Search Results (196)

Hydrothermally treated chitosan/polyvinyl alcohol beads (H-CS/PVA) were used as filler material in a fixed-bed column for continuous Cr (VI) removal. The effects of main operational parameters, namely bed height, initial concentration and flow rate, were evaluated in the respective ranges of 2–6 cm, 20–60 mg/L and 2.5–7.5 mL/min. Maximum removal efficiency and adsorption capacity were calculated as 64.2% and 15.53 mg/g, respectively. The corresponding breakthrough curves were analyzed by Yoon–Nelson, Adams–Bohart, Thomas and BDST (Bed Depth–Service Time) models, out of which the highest consistency was achieved with the Yoon–Nelson model for all studied conditions. The adsorbent maintained strong reusability, showing minimal loss (~2.5%) in desorption efficiency across three successive regeneration cycles with 0.1 M NaOH as the eluent. SEM and SEM–EDX analyses confirmed the presence of chromium on the H-CS/PVA surface at an elemental fraction of 1.03% (w.). Furthermore, FTIR and XPS analyses verified the role of amine and hydroxyl functionalities in the complexation and adsorption of Cr (VI). Overall, a column system operated under optimal conditions (H_bed: 6 cm, C₀: 40 mg/L, and column diameter: 2.5 cm) and regenerated three times can efficiently treat 20 L of Cr (VI)-contaminated wastewater, resulting in an associated environmental impact of 0.896 kg CO₂-eq. Full article

Propyl-paraben (PrP) is a common preservative found in cosmetics and pharmaceutical products. It is classified as a category 1 endocrine-disrupting compound, which highlights the importance of efficiently removing it from water during treatment processes. This study investigates the potential of using Leptolyngbya sp. dominated cyanobacterial biomass residues, in both their raw and hydrothermally treated (hydrochar) forms, for the removal of PrP from aqueous media. Batch and fixed-bed column experiments were carried out under varying conditions to assess adsorption kinetics and equilibrium behavior. Both raw biomass and hydrochar exhibited satisfactory PrP removal, achieving maximum adsorption capacities of 224.58 and 258.55 mg/g respectively, at 10 mg/L initial PrP concentration and 23.33 mg/L adsorbent dosage. Equilibrium data were best described by the Freundlich isotherm model, indicating a heterogeneous surface and multilayer adsorption. The kinetic analysis revealed that the adsorption behavior, for both adsorbents, was best described by the pseudo-second-order model, while the thermodynamic evaluation revealed negative ΔH° and ΔS° values, confirming an exothermic, physisorption-driven process. The adsorption mechanism was further investigated through surface characterization techniques, including Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, N₂ physisorption, and zeta potential analysis. The findings demonstrate the potential of microalgal biomass as a low-cost, sustainable biosorbent, for emerging contaminants, reinforcing its role in advanced water treatment and circular economy strategies. Full article

Metanil Yellow (MY), a highly toxic azo dye used in food products, was removed from aqueous solution using a metal- and halide-free ordered mesoporous carbon (OMC) adsorbent. MY exhibited a strong affinity towards OMC in batch as well as column operations, and OMC performed much better than previously reported adsorbents. The pH, dye concentration, adsorbent dosage, and contact time were optimised, and detailed adsorption experiments were performed under these conditions. Several isotherm models were fitted to the adsorption data, showing that the Langmuir and the Freundlich adsorption models were followed. Adsorption was spontaneous and endothermic at all measurement temperatures. On the basis of pH studies, enthalpy data, and adsorption isotherm analysis, adsorption was determined to be by physisorption. In kinetics studies, the adsorption process was found to be pseudo-second order with interparticle diffusion as the rate-limiting step. Column experiments using a fixed bed of OMC resulted in almost 100% column efficiency and a fractional column capacity of 0.999. During adsorption/desorption cycles of the exhausted column, 99.71% of the dye was recovered after the first cycle and 97.66% after the eleventh. These findings indicate that OMC is a promising and efficient material for the adsorptive removal of toxic MY dye. Full article

With the increase in the demand for electronic-grade high-purity silane in the semiconductor chip industry, it is of great significance to develop a green and economical method for silane production. Therefore, a novel energy-saving fixed-bed process was proposed innovatively. In this paper, the thermodynamics and kinetics of the trichlorosilane disproportionation system were studied, and the optimal reaction conditions for the resin catalyst were determined, which were used for the subsequent simulation. Based on the conventional DR1 + DR2 process (which includes one trichlorosilane disproportionation reactor (DR1) and one dichlorosilane disproportionation reactor (DR2)), by adding an additional disproportionation reactor to the TCS recycle loop and/or DCS recycle loop, three improved process configurations were designed, including 2DR1 + DR2, DR1 + 2DR2, and 2DR1 + 2DR2 processes. Then, combined with four-column heat integration, the HI + 2DR1 + 2DR2 process was proposed to solve the bottleneck problems of high energy consumption and large circulation flow rate. The results show that the HI + 2DR1 + 2DR2 process achieved the best energy-saving effect. The TCS recycle loop flow rate reduced by 36.87%, the DCS recycle loop flow rate reduced by 12.41%, total energy consumption decreased by 62.8%, and CO₂ emissions decreased by 56.72%. The unit energy consumption is 13.8 kg steam/kg SiH₄, and the silane purity is greater than 99.9999%. This design can be easily applied to the existing production process of the silane plant, achieving energy-saving and low-cost production of silane. Full article

The aim of this study was to investigate the ability of sewage sludge-derived biochar to remove PO₄-P from real biologically treated wastewater. Biochar was produced via the pyrolysis of anaerobically digested sewage sludge pretreated with nanoscale zero-valent iron (nZVI) at concentrations of 3%, 1.5%, and 0.5% (w/w, based on total solids). A sample without nZVI addition was used as a control. The properties of biochar samples were analyzed, including elemental composition, specific surface area, and pore size. PO₄-P removal was evaluated using both batch adsorption and column experiments. The highest adsorption capacity determined in the batch experiment was 2.5 mg/g. When wastewater was passed through columns packed with 0.3–0.6 mm biochar particles at a hydraulic loading rate of 1 m/h, a 3-fold-higher phosphorus retention capacity was obtained in the range of 7.26–7.82 mg/g. The column containing biochar derived from sewage sludge with 3% nZVI accumulated 7% more PO₄-P than the biochar without nZVI. All columns effectively removed phosphates from wastewater (efficiency > 80%) due to the chemical composition of biochar, which mainly contained Fe and Ca elements. In contrast to the batch experiment, the columns were subject to the biological sorption of phosphates via microorganisms, physical retention between particles, and the formation of precipitates on the surface of a column. Full article

Water contamination by heavy metals remains a major global challenge, requiring efficient, sustainable, and low-cost remediation materials. Chitosan and cellulose are recognized as effective biosorbents due to their high affinity toward metal ions, biodegradability, and availability. However, their individual limitations motivate the design of composite with enhanced properties. In this study, chitosan/cellulose composite hydrogel beads crosslinked with glutaraldehyde (CHB-CF-GLA) were synthesized and evaluated for Cu(II) removal under batch and dynamic conditions. The composite was characterized by FESEM-EDS, ATR-FTIR, XRD, swelling analysis, and determination of pH_pzc to elucidate its structural and physicochemical features. Batch experiments optimized pH, initial Cu(II) concentration, and adsorption capacity, while non-linear kinetic and isotherm models described the adsorption mechanism. The adsorbent exhibited good stability and reusability over multiple cycles. Fixed-bed column studies demonstrated that increasing bed height prolonged breakthrough and exhaustion times, while higher influent concentrations and flow rates led to earlier column saturation. The experimental breakthrough curves were well described by the Thomas and Yoon–Nelson models, whereas the Adams–Bohart model showed limited applicability. COMSOL Multiphysics 3.5 simulations validated the experimental data and predicted column performance. Overall, CHB-CF-GLA is an efficient and functional adsorbent with strong potential for continuous Cu(II) removal in water treatment applications. Full article

l-menthol is one of the most popular flavors in the world. The separation of menthol enantiomers is crucial because of the unpleasant taste of d-menthol. This work presents the chiral separation of racemic menthol by simulated moving bed chromatography for the first time. Six preparative columns packed with amylose 3,5-dimethylphenylcarbamate coated on silica gel were used for separation, and a mixture of n-hexane/isopropanol was selected as the mobile phase. The hydrodynamic properties of the SMB columns were studied to minimize the packing asymmetry in the SMB experiment. The binary adsorption isotherm of menthol enantiomers was measured by the adsorption–desorption method. Fixed-bed batch chromatography was carried out to evaluate the adsorption kinetic behavior. Mathematical models, considering the mass transfer resistance and axial dispersion, were applied to describe the dynamics of the chromatographic separation process. The SMB process for chiral separation of racemic menthol was designed by evaluating the separation region using simulations. Reasonable agreements were achieved between the predicted results and the experimental results. Purities for both the extract and raffinate were above 99.0%, and a productivity of 0.267 g_racemate/(L_CSP∙min) and a solvent consumption of 0.431 L/g_racemate were achieved. Full article

This work presents a comprehensive analysis of reactor modeling studies for the methanation of CO_x, with the aim of identifying trends, evaluating modeling strategies, and suggesting a generalized modeling framework. The analysis spans a wide range of configurations, including packed/fixed-bed reactors (immobilized catalyst pellets/particles), fluidized-bed reactors, and structured catalyst reactors, as well as membrane and slurry/bubble-column configurations when applicable. This highlights the diversity of modeling approaches used, ranging from simple 1D pseudo-homogeneous models to complex 2D heterogeneous simulations. Emphasis is placed on the governing assumptions, dimensional formulations, transport phenomena, and kinetic models employed across studies. By systematically comparing these models, this work identifies the most critical modeling assumptions and parameters that govern the prediction reliability of reactor performance (e.g., conversion and temperature profiles) and inform reactor design. The proposed reactor model integrates insights from the literature, balancing model fidelity and computational feasibility, and serves as a foundational tool for future modeling efforts and industrial applications. This work contributes to the field by offering a unified perspective that links model complexity to physical realism, providing valuable guidance in the development of predictive tools for CO_x methanation systems. Full article

The selective removal of radioactive cesium-137 and strontium-90 from high-salinity radioactive wastewater remains a critical challenge, as competing ions reduce adsorption efficiency and selectivity. In this study, high-performance granulated adsorbents were developed based on alkali-activated geopolymer matrices to enhance sorption performance. The adsorbents were synthesized by inorganic polymerization, and mechanically robust granules with controlled porosity and surface chemistry were obtained. Batch sorption experiments conducted in simulated seawater demonstrated greater than 99% removal efficiencies for cesium and strontium. Isotherm modeling confirmed high maximum sorption capacities (up to 0.41 meq/g for Cs⁺ and 5.07 meq/g for Sr²⁺). Continuous fixed-bed column tests demonstrated sustained removal efficiencies for the optimized adsorbents. Structural analyses, including scanning electron microscopy, energy-dispersive X-ray spectroscopy mapping, and X-ray diffraction, confirmed uniform elemental distribution and crystalline phases consistent with selective sorption mechanisms. Assessment of mechanical strength revealed sufficient compressive strengths to ensure operational durability under hydraulic stress. These findings demonstrate that the synthesized geopolymer-based granules are a potentially effective and versatile solution for the comprehensive treatment of radioactive wastewater. Full article

The use of white-rot fungi Pleurotus spp. and Trametes versicolor in continuous-flow fixed-bed systems has emerged as a promising and sustainable approach for the removal of different pollutants from aqueous media. This overview presents the most important design and operating parameters, the efficiency of fixed-bed systems using these fungi and their spent substrate, and the effect of operating parameters on changes in removal efficiency. After a literature screening based on the Scopus database, the overview focuses specifically on 55 studies that present the results of several hundred tests, meeting the criteria for continuous-flow fixed-bed systems, which include ensuring uninterrupted flow, constant adsorbent mass, and continuous interaction between the stationary and mobile phases. Results reported in the literature show the varying importance of biodegradation and biosorption processes in the removal of metals and organic pollutants (e.g., dyes, pharmaceuticals, pesticides, volatile compounds). The overview highlights the impact of operational parameters on removal efficiency, including bed depth, flow rate, type of polluted water, and initial concentration. It also determines that these fixed-bed systems using Pleurotus spp. and Trametes versicolor are primarily suitable for modelling the adsorption-based removal of given pollutants and the bioremediation of smaller amounts of municipal, industrial, or agricultural wastewater. Full article

The competitive adsorption of two model herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA), onto Activated Carbons (ACs) derived from pomegranate peels through chemical activation with phosphoric acid (H₃PO₄) was investigated in fixed-bed column mode. The prepared activated carbon (AC-PA) exhibited a high apparent surface area (up to 1409 m²/g) and a predominantly microporous structure. Morphological and chemical analyses (micrographic observation, X-ray difraction, N₂ adsorption–desorption) confirmed the presence of well-developed pore networks and surface oxygenated functionalities. Column adsorption experiments were performed under varying flow rates (0.25–3 mL/min) for both single and binary solutions. The breakthrough data were modeled using the Thomas and Yoon–Nelson equations, achieving high determination coefficients (R² = 0.91–0.99). Lower flow rates favored higher adsorption capacities, reaching 193.61 mg/g for 2,4-D at 0.25 mL/min. Under similar conditions (flow rate of 1.5 mL min⁻¹), the AC provided a better adsorption for 2,4-D than for MCPA in single systems, which was attributed to stronger affinity based on its greater hydrophobicity and prominence to dispersive interactions. In binary systems, competitive effects shifted the results and a noticeable roll-up phenomenon was observed for 2,4-D, attributed to its displacement by MCPA along the bed; this made the adsorbent more effective for MCPA in binary mixtures than in single ones. These findings highlight the potential of pomegranate-based activated carbon as a cost-effective and sustainable adsorbent for herbicide removal in continuous water treatment systems. Full article

Carbon capture and storage (CCS) technologies are an important step to mitigate CO₂ emissions. This study focuses on CO₂ capture from biomass combustion in fluidized bed boilers using a vacuum pressure swing adsorption (VPSA) process. A pilot-scale VPSA unit was used to evaluate the dynamic adsorption behavior of zeolite 13X and clinoptilolite under realistic operating conditions. Moreover, a simplified one-dimensional isothermal mathematical model of a fixed-bed adsorption column was developed to simulate breakthrough curves to validate whether the model reproduces the observed experimental trends. Experimental results confirmed that fresh zeolite 13X exhibited the highest CO₂ adsorption capacity, while clinoptilolite showed moderate uptake. For both sorbents, a decrease in derived adsorption capacity was observed after prior use. The developed mathematical model successfully reproduced the experimental breakthrough curves, achieving coefficients of determination (R²) up to 0.99 and percentage fit (%Fit) values close to 94% for fresh sorbents, while lower correlations were observed for used sorbents. The model reliably captured the breakthrough curves, validating its applicability for process prediction. These results highlight the effectiveness of combining experimental measurements with modeling to assess sorbent performance and guide further optimization of VPSA processes under realistic flue gas conditions. Full article

Heavy metals release in the environment represents a growing threat to human health and nature, particularly due to industrial activities contributing to soil and water contamination. In this study, Ganoderma lucidum heteropolysaccharides (GLHP) were evaluated as a biosorbent for cadmium removal. The biomass was acquired following the production of Ganoderma lucidum fruiting bodies and consisted of remnants from the fungus and cultivation substrate. Cd(II) and elemental analysis were carried out by atomic adsorption spectrometry (AAS) and inductively coupled plasma mass spectroscopy (ICP-MS), respectively. The biosorption efficiency was critically evaluated, optimizing physical adsorption parameters for batch, column, and percolation configuration, as well as application in real environmental water. Utilizing a simple pre-rinsing step, completely omitting any chemical pretreatment, the Cd(II) removal efficiency was improved from 41.2% to 78.4% in a batch system and up to 98.4% in a fixed-bed column, making it suitable not only for wastewater treatment but also for drinking water purification. The adsorption kinetics were described by a pseudo-second-order (PSO) model and further analyzed using a revised PSO (rPSO) model, which explicitly accounts for adsorbate and adsorbent concentrations. A global fit to the PSO model demonstrated that the rate constant was independent of the adsorbent concentration, supporting its application as a robust descriptor of the adsorption process. GLHP showed good adsorption performance, following the Sips adsorption isotherm and Thomas model for batch and column setup, respectively, demonstrating the potential as a scalable, low-cost biosorbent for fast and efficient Cd(II) removal from contaminated waters. Full article

Fixed-bed adsorption is widely employed in the scaling-up of liquid-phase adsorption processes because it offers significant operational advantages over batch systems. However, conventional approaches for scaling up adsorption columns are subject to important limitations. In this regard, the Axial Dispersion Model (ADM) coupled with the Pore Volume and Surface Diffusion Model (PVSDM) provides a framework capable of overcoming these constraints. In this study, ADM–PVSDM was applied predictively using equilibrium relationships and diffusion coefficients obtained from batch experiments. Model validity was assessed against nine experimental breakthrough curves, yielding an average deviation of 7.6% in breakthrough time. Furthermore, the model successfully predicted system behavior across a feed-flux range of 18–174 g h⁻¹m⁻². The integration of ADM–PVSDM was supported by the characterization of the Mass Transfer Zone (MTZ), which underpins the scaling approach proposed herein. The predicted breakthrough curves were also used to estimate MTZ length and velocity, which ranged from 0.97 to 8.7 cm and from 0.56 × 10⁻³ to 20 × 10⁻³ cm min⁻¹, respectively, with mean percentage deviations of 6.4% and 7.3%. These predictions enabled the development of a methodology which is capable of scaling adsorption columns over a wide operational range while requiring substantially fewer experiments compared to conventional scaling methods. Finally, it was demonstrated that commonly used empirical models, such as the Bohart–Adams model, failed to predict breakthrough curves with sufficient accuracy, thus rendering them unsuitable for developing this scaling methodology. Full article

Surplus cyanobacterial biomass can serve as a low-cost sorbent for polishing nitrate-contaminated waters. We compared raw cyanobacterial biomass (Leptolyngbya sp.) with its hydrochar produced by hydrothermal carbonization. Despite an approximately tenfold increase in BET area after carbonization (4.08 vs. 0.5 m² g⁻¹), the hydrochar performed worse than the native material under all tested conditions. Batch tests (C₀ = 20 to 100 mg N L⁻¹; dose = 0.067 g L⁻¹) reached equilibrium within 25 min, achieving removal rates ranging from 40% up to 56%. Nonlinear fits showed that the pseudo-first-order model simulates the time courses with physically consistent parameters, while the equilibrium data in the studied window were represented by the Freundlich isotherm. In fixed-bed trials, the biomass treated 58 bed volumes to the nitrate-N compliance value of 11.3 mg N L⁻¹, compared with 27 bed volumes for the hydrochar; the breakthrough profiles were modeled using the Yoon–Nelson equation and nonlinear regression. Over the conditions examined, performance tracked surface chemistry and charge characteristics rather than area, consistent with contributions from specific interactions and uptake within the cellular matrix. These results support minimally processed cyanobacterial biomass as a practical option for energy-lean nitrate polishing under the frame of the circular economy. Full article