Synthesis of Luffa cylindrica biomass-based adsorbent for PFOA removal from aqueous matrices

Global concern about perfluoroalkyl substances (PFAS) has increased due to their very high environmental stability, recalcitrance to conventional water and wastewater treatment technologies and adverse effects on aquatic ecosystems, as well as potential risks to human health. These factors underscore the need for control measures and development of efficient and sustainable technologies to remove these persistent organic pollutants, especially from aqueous matrices. Among various PFAS, perfluorooctanoic acid (PFOA) is one of the most detected compounds in different environmental matrices such as water, air, soil, sediments and biota. Despite the restrictions and controls proposed by the European Commission (Stockholm Convention) and the US Environmental Protection Agency (EPA), PFOA continues to be widely used by the polymer and surfactant industries in many countries. Polishing techniques, such as oxidative processes, membrane filtration, and biological reactors, have been investigated for PFOA removal. However, many of these technologies involve high implementation costs, operational complexity, and, in some cases, the result is the partial degradation of PFOA, generating even more stable and toxic by-products. In this context, adsorption processes stand out as a feasible and efficient alternative, especially if low-cost biomass-based adsorbent materials is applied, offering a sustainable and cost-effective solution. This study aims to evaluate the optimal synthesis conditions for the preparation of an adsorbent material derived from Luffa cylindrica (plant sponge) for the removal of PFOA in aqueous matrices. To find the best synthesis conditions, thermochemical modifications of the biomass were tested using a Central Composite Design (CCD) with three independent variables: (i) temperature; (ii) residence time in the furnace; and (iii) type of activation. Removal efficiencies were evaluated at 30, 60, 120 and 180 min of contact time. Temperature and furnace residence time were identified as the most significant variables, with a 90% confidence level. The design of experiment (DoE) showed that setting the temperature at 400°C, residence time of 20 min and acid activation resulted in the removal of 87.7 ± 6.5% of PFOA in water at an initial concentration of 5 mg L⁻¹. This approach offers a sustainable and promising alternative for the synthesis of biomass-based biosorbents capable of efficiently removing PFOA, thereby minimizing potential environmental and public health impacts. Future experiments with focus on the performance of such adsorbent in removing other contaminants of the PFAS group from water is recommended.