Binary coagulation system (graphene oxide/chitosan) for polluted surface water treatment

Coagulative removal of polystyrene microplastics from aqueous matrices using FeCl3-chitosan system: Experimental and artificial neural network modeling

Effluent from sewage treatment plants (STPs) is a significant source of microplastics (MPs) re-entry into the environment. Coagulation-flocculation-sedimentation (CFS) process as an initial tertiary treatment step requires investigation for coagulative MPs removal from secondary-treated sewage effluents. In this study, experiments were conducted on synthetic water containing 25 mg/L polystyrene (PS) MPs using varying dosages of FeCl3 (1-10 mg/L) and chitosan (0.25-9 mg/L) to assess the effect of process parameters, such as pH (4-8), stirring speed (0-200 rpm), and settling time (10-40 min). Results revealed that ∼89.3% and 21.4% of PS removal were achieved by FeCl3 and chitosan, respectively. Further, their combination resulted in a maximum of 99.8% removal at favorable conditions: FeCl3: 2 mg/L, chitosan: 7 mg/L, pH: 6.3, stirring speed: 100 rpm, and settling time: 30 min, with a statistically significant (p < 0.05) effect. Artificial neural network (ANN) validated the experimental results with RMSE = 1.0643 and R2 = 0.9997. Charge neutralization, confirmed by zeta potential, and adsorption, ascertained by field-emission scanning electron microscope (FESEM) and Fourier-transform infrared spectroscopy (FTIR), were primary mechanisms for efficient PS removal. For practical considerations, the application of the FeCl3-chitosan system on the effluents from moving bed biofilm reactor (MBBR) and sequencing batch reactor (SBR)-based STPs, spiked with PS microbeads, showed > 98% removal at favorable conditions.

Graphene oxide affects bacteriophage infection of bacteria by promoting the formation of biofilms

Graphene oxide (GO) is increasingly used in a range of fields, such as electronics, biosensors, drug delivery, and water treatment, and the likelihood of its release into the environment is increasing correspondingly. GO is involved in the formation of biofilms and leads bacteria to over proliferate, but the effects of GO on bacteriophage infection remain unexplored. We noted bacterial overgrowth in experiments when GO was used to treat the bacterial culture medium, leading us to question whether bacterial proliferation caused by GO affects phage infection of target bacteria. Treating Pseudomonas aeruginosa with GO at a low dosage (0.02 mg/mL) led to biofilm expansion in LB medium. Biofilm formation in the presence of GO affected the ability of bacteriophages to kill bacteria and reproduce. Similarly, the presence of GO deposits increased the ratio of bacteria to phage, providing a favorable environment for bacterial growth. Additionally, increasing the positive electrical charge in the culture environment inhibited the rejection of bacteriophages by negatively charged GO, improving phage reproduction. Finally, adding GO to sewage in imitation field experiments significantly increased the bacterial diversity and richness in the sewage, stimulating a significant increase in the variety and number of bacteria. Collectively, these results indicate that GO hinders phage infection by providing a bacterial refuge. The results of this study provide valuable insights into how GO interacts with bacteriophages to explore the effects on bacterial growth.

In situ anchoring of iron and zinc oxides nanoparticles onto rice husk cellulose for efficient wastewater remediation

The development of effective and economical technologies for the treatment of contaminated wastewater has been of great significance to researchers. Therefore, an equal molar ratio of iron and zinc oxides nanoparticles was hydrothermally immobilized on the cellulose fibers of rice husk. Using XRD, SEM, FTIR, EDX, TEM, VSM, BET, and TGA/DTG, the structure, and characteristics of Cel/α-Fe₂O₃-ZnO, a ternary nanocomposite, were affirmed. The nanocomposite displayed a mesoporous structure with a substantial surface area. The efficiency of nanocomposite as a new adsorbent has been studied for the extraction of reactive black 5 (RB5), which is a diazo-anionic dye from simulated wastewater. The medium's pH was the dominant factor of RB5 adsorption, and the optimal removal effectiveness was acquired at pH 2. The adsorption values of RB5 correspond to second-order kinetics. They also matched Langmuir with a maximum capacity of 99.30 mg g^-1. For real industrial wastewater, Cel/α-Fe₂O₃-ZnO has successfully reduced a number of major pollutants, including ammonia (92.73 %), color (92.88 %), COD (91.53 %), BOD₅ (84.97 %), TSS (96.27 %), TP (52.17 %) and TN (47.23 %). These results illustrate the effective application of the ternary nanocomposite in wastewater treatment.

Polyols and Polyurethane Foams Based on Water-Soluble Chitosan

At present, majority of polyols used in the synthesis of polyurethane foams are of petrochemical origin. The decreasing availability of crude oil imposes the necessity to convert other naturally existing resources, such as plant oils, carbohydrates, starch, or cellulose, as substrates for polyols. Within these natural resources, chitosan is a promising candidate. In this paper, we have attempted to use biopolymeric chitosan to obtain polyols and rigid polyurethane foams. Four methods of polyol synthesis from water-soluble chitosan functionalized by reactions of hydroxyalkylation with glycidol and ethylene carbonate with variable environment were elaborated. The chitosan-derived polyols can be obtained in water in the presence of glycerol or in no-solvent conditions. The products were characterized by IR, 1H-NMR, and MALDI-TOF methods. Their properties, such as density, viscosity, surface tension, and hydroxyl numbers, were determined. Polyurethane foams were obtained from hydroxyalkylated chitosan. The foaming of hydroxyalkylated chitosan with 4,4′-diphenylmethane diisocyanate, water, and triethylamine as catalysts was optimized. The four types of foams obtained were characterized by physical parameters such as apparent density, water uptake, dimension stability, thermal conductivity coefficient, compressive strength, and heat resistance at 150 and 175 °C. It has been found that the obtained materials had most of the properties similar to those of classic rigid polyurethane foams, except for an increased thermal resistance up to 175 °C. The chitosan-based polyols and polyurethane foams obtained from them are biodegradable: the polyol is completely biodegraded, while the PUF obtained thereof is 52% biodegradable within 28 days in the soil biodegradation oxygen demand test.

Synergistic Effect of Iron and Copper Oxides in the Removal of Organic Dyes Through Thermal Induced Catalytic Degradation Process

This study proposes a new method for producing α-Fe2O3–CuO nanocatalyst that is both cost-effective and ecologically benign. The α-Fe2O3–CuO nanocomposite was prepared via moderate thermal oxidative decomposition of copper hexacyanoferrate. Its structure and surface morphology are affirmed via XRD, SEM, FTIR, EDX, TEM, XPS, and VSM. In the presence of H2O2, α-Fe2O3–CuO is employed as a heterogeneous catalyst to stimulate thermally induced degradation of dyes such as direct violet 4, rhodamine b, and methylene blue. The synergistic effect of Fe2O3 and CuO enhanced the catalytic activity of the nanocomposite compared to Fe2O3 and CuO separately. The effectiveness of DV4 degradation is optimized by evaluating multiple reaction parameters. The reaction rate increased substantially with the temperature, revealing its key role in the degradation process. Higher H2O2 levels and the inclusion of inorganic anions like chloride or nitrate also sped up the degradation process. While sulfate and humic acid, particularly at high doses, slowed it. The mechanism of H2O2 activation on α-Fe2O3–CuO is studied. The measurements of chemical oxygen demand and total organic carbon indicate that all dyes are highly mineralized. The remarkable performance and stability of this nanocomposite in removing diverse dyes render it a promising option for wastewater remedy.

Magnetic Field Effect on Coagulation Treatment of Wastewater Using Magnetite Rice Starch and Aluminium Sulfate

The use of synthetic coagulants to reduce suspended particles from drinkable water and wastewater is prompting new issues because it poses many health and environmental risks. Hence, improving the coagulation process using sophisticated nanotechnology with a magnetic field (MF) for quick recoverability emerges as being useful. In this study, the effects of magnetite rice starch (MS) and aluminum sulfate (alum) were investigated at a constant dose (3 g or 3000 mg/L) using a Jar test (six beakers) as potential low-cost coagulants for industrial wastewater treatment. At a high magnification of 1000× and a surface pore size of 298 µm, scanning electron microscopy and energy dispersive X-ray (SEM/EDX) analyses were utilized to elucidate the morphology of the coagulants. Coagulation was performed at 150 rpm (quick mixing) for 2 min, and 30 rpm (slow mixing) for 15 min. Thereafter, samples were allowed to settle (10-60 min) with and without MF. The findings showed more than 65% contaminants removal (turbidity and TSS) and 30% chemical oxygen demand (COD) removal using alum while MS showed 80% contaminants removal (turbidity and TSS) and 50% COD removal. MS showed an increase of more than 3% in contaminants removal (COD, turbidity, and TSS) when exposed to MF. As a result, the use of MS together with MF in water and wastewater treatment is anticipated as an environmentally benign and effective coagulant.

Effect of Magnetized Coagulants on Wastewater Treatment: Rice Starch and Chitosan Ratios Evaluation

Coagulation with synthetic chemicals has been used to treat a wide range of industrial effluents. Herein, the unique characteristics of industrial effluents being detrimental to the environment warrants urgent resource-efficient and eco-friendly solutions. Therefore, the study investigated the use of two magnetized coagulants (chitosan magnetite (CF) and rice starch magnetite (RF)), prepared via co-precipitation in three different ratios (1:2, 1:1 and 2:1) of natural coagulants (chitosan or rice starch) and magnetite nanoparticles (F) as alternative coagulants to alum for the treatment of wastewater. A Brunauer–Emmett–Teller (BET) analyzer, an X-ray diffraction (XRD) analyzer, and energy-dispersive X-ray (EDX) spectroscopy were used to characterize the surface area, crystal structure, and elemental composition of the coagulants. The influences of settling time (10–60 min) on the reduction of turbidity, color, phosphate, and absorbance were studied. This was carried out with a jar test coupled with six beakers operated under coagulation conditions of rapid stirring (150 rpm) and gentle stirring (30 rpm). Wastewater with an initial concentration of 45.6 NTU turbidity, 315 Pt. Co color, 1.18 mg/L phosphate, 352 mg/L chemical oxygen demand (COD), and 73.4% absorbance was used. The RF with a ratio of 1:1 was found to be the best magnetized coagulant with over 80% contaminant removal and 90% absorbance. The treatability performance of RF (1:1) has clearly demonstrated that it is feasible for wastewater treatment.

Adsorptive removal of pollutants from water using magnesium ferrite nanoadsorbent: a promising future material for water purification

Nanoadsorbents having large specific surface area, high pore volume with tunable pore size, affordability and easy magnetic separation gained much popularity in recent time. Iron-based nanoadsorbents showed higher adsorption capacity for different pollutant removal from water among other periodic elements. Spinel ferrite nanomaterials among iron-bearing adsorbent class performed better than single iron oxide and hydroxides due to their large surface area, mesoporous pore, high pore volume and stability. This work aimed at focusing on water treatment using magnesium ferrite (MgFe₂O₄) nanomaterials. Synthesis routes, properties and pollutant adsorption were critically investigated to explore the performance of magnesium ferrite in water treatment. Structural and surface properties were greatly affected by the factors involved in different synthesis routes and iron and magnesium ratio. Complete removal of pollutants through adsorption was achieved using magnesium ferrite. Pollutant adsorption capacity of MgFe₂O₄ and its modified forms was found several folds higher than Fe₂O₃ and Fe₃O₄ nanomaterials. In addition, MgFe₂O₄ showed strong stability in water than other pure iron oxide and hydroxide. Modification with graphene oxide, activated carbon, biochar and silica was demonstrated to be beneficial for enhanced adsorption capacity. Complex formation was suggested as a dominant mechanism for pollutant adsorption. These nanomaterials could be a viable and competitive adsorbent for diverse pollutant removal from water.

Immobilization of Trametes versicolor laccase on chitosan/halloysite as a biocatalyst in the Remazol Red RR dye

In this study, the laccase obtained from Trametes versicolor was immobilized onto the chitosan(CTS)/halloysite (HNT) beads. In the immobilization step, the effects of chitosan (1-3% w/v), halloysite (0-2% w/v), glutaraldehyde (0.5-1.5% v/v) and enzyme concentrations (1-3%) on loading and immobilization efficiency were investigated. SEM, FT-IR, XRD, TGA and XPS analyses were performed to examine the structure of beads. In addition, the effects of parameters such as pH (4-10), temperature (25-55 °C), storage life on the activity of free and immobilized laccase were also investigated. The activities of free and immobilized laccase preserved 23% and 56% of its initial activity at the end of 59 days of storage. The effects of mediators such as 2.2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), 1-Hydroxybenzotriazole hydrate (HBT), 2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO) and violuric acid (VLA) on the dye removal efficiency were investigated. Reusability of the CTS/HNT/Lac in the presence of HBT and VLA mediators, which enable the highest dye removal, was tested. After 15 cycles, 42% and 54% dye removal were achieved with the CTS/HNT/Lac in the medium containing HBT and VLA, and 42% and 49% of the activity is preserved, respectively. This study showed that CTS/HNT/Lac can be used repeatedly for Remazol Red RR dye removal.