Nancy Acelas

Rice husk, an abundant agro-industrial by-product rich in SiO₂, represents a promising precursor for the sustainable synthesis of zeolites. In this study, rice husk ash was used to synthesize faujasite-type X and faujasite-type Y, and their performance for Hg²⁺ removal from aqueous solutions was comparatively evaluated. X-ray diffraction confirmed the successful formation of the faujasite structures, while physicochemical characterization revealed differences in pore structure and surface chemistry. FAU-type X exhibited higher Hg²⁺ removal than FAU-type Y, consistent with the combined influence of its lower Si/Al ratio, higher framework charge density and ion-exchange capacity, as well as its larger pore volume and average pore diameter. Based on its higher Hg²⁺ removal, FAU-type X was selected for a comprehensive evaluation of its adsorption performance and applicability under environmentally relevant conditions. The pseudo-second-order model best described adsorption kinetics for both zeolites, whereas thermodynamic analyses indicated that the adsorption process was spontaneous and endothermic. Optimal adsorption conditions for FAU-type X were achieved at pH 6.8, using an adsorbent dosage of 0.75 g L⁻¹, a contact time of 24 h, and an initial Hg²⁺ concentration of 1 mg L⁻¹. Equilibrium data were best fitted by the Sips isotherm model, indicating adsorption on a heterogeneous surface with a maximum adsorption capacity of 83.14 mg g⁻¹. FAU-type X retained appreciable adsorption performance after four regeneration cycles, although Hg²⁺ removal efficiency decreased in Caquetá River water because of competition from coexisting metal ions. To assess the environmental implications of the treated water beyond Hg²⁺ removal efficiency, ecotoxicological assays demonstrated the sensitivity of Daphnia magna to residual Hg²⁺ concentrations, whereas reductions in Escherichia coliforms were mainly attributed to the adsorption process. In addition, Lactuca sativa seedlings exhibited approximately 50% inhibition of elongation after treatment. Overall, these findings demonstrate the potential of rice husk-derived faujasite-type X as a sustainable adsorbent for Hg²⁺ removal, while highlighting the need for complementary treatment strategies to ensure the environmentally safe discharge of water and its agricultural reuse.

Mercury contamination in water poses severe environmental and health risks, requiring efficient and sustainable removal strategies. In this study, rice husk (RH), rice husk-derived materials, including rice ash (RHA), and Mobil Composition of Matter No. 41 (MCM-41) were evaluated as adsorbents for Hg(II) removal in aqueous systems. Among the tested materials, MCM-41 exhibited superior adsorption performance, achieving up to 98% Hg(II) removal under optimal conditions (pH 6.8, 3 g L⁻¹ of adsorbent, and a pollutant concentration of 0.90 mg L⁻¹). Adsorption followed a pseudo-second-order kinetic model and was best described by the Langmuir isotherm, indicating monolayer adsorption. The maximum adsorption capacity reached 0.80 mg g⁻¹. Thermodynamic analysis revealed that the process was spontaneous and exothermic, primarily governed by coordination interactions and hydrogen bonding with surface silanol groups. The adsorbent’s applicability was further assessed in distilled water, synthetic industrial wastewater, and river water. Although high removal efficiencies were maintained, a decrease was observed in complex matrices due to competition from coexisting ions. Reusability tests demonstrated that MCM-41 retained its performance over four adsorption cycles. Environmental safety was evaluated through ecotoxicological and microbiological assays. Daphnia magna exhibited high sensitivity to Hg(II) (EC₅₀ values of 0.0220 mg L⁻¹ at 24 h and 0.0158 mg L⁻¹ at 48 h), while treated samples showed improved germination indices of Lactuca sativa, particularly in distilled and river water. However, residual toxicity persisted in industrial wastewater matrices. Overall, rice husk-derived MCM-41 is a promising and sustainable adsorbent for Hg(II) removal, though further optimization is needed to mitigate residual toxicity in complex water matrices.

This study elucidates the competitive adsorption dynamics of ciprofloxacin (CIP) and acetaminophen (ACE) onto coffee husk activated with potassium (CH–KOH, BET surface area = 1145 m² g⁻¹, pH_PZC = 7.36), providing mechanistic insights into the removal of pharmaceuticals in complex aqueous matrices. The Modified Langmuir multicomponent isotherm effectively captured the competitive equilibrium behavior (deviation = 25.8%), showing a higher affinity for ACE (η_ACE = 0.7) than for CIP (η_CIP = 4.9), the qT was 1.25 mmol g⁻¹ across the entire evaluated concentration range, which is similar to the observed in mono-component systems, Q_max 1.26 mmol g⁻¹ for ACE and 0.58 mmol g⁻¹ for CIP, with removal efficiencies of 91–99% and 75–99%, respectively. In real matrices such as synthetic hospital wastewater and urine, high efficiencies (84–97%) were maintained. Fixed-bed column studies confirmed the strong performance under continuous-flow conditions, with saturation capacities (q_s) up to 1.46 mmol g⁻¹ for ACE and 0.61 mmol g⁻¹ for CIP, mass transfer zones ranging from 0.42 to 1.53 cm, and breakthrough times between 91 and 1463 min depending on flow rate (1–3 mL min⁻¹) and bed height (1–3 cm). The Thomas model accurately predicted breakthrough curves, revealing faster kinetics for ACE. Physisorption predominates, involving synergistic π–π stacking interactions, hydrogen bonding networks, and hydrophobic association, with ACE showing greater selectivity in both mono and multicomponent systems. CH–KOH exhibited high stability and reusability, stabilizing at approximately 70% of its initial capacity by the third cycle, with no further decrease observed in the fourth cycle. Comprehensive physicochemical characterization revealed that physisorption predominates, involving synergistic π–π stacking interactions, hydrogen bonding networks, and hydrophobic associations. These results confirm the potential of CH–KOH as a sustainable adsorbent for pharmaceutical contaminant removal in real-world scenarios, integrating circular economy principles into advanced water treatment.

This study shows the efficiency of WH-C450, an adsorbent obtained from water hyacinth (WH) biomass, in the removal of sulfamethoxazole (SMX) from aqueous solutions. The process involves calcination of WH at 450 °C to produce an optimal adsorbent material capable of removing up to 73% of SMX and maximum SMX adsorption capacity of 132.23 mg/g. Fourier-transform infrared (FTIR) characterization reveals the involvement of various functional groups in the adsorption process through hydrogen bonds and electron-donor–acceptor (EDA) interactions. X-ray diffraction (XRD) analysis confirms the presence of phases containing CO₃²⁻, PO₄³⁻ ions, as well as elements such as Si and Fe, which contribute to the adsorption mechanism through hydrogen bonding and complexation, respectively. X-ray photoelectron spectroscopy (XPS) analysis further supports these interactions. Kinetic analysis shows rapid adsorption, which combines physical and chemical processes and leads to rapid attainment of equilibrium. This is due to the high affinity of WH-C450 for SMX, which allows for a fast and efficient adsorption process. Isothermal modeling reveals multilayer adsorption with favorable interactions. Thermodynamic analysis confirms the endothermic and temperature-dependent nature of the process. In addition, pH, adsorbent dose, and initial concentration are important in adsorption. Lower pH levels enhance cationic SMX adsorption, while higher adsorbent doses improve efficiency. Optimal conditions were identified by experimental design, enabling the establishment of a predictive model. Consequently, the SMX removal capacity is strongly correlated with the initial concentration. This research underscores the potential of WH-C450 for antibiotic removal in water treatment applications. Graphical Abstract

In this study, we utilized drinking water treatment sludge (WTS) to produce adsorbents through the drying and calcination process. These adsorbents were then evaluated for their ability to remove azithromycin (AZT) from aqueous solutions. The L-500 adsorbent, derived from the calcination (at 500°C) of WTS generated under conditions of low turbidity in the drinking water treatment plant, presented an increase in the specific surface area from 70.745 to 95.471 m² g^-1 and in the total pore volume from 0.154 to 0.211 cm³ g^-1, which resulted in a significant AZT removal efficiency of 65% in distilled water after 60 min of treatment. In synthetic wastewater, the rate of AZT removal increased to 80%, in comparison, in a real effluent of a municipal wastewater treatment plant, an AZT removal of 56% was obtained. Kinetic studies revealed that the experimental data followed the pseudo-second-order model (R²: 0.993–0.999, APE: 0.07–1.30%, and Δq: 0.10–2.14%) suggesting that chemisorption is the limiting step in the adsorption using L-500. This finding aligns with FTIR analysis, which indicates that adsorption mechanisms involve π-π stacking, hydrogen bonding, and electrostatic interactions. The equilibrium data were analyzed using the nonlinear Langmuir, Freundlich, and Langmuir-Freundlich isotherms. The Langmuir-Freundlich model presented the best fitting (R²: 0.93, APE: 2.22%, and Δq: 0.06%) revealing numerous interactions and adsorption energies between AZT and L-500. This adsorbent showed a reduction of 19% in its AZT removal after four consecutive reuse cycles. In line with the circular economy principles, our study presents an interesting prospect for the reuse and valorization of WTS. This approach not only offers an effective adsorbent for AZT removal from water but also represents a significant step forward in advancing sustainable water treatment solutions within the framework of the circular economy.

This study introduces calcined water hyacinth (CWH), processed at 650°C, as a novel and environmentally friendly adsorbent for phosphorus (P) removal from wastewater. Building on previous findings that identified CWH as a rich source of metal oxides and hydroxides (e.g., Ca(OH)₂, Al₂O₃, MgO, Fe₃O₄), this research explores its application in fixed-bed column systems for continuous adsorption processes. The study demonstrates that CWH effectively removes phosphorus through apatite formation, showcasing its potential for real-world water treatment. The phosphorus adsorption capacity increased from 23.64 to 26.55 mg/g when the flow rate was reduced from 1.5 to 0.5 mL/min. Breakthrough curves fitted to the Thomas, Adams-Bohart, and Yoon-Nelson models provided critical insights into column performance, while the Bed Depth Service Time (BDST) model confirmed the feasibility of employing CWH in continuous-flow systems. The practical tests on synthetic municipal wastewater, which revealed a maximum adsorption capacity of 5.20 mg/g, further demonstrated CWH’s effectiveness for treating wastewater with low phosphorus concentrations, providing reassurance about its real-world applicability. Furthermore, the study found that increasing the adsorbent height improved column performance by extending breakthrough and exhaustion times, whereas higher flow rates led to faster saturation and reduced capacity. The exhausted CWH material can be repurposed as a soil amendment or fertilizer feedstock, supporting nutrient recycling.