Coagulation/flocculation process for dye removal using sludge from water treatment plant: optimization through response surface methodology

Electrochemical Recovery to Overcome Direct Osmosis Concentrate-Bearing Lead: Optimization of Treatment Process via RSM-CCD

The use of electrochemistry is a promising approach for the treatment of direct osmosis concentrate that contains a high concentration of organic pollutants and has high osmotic pressure, to achieve the safe discharge of effluent. This work addresses, for the first time, this major environmental challenge using perforated aluminum electrodes mounted in an electrocoagulation–flotation cell (PA-ECF). The design of the experiments, the modeling, and the optimization of the PA-ECF conditions for the treatment of DO concentrate rich in Pb were explored using a central composite design (CCD) under response surface methodology (RSM). Therefore, the CCD-RSM was employed to optimize and study the effect of the independent variables, namely electrolysis time (5.85 min to 116.15 min) and current intensity (0.09 A to 2.91 A) on Pb removal. Optimal values of the process parameters were determined as an electrolysis time of 77.65 min and a current intensity of 0.9 A. In addition to Pb removal (97.8%), energy consumption, electrode mass-consumed material, and operating cost were estimated as 0.0025 kWh/m3, 0.217 kg Al/m3, and 0.423 USD/m3, respectively. In addition, it was found that DO concentrate obtained from metallurgical wastewater can be recovered through PA-ECF (almost 94% Pb removal). This work demonstrated that the PA-ECF technique could became a viable process applicable in the treatment of DO concentrate containing Pb-rich for reuse.

Preparation of clinoptilolite/starch/CoFe2O4 magnetic nanocomposite powder and its elimination properties for cationic dyes from water and wastewater

A new magnetic nanocomposite clinoptilolite (CLT)/Starch/CoFe₂O₄ was synthesized using co-precipitation method. The prepared magnetic composite powder was utilized for decontamination of methylene blue dye (MBD), methyl violet dye (MVD), and crystal violet dye (CVD) from water media. The BET analysis showed that CLT modification using starch and CoFe₂O₄ nanoparticles improved its specific surface and the amount of specific surface area for CLT, CoFe₂O_4, and CLT/Starch/CoFe₂O₄ powder was reported to be 18.82 m².g^-1, 151.4 m².g^-1, and 104.75 m².g^-1, respectively. Experimental results showed that pH 9 had a vital role in the adsorption process of all three types. Langmuir and Redlich-Petersen isotherm models were well fitted with experimental data. Also, the maximum adsorption capacity of CVD, MBD, and MVD to the desired composite was determined as 32.84 mg.g^-1, 31.81 mg.g^-1, and 31.15 mg.g^-1, respectively. In addition, the kinetic data of the removal process followed a pseudo-first order (PFO) kinetic model. Negative thermodynamic parameters were indicated that the process is spontaneous and exothermic. Finally, ad(de)sorption experiments' results showed that the synthesized nanocomposite adsorbent has an excellent ability to adsorb cationic dyes after several consecutive cycles.

Molecular Dynamics Study of the Conformation, Ion Adsorption, Diffusion, and Water Structure of Soluble Polymers in Saline Solutions

Polymers have interesting physicochemical characteristics such as charge density, functionalities, and molecular weight. Such attributes are of great importance for use in industrial purposes. Understanding how these characteristics are affected is still complex, but with the help of molecular dynamics (MD) and quantum calculations (QM), it is possible to understand the behavior of polymers at the molecular level with great consistency. This study was applied to polymers derived from polyacrylamide (PAM) due to its great use in various industries. The polymers studied include hydrolyzed polyacrylamide (HPAM), poly (2-acrylamido-2-methylpropanesulfonate) (PAMPS), polyacrylic acid (PAA), polyethylene oxide polymer (PEO), and guar gum polysaccharide (GUAR). Each one has different attributes, which help in understanding the effects on the polymer and the medium in which it is applied along a broad spectrum. The results include the conformation, diffusion, ion condensation, the structure of the water around the polymer, and interatomic polymer interactions. Such characteristics are important to selecting a polymer depending on the environment in which it is found and its purpose. The effect caused by salinity is particular to each polymer, where polymers with an explicit charge or polyelectrolytes are more susceptible to changes due to salinity, increasing their coiling and reducing their mobility in solution. This naturally reduces its ability to form polymeric bridges due to having a polymer with a smaller gyration radius. In contrast, neutral polymers are less affected in their structure, making them favorable in media with high ionic charges.

In-situ investigation of dye pollutant adsorption performance on graphitic carbon nitride surface: ATR spectroscopy experiment and MD simulation insight

The adsorption performances on graphitic carbon nitride (g-C₃N₄) surface were investigated for organic dye pollutants by both experimental and calculation methods. For experimental investigation, adsorption thermodynamics and kinetics results were in-situ obtained and evaluated. With [Formula: see text] by Langmuir modeling^, g-C₃N₄ showed superior adsorption spontaneity of MB⁺ >MO^-. With linear and exponential modeling, g^-C₃N₄ showed only adsorption process for MB⁺ but both diffusion and adsorption processes for MO^-. For simulation insight, all MB⁺ molecules but only parts of MO^- molecules were inclined to orient in parallel position at g-C₃N₄ surface after optimization during low concentration. And both MB⁺ and MO^- molecules were inclined to orient in perpendicular position at g-C₃N₄ surface after optimization during high concentration. Combined with experimental and calculation results, a molecular-orientation and force-dominance mechanism adsorption model are proposed to explain the surface interaction processes between dyes and g-C₃N₄. Electrostatic interaction and π-π stacking interaction were revealed to dominate for MB⁺ adsorption, and π-π stacking interaction and van der Waals force were revealed to dominate for MO^- adsorption. This work obtained 'localized' interfacial information and elucidated in-situ intermolecular interactions at g-C₃N₄ interface, which can provide fundamental basis for operation removal of organic dye pollutants by g-C₃N₄.

Understanding the by-product formation potential during phenol oxidation from in-situ electro-generated radicals by microalgae harvesting

Advanced oxidation processes have gained colossal attention owing to the prospect of accessible mineralization, but by-product formation and its toxicity evaluation are still inconclusive. The present study demonstrated the performance of electrochemical oxidation process supported with graphite electrodes for the oxidation of phenol from modulated coke oven wastewater. The results suggested that the hydrogen peroxide along with the in-situ synthesized oxidizing agents has the ability to increase the phenol mineralization 1.5 times and by-product toxicity potential on microalgae, Scenedesmus sp. CBIIT(ISM) also revealed that chlorophyll-a synthesis has increased after the electro-oxidation process in coke oven wastewater. The experimental results for phenol mineralization and by-product formation were validated using a mass spectrophotometer.

Multicomponent transport model-based scaling up of long-term fixed bed adsorption of reactive dyes from textile effluent using aminated PAN beads

Novel functionalized polymeric beads have been prepared by a simple phase inversion technique and its potential as an effective sorbent for reactive dyes is studied. Polyacrylonitrile was used as the base polymer for the beads that were further functionalized using diethylenetriamine. Scanning electron microscopy, FTIR spectroscopy, BET technique, TGA analysis, and zeta potential measurement were used for characterization of the functionalized beads. The adsorption characteristics of the beads were analyzed through adsorption isotherms. A first-principle-based pore diffusion-adsorption model was employed to study adsorption process of the functionalized beads and to determine various mass transfer parameters, i.e., mass transfer coefficient and effective pore diffusivity, in both single and multicomponent cases. For different reactive dyes, the beads have adsorption capacities in the range of 170-230 mg/g. Effects of different operating parameters, i.e., inlet concentration of solute, influent rate, and bed depth were studied to determine the breakthrough performance of the columns prepared with the beads. Industrial dye effluent, containing four reactive dyes at different initial concentrations, was used to study multicomponent adsorption in the columns. The regeneration efficiency of the beads was determined using aqueous cationic surfactant solution. Finally, scaling up of the fixed bed columns was carried out using a first principle-based transport model based on pore diffusion-adsorption processes.

Pilot-Scale Study of Real Domestic Textile Wastewater Treatment Using Cassia fistula Seed-Derived Coagulant

Plant-derived coagulants have exhibited a good potential in wastewater treatment due to their “green” characteristics, high coagulating-flocculating activity, cost-effectiveness, and biodegradability. Nevertheless, research studies have focused mainly on bench-scale experiments; pilot-scale and full-scale simulations are still limited. Herein, we firstly report a pilot-scale study of real domestic textile wastewater treatment using Cassia fistula coagulant. The material characterizations using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and dynamic light scattering (DLS) revealed that the natural gum extracted from C. fistula seed possessed a rough and irregular surface containing a high molecular weight galactomannan. The bench-scale investigation was initially conducted to determine the optimal pollutant concentration, initial pH, and coagulant dosage in the coagulation-flocculation process. The pilot-scale study revealed that C. fistula coagulant is an effective material for real textile wastewater treatment, showing percentage removal of 93.83% at a volume of 30 L and a coagulant dosage of 1.17 mg·L−1. Coagulation-flocculation using C. fistula seed gum could be an efficient primary wastewater treatment prior to membrane or biological methods to meet Vietnamese environmental standards. The main mechanisms of textile wastewater treatment involve adsorption/bridging interactions via hydrogen bonding and electrostatic attraction between negatively charged carboxylate groups of the coagulant and positively charged pollutants.

Coagulated Mineral Adsorbents for Dye Removal, and Their Process Intensification Using an Agitated Tubular Reactor (ATR)

The aim of this study was to understand the efficacy of widely available minerals as dual-function adsorbers and weighter materials, for the removal of toxic azo-type textile dyes when combined with coprecipitation processes. Specifically, the adsorption of an anionic direct dye was measured on various mineral types with and without the secondary coagulation of iron hydroxide (‘FeOOH’) in both a bench-scale stirred tank, as well as an innovative agitated tubular reactor (ATR). Talc, calcite and modified bentonite were all able to remove 90–95% of the dye at 100 and 200 ppm concentrations, where the kinetics were fitted to a pseudo second-order rate model and adsorption was rapid (<30 min). Physical characterisation of the composite mineral-FeOOH sludges was also completed through particle size and sedimentation measurements, as well as elemental scanning electron microscopy to determine the homogeneity of the minerals in the coagulated structure. Removal of >99% of the dye was achieved for all the coagulated systems, where additionally, they produced significantly enhanced settling rates and bed compression. The greatest settling rate (9 mm min−1) and solids content increase (450% w/w) were observed for the calcium carbonate system, which also displayed the most homogenous distribution. This system was selected for scale-up and benchmarking in the ATR. Dye removal and sediment dispersion in the ATR were enhanced with respect to the bench scale tests, although lower settling rates were observed due to the relatively high shear rate of the agitator. Overall, results highlight the applicability of these cost-effective minerals as both dye adsorbers and sludge separation modifiers to accelerate settling and compression in textile water treatment. Additionally, the work indicates the suitability of the ATR as a flexible, modular alternative to traditional stirred tank reactors.

Low cost effective heterogeneous photo-Fenton catalyst from drinking water treatment residuals for reactive blue 19 degradation: Preparation and characterization

Four different catalysts from drinking water treatment residuals (DWTR) were prepared via impregnation in the iron nitrate, calcined at different temperatures ranged from 200°C to 500°C, and tested for the reactive blue 19 oxidation using the heterogeneous photo-Fenton, under UVA light source. XRD and XPS results revealed that iron nature was found under a ferric oxide form (Fe³⁺ ) similar to the magnetite. Calcination temperature results showed a significant effect on the activity of the catalysts. RB19 and TOC removals were 99% and 79%, respectively, with the best catalyst that calcined at 500°C in optimal conditions as follows: initial pH solution = 3, 10 mM of H₂ O₂ dosage, 0.5 g/L of catalyst loading, reaction temperature 35°C, and I_UVA  = 3.55 MW/cm² for 50 mg/L of RB19. The reusability of the catalyst after three cycles showed complete removal of RB19 and 65% TOC removal. PRACTITIONER POINTS: Synthetized heterogeneous photo-Fenton catalyst from drinking water treatment residuals for the photo Fenton oxidation. The calcination temperatures plays a crucial role in catalyst photocatalytic activity. Degradation of reactive blue 19 with Fe/DWTR-500 in presence of H₂ O₂ . The Fe/DWTR-500 catalyst exhibited the best photocatalytic activity. Reusability studies of Fe/DWTR-500 and the kinetics of reactive blue 19 degradation were investigated.

Insight into Organic Pollutant Adsorption Characteristics on a g-C3N4 Surface by Attenuated Total Reflection Spectroscopy and Molecular Dynamics Simulation

Herein the adsorption characteristics of zwitterionic dye pollutant Rhodamine B (Rh⁺B^-) on a g-C₃N₄ surface were investigated by both an attenuated total reflection spectroscopy (ATRS) experiment and a molecular dynamics simulation (MDS). For experimental investigation, g-C₃N₄ was coated on a silica optical fiber (SOF) surface to fabricate an adsorption film. According to the ATRS response, adsorption thermodynamics and thermodynamics results were in situ obtained and evaluated. The isothermal Langmuir model was used to calculate the adsorption equilibrium constants (K_ads) and adsorption energies (ΔG_ads) for Rh⁺B^- as 27.25 × 10⁴ M^-1 and -31.01 kJ mol^-1, respectively, which indicated the spontaneous adsorption behavior of Rh⁺B^- at the g-C₃N₄ surface. Using dynamic Elovich modeling, the rate constants of Rh⁺B^- were found to be k₁ = 0.0063 min^-1 and k₂ = 0.0004 min^-1, which indicated two-stage adsorption at the g-C₃N₄ surface. For theoretical simulation, adsorption configurations and adsorption energies were systematically calculated by a molecular dynamics simulation (MDS) . Rh⁺B^- molecules were inclined to orient in a parallel position at the g-C₃N₄ surface during low concentration but a perpendicular position at the g-C₃N₄ surface during high concentration. Combined with experimental and calculation results, this work revealed the microscopic adsorption performance and elucidated the intermolecular interaction between localized interfaces of g-C₃N₄ and hazardous dye pollutant. We propose an adsorption model to explain the process of surface interaction, which is based on molecular orientation and a force-driven mechanism. Electrostatic attraction and π-π interaction dominated the adsorption interaction with an adsorption energy of ΔG_low(ads) = -38.96 kJ mol^-1 for low Rh⁺B^- concentration, and electrostatic attraction dominated the adsorption interaction with an adsorption energy of ΔG_high(ads) = -25.76 kJ mol^-1 for high Rh⁺B^- concentration. This work can provide a fundamental basis for a dye-pollutants removal application by g-C₃N₄ in both adsorption and photocatalyzation.

Dye degradation, antibacterial and in-silico analysis of Mg/cellulose-doped ZnO nanoparticles

Various concentrations of Mg into fixed amount of cellulose nanocrystals (CNC)-doped ZnO were synthesized using facile chemical precipitation. The aim of present study is to remove dye degradation of methylene blue (MB) and bactericidal behavior with synthesized product. Phase constitution, functional group analysis, optical behavior, elemental composition, morphology and microstructure were examined using XRD, FTIR, UV-Vis spectrophotometer, EDS and HR-TEM. Highly efficient photocatalytic performance was observed in basic medium (98%) relative to neutral (65%), and acidic (83%) was observed upon Mg and CNC co-doping. Significant bactericidal activity of doped ZnO nanoparticles depicted inhibition zones for G -ve and +ve bacteria ranging (2.20 - 4.25 mm) and (5.80-7.25 mm) for E. coli and (1.05 - 2.75 mm) and (2.80 - 4.75 mm) for S. aureus at low and high doses, respectively. Overall, doped nanostructures showed significant (P < 0.05) bactericidal efficacy against G +ve relative to G -ve. Furthermore, the molecular docking studies were employed to rationalize possible mechanism behind these in vitro bactericidal activities. In silico findings suggested CNC doped ZnO nanocomposites as possible inhibitors of β-lactamase (Binding score: -7.936 kcal/mol), DHFR (Binding score: -5.691 kcal/mol) and FabI (Binding score: -8.673 kcal/mol).

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

In this study, chitosan (CS) is used as a natural coagulant aid alongside graphene oxide (GO) to remove turbidity and numerous pollutants from raw and artificially contaminated surface water. The coagulation capability of the system (GO/CS) was assessed with respect to a water sample's turbidity, pH, coagulant dose, settling velocity, and temperature. The presence of CS enhanced the coagulation capacity of GO at varied pH levels and no GO residue was detected in the water after the treatment. The proposed system achieved high turbidity removal efficiency (≥98.3%) for all turbidity levels. A mixture of GO (8 mg/L) and CS (2 mg/L) was ideal to remove algae (99.5%) and bacteria (≥95.0%). Furthermore, it demonstrated a high coagulation capacity to remove dyes, direct brown-2 (DB-2), methylene blue (MB), and Pb(II) ions from artificially contaminated surface water. Interestingly, the sludge exhibited an extraordinary adsorption capacity for DB-2, MB, and Pb(II) ions. The adsorption process followed the pseudo-second-order kinetic model, and was consistent with the Langmuir model, with an adsorption capacity of up to 667.8, 400.7, and 459.1 mg/g for DB-2, MB, and Pb(II) ions, respectively. Therefore, the presented binary coagulation system is of great potential economic value for the treatment of raw surface water and wastewater.

Adsorption of Reactive Red 195 from aqueous medium using Lotus (Nelumbo nucifera) leaf powder chemically modified with dimethylamine: characterization, isotherms, kinetics, thermodynamics, and mechanism assessment

NOVELTY STATEMENT

In the modern era, dyes are inevitable and their surging usage leads to colossal contamination of aqueous streams, thereby threatening both the land and aquatic species. One among such dye is anionic Reactive Red 195 (RR 195), and traceable even at minute concentrations of aqueous streams, posing a severe threat to living species. Moreover, RR 195 is highly recalcitrant offering resistance to biodegradation due to the presence of an azo (-N=N-) group within its structure. Thus, there is a definite need to address the issue of eliminating RR 195 from industrial wastewater effluents. In lieu of this, the primitive objective of this study is to test the effectiveness of the natural adsorbent lotus leaf (Nelumbo nucifera) for the selective sorption of RR 195 from the aqueous stream. Although ample literature is available on the direct utilization of lotus leaf as adsorbent, yet no study was performed on the chemical modification (dimethylamine) of the aforementioned adsorbent. Hence, an attempt has been made in this direction to add a new sorbent into the adsorbents database.

Magnetic seeding coagulation: Effect of Al species and magnetic particles on coagulation efficiency, residual Al, and floc properties

Magnetic seeding coagulation (MSC) process has been used to accelerate flocs sedimentation with an applied magnetic field, offering large handling capacity and low energy consumption. The interactions of three typical Al species, aluminum chloride (AlCl₃), Al₁₃O₄(OH)₂₄⁷⁺ polymer (Al₁₃), and (AlO₄)₂Al₂₈(OH)₅₆¹⁸⁺ polymer (Al₃₀), with magnetic particles (MPs) were examined to clarify the MSC process. In traditional coagulation (TC) process, the aggregation of primary Al_a-dissolved organic matter (DOM) complexes with in-situ-formed polynuclear species generated a large average floc size (226 μm), which was proved to be efficient for DOC removal (52.6%). The weak connections between dissolved Al_a-DOM complexes and MPs led to the negligible changes of dissolved Al after seeding with MPs in AlCl₃. A significant interaction between MPs and Al₁₃ was observed, in which the MPs-Al₁₃-DOM complexes were proposed to be responsible for the significant improvement of DOC removal (from 47% to 52%) and residual total Al reduction (from 1.05 to 0.27 mg Al L^-1) with MPs addition. Al₃₀ produced a lower floc fractal dimension (D_f = 1.88) than AlCl₃ (2.08) and Al₁₃ (1.99) in the TC process, whereas its floc strength (70.9%) and floc recovery (38.5%) were higher than the others. Although more detached fragments were produced with MPs addition, the effective sedimentation of these fragments with the applied magnetic field led to the decrease of residual turbidity and colloidal Al in Al₃₀. The dependence of coagulation behavior to MPs and different Al species can be applied to guide the application of an effective MSC process.

Adsorption of Malachite Green Dye onto Mesoporous Natural Inorganic Clays: Their Equilibrium Isotherm and Kinetics Studies

Contamination of water with organic dyes is a major environmental concern as it causes serious life-threatening environmental problems. The present research was designed to evaluate the potential of three different natural inorganic clays (NICs) i.e., Pakistani bentonite clay (PB), bentonite purchased from Alfa Aesar (BT), and Turkish red mud (RM) for malachite green (MG) dye removal from an aqueous solution. Various analytical techniques, namely X-ray fluorescence spectrometry (XRF), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller surface area measurement (BET), and thermogravimetric analysis (TGA), were used to investigate the physicochemical properties of the NICs samples. The effect of adsorption operational parameters such as contact time, aqueous phase pH, dye concentration, and amount of NICs on the adsorption behavior of MG onto NICs samples were investigated under the batch adsorption system. The equilibrium and kinetic inspection reflected the best description of MG adsorption behavior by the Langmuir isotherm model and pseudo-first-order kinetic model, respectively. The results indicated that the adsorption was favorable at higher pH. The maximum adsorption capacities calculated by Langmuir isotherm for PB, BT, and RM were found to be 243.90 mg/g, 188.68 mg/g, and 172.41 mg/g, respectively. It can be concluded that natural inorganic clays with a higher surface area can be used as an effective adsorbent material to remove the MG dye from an aqueous solution.

Complex interior and surface modified alginate reinforced reduced graphene oxide-hydroxyapatite hybrids: Removal of toxic azo dyes from the aqueous solution

In this study, alginate reinforced reduced graphene oxide@hydroxyapatite (rGO@HAP-Alg) hybrids have been fabricated via co-precipitation technique. The developed adsorbent was effectively utilized for the removal of Reactive Blue 4 (RB4), Indigo Carmine (IC) and Acid Blue 158 (AB158) azo dyes from aqueous solution, and found to have the adsorption efficiency of 45.56, 47.16 and 48.26 mg/g, respectively. The thermodynamic parameters demonstrated the endothermic and spontaneous nature of the adsorption process. The adsorption system was pH-dependent and showed maximum dye removal at pH 6-7, which was indicative of the electrostatic interactions, surface complexation and the hydrogen bonding mechanisms involved between the adsorbate and adsorbent during the adsorption process. Furthermore, the renewability studies demonstrated the reusability and stability of rGO@HAP-Alg hybrids up to five successive cycles. This study delivers a promising strategy for removing dye molecules and extends the potential application of rGO@HAP-Alg hybrids to treat practical dye contaminated water/wastewater.

Biodegradable macro-porous CMC-polyaniline hydrogel: synthesis, characterization and study of microbial elimination and sorption capacity of dyes from waste water

Certainly water pollution control will play a key role in environmental health. Therefore, researchers are attempting to reduce the ecological effects of water pollution by creating restrictions in the use of chemicals or water reuse. Among all the available techniques, adsorption method attracted much attention due to the higher efficiency, cost-effectiveness and simplicity. So, in this work, novel biodegradable hydrogel based on carboxymethyl cellulose (CMC) and polyaniline (PANI) was introduced to remove toxic dyes from wastewater. The synthesis process was accomplished in two steps: free radical polymerization of acrylic acid (AA) on the CMC (0.25 g) in the presence of ammonium per sulfate (APS) as radical initiator (0.2 g) and N,N-methylene-bis-acrylamide (MBA) as crosslinker (0.1 g) at 70 °C, and after 30 min, growing PANI chains on the synthesized CMC-PAA hydrogel by radical polymerization of aniline (1.0 mL) in acidic condition (20 mL of hydrochloric acid 1.0 M) to form macro-porous conductive hydrogel (CMC-PAA-PANI). The resulted hydrogel showed high antibacterial activity and excellent biodegradability by natural soil microorganisms with decomposition to 91.7 %. Also, the final hydrogel exhibited reasonable conductivity and pH sensitivity properties.

Cucurbituril-Functionalized Nanocomposite as a Promising Industrial Adsorbent for Rapid Cationic Dye Removal

A supramolecular cucurbit[6]uril (CB[6])-enriched magnetic montmorillonite (CBCM) nanocomposite was prepared and characterized. CB[6] played a prominent role as a capping agent, helping in better distribution of the nanoparticles, and as a binder between nanoparticles. Montmorillonite provided structural stability and fortified ultrafast adsorption toward dyes. Its application in the removal of cationic dyes from wastewater was systematically assessed. Process parameters such as pH, initial dye concentration, dosage, temperature, and time were optimized. Kinetics and isotherms of the process were described using pseudo-second-order kinetics and the Langmuir isotherm, respectively. CBCM exhibited rapid dye removal capacity in short reaction times with q max of 199.20, 78.31, and 55.62 mg g-1 and K2 of 0.0281, 0.0.0823, and 0.0953 L mg-1 min-1 for crystal violet, methylene blue, and rhodamine B, respectively. Benefiting from the synergetic effects of montmorillonite surface hydrophobicity, abundant carbonyl groups of CB[6], and magnetic properties of copper ferrite, CBCM demonstrated outstanding dye removal capacity, negligible leaching at saturation, and high tolerance toward harsh conditions. This intrinsic nature is expedient in prolonged industrial operations. To demonstrate industrial viability, syringe filtration and continuous flow fixed-bed column operations were validated. The CBCM fixed-bed column demonstrated stable dye removal efficiency with 10-100 mg mL-1 dye at 10-50 mL min-1 flow rates. Utilizing the magnetic and catalytic activities of the copper ferrite nanoparticles, CBCM was recycled using a magnet, regenerated, and reused for several cycles. CB[6] remarkably improved the performance of the nanocomposite and made it suitable for different effluent treatment techniques. This may pave a sustainable way toward the efficient onsite treatment of effluent at the industrial scale.

Dewaterability of sewage sludge conditioned with a graft cationic starch-based flocculant: Role of structural characteristics of flocculant

Coagulation/flocculation is one of the most extensive and cost-effective pretreatments to improve the dewaterability of sludge in water treatment plants. In this study, three series of graft cationic starch (St)-based flocculants with distinct structural characteristics including charge density (CD), graft-chain length (L), and graft-chain distribution (N) were synthesized by graft copolymerization of [(2-methacryloyloxy-ethyl) trimethyl ammonium chloride] and acrylamide onto St backbone. The structural effects of these St-based flocculants on the sludge dewaterability have been quantitatively analyzed by using a second-order polynomial model according to phenomenological theory. The predicted dewatering performance and optimal dose were fully consistent with the experimental results. On the basis of this established model, the dewatering mechanisms were discussed in detail by combination of the analysis of the changes in filter cake moisture content, specific resistance of filtration, bound water content, compression coefficient, extracellular polymeric substances fractions and components, spatial distributions of proteins and polysaccharides, microstructures of sludge cake, and flocs properties in the dewatering process. This graft St-based flocculant, with the structural characteristics of high CD, long L, and low N, exhibited superior sludge dewaterability because of the enhanced charge neutralization and bridging flocculation effects. Among these three structural factors, CD played a more important role in improvement of sludge dewaterability than L and N due to the dominant effect of charge neutralization. This study provided a better understanding of structure-activity relationship of these grafting modified flocculants, which was of significant guidance for the exploit and design of novel and efficient flocculants for improvement of sludge dewaterability.

Modeling of Degradation of Diazo Dye in Swirl-Flow Photocatalytic Reactor: Response Surface Approach

Photocatalytic degradation of Direct Blue 15 (DB15), an azo dye, was studied using a swirl-flow monolithic reactor under UV irradiation. The degradation reactions were carried out to investigate effects of initial dye concentration, catalyst loading, and light intensity at an optimal pH. The experiments were designed and mathematically modelled by CCD-RSM (central composite design-response surface methodology) approach. It was found that the selected parameters significantly affect DB15 degradation. In terms of the linear term, catalyst loading and light intensity had a synergistic effect, while dye concentration registered the opposite effect. Strong interaction was observed between catalyst loading and both light intensity and initial dye concentration compared with the interaction of light intensity and initial dye concentration. Based on the experimental results, a quadratic model was developed to predict the percentage removal of DB15. The predicted values of the model were in good agreement with the experimental values (R2 = 0.987), indicating the model fits well for the parameter space for which experiments were performed. According to diagnostic plots, the model credibility was valid because its residuals were distributed normally and exhibited a random pattern based on their examination versus the predicted values. The results revealed that the initial dye concentration and catalyst concentration have a significant effect on the mineralization time.

A review on MXene-based nanomaterials as adsorbents in aqueous solution

Environmental pollution has intensified and accelerated due to a steady increase in the number of industries, and finding methods to remove hazardous contaminants, which can be typically divided into inorganic and organic compounds, have become inevitable. One of the widely used water treatment technologies is adsorption and various kinds of adsorbents for the removal of inorganic and organic contaminants from water have been discovered. Recently, MXene, as an emerging nanomaterial, has gained rapid attention owing to its unique characteristics and various applicability. Particularly, in the area of adsorptive application, MXene and MXene-based adsorbents have shown great potential in a large number of studies. In this regard, a comprehensive understanding of the adsorptive behavior of MXene-based nanomaterials is necessary in order to explain how they remove inorganic and organic contaminants in water. Adsorption by MXene-based adsorbents tends to be highly influenced by not only the physicochemical properties of these adsorbents but also water quality, such as pH value, temperature, background ion, and natural organic matter. Therefore, in this review paper, the effect of various water quality on the adsorption of inorganic and organic contaminants by various types of MXene and MXene-based adsorbents is explored. Furthermore, this review also covers general trends in the synthesis of MXene and regeneration of MXene-based adsorbents in order to assess their stability.

Tio2/SiO2/Fe3O4 magnetic nanoparticles synthesis and application in methyl orange UV photocatalytic removal

Three main parameters affecting TiO₂/SiO₂/Fe₃O₄ nanoparticles activity in photocatalytic degradation of methyl orange were investigated using response surface methodology (SRM). Precipitation method and sol-gel technique were used to prepare SiO₂/Fe₃O₄ electromagnetic composite support and TiO₂/SiO₂/Fe₃O₄ photocatalytically active nanoparticles. The specific surface area, pore volume, and average pore size of the synthesized nanoparticles were respectively equal to 56 m²/g, 0.12 cm³/g and 9.4 nm. The point of zero charge (PZC) of the catalyst was measured to be 5.9. The maximum and minimum photocatalytic degradation of methyl orange using the synthesized nanoparticles were 100% and 30%, respectively. A linear model was fitted to the obtained results with R²_adjusted equal to 0.87. The results of analysis of variance (ANOVA) revealed that catalyst concentration, reaction media pH and aeration rate were significantly affected the photocatalytic activity. Optimization was performed considering photocatalytic activity as the main objective functions. In order to maximize photocatalytic activity, catalyst loading, reaction media pH and aeration rate were respectively adjusted to 2,000 ppm, 3 and 2.5 L/min, which resulted in total methyl orange removal. Considering promising photocatalytic activity of TiO₂/SiO₂/Fe₃O₄ along with core-sell nanocomposite separation performance led us to propose this photocatalyst as an alternative solution for treating waste waters.

Fabrication of thermostable and reusable nanobiocatalyst for dye decolourization by immobilization of lignin peroxidase on graphene oxide functionalized MnFe2O4 superparamagnetic nanoparticles

In view of the potential applications of immobilized enzymes, partially purified Lignin Peroxidase (LiP) from Pseudomonas fluorescens LiP-RL5 was immobilized on Graphene Oxide functionalized MnFe₂O₄ nanoparticles (10 nm, synthesized by sol-gel auto-combustion) to fabricate a new hyperactive and thermostable nanobiocatalyst and thereafter characterized by using standard techniques. Immobilized LiP was quite stable at 50 °C with the half-life of 14 h and showed higher tolerance towards various metal ions and solvents than free LiP. Immobilized LiP retained 50% of enzyme activity even after nine consecutive runs. When tested against various textile dyes, the immobilized LiP was found quite effective with higher dye decolourization efficiency (up to 88%) within 1 h of incubation at 30 °C. The results of this research effort confirmed that the immobilization of LiP and fabrication of nanobiocatalyst increase the efficacy, stability, and reusability of the enzyme which could be efficiently utilized under harsh industrial conditions.

Fabrication of hybrid chitosan encapsulated magnetic-kaolin beads for adsorption of phosphate and nitrate ions from aqueous solutions

Phosphate and nitrate are commonly used industrial and agricultural nutrients that are of great anxiety because of their ubiquitous existence in water and wastewater sources and association with harmful health effects. Herein, we aimed to fabricate a novel and environmental-friendly chitosan encapsulated magnetic kaolin beads for the first time and applied for the adsorption of phosphate and nitrate ions from water. The physico-chemical properties of MK-chitosan beads were established by XRD, FTIR, and TGA-DSC techniques. Surface area (BET) analysis shows that MK-chitosan beads have a specific surface area of 2.12 m²/g. Surface morphology and elemental studies (SEM and EDAX) revealed the porous nature of MK-chitosan beads. The synthesized bead material employed as selective and effective adsorbent material for the remediation of phosphate and nitrate from water/ wastewater. The impact of external adsorption influencing effects likes, adsorbent dose, contact time, co-anions, pH of the solution, and temperature experiments have been performed. Adsorption isotherm and kinetic experiments have been studied and the data have been well tailored by the Freundlich isotherm and pseudo-second-order kinetic models. Thermodynamic parametric studies revealed endothermic and spontaneous nature of the overall sorption system. Besides, MK-chitosan beads were found to regeneration performance up to eight consecutive cycles. Furthermore, the adsorbent-adsorbate system implying that MK-chitosan beads could be a promising candidate for the removal of phosphate and nitrate ions from aqueous solutions.

Synthesis, characterization and flocculation performance of a novel sodium alginate-based flocculant

In this study, a natural polymer-based organic flocculant (sodium alginate-methacrylatoethyl trimethyl ammonium chloride, SA-PDMC) was synthesized by graft copolymerization. The optimum preparation procedures were determined by single factor experiments. The flocculation behaviors of SA-PDMC were investigated in humic acid (HA) and kaolin suspension considering the effects of flocculant doses and initial pH. The results indicated that charge neutralization and bridging action played an important role in the removals of HA and kaolin. Also, SA-PDMC performed well in a wide pH range of 5.0-10.0. Besides, SA-PDMC, as polyaluminium (PAC) aid, was investigated in the lake water treatment. The ratio of PAC and SA-PDMC was optimized through response surface methodology based on a central composite design. Results showed that SA-PDMC and PAC have a strong synergy, under optimal conditions SA-PDMC can reduce the dose of PAC by 40 % while ensuring the water quality.

Self-Nitrogen-Doped Nanoporous Carbons Derived from Poly(1,5-diaminonaphthalene) for the Removal of Toxic Dye Pollutants from Wastewater: Non-Linear Isotherm and Kinetic Analysis

The high surface area and porosity of self-nitrogen-doped porous carbons (SNPCs) nominates them for potential application in water treatment due to their high efficiency towards the removal of various pollutants. In this study, SNPCs were fabricated from poly(1,5-diaminonaphthalene) (P(1,5-DANPh) by single and simultaneous carbonization at the activation step at different temperatures (600, 700, and 800 °C). The carbonization's temperature plays a vital role in controlling the nitrogen-doping, surface area, porosity, and morphology of SNPCs. The SNPCs-7 sample prepared at 700 °C showed the highest surface area (1678.8 m² g^-1) with pore volume (0.943 cm³ g^-1) with a micro/meso porous structure. The prepared SNPCs were used as an effective adsorbent for removal of crystal violet dye (CV) from contaminated water. SNPCs-7 showed the highest adsorption of 487.53 mg g^-1 and the adsorption capacity of the SNPCs samples follows the order SNPCs-7 > SNPCs-8 > SNPCs-6, which is consistent with the results of their surface area and porosity. The adsorption for CV dye followed Freundlich isotherm models and a pseudo second order kinetic model. The negative values of Gipps free energy (ΔG°) and positive value of enthalpy (ΔH°) indicated that the adsorption of CV dye onto the surface of SNPCs was a spontaneous and endothermic process, respectively. Based on the results, the adsorption mechanism of CV dye onto the surface of SNPCs was proposed.