Alexandre Diório

Wastewater treatment remains a pressing global challenge due to the continuous discharge of recalcitrant pollutants from anthropogenic activities. Among these, synthetic dyes are particularly problematic due to their persistence and toxicity, requiring advanced and sustainable removal strategies. In this study, a novel bio-based hydrogel was synthesized via a green process, avoiding the use of harmful chemicals. The hydrogel, composed of alginate and mucilage extracted from Opuntia ficus-indica, was applied as an adsorbent for the removal of Neutral Red dye from a synthetic aqueous solution. Characterization revealed a rough surface morphology, mesoporosity, and a specific surface area of 0.14 m²/g. The material exhibited a point of zero charge at pH 9.0, and its surface was rich in functional groups, including hydroxyl, deprotonated carboxyl, and ether groups, which contributed to dye adsorption through non-electrostatic mechanisms. Optimal removal was achieved at acidic pH, with a maximum adsorption capacity of 26.6 mg/g at pH 5.0. The adsorption kinetics followed a pseudo-second-order model, reaching equilibrium within 200 min, with a maximum uptake of 24.8 mg/g after 720 min. Thermodynamic analysis indicated a spontaneous, exothermic, and reversible adsorption process, with maximum capacities of 1420, 1432, and 1308 mg/g at 25, 35, and 45 °C, respectively. Competitive adsorption studies showed a decrease in capacity in the presence of electrolytes (KCl, NaCl, and MgCl₂). The hydrogel demonstrated excellent reusability, retaining over 90% efficiency after five consecutive cycles, and showed no toxicity in lettuce seed germination tests. These results highlight the potential of alginate-Opuntia ficus-indica hydrogel as a sustainable, non-toxic, and efficient adsorbent for dye removal in water treatment applications.

Biogas from municipal solid waste is a promising pathway for renewable energy production while mitigating environmental pollution and public health risks. In this study, biogas emissions from a sanitary landfill in Maringá, southern Brazil, were evaluated using three models (IPCC, LandGEM, and CETESB tool) to estimate methane generation and energy recovery potential. Experimental analysis revealed methane concentrations from 51.10 ± 8.89% to 57.06 ± 1.19% across collection drains, indicating favorable conditions for energy utilization. Methane generation was estimated under different scenarios, reaching up to 1.30 × 10⁴ tonnes of CH₄, with peak production projected over 25–26 years depending on the model. Beyond energetic relevance, controlled biogas recovery can substantially reduce methane emissions, a key precursor of tropospheric ozone, and limit hazardous trace gas release, improving air quality and reducing population exposure to harmful pollutants. These findings are particularly relevant in developing countries, where insufficient waste management infrastructure leads to uncontrolled emissions, posing elevated environmental and health risks. This study supports integrating landfill biogas recovery into waste management and climate strategies, contributing to Sustainable Development Goals related to clean energy (SDG 7), climate action (SDG 13), and health (SDG 3), demonstrating it as a scalable solution for sustainable urban development.

3D-printing enables the fabrication of membranes with desired shapes and geometrical parameters. In this study, a membrane for pressure-driven processes was manufactured in a single step using the fused deposition modeling (FDM) technique. The membrane was produced from a mixture of polylactic acid (PLA) with sucrose as a pore-forming agent. Sucrose was removed from the final membrane by washing it with water. The membrane consists of three layers, and this sandwich-like structure ensures its mechanical stability. The material obtained was characterized using SEM and AFM imaging, as well as nitrogen adsorption-desorption and contact angle measurements. The porosity of each layer of the membrane is due to a loose region, which is coated on both sides with a dense film formed during printing. The pores responsible for rejection capability can be found in grooves between the polymer stripes in the dense layer. The membrane exhibits a water permeability of 64 L m⁻²h⁻¹bar⁻¹, with a molecular weight cut-off of 69 kDa. The PLA membrane can be used for polyphenol concentration, demonstrating a permeability of 2–3.4 L m⁻²h⁻¹bar⁻¹ and a selectivity towards these compounds of 78–98% at 0.5 bar, with a flux decline ratio of up to 50%.

The increased production and consumption of pharmaceuticals represent a potential environmental threat. Thus, advanced treatments are necessary to remove pharmaceutical products from water. A promising removal alternative is low-cost adsorbents, due to their availability, low processing, and favorable results. This study used sunflower seed husks (SSH) and chemically treated sunflower seed husks (TSSH) as bioadsorbents to remove chloroquine from water. Results showed that the pseudo-second-order is the kinetic model with the best fit for both adsorbents. As for isothermic models, the best fit for SSH was Langmuir, and for TSSH, Freundlich. Maximum adsorption capacities of qe=168.09±22.98 mg/g and qe=185.91±27.23 mg/g were found through the isothermic models for SSH and TSSH, respectively. In addition, SSH reached 80% of its initial adsorption capacity after three adsorption-desorption cycles, indicating physisorption and good applicability due to its reusability. Thus, SSH is an efficient adsorbent for chloroquine removal with excellent regeneration capacity, low production cost, and low waste production. This study serves as a model for the use of SSH in the removal of contaminants of emerging concern.

The development of industrial process in line with the circular economy and the environmental, social and corporate governance (ESG) is the foundation for a sustainable economic development. Alternatives that make feasible the transformation of residues in added value products are promising and contributes to the repositioning of the industry towards sustainability, due to financial leverage obtained from lesser operational costs when compared with conventional processes, therefore increasing the company competitivity. In this study is presented a promising and innovative technology for the recycling of agro-industrial residues, the sugarcane bagasse and the high-pressure water boiler effluent, in the development of a low-cost adsorbent (HC-T) using the hydrothermal carbonization process and its application in the adsorption of herbicide Diuron and Methylene Blue dye from synthetic contaminated water. The hydrothermal carbonization was performed in a Teflon contained inside a sealed stainless-steel reactor self-pressurized at 200 °C, biomass-to-effluent (m/v) ratio of 1:3 and 24 h. The synthesized material (HC) was activated in an oven at 450 °C for 10 min, thus being named adsorbent (HC-T) and characterized by textural, structural and spectroscopic analysis. The low-cost adsorbent HC-T presented an 11-times fold increase in surface area and ∼40% increase total pore volume in comparison with the HC material. The kinetic and isotherm adsorption experiments results highlighted that the HC-T was effective as a low-cost adsorbent for the removal of herbicide Diuron and Methylene Blue dye from synthetic contaminated waters, with an adsorption capacity of 35.07 (63.25% removal) and 307.09 mg g^-1 (36,47% removal), respectively.

Atrazine (ATZ) is an herbicide used for increased food production due to its weed and pesticide control capacity in different crops. However, ATZ is a chemical compound that is harmful to the environment and human health, and, unfortunately, it has been detected in surface and groundwater. Therefore, the aim of this paper was to perform the adsorption of Atrazine from a synthetically contaminated water sample using a packed-bed column with a low-cost adsorbent prepared from Moringa oleifera Lam. seeds. The synthesized adsorbent presented an increase in the surface specific area (S_BET) of 37% in comparison with the in natura material. The effects of the peristaltic pump flow rate (Q), concentration of the ATZ inlet ([ATZ]_inlet) solution, and bed height (H) were studied, with the highest percentage of ATZ removed through the adsorption column (50, 0%) obtained with a packed-bed column with H = 13 cm bed height, Q = 1 mL/min, [ATZ]_inlet = 2.0 mg/L, pH = 5.0, a breakthrough time of 25 min, and a saturation time of 420 min. The logistic model was used to best fit the experimental data with an R² > 0.99, and the Bohart–Adams, Thomas, and Yoon–Nelson models were used to explain and analyze the obtained effects in the continuous adsorption of ATZ. Therefore, the Moringa oleifera Lam. seeds provided a low-cost adsorbent for the continuous adsorption of the herbicide Atrazine in a packed-bed column.

The discharge of harmful dyes in water bodies is a serious pollution problem, dangerous for the ecosystem’s equilibrium and human health. In this sense, the aim of this work was to determine the influence of electrolytes (NaCl, KCl, CaCl₂ and MgCl₂) in the adsorption of Reactive Blue BF-5G dye, the most common dye used in industrial process for fabric colouring, using bovine bone char as the adsorbent. The bovine bone char was characterized by pH of point of zero charge (pH_PZC), N₂ adsorption–desorption isotherms, Fourier transform-infrared spectroscopy (FT-IR) and X-ray diffractometry (XDR). The characterization revealed a mesoporous structure (pore mean diameter of 94 Å and S_BET ∼107 m² g^-1) with negative charge distribution at the surface (pH_PZC= 3.8). The adsorption experiments revealed that the presence of KCl enhanced the material adsorption capacity (q_max = 195 mg g⁻¹), that the Sips isotherm best fitted the experimental data (R² > 0.9 except for KCl solution) and the adsorption process was mono- and multilayered. The kinetic adsorption experiments indicated that the inorganic electrolytes increased the initial adsorption velocity and the data was best modelled by the surface diffusional model (SDM), implying a resistance (aqueous > CaCl₂> NaCl > MgCl₂> KCl) to mass transfer at the surface of the pores which, in turn, prevented the dye diffusion to the interior of the adsorbent (q_e = 71 mg g⁻¹). Therefore, small quantities of KCl can be used to lower the mass transfer resistance and provide higher adsorption capacity with reduced time of operation, thus increasing the overall process efficiency. GRAPHICAL ABSTRACT

The clinoptilolite natural zeolites (NZs) posses low herbicide adsorption capacity demanding acid-, alkali-, or salt chemical modifications that enhance its adsorption. However, this may affect the material structure and charge distribution. Alternatively, zeolites may be synthesized at a high cost and time-consuming process. Consequently, new methods, such as the hydrothermal method, for NZ modification needs to be studied. In this sense, a novel surface-modified zeolite (SMZ), using hexadecyltrimethylammonium bromide (CTAB), in acid media was produced by the hydrothermal method and applied for the adsorption of Atrazine (ATZ), Diuron (DIU) and 2,4-D. Commercial NZ and SMZ were characterized by SEM, XRD, TGA, FT-IR, AA spectroscopy, pH_PZC, Zeta potential and N₂-physisorption. The SMZ chosen for the adsorption experiments was the one with the highest modification yield and adsorption capacity obtained from a complete design of experiments (CTAB=0.74 ; D=12 Mesh; HCl=0.1 M; t=6 h and T=205 ºC). The adsorption experiments revealed that the SMZ adsorption capacity for the herbicide 2,4-D (q_max=9.02 mg/g) was greater than that obtained for ATZ (q_max=2.11 mg/g) and DIU (q_max=1.85 mg/g), which was explained by the presence of the hydroxyl group and by geometric characteristics of the 2,4-D. Adsorption models’ fitting showed that the adsorption of 2,4-D onto SMZ were best described by pseudo-second order kinetic (k₂=0.005-0.006 g/mg.min; q_e,exp=7.122-8.614 mg/g) and Langmuir isothermal model (K_L=0.283-0.499 L/mg; q_m=7.167-7.995 mg/g). These results indicate that the hydrothermal method is a viable alternative to enable the use of NZs for the adsorption of emerging contaminants from wastewater. GRAPHICAL ABSTRACT