A simple method for assaying anaerobic biodegradation of dyes

Shewanella oneidensis: Biotechnological Application of Metal-Reducing Bacteria

What is an unconventional organism in biotechnology? The γ-proteobacterium Shewanella oneidensis might fall into this category as it was initially established as a laboratory model organism for a process that was not seen as potentially interesting for biotechnology. The reduction of solid-state extracellular electron acceptors such as iron and manganese oxides is highly relevant for many biogeochemical cycles, although it turned out in recent years to be quite relevant for many potential biotechnological applications as well. Applications started with the production of nanoparticles and dramatically increased after understanding that electrodes in bioelectrochemical systems can also be used by these organisms. From the potential production of current and hydrogen in these systems and the development of biosensors, the field expanded to anode-assisted fermentations enabling fermentation reactions that were - so far - dependent on oxygen as an electron acceptor. Now the field expands further to cathode-dependent production routines. As a side product to all these application endeavors, S. oneidensis was understood more and more, and our understanding and genetic repertoire is at eye level to E. coli. Corresponding to this line of thought, this chapter will first summarize the available arsenal of tools in molecular biology that was established for working with the organism and thereafter describe so far established directions of application. Last but not least, we will highlight potential future directions of work with the unconventional model organism S. oneidensis.

Facile Synthesis of a Crystalline Zinc Sulfide/Chitosan Biopolymer Nanocomposite: Characterization and Application for Photocatalytic Degradation of Textile Dyes and Anticancer Activity

In the present study, we have synthesized a zinc sulfide/chitosan (ZS/CS) nanocomposite by utilizing simple, economical, and environmentally friendly methods. The synthesized nanomaterials were characterized by different analytical techniques such as XRD, FE-SEM, EDS, and FTIR to determine the phase structure, morphology, and elemental composition. FTIR spectroscopy was used to confirm the functional groups of the synthesized zinc sulfide (ZS) nanoparticles and ZS/CS composite. Besides, the optical properties of the as-synthesized nanocomposite was analyzed by a UV-visible spectrophotometer, and the estimated band gap energy is ∼3.03 eV. The photocatalytic efficiency of the synthesized ZS/CS nanocomposite was investigated against two textile dyes, Crystal Violet (CV) and Acid Red-I (AR-I), under UV-visible light irradiation. The nanocomposite showed excellent photocatalytic activity against the dyes, and photodegradation was estimated to be about 93.44 and 90.67% for CV and AR-I, respectively. The nanocomposite was reused for three consecutive cycles. The results revealed that the photocatalyst displayed good reusability during the photocatalytic decomposition and thus is considered a cost-effective and promising photocatalyst in degrading dye pollutants. The kinetic study proved that the pseudo-first-order reaction kinetics was followed by the degradation process. We also examined the anticancer activity of ZS and ZS/CS against human breast and myelogenous leukemia cancer cell lines, namely, MCF-7 and K-562, and the half minimal inhibitory concentrations were found to be less than 50 μg/mL.

Toxic effects and mechanisms of cationic blue SD-GSL on Chlorella vulgaris before and after the biological decolorization process

Biodegradation is regarded as an efficient way to decolorize azo dyes. However, the changes in the algal toxicity of azo dyes during biodecolorization are still unclear. In this study, the physiological responses of Chlorella vulgaris to the hydrophobic and hydrophilic components of cationic blue SD-GSL (a typical monoazo dye) and its biodecolorization products were investigated. The toxicity of each component to Chlorella vulgaris and the sources of the toxicity were analyzed. The cationic blue SD-GSL components inhibited the algal cell division and superoxide dismutase (SOD) activity at all concentrations, and inhibited the synthesis of chlorophyll-a (Chl-a) at concentrations >100 mg/L, whereas increased the malondialdehyde (MDA) content. The hydrophobic and hydrophilic components of its biodecolorization products had enhanced inhibition rates on cell density (10.7% and 15.6%, respectively), Chl-a content (31.2% and 8.4%, respectively), and SOD activity (13.5% and 1.9%, respectively) of Chlorella vulgaris, and further stimulated an increase in MDA content (4.4% and 7.0%, respectively), indicating that the biodecolorization products were more toxic than the pristine dye. Moreover, the toxic effect of hydrophobic components on Chlorella vulgaris was stronger than that of hydrophilic components. The sensitivity sequence of Chlorella vulgaris to the toxicity of cationic blue SD-GSL and its biodecolorization product components was: Chl-a synthesis > SOD activity > cell division. SUVA analysis and 3D-EEM analysis revealed that the enhanced algal toxicity of the biodecolorization products of cationic blue SD-GSL was attributed to the aromatic compounds, which were mainly concentrated in the hydrophobic components. UPLC-Q-TOF-MS was used to verify dye biodecolorization byproducts. The information obtained from this study helps to understand the decolorization products toxicities of the biologically treated azo dyes, thereby providing new insights into the environmental safety of textile wastewater after traditional biological treatment.

Performance and cost-benefit analysis of anaerobic moving bed biofilm reactor for pretreatment of textile wastewater

Performance of an anaerobic moving bed biofilm reactor (AnMBBR) was evaluated for pretreatment of real textile desizing wastewater at organic loading rate (OLR) of 1±0.05 to 6.3±0.37 kgCOD/m3/d. After OLR optimization, the performance of AnMBBR was evaluated for biodegradation of reactive dyes. AnMBBR was operated under a mesophilic temperature range of 30 to 36 °C, while the oxidation-reduction potential (ORP) and pH were in the range of 504 to 594 (-mV) and 6.98 to 7.28, respectively. By increasing the OLR from 1±0.05 to 6.3±0.37 kgCOD/m3/d, COD and BOD5 removal was decreased from 84 to 39% and 89 to 49%, respectively. While the production of biogas was increased from 0.12 to 0.83 L/L·d up to an optimum OLR of 4.9±0.43 kgCOD/m3/d. With increase in the dye concentration in the feed, COD, BOD5, color removal and biogas production reduced from 56, 63, 70% and 0.65 L/L·d to 34, 43, 41% and 0.08 L/L·d, respectively. Based on the data obtained, a cost-benefit analysis of AnMBBR was also investigated for the pretreatment of real textile desizing wastewater. Cost estimation of anaerobic pretreatment of textile desizing wastewater indicated a net profit of 21.09 million PKR/yr (114,000 €/yr) and a potential payback period of 2.54 years.

Extracellular pollutant degradation feedback regulates intracellular electron transfer process of exoelectrogens: Strategy and mechanism

Exoelectrogens possess extraordinary degradation ability to various pollutants through extracellular electron transfer (EET). Compared with extracellular electron release process, intracellular electron transfer network is not yet fully recognized. Especially, controversy remains regarding the role of CymA, an essential electron-transfer hub of Shewanella oneidensis MR-1, in EET process. In this study, we thoroughly surveyed the intracellular transfer strategies during EET through dye decolorization. Loss of CymA severely impaired the reduction ability of S. oneidensis MR-1 to methyl orange (MO), but hardly affected the decolorization of aniline blue (AB). Complement of cymA fully restored the MO decolorization ability of ΔcymA mutant. The contribution of CymA to extracellular decolorization was subjected to MO concentrations. The defect in the decolorization ability of ΔcymA mutant was not evident at low MO concentration, but severe at high MO concentration. Further investigation revealed that EET rate determined the significance of CymA in the extracellular bioremediation by S. oneidensis MR-1. Coupled with MO concentrations increasing from 15 to 120 mg/L, the initial electron transfer rates of S. oneidensis MR-1 increased accordingly from 2.69 × 10⁴ to 11.21 × 10⁴ electrons CFU^-1 s^-1, which led to a gradual increase of the dependency_CymA. Thus, we first revealed that extracellular degradation performance could feedback regulate the intracellular electron transfer process of S. oneidensis MR-1. This work is helpful to fully understand the complex EET process of exoelectrogens and facilitates the application of exoelectrogens in bioremediation of environmental pollutants.

Versatile mechanisms and enhanced strategies of pollutants removal mediated by Shewanella oneidensis: A review

The removal of environmental pollutants is important for a sustainable ecosystem and human health. Shewanella oneidensis (S. oneidensis) has diverse electron transfer pathways and can use a variety of contaminants as electron acceptors or electron donors. This paper reviews S. oneidensis's function in removing environmental pollutants, including heavy metals, inorganic non-metallic ions (INMIs), and toxic organic pollutants. S. oneidensis can mineralize o-xylene (OX), phenanthrene (PHE), and pyridine (Py) as electron donors, and also reduce azo dyes, nitro aromatic compounds (NACs), heavy metals, and iodate by extracellular electron transfer (EET). For azo dyes, NACs, Cr(VI), nitrite, nitrate, thiosulfate, and sulfite that can cross the membrane, S. oneidensis transfers electrons to intracellular reductases to catalyze their reduction. However, most organic pollutants cannot be directly degraded by S. oneidensis, but S. oneidensis can remove these pollutants by self-synthesizing catalysts or photocatalysts, constructing bio-photocatalytic systems, driving Fenton reactions, forming microbial consortia, and genetic engineering. However, the industrial-scale application of S. oneidensis is insufficient. Future research on the metabolism of S. oneidensis and interfacial reactions with other materials needs to be deepened, and large-scale reactors should be developed that can be used for practical engineering applications.

Synthesis, Characterization, and Solar Photo-Activation of Chitosan-Modified Nickel Magnetite Bio-Composite for Degradation of Recalcitrant Organic Pollutants in Water

Photocatalysis is a promising process for decomposing harmful organic pollutants in water. In this study, solar/photocatalytic degradation of two model azo dyes, i.e., methylene blue (MB) and methyl red (MR), in water usinga nanostructured chitosan-modified nickel magnetite (CS-NM) bio-composite was investigated. The CS-NM bio-composite was synthesized through a co-precipitation method and characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), thermogravimetry (TGA), and UV-Vis spectroscopy. FTIR analysis showed the uniform incorporation and conjugation of nickel magnetite (NM) into the chitosan (CS) polymer matrix. SEM showed that the average particle size was 0.5 μm. The TGA results revealed the good thermal stability of the prepared bio-composite at 300 °C. The point of zero charge was calculated as 7.5. The effect of water quality and process parameters, such as concentration of dyes, catalyst dose, solution pH, and temperatures, was investigated, for application purposes. The solar/CS-NM photocatalysis resulted in 99 and 96% degradation of individual MB and MR (C0 = 50 ppm), respectively, in 90 min. The degradation of MB and MR by solar/CS-NM photocatalysis followed pseudo-first-order kinetics, with observed rate constants (k) of 0.077 and 0.072 min−1, respectively. The CS-NM photocatalyst showed high recyclability, represented by only a 4–6% loss in the photocatalytic efficiency, after four cycles. The results showed that solar/CS-NM photocatalysis is an efficient technique for degrading recalcitrant organic pollutants, such as azo dyes, in water environments.

A Study of Methylene Blue Dye Interaction and Adsorption by Monolayer Graphene Oxide

The graphene oxide (GO) interaction with methylene blue (MB) cationic dye was studied in an aqueous solution at different pH during MB adsorption. The mutual interaction of MB with GO surface was studied and evaluated by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The π-π and electrostatic interaction of MB with GO surface are the main types of interactions, and the XRD data show the monomeric arrangement of MB cation with GO. The GO surface functional groups and point of zero charge (PZC) were determined by acid-base titration. Suitability of zeta-potential measurement and acid-base titration method was briefly discussed. The quality of prepared GO was evaluated by Raman spectroscopy, XRD, and atomic force microscope (AFM). The experimental adsorption equilibrium data were analyzed using Langmuir, Langmuir-Freundlich, Freundlich, and Temkin isotherms. The GO maximum adsorption capacity increases with higher pH, that is ascribed to the facile interaction of negatively charged GO with positively charged MB structure.

Enhanced Bioremediation Potential of Shewanella decolorationis RNA Polymerase Mutants and Evidence for Novel Azo Dye Biodegradation Pathways

Bioremediation has been considered as a promising method for recovering chemical polluted environments. Here Shewanella decolorationis strain Ni1-3 showed versatile abilities in bioremediation. To improve the bioremediation activity, RNA polymerase (RNAP) mutations of strain Ni1-3 were screened. Eleven mutants were obtained, of which mutant #40 showed enhanced Amaranth (AMR) degradation capacity, while mutant #21 showed defected capacity in AMR degradation but greatly enhanced capacity in cathodic metal leaching which is three to four times faster than that of the wild-type (WT) strain Ni1-3, suggesting that different pathways were involved in these two processes. Transcriptional profiling and gene co-expression networks between the mutants (i.e., #40 and #22) and the WT strain disclosed that the non-CymA-Mtr but cytochrome b- and flavin-oxidoreductase-dominated azo dye degradation pathways existed in S. decolorationis, which involved key proteins TorC, TorA, YceJ, YceI, Sye4, etc. Furthermore, the involvement of TorA was verified by trimethylamine N-oxide reduction and molybdenum enzyme inhibitory experiments. This study clearly demonstrates that RNAP mutations are effective to screen active microbial candidates in bioremediation. Meanwhile, by clarifying the novel gene co-expression network of extracellular electron transfer pathways, this study provides new insights in azo dye degradation and broadens the application of Shewanella spp. in bioremediation as well.

Compact Carbon-Based Membrane Reactors for the Intensified Anaerobic Decolorization of Dye Effluents

Carbon-based membranes integrated with anaerobic biodegradation are presented as a unique wastewater treatment approach to deal with dye effluents. This study explores the scope of ceramic-supported carbon membrane bioreactors (B-CSCM) and ceramic-supported graphene oxide membrane bioreactors (B-CSGOM) to decolorize azo dye mixtures (ADM) and other dyes. The mixture was prepared using an equimolar composition of monoazo Acid Orange 7, diazo Reactive Black 5, and triazo Direct Blue 71 dye aqueous solution. Afterwards, as in the ADM experiment, both compact units were investigated for their ability in the biodecolorization of Methylene Blue (MB) and Rhodamine B (RhB) dye solutions, which do not belong to the azo family. The obtained outcomes revealed that the conductive surface of the graphene oxide (GO) membrane resulted in a more efficient and higher color removal of all dye solutions than B-CSCM under a wide feed concentration and permeate flux ranges. The maximum color removal at low feed concentration (50 mg·L⁻¹) and permeate flux (0.05 L·m⁻²·h⁻¹) was 96% for ADM, 98% for MB and 94% for RhB, whereas it was 89%, 94% and 66%, respectively, for B-CSCM. This suggests that the robust, cost-effective, efficient nanostructures of B-CSGOM can successfully remove diverse azo dye solutions from wastewater better than the B-CSCM does.

Construction of porous 2D MOF nanosheets for rapid and selective adsorption of cationic dyes

Porous two-dimensional metal-organic framework (2D-MOF) nanosheets Zr-BTB-H4TBAPy and PCN-134-2D were synthesized and characterized by X-ray diffraction (XRD), N2 adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and zeta potential and subjected to dye adsorption and separation investigation. These 2D-MOF nanosheets are ultrathin, have large surface area and high water stability and can selectively adsorb cationic dyes, rhodamine B (RhB) and methylene blue (MLB), from aqueous solutions, with removal rates of nearly 100% within 10 min. The adsorption kinetic results showed that Zr-BTB-H4TBAPy and PCN-134-2D could effectively and selectively remove cationic dyes from water, followed a pseudo-second-order kinetic model and fitted well with the Freundlich isotherm. The adsorption mechanism studies further indicated that their excellent adsorption and separation performance could be ascribed to their ultrathin and porous features, plentiful exposed surface-active sites, and favorable electrostatic interactions between the adsorbents and cationic dyes. Moreover, the porous 2D MOF nanosheets displayed excellent recyclability and reusability. These outstanding features make them potentially applicable for rapid and selective cationic dye adsorption and separation.

Chitosan‑zinc sulfide nanoparticles, characterization and their photocatalytic degradation efficiency for azo dyes

Herein, chitosan‑zinc sulfide nanoparticles (CS-ZnS-NPs) were developed as an efficient photocatalyst for the degradation of toxic dyes. The as-synthesized CS-ZnS-NPs were analyzed using XRD, FTIR, SEM, and EDS. The functional groups of CS-ZnS-NPs were validated with FTIR spectroscopy. The SEM envisaged the average particle size as 40 nm, whereas EDS interpreted the compositional analysis of the nanocomposite. XRD analysis illustrated the crystallinity and hexagonal crystal structure of the CS-ZnS-NPs. The photocatalytic efficiency of CS-ZnS-NPs was evaluated using two carcinogenic azo dyes, Acid Brown 98 and Acid Black 234. A UV lamp (254 nm) was used as an irradiation source during the photocatalytic degradation of dyes. At the optimum conditions, the synthesized CS-ZnS-NPs showed 96.7% degradation for Acid Black 234 in 100 min and 92.6% for Acid Brown 98 in 165 min. The degradation phenomena followed pseudo-first-order kinetics. The values of rate constant (k) were 0.01464 and 0.04096 min^-1 with correlation coefficient (R²) of 0.98891 and 0.99406 for Acid Brown 98 and Acid Black 234, respectively. The CS-ZnS-NPs were easily recovered and recycled for four successive batches. The results showed that CS-ZnS-NPs are considered as highly productive, cost-effective and promising photocatalyst in degrading pollutants in several consecutive cycles.

Simultaneous capture of methyl orange and chromium(vi) from complex wastewater using polyethylenimine cation decorated magnetic carbon nanotubes as a recyclable adsorbent

Most recently, the continuous deterioration of the aquatic environment triggered by both heavy metals and synthetic organic dyes has imparted serious threats to the ecosphere and drinking water safety. However, it is still extremely challenging to treat complex wastewater containing these two classes of pollutants via a one-step method owing to the significant differences in their physicochemical properties. In the current work, versatile magnetic MWCNTs decorated with PEI (denoted as MWCNTs@Fe3O4/PEI) was fabricated by a facile, rapid and reproducible strategy and applied to as a robust adsorbent for simultaneously removing methyl orange (MO) and Cr(vi) from aqueous solutions. The physicochemical properties of the as-designed nanohybrid were investigated using various analytical techniques, i.e. XRD, FT-IR, SEM, TEM, VSM, zeta potential, etc. It was found that the surface charge properties of the MWCNTs as well as its dispersion in aqueous solution were greatly changed after the introduction of PEI molecules. The resulting nanohybrid exhibited attractive adsorption capabilities toward anionic MO and Cr(vi). In the perspective of a mono-pollutant system, the time-dependent adsorption process matched well with a pseudo-second-order kinetics equation, the adsorption isotherm data at r.t. were well fitted by a Langmuir model with maximum monolayer uptake capacity of 1727.6 mg g-1 for MO and 98.8 mg g-1 for Cr(vi), and the removal process of both pollutants was thermodynamically spontaneous and exothermic. In the MO-Cr(vi) binary system, the uptake of Cr(vi) by the as-prepared adsorbent was evidently enhanced by the presence of MO, while the coexisting Cr(vi) exerted a small negative effect on the sorption of MO; which was attributed to the different adsorption mechanisms of both pollutants on the as-recommend adsorbent. The much better adsorbing performance of the resulting MWCNTs@Fe3O4/PEI for MO and Cr(vi) than that of the pristine MWCNTs or the MWCNTs/Fe3O4 composite was mainly ascribed to the high surface area of the MWCNTs, the high density of protonated N-rich groups of PEI as well as the excellent dispersion and solubility of the resulting nanocomposites. Moreover, the obtained nanohybrids can be easily recovered after being used by a permanent magnet and still retained high stability and excellent reusability after consecutive adsorption-desorption cycles, implying its great potential in practical applications. Therefore, the as-fabricated MWCNTs@Fe3O4/PEI composite could be recommended as a promising candidate adsorbent for the simultaneous capture of MO and Cr(vi) from complex wastewater via multiple uptake mechanisms (e.g. electrostatic attraction, π-π stacking and hydrogen bonding).

Removal of Patent Blue (V) Dye Using Indian Bael Shell Biochar: Characterization, Application and Kinetic Studies

The prospective utilization of bael shell (Aegle marmelos) as an agro-waste for the production of biochar was investigated along with its characterization and application for the abatement of hazardous aqueous Patent Blue (PB) dye solution. The sorptive removal of PB on bael shell biochar (BSB) was investigated under the following operational conditions: (pH, 2.7–10.4; biochar dosage, 2–12 g/L; and contact time, 0–60 min). The removal efficiency of PB by BSB in a batch adsorption experiment was 74% (pH 2.7 and 30 ± 5 °C). In addition, a clear relationship between the adsorption and pH of the solution was noticed and the proposed material recorded a maximum sorption capacity of 3.7 mg/g at a pH of 2.7. The adsorption of PB onto BSB was best explained by the pseudo-second order kinetic model (R2 = 0.972), thereby asserting the predominant role of chemisorption. The active role of multiple surface-active functionalities present on BSB during PB sorption was elucidated with the help of Freundlich isotherm (R2 = 0.968). Further, an adsorption mechanism was proposed by utilizing Fourier transform infrared spectroscopy (FTIR).