Flocculation of combined contaminants of dye and heavy metal by nano-chitosan flocculants

Rational design of a dual-bacterial system for synchronous removal of antibiotics and Pb(Ⅱ)/Cd(Ⅱ) from water

Facing the combined pollution of antibiotics and heavy metals caused by livestock excrement and industrial effluents, how to use microbial technology to remove these pollutants simultaneously is an important research topic in environmental remediation. In addition, quick separation of the bacteria-water after remediation is also an urgent problem. In this study, we gradually developed a dual-bacteria microbial treatment technology capable of removing Pb(Ⅱ), Cd(Ⅱ) and common antibiotics, as well as self-settling after treatment. The key technology in this study mainly includes modifying the bacterial membrane proteins using Pb-binding protein PbrR, Cd-binding protein CadR and bacterial laccase CotA via surface-display technology to maximize the removal of Pb(Ⅱ), Cd(Ⅱ) and antibiotics, separately. Besides, the introduction of nanobody-antigen adhesion facilitated the self-settling in dual-bacterial system. Then, we studied its effectiveness in removing single pollutants, analyzed the influence of different heavy metal ions, and conducted detailed studies on the kinetics. Further characterization of heavy metal biosorption behavior was conducted using SEM, SEM-EDS, FTIR, and XPS techniques. Via protein fusion and dual vector expression, we constructed a dual-bacteria treatment system that could achieve rapid, selective removal of combined pollutants at a wide pH range temperature range, ultimately precipitating at bottom. Finally, molecular dynamics simulation was employed to elucidate the molecular mechanism underlying the selective biosorption by metal-binding proteins. The findings in this study hold significant implications for achieving selective pollutant removal using engineering bacteria in complex water environments.

Preparation of dandelion flower extract-based polyvinyl alcohol-chitosan-dandelion-CuNPs composite gel for efficient bacteriostatic and dye adsorption

A multifunctional composite gel with efficient bacteriostatic and dye adsorption properties was prepared using polyvinyl alcohol, chitosan, and soybean isolate protein as carriers, CuNPs prepared by green reduction of dandelion extract as bacteriostatic agent, and glutaraldehyde as cross-linking agent. The composite gel showed good inhibition capacity of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa with the diameter of inhibition zone of 27.0-28.3 mm by agar diffusion method. The composite gel antibacterial rate remained above 90 % after 14 days of preparation. After 6 times reuse of composite gel in water, the antibacterial rate remained above 90 %, proving its good stability and reusability. Adding dandelion extract and CuNPs greatly improved the gel antioxidant property, acquiring free radical scavenging rate at 95.6 %. This composite gel had good biocompatibility and adsorption performance, and the maximum adsorption amount of methylene blue and methyl orange was 40.36 mg/g and 41.81 mg/g, respectively. To sum up, the green composition of composite gel has good antimicrobial performance and high dye adsorption, which holds significant promising for treating the water body pollution and protecting the environment. To build cost-effective antibacterial and dye adsorption process on a large-scale, in-depth exploration about this topic is still needed to develop.

Investigation of adsorption potential of waste jewelry meerschaum powder for Cu(II) and cationic dye

The presence of heavy metals and pollutant dyes can have detrimental effects on aquatic ecosystems and compromise aquatic aesthetics. This study investigates the use of unprocessed waste gem meerschaum powder as a new adsorbent in the removal of both Cu(II) and methylene blue (MB) from aqueous solutions to reduce water pollution. The structure of the waste powder was characterized by FT-IR, XRD, SEM and BET methods. Optimization of Cu(II) and MB dye removal was carried out using design of experiment technique. Under optimum conditions, remarkable removal efficiencies of 95.5% (± 3.7) for Cu(II) and 97.8% (± 0.4) for MB were achieved. The removal of Cu(II) followed the Freundlich isotherm model, while the removal of MB dye adhered to the Langmuir isotherm model. Both adsorption processes obeyed the pseudo-second-order kinetic model and occurred spontaneously. This innovative approach offers a promising solution to water pollution by highlighting the importance of sustainable and cost-effective waste use.

The performance of quaternary-ammonium chitosan in wastewater treatment: The overlooked role of solubility

Quaternary-ammonium chitosan (CT-CTA) is a popular water treatment agent, and its electropositivity and cation strength are improved compared with chitosan. The use of CT-CTA is widely advocated to remove suspended particles and organic matter from wastewater. However, the solubility of CT-CTA is an important factor affecting the performance of CT-CTA, which is a neglected problem in previous studies. In the study, CT-CTA with different solubilities were prepared by adjusting pH from 2 to 7 in preparation, and their applications were explored in wastewater. When the pH was 2, 2.5, or 3, the obtained CT-CTA was a dissolved state. The turbidity and color removal were 95 % - 98 % and 60 % - 74 %, respectively. When the pH was 4, 5, 6, or 7, the obtained CT-CTA was a solid state. The turbidity and color removal were 30 % - 63 % and 90 % - 97 %, respectively. For domestic-wastewater treatment, CT-CTA in a dissolved state removed 92 % of turbidity and 50 % of chemical oxygen demand (COD). CT-CTA in a solid state removed 86 % of turbidity and 64 % of COD with poly aluminum chloride (PAC). The results illustrated the performance of CT-CTA with different solubilities, which can broaden its application in wastewater treatment.

Harnessing the Potential of Chitosan and Its Derivatives for Enhanced Functionalities in Food Applications

As one of the most abundant natural polysaccharides that possess good biological activity, chitosan is extracted from chitin. Its application in the food field is being increasingly valued. However, chitosan extraction is difficult, and its poor solubility limits its application. At present, the extraction methods include the acid-base method, new chemical methods, and biological methods. The extraction rates of chitin/chitosan are 4-55%, 13-14%, and 15-28%, respectively. Different chemical modifications have different effects on chitosan, making it applicable in different fields. This article reviews and compares the extraction and chemical modification methods of chitosan, emphasizing the importance of green extraction methods. Finally, the application prospects of chitosan in the food industry are discussed. This will promote the understanding of the advantages and disadvantages of different extraction methods for chitosan as well as the relationship between modification and application, providing valuable insights for the future development of chitosan.

Facile synthesis of S, N-co-doped carbon dots for bio-imaging, Fe3+ detection and DFT calculation

Turning waste into wealth, herein, two highly fluorescent N and S co-doped carbon dots (N, S-CDs-A and N, S-CDs-B) were synthesized by the hydrothermal reaction of contaminant reactive red 2 (RR2) and L-cysteine or L-methionine, respectively. The detailed morphology and structure of N, S-CDs were characterized by XRD, Raman spectrum, FTIR spectra, TEM, HRTEM, AFM and XPS. The maximum fluorescent of N, S-CDs-A and N, S-CDs-B are 565 and 615 nm under different excitation wavelengths with moderate fluorescence intensity of 14.0 % and 6.3 %, respectively. The microstructure models of N, S-CDs-A and N, S-CDs-B, which were induced by FT-IR, XPS and element analysis, had been applied in DFT calculation. The result indicated that the doping of S and N is beneficial to obtain the red-shift of fluorescent spectra. Both N, S-CDs-A and N, S-CDs-B showed highly sensitive and selective to Fe3+. N, S-CDs-A can also detect Al3+ ion with high sensitivity and selectivity. Finally, N, S-CDs-B was successfully applied in cell imaging.

Superior performance of novel chitosan-based flocculants in decolorization of anionic dyes: Responses of flocculation performance to flocculant molecular structures and hydrophobicity and flocculation mechanism

To achieve economical and efficient decolorization, two novel flocculants, weakly hydrophobic comb-like chitosan-graft-poly (N, N-Dimethylacrylamide) (CSPD) and strongly hydrophobic chain-like chitosan-graft-L-Cyclohexylglycine (CSLC) were synthesized in this study. To assess the effectiveness and application of CSPD and CSLC, the impacts of factors, including flocculant dosages, initial pH, initial dye concentrations, co-existing inorganic ions and turbidities, on the decolorization performance were explored. The results suggested that the optimum decolorizing efficiencies of the five anionic dyes ranged from 83.17% to 99.40%. Moreover, for accurately controlling flocculation performance, the responses to flocculant molecular structures and hydrophobicity in flocculation using CSPD and CSLC were studied. The Comb-like structure gives CSPD a wider dosage range for effective decolorization and better efficiencies with large molecule dyes under weak alkaline conditions. The strong hydrophobicity makes CSLC more effective in decolorization and more suitable for removing small molecule dyes under weak alkaline conditions. Meanwhile, the responses of removal efficiency and floc size to flocculant hydrophobicity are more sensitive. Mechanism studies revealed that charge neutralization, hydrogen bonding and hydrophobic association worked together in the decolorization of CSPD and CSLC. This study has provided meaningful guidance for developing flocculants in the treatment of diverse printing and dyeing wastewater.

Influence of structure and functional group of modified kraft lignin on adsorption behavior of dye

Utilization of kraft lignin to produce bio-based adsorptive material for effective dye adsorption from industrial wastewater is essential to fulfilling the significant environmental protection needs. Lignin is the most abundant byproduct material with a chemical structure containing various functional groups. However, the complicated chemical structure makes it somewhat hydrophobic and incompatible, which limits its direct application as an adsorption material. Chemical modification is a common way to enhance lignin properties. In this work, the kraft lignin was modified through direct amination using Mannich reaction and oxidization followed by amination as new route of lignin modification. The prepared lignins, including aminated lignin (AL), oxidized lignin (OL), and aminated-oxidized lignin (AOL), as well as unmodified kraft lignin, were analyzed by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), elemental analysis and ¹H-nuclear magnetic resonance measurements (¹HNMR). The adsorption behaviors of modified lignins for the malachite green in aqueous solution were investigated well and discussed, as well as the adsorption kinetics and thermodynamic equations. Compared with other aminated lignin (AL), the AOL displayed a high adsorption capacity of 99.1 % dye removal, due to its more effective functional groups. The change in structure and functional groups on the lignin molecules during oxidation and amination had no effect on its adsorption mechanisms. The adsorption process of malachite green on different kinds of lignin belongs to endothermic chemical adsorption, which mainly consists of monolayer adsorption. The modification of lignin through oxidation followed by amination process, afforded kraft lignin a broad potential application in the field of wastewater treatment.

Recent advances in nanomaterials based sustainable approaches for mitigation of emerging organic pollutants

Emerging organic pollutants (EOPs) are a category of pollutants that are relatively new to the environment and recently garnered a lot of attention. The majority of EOPs includes endocrine-disrupting chemicals (EDCs), antibiotic resistance genes (ARGs), pesticides, dyes and pharmaceutical and personal care products (PPCPs). Exposure to contaminated water has been linked to an increase in incidences of malnutrition, intrauterine growth retardation, respiratory illnesses, liver malfunctions, eye and skin diseases, and fatalities. Consequently, there is a critical need for wastewater remediation technologies which are effective, reliable, and economical. Conventional wastewater treatment methods have several shortcomings that can be addressed with the help of nanotechnology. Unique characteristics of nanomaterials (NMs) make them intriguing and efficient alternative in wastewater treatment strategies. This review emphasis on the occurrence of divers emerging organic pollutants (EOPs) in water and their effective elimination via different NMs based methods with in-depth mechanisms. Furthermore, it also delves the toxicity assessment of NMs and critical challenges, which are crucial steps for practical implementations.

Aleppo pine seeds (Pinus halepensis Mill.) as a promising novel green coagulant for the removal of Congo red dye: Optimization via machine learning algorithm

Consideration is now being given to the use of metal coagulants to remove turbidity from drinking water and wastewater. Concerns about the long-term impact of non-biodegradable sludge on human health and the potential contamination of aquatic systems are gaining popularity. Recently, alternative biocoagulants have been suggested to address these concerns. In this study, using a 1 M sodium chloride (NaCl) solution, the active coagulating agent was extracted from Pinus halepensis Mill. Seed, and used for the first time to remove Congo red dye, the influence of numerous factors on dye removal was evaluated in order to make comparisons with conventional coagulants. The application of biocoagulant was shown to be very successful, with coagulant dosages ranging from 3 to 12 mL L^-1 achieving up to 80% dye removal and yielding 28 mL L^-1 of sludge. It was also found that biocoagulant is extremely pH sensitive with an optimum operating pH of 3. Ferric chloride, on the other hand, achieved similar removal rate with higher sludge production (46 mL L^-1) under the same conditions. A Fourier Transform Infrared Spectroscopy and proximate composition analysis were undertaken to determine qualitatively the potential active coagulant ingredient in the seeds and suggested the involvement of proteins in the coagulation-flocculation mechanism. The evaluation criteria of the Support vector machine_Gray wolf optimizer model in terms of statistical coefficients and errors reveals quite interesting results and demonstrates the performance of the model, with statistical coefficients close to 1 (R = 0.9998, R² = 0.9995 and R² adj = 0.9995) and minimal statistical errors (RMSE = 0.5813, MSE = 0.3379, EPM = 0 0.9808, ESP = 0.9677 and MAE = 0.2382). The study findings demonstrate that Pinus halepensis Mill. Seed extract might be a novel, environmentally friendly, and easily available coagulant for water and wastewater treatment.

Amidoxime functionalized PVDF-based chelating membranes enable synchronous elimination of heavy metals and organic contaminants from wastewater

Aiming at the synchronous elimination of heavy metals and organic contaminants from wastewater, the amidoxime functionalized PVDF-based chelating membrane was fabricated in this study. The structure and morphology of the chelating membrane were characterized using infrared spectroscopy (FT-IR), nuclear magnetic resonance spectrometer (NMR) and scanning electron microscopy (SEM). The SEM results show that the chemical modification with amidoxime groups did not damage the structure of the PVDF-based membrane. The chelating membrane has a high removal efficiency for Cu²⁺ (77.33%) and Pb²⁺ (79.23%) owing to the chemisorption through coordination bonds. However, the chelating membrane exhibits a low removal efficiency for Cd²⁺ (29.88%) due to the physical adsorption. The chelating membrane has a high rejection efficiency of BSA (95.17%) and lysozyme (70.09%), which is attributed to the sieving effect and increased hydrophobicity. Furthermore, the membrane performance for simultaneously removing metals and proteins from simulated wastewater was examined. The interaction of metal ions with proteins (BSA and lysozyme) can enhance the ion removal efficiency of the chelated membrane, but decrease the protein rejection efficiency due to the destructive effect. The amidoxime functionalized PVDF-based chelating membrane has a high potential for application in wastewater treatment.