Separation Processes for Environmental Preservation: Advances in Sustainable Technologies, Waste Valorization, and Circular Economy

Environmental pollution remains one of the most pressing challenges faced by modern society, particularly due to the increasing occurrence of emerging contaminants, hazardous compounds, pathogenic microorganisms, toxic metals, dyes, and complex industrial effluents. These pollutants may originate from several anthropogenic activities, including industrial production, agriculture, healthcare, petroleum processing, and the inappropriate disposal of waste streams. In this context, separation processes play a central role in environmental preservation, since they enable contaminant removal, effluent treatment, resource recovery, and the valorization of residues within more sustainable and circular production systems.

The Special Issue “Separation Processes for Environmental Preservation” was conceived to gather contributions focused on novel materials, green technologies, and integrated separation strategies for environmental applications. The published articles cover adsorption-based treatments, pilot-scale flotation systems, particle-separation technologies, green solvent-based fractionation, and computational modeling approaches. Together, these studies illustrate how separation processes can be designed and optimized not only to improve treatment efficiency, but also to reduce environmental impacts and promote the sustainable use of resources [1,2,3,4,5,6,7,8].

A major theme emerging from this Special Issue is the development and assessment of low-cost, waste-derived, and multifunctional materials for contaminant removal. Alvarino et al. investigated activated carbon impregnated with garlic extract as an antibacterial material for the treatment of synthetic hospital wastewater, demonstrating the potential of combining carbonaceous supports with natural biocidal compounds [1]. Hawerroth et al. evaluated granitic rock powder, a mining waste, as an eco-friendly adsorbent for the removal of Basazol Yellow 5G dye and further explored the reuse of the post-adsorption residue in mortars, directly connecting effluent treatment with circular-economy principles [2]. Similarly, da Silva et al. synthesized activated biochars from Moringa oleifera seed shells and assessed their application in the adsorption of metronidazole from aqueous medium, highlighting the potential of biomass residues for the production of efficient adsorbent materials [3]. Complementing these experimental approaches, Tejada-Tovar et al. used Aspen Adsorption to simulate packed-bed columns for the removal of Pb(II) and Ni(II), reinforcing the relevance of predictive tools for evaluating adsorption systems at larger scales [4].

Beyond adsorption, this Special Issue also includes contributions addressing other separation routes and process-engineering challenges. Vlotman et al. investigated a pilot-scale shear-enhanced flotation separation system for winery wastewater treatment, integrating hydrodynamic shear, coagulation, flocculation, and dissolved air flotation as a primary treatment strategy [5]. Jordan et al. reconstructed and evaluated a fluidized-bed device for separating granular material generated from the grinding of rapid antigen tests, combining experimental characterization with CFD–DEM modeling to support the development of recycling strategies [6]. Cen et al. examined particle–wall collision behavior for non-spherical particles, providing relevant information for gas–solid flows, particle classification, and separation systems [7]. Ferreira et al. proposed D-limonene as a renewable solvent for cold asphaltene precipitation, offering a greener route for selective fractionation and molecular characterization when compared with conventional petroleum-derived precipitants [8].

Collectively, these contributions demonstrate that separation processes for environmental preservation are increasingly moving beyond conventional treatment approaches. The studies gathered in this Special Issue emphasize the valorization of residues, the design of alternative and multifunctional materials, the use of greener solvents, the intensification of physical–chemical treatment routes, and the integration of experimental data with computational tools. This convergence reflects a broader transition toward separation technologies that are not only efficient in contaminant removal, but also aligned with sustainability, circular economy, and process intensification.

Another relevant aspect of this Special Issue is the diversity of contaminants, matrices, and separation targets addressed by the published studies. The contributions encompass pharmaceutical compounds, dyes, heavy metals, pathogenic microorganisms, winery wastewater, petroleum fractions, and solid residues derived from healthcare-related materials. This diversity reinforces the broad applicability of separation processes in environmental preservation, extending from water and wastewater treatment to waste valorization, material recovery, and greener analytical or industrial routes. Moreover, the combination of experimental characterization, process evaluation, and computational modeling observed in several studies highlights the importance of multidisciplinary approaches for developing technologies that are both technically robust and environmentally responsible [1,2,3,4,5,6,7,8].

Despite these advances, several challenges remain for the implementation of separation processes in real environmental applications. Future studies should further address the performance of materials and technologies in complex real matrices, the regeneration and reuse of adsorbents, the management of spent materials, and the long-term stability of treatment systems. In addition, scale-up studies, techno-economic assessments, life-cycle perspectives, and robust modeling frameworks are essential to bridge the gap between laboratory-scale performance and industrial application. The integration of complementary separation processes may also represent an important pathway for treating complex effluents and improving overall process feasibility.

In conclusion, the articles collected in this Special Issue highlight the relevance and versatility of separation processes as tools for environmental preservation. By combining waste valorization, contaminant removal, green solvents, process modeling, and pilot-scale treatment strategies, these contributions provide valuable insights for the development of more sustainable and efficient environmental technologies.