Editorial: Activated Carbon: Contaminant Removal for Environmental Sustainability

1. Introduction

Population growth, industrialization, and increasing living standards have intensified the release of agricultural, industrial and pharmaceutical contaminants into aquatic environments. The produced effluents often contain a complex mixture of contaminants, including metallic ions, phenolic compounds, dyes, solvents, surfactants, pesticides, petrochemicals, pharmaceuticals and other hazardous chemicals [1]. The growing diversification of industrial processes has further increased the occurrence of these pollutants in aquatic environments. Due to their persistence, toxicity, and resistance to conventional treatment technologies, these contaminants may pose significant risks to ecosystems, environmental quality, aquatic organisms, and human health [1].

The presence of chemical and biological contaminants in water bodies is a major concern to public authorities, water utilities, and society. Effective management and treatment of wastewater have become essential to ensure environmental protection, safeguard water resources, and promote sustainable development. Among the numerous treatment technologies available for this purpose, adsorption onto activated carbons (ACs) has emerged as one of the most promising approaches due to its simplicity [2,3], versatility, and high efficiency in removing a broad spectrum of pollutants [3]. However, the high cost of commercial ACs limits their widespread application, prompting the search for alternative, cost-effective adsorbents. Nevertheless, over recent decades, significant progress has been made in the development of ACs derived from renewable resources, agricultural biomass [3], industrial by-products, and synthetic residues. The applications of ACs have been expanding beyond conventional pollutant removal, encompassing emerging contaminants, resource recovery, and circular economy strategies [4]. Aligned with the circular economy, more attention is being given to modification, regeneration, reuse and optimization of Acs’ production to improve their environmental and economic sustainability [5].

Recent reviews have highlighted the rapid development of biomass-derived carbon materials produced from agricultural residues, lignin, algae, forestry by-products, and other renewable feedstocks. These sustainable adsorbents combine high adsorption performance with low production costs while contributing to waste valorization and circular economy strategies. Advances in precursor selection, activation methods, surface functionalization, regeneration, and life-cycle assessment have further strengthened their potential for water and wastewater treatment [1,6,7,8].

The papers included in this Special Issue are aligned with the current research trends identified in recent reviews, namely, the development of sustainable adsorbents, the treatment of increasingly complex wastewaters, and the integration of adsorption with complementary treatment technologies to enhance process efficiency. This Special Issue, “Activated Carbon: Contaminant Removal for Environmental Sustainability”, was created to provide a platform for the dissemination of recent advances related to the preparation, characterization, modification, regeneration, reuse and application of AC materials in the removal of a diversity of pollutants from water. Emphasis was placed on the development of ACs from novel precursors, including biomass-derived and waste-derived materials, as well as on their application to drinking water purification and wastewater treatment. The contributions collected in this Special Issue are aligned with these objectives and provide valuable insights into current trends and future opportunities in the field of activated carbon-based environmental remediation.

The nine papers published in this Special Issue cover experimental studies on the removal of pharmaceuticals, pesticides, industrial organic pollutants, heavy metals, and emerging contaminants, together with review articles addressing green adsorbents, dye-contaminated wastewater treatment, and the recovery of valuable resources. The contribution of different papers can be found in

Table 1. Main contributions of the papers included in this Special Issue.

Reference	Target Pollutants	Precursor or Adsorbents	Focus
Ledesma et al. [10]	p-Nitrophenol	Activated carbon	Particle size impact, column dynamics
Ferreira et al. [11]	Paracetamol and Cu2+	Agrowaste porous carbons	High removal without acute ecotoxicity
Liu et al. [12]	Multiple pollutants	Green adsorbents/Biochar	Comprehensive review on sustainability and LCA
Rocha et al. [13]	Octocrylene	Spent coffee grounds biochar	Emerging organic contaminant removal
Moraes et al. [14]	Diuron, Linuron	Spent coffee grounds AC	Herbicide removal and adsorption modeling
Nogueira et al. [15]	Rare earth elements	Pyrolytic carbons	Critical raw material recovery
Doczekalska et al. [16]	Paracetamol	Nutshell-derived ACs	Agricultural waste valorization
Cansado et al. [17]	Synthetic dyes	Various ACs/methods	Review on dye wastewater treatment pathways
Hao et al. [18]	Carbon emissions	Economic framework	Decoupling strategies in carbon economy

. These contributions, in alignment with the recent literature, demonstrate the actual and continuing importance of ACs technologies in addressing contemporary environmental challenges while supporting sustainability and circular economy purposes [9].

2. Contributions to This Special Issue

The articles published in this Special Issue collectively illustrate the rapid evolution of activated carbon research toward sustainable water treatment. Although they address different contaminants and adsorption systems, the nine contributions converge around five major points: (i) sustainable production of activated carbon from waste resources, (ii) removal of conventional and emerging contaminants, (iii) process understanding and scale-up on adsorbents production, (iv) sustainability, cost and circular economy, and (v) future perspectives for adsorption technologies.

One of the strongest points emerging from this Special Issue is the increasing use of renewable and waste-derived feedstocks as precursors for activated carbon production. Agricultural residues, nutshells, and spent coffee grounds were successfully converted into high-performance adsorbents capable of replacing commercial ACs in several applications. These studies demonstrate that biomass valorization not only reduces production costs but also contributes to waste management, wastewater remediation, and circular economy strategies.

The studies by Ferreira et al., Rocha et al., Moraes et al., and Doczekalska et al. [11,13,14,16] jointly show that ACs and biochar prepared from agro by-products can effectively remove organic and inorganic contaminants while preserving competitive adsorption performances. Particularly significant is the use of spent coffee grounds as a versatile precursor across two different manuscripts, illustrating the growing interest in transforming urban biowaste into valuable ACs [13,14].

This Special Issue includes the investigation of a diversity of contaminants. Instead of focusing on a single pollutant class, the included papers describe the removal of pharmaceuticals, herbicides, phenolic compounds, UV filters, heavy metals, dyes, and rare earth elements, reflecting the complexity of modern wastewater streams [10,11,12,13,14,15,16,17,18].

The studies published in this Special Issue demonstrated that AC-based materials remain one of the few adsorption technologies, under optimized conditions, that can remove almost all contaminants from the aqueous phase. While pharmaceuticals such as paracetamol received considerable attention [11,16], other contributions extended adsorption applications to pesticides (diuron and linuron), p-nitrophenol, octocrylene, synthetic dyes, copper ions, and even valuable rare earth elements, highlighting the expanding applications of ACs [10,11,12,13,14,15,16,17,18].

The limitations concerning expanding the results from the laboratory to an industrial scale were also discussed. Several contributions move beyond simply reporting adsorption capacities and instead address aspects that are essential for real-world implementation. In this field, the work of Ledesma et al. must be highlighted, which investigated both batch and continuous fixed-bed adsorption, providing valuable information for process scale-up and demonstrating the influence of adsorbent particle size on column performance [10]. Likewise, Ferreira et al. evaluated pollutant removal from binary contaminant systems (paracetamol and Cu²⁺) and complemented adsorption experiments with ecotoxicity tests, showing that adsorption efficiency should be assessed together with environmental safety [11]. Other studies employed adsorption isotherms, kinetic modeling, and numerical simulations to better understand adsorption mechanisms and optimize process design [13]. Together, these contributions reflect the increasing relevance of adsorption research, where process engineering and environmental assessment are becoming as important as adsorption capacity itself.

All manuscripts in this Special Issue placed emphasis on sustainability. Beyond developing efficient adsorbents, several papers consider regeneration, waste valorization, life-cycle thinking, and resource recovery. The review by Liu et al. provides a comprehensive framework for evaluating green adsorbents by integrating synthesis methods, ecotoxicity, regeneration, and environmental impacts [12]. In the same perspective, Nogueira et al. expand the use of the adsorption process by demonstrating its potential for recovering rare earth elements from secondary resources [15]. The review by Cansado et al. further reinforces the importance of adsorption technologies for dye-contaminated wastewater and identifies future opportunities for improving process sustainability [17]. Jointly, these papers illustrate the transition from adsorption as a simple separation and remediation process to adsorption as a facilitating technology for circular resource management and valorization. Linking technological innovation with macro-environmental policy, the study by Hao et al. highlights the structural drivers of carbon emissions in catch-up economies, offering actionable pathways for energy transition and decarbonization that reinforce the broader sustainability goals of this Special Issue [18].

The contributions in this Special Issue reveal several emerging trends that are influencing the future of ACs research. These include the increasing utilization of biomass-derived precursors, the treatment of complex mixtures of emerging contaminants, the integration of adsorption with modeling and continuous-flow systems, and the growing importance of regeneration, life-cycle assessment, and resource recovery [10,11,12,13,14,15,16,17,18].

These trends are fully consistent with the recent literature review and indicate that future developments will increasingly focus on designing multifunctional carbon materials, improving process scalability, integrating adsorption with complementary treatment technologies, and supporting circular economy principles through adsorbent production and reuse.

This Special Issue also discussed the role of green adsorbents within circular economy strategies and their alignment with the United Nations Sustainable Development Goals.

Collectively, recent reviews demonstrate that adsorption research is moving beyond the development of high-capacity adsorbents toward sustainable material production, life-cycle assessment, regeneration, resource recovery, and integration with complementary treatment technologies [1,2,4,5,6,7,8], which is aligned with the manuscripts included in this Special Issue.

3. Conclusions

The articles published in this Special Issue demonstrate that ACs continue to play a central role in water treatment. Beyond improving adsorption performance, current research increasingly emphasizes renewable feedstocks, material regeneration, environmental assessment, resource recovery, and process integration. These advances support the transition toward circular and resource-efficient water treatment technologies. Future research should focus on scaling up promising laboratory findings, integrating adsorption with complementary treatment processes, and developing cost-effective, environmentally sustainable adsorbents capable of addressing emerging contaminants under real operating conditions.