Graphene hydrogel improves S. putrefaciens' biological treatment of dye wastewater: Impacts of extracellular electron transfer and function of c-type cytochromes

Design of cross-linked chitosan-adipic acid/Al2O3 nanoparticles for highly efficient removal of bromothymol blue dye: Physicochemical properties, isotherms, and adsorption kinetics

In the present work, an eco-friendly cross-linked chitosan-adipic acid/Al2O3 nanoparticles (CTS-ADP/Al2O3) nanocomposite was designed for the highly efficient removal of bromothymol blue (BTB) dye from an aquatic medium. Several analytical approaches including Zeta potential, BET, XRD, FTIR, pHpzc, and FESEM-EDX were adopted to investigate the CTS-ADP/Al2O3's physicochemical properties. The response surface methodology approach was used to conduct a comprehensive study on the capability of CTS-ADP/Al2O3 to remove BTB dye. This research took into account the factors that impact adsorption, including the CTS-ADP/Al2O3 dosage (0.02-0.08 g), the duration (10-50 min), and the pH (4-10). The BTB equilibrium data fitted well with the Freundlich isotherm. A reasonable agreement of the kinetics data of BTB adsorption by CTS-ADP/Al2O3 was provided using a pseudo-first-order model. The adsorption capability of CTS-ADP/Al2O3 was outstanding (527.3 mg/g). It is possible to attribute the effective adsorption of BTB on the positively charged CTS-ADP/Al2O3 to the electrostatic attraction between the BTB anions and the positively charged CTS-ADP/Al2O3, as well as to n-π, and H-bond interactions. This work reveals that CTS-ADP/Al2O3 has a surprising potential as an effective bio-adsorbent to treat industrial wastewater.

Synergizing Monte Carlo simulations and experimental insights for efficient cationic dye removal using natural fluorapatite

CONTEXT

Natural fluorapatite (FAP) has been investigated as an adsorbent for the removal of dyes such as methylene blue (MB) and crystal violet (CV) from aqueous solutions. Effective dye removal is crucial for water treatment, particularly for industrial wastewater containing toxic dyes. FAP, a naturally abundant material, was characterized using XRD, FTIR, and SEM analysis. The maximum adsorption efficiency achieved was 97% (23 mg/g) for CV and 95% (13 mg/g) for MB under optimal conditions within an equilibrium time of 50 min. The adsorption capacity increased with the ionic strength of the dye solution, reaching 35 mg/g for CV and 28 mg/g for MB. The kinetic study showed that the adsorption of CV and MB is well described by the pseudo-second-order kinetic model (R2 = 0.999) and fits the Freundlich model significantly, with an R2 = 0.99 for both studied molecules. The thermodynamic analysis (ΔH° = 22.647 and 14.907 kJ.mol-1, ΔS° = 88.627 and 47.330 J.mol-1.K-1 for CV and MB, respectively) revealed that the adsorption process is spontaneous and endothermic, with significant randomness at the adsorbent-adsorbate interface. However, desorption and regeneration tests showed that the efficiency of FAP decreases upon reuse. Despite this, the abundance of natural FAP balances its drawbacks. MD simulations confirmed that adsorption is exothermic and spontaneous, especially in basic conditions, where Van der Waals interactions dominate. These findings suggest that natural FAP has significant potential for dye removal in wastewater treatment applications.

METHODS

The effects of various parameters, including dye concentration, temperature, adsorbent mass, and pH, on the adsorption capacity of FAP were studied. Experimental conditions included an initial dye concentration of 20 mg/L, adsorbent mass of 1 g/L, pH of 12, and temperature of 298 K. The Freundlich model was used to describe the adsorption process, while MD simulations provided insights into the adsorption mechanism.

Removal of Hazardous Organic Dyes from Liquid Wastes Using Advanced Nanomaterials

The presence of organic dyes in aqueous environments is extremely hazardous to life due to the toxicity of these compounds. Thus, its removal from these various aquatic media is of the utmost importance, and several technologies are constantly being tested to meet this goal. Among these technologies, various types of degradation and adsorption techniques are typically used, and of the various types of materials used within these technologies, nanomaterials are constantly being developed and investigated, likely due to the various properties that these nanomaterials have. This work reviewed recent developments (in 2023) about the use of these nanomaterials in the treatment of solutions contaminated with these toxic organic dyes.

Distinctive effects of graphene oxide and reduced graphene oxide on methane production kinetics and pharmaceuticals removal in anaerobic reactors

Graphene oxide (GO) addition to anaerobic digestion has been suggested to enhance direct electron transfer. The impact of GO (0.075 g GO g-1 VS) and biologically and hydrothermally reduced GO (bio-rGO and h-rGO, respectively) on the methane production kinetics and removal of 12 pharmaceuticals was assessed in Fed-batch reactors. A decrease of 15 % in methane production was observed in the tests with GO addition compared with the control and the h-rGO. However, bio-rGO and h-rGO substantially increased the methane production rate compared to the control tests (+40 %), in the third fed-batch test. Removal of pharmaceuticals was enhanced only during the bio-reduction of GO (1st fed-batch test), whereas once the GO was bio-reduced, it followed a similar trend in the control and h-rGO tests. The addition of GO can enhance the methane production rate and, therefore, reduce the anaerobic treatment time.

Preparation and characterization of acetate cellulose electrospun nanofibers membrane: Potential application on wastewater treatment

Development of nanofiber membranes with the ability to remove organic dye such as Indigo Carmine (IC) from effluent wastewater is of immense help to the textile industry. In the present study, we investigate the preparation of cellulose acetate (CA) nanofiber membranes with optimized performances using electrospinning technique for effective removal of Indigo Carmine (IC) dye. Electrospinning parameters and solvent system containing acetic acid were adjusted to obtain CA nanofibers membranes which better suits dye removal application. The obtained nanofiber membranes were characterized using Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FT-IR) and contact angle analysis. Results show that nanofiber webs with optimized electrospinning parameters were continuously formed and are substantially free of defects such as beading, with an average diameter of 950 ± 50 nm. Hydrophobicity of membranes were successfully modified and showed important increase of contact angle values from 37° to 107°. The stirring time was varied to improve the solution homogeneity and consequently the response of membranes in filtration treatment. The CA membranes performance was evaluated through water flux and permeability measurement and tested on IC dye removal. The results showed a rate of dye removal around 83 % and a maximum adsorption capacity (Qm) of 13.09 mg/g for the optimized CA membranes.

Bidirectional extracellular electron transfer pathways of Geobacter sulfurreducens biofilms: Molecular insights into extracellular polymeric substances

The basis for bioelectrochemical technology is the capability of electroactive bacteria (EAB) to perform bidirectional extracellular electron transfer (EET) with electrodes, i.e. outward- and inward-EET. Extracellular polymeric substances (EPS) surrounding EAB are the necessary media for EET, but the biochemical and molecular analysis of EPS of Geobacter biofilms on electrode surface is largely lacked. This study constructed Geobacter sulfurreducens-biofilms performing bidirectional EET to explore the bidirectional EET mechanisms through EPS characterization using electrochemical, spectroscopic fingerprinting and proteomic techniques. Results showed that the inward-EET required extracellular redox proteins with lower formal potentials relative to outward-EET. Comparing to the EPS extracted from anodic biofilm (A-EPS), the EPS extracted from cathodic biofilm (C-EPS) exhibited a lower redox activity, mainly due to a decrease of protein/polysaccharide ratio and α-helix content of proteins. Furthermore, less cytochromes and more tyrosine- and tryptophan-protein like substances were detected in C-EPS than in A-EPS, indicating a diminished role of cytochromes and a possible role of other redox proteins in inward-EET. Proteomic analysis identified a variety of redox proteins including cytochrome, iron-sulfur clusters-containing protein, flavoprotein and hydrogenase in EPS, which might serve as an extracellular redox network for bidirectional EET. Those redox proteins that were significantly stimulated in A-EPS and C-EPS might be essential for outward- and inward-EET and warranted further research. This work sheds light on the mechanism of bidirectional EET of G. sulfurreducens biofilms and has implications in improving the performance of bioelectrochemical technology.