of these metals in wheat roots and shoots decreased by 62.43% and 79.83% for Cd, 73.21% and 66.32% for Pb, 57.98% and 68.92% for Cu, and 40.42% and 43.66% for Zn. Furthermore, BCM application decreased the abundance and alpha diversity of soil bacteria and changed the soil bacterial community structure dramatically. Overall, BCM has great potential for the remediation of metal-contaminated soils, but its long-term impact on soil metals and biota need further research.

Simultaneous anaerobic decolorization/degradation of Reactive Black-5 azo dye and chromium(VI) removal by Bacillus cereus strain MS038EH followed by UV-C/H2O2 post-treatment for detoxification of biotransformed products

The existence of synthetic dyes and heavy metals in textile wastewater is a serious problem. These compounds should be removed before discharge into the environment by an appropriate method. The present study was conducted for the characterization of efficient multi-functional strain Bacillus cereus MS038EH for the simultaneous removal of Reactive Black-5 and Chromium(VI). Maximum decolorization efficiency of 94.74% was achieved at pH 7, 35 °C, and 4% inoculum size for 900 mg/L of Reactive Black-5. Also, 94.10% efficiency was observed in the presence of 8 g/L of yeast extract as an optimum nitrogen source, while carbon sources had no significant effect on decolorization. It should be pointed out that the decolorization efficiency was decreased from 94 to 64% by increasing NaCl concentrations from 0 to 50 g/L, respectively. Bacillus cereus strain MS038EH could decolorize 94.31% of Reactive Black-5 (900 mg/L) and remove 87.31% of chromium(VI) (30 mg/L) within 36 h. Results of Gas chromatography-mass spectrometry and Fourier transform-infrared spectroscopy proved that Reactive Black-5 was cleaved into the lower molecular weight products without any azo bonds. However, the phyto-toxicity analysis showed that Reactive Black-5 was not toxic for Triticum aestivum and Maize, while biologically treated Reactive Black-5 was toxic for seeds. Therefore, ultraviolet-C/H₂O₂ was applied for the detoxification of biotransformed products. When ultraviolet-C/H₂O₂ was applied as post-treatment, the seeds were germinated completely. It is demonstrated that the application of ultraviolet-C/H₂O₂ after anaerobic treatment is effective for toxicity reduction of textile wastewater.