Heavy metal pollution in water resources, particularly cadmium and lead, poses a significant environmental and public health challenge, requiring the development of sustainable, efficient, and cost-effective water treatment methods. Therefore, this study investigates the biosorption capabilities of natural (SN) and surfactant-modified (SM) guava seed biosorbents to remove Cd and Pb from aqueous solutions. Guava seeds, an agricultural waste material, were treated with hexadecyltrimethylammonium bromide (HDTMA-Br) to enhance their adsorption efficiency. The biosorbents were characterized by FTIR, SEM-EDS, and zeta potential analysis to explain the surface modifications and their influence on the adsorption mechanisms. Batch experiments were performed to evaluate the effects of pH, contact time, temperature, biosorbent dosage, and concentration on Cd and Pb removal efficiencies. Adsorption isotherm and kinetic data were analyzed using mathematical models to obtain the basic parameters of the systems under study. The results showed that SM exhibited superior adsorption capacities of 328 mg/g for Cd and 594 mg/g for Pb at 25 °C, significantly outperforming SN. The study analyzed the thermodynamic parameters of adsorption systems, revealing endothermic and exothermic properties for SN and SM. Functional groups like hydroxyl and carbonyl were crucial for metal ion binding. HDTMA-Br introduced active sites and enhanced surface charge interactions. Regeneration tests showed reusability, maintaining over 85% efficiency after four cycles. Guava seeds could be cost-effective and sustainable biosorbents for heavy metal removal.

The persistent pharmaceutical diclofenac (DCF) presents a significant environmental challenge due to its widespread presence and biological activity in water systems. This study aimed to develop and characterize a novel, low-cost biosorbent by modifying waste guava seeds (GS) with the cationic surfactant cetyltrimethylammonium bromide (CTAB) to enhance the removal of DCF from aqueous solutions. GS and seeds modified with CTAB at 2 mmol/L (MGS-2) and 10 mmol/L (MGS-10) were prepared and characterized using FTIR, SEM-EDS, TGA, and Zeta Potential measurements. Batch adsorption experiments were conducted to assess the effects of contact time, biosorbent dosage, and solution pH. CTAB modification changed the biosorbent’s surface charge from negative to positive, thereby enhancing DCF removal. The MGS-10 biosorbent demonstrated the fastest kinetics. Critically, an intermediate level of surfactant modification (MGS-2) proved optimal, achieving a maximum adsorption capacity of 38.0 mg/g at 45 °C. This capacity significantly surpassed both the GS (29.7 mg/g) and the MGS-10 (32.7 mg/g). This superior performance is attributed to a favorable multi-stage adsorption mechanism, which combines electrostatic attraction and hydrophobic interactions, and is determined to be an endothermic and entropy-driven process. While highly effective, the biosorbents showed poor regenerability with NaOH, indicating a need to explore alternative regeneration methods. This work demonstrates that optimally modified guava seeds are a promising and sustainable material for remediating pharmaceutical contaminants from water.

In developing countries, landfills of urban solid waste (USW) are a major source of contamination. One reason is the common practice of the illegal confinement of hazardous waste (HW). The contamination is mainly due to deficitary design location, operation and lack of liner, which enables the dispersion of pollutants. The aim of our work is to demonstrate the presence of heavy metals (HM) and arsenic (As) in USW of the closed dump of Morelia, which clandestinely confined HW for 20 years. Solid samples of USW were collected from eight opencast wells with different age of confinement. Composition, degradation status, physical-chemical characterization and analysis of HM and As were carried out. The results showed the presence of Pb, Cu, Ni, Zn, Cr, Fe and high concentrations of As. This study provides evidence about the usual and illegal practice of landfill HW together with USW; the hazard due to the presence of HM and As; the deficiency in the operation and closure; and, the lack of competent legislation on the subject. This information is essential to establish background information for improving laws and help decision makers in territorial planning to improve public and environment health.

Valorization of agro-industrial waste into functional materials is fundamental to the circular economy, especially for addressing the persistent contamination by anionic azo dyes in textile wastewater. This study evaluates guava seeds modified with hexadecyltrimethylammonium bromide (GS-M) as low-cost biosorbents for the removal of Direct Blue 71 (DB71), comparing their performance with that of natural seeds (GS-N) in batch systems and fixed-bed columns. Characterization by infrared spectroscopy (FTIR) and electron microscopy (SEM-EDS) confirmed successful surfactant immobilization, thereby creating a cationic surface with strong electrostatic affinity for anionic dye molecules. Batch experiments showed that GS-M achieved 98% DB71 removal within 120 min, whereas GS-N reached only 58% after 300 min. For GS-M, both pseudo-first-order and pseudo-second-order models fit the kinetic data well, consistent with concurrent electrostatic and hydrophobic interactions; GS-N was best described by the Elovich model, indicating rate limitation by electrostatic repulsion. GS-M maintained removal efficiency above 84% across pH 3–9, whereas GS-N was effective under acidic conditions. Langmuir maximum adsorption capacity (Q_o) values for GS-M were 6.02 mg/g at pH 4 and 7.87 mg/g at pH 8, a 1.5- to 2.2-fold increase over GS-N under matched conditions. Three adsorption–desorption cycles retained ~49% of the initial GS-M capacity, supporting a short-cycle reuse profile rather than indefinite multi-cycle operation. Fixed-bed column performance was highly sensitive to the hydraulic loading rate (v_c), with breakthrough times increasing nearly eightfold as v_c decreased. The Bed Depth Service Time (BDST), Thomas, and Yoon–Nelson models described the dynamic data consistently, yielding a maximum dynamic capacity of 165.6 mg/L under optimal conditions and providing a quantitative basis for scale-up. These results establish surfactant-modified guava seeds as a low-cost, pH-resilient biosorbent system aligned with circular-economy principles for the sustainable remediation of textile wastewater.

The contamination of groundwater by fluoride poses a serious global health concern. This research investigates the enhancement of guava seed microparticles (GSM) for fluoride adsorption by modifying them with a cationic surfactant (HDTMA-Br) and iron nanoparticles (MNP), resulting in a functionalized biosorbent (GSM-Fe). The research evaluates the process’s fluoride adsorption capacity, mechanisms, and thermodynamics. Characterization techniques confirmed successful surface modifications, including SEM, FTIR, and zeta potential measurements. Batch experiments assessed the impact of contact time, adsorbent dosage, solution pH, and temperature on fluoride removal. GSM-Fe exhibited a maximum adsorption capacity of 559.9 mg/g at 25°C, significantly higher than unmodified GSM (89.2 mg/g). The adsorption followed the Langmuir-Freundlich isotherm and pseudo-second-order kinetics. Fluoride adsorption primarily occurs through hydrogen bonding, electrostatic attraction, and interactions with functional groups such as hydroxyl and carboxyl groups on the biosorbent surface. The process was endothermic, with higher fluoride removal efficiency at elevated temperatures. Thermodynamic analysis confirmed the spontaneity of adsorption at higher temperatures. This study demonstrates that GSM-Fe is a highly efficient, cost-effective, and sustainable biosorbent for fluoride removal from water, offering a promising solution for managing fluoride contamination, particularly in developing regions.