Advanced Technologies of Water and Wastewater Treatment (2nd Edition)

Water is one of the most vital resources for life on Earth, yet a growing population, industrialization, and pollution from industries, agriculture, and households are dramatically increasing demand while threatening the quality of water [1]. Traditional treatment methods are often insufficient, leaving communities exposed to health risks from waterborne diseases and emerging contaminants that conventional processes cannot fully remove [2]. In response, researchers are developing innovative and sustainable technologies that offer higher purification efficiency and reliability. Natural and bio-based materials, such as chitosan [3], pinecones, and agricultural residues [4], serve as effective coagulants and biosorbents for microorganisms, heavy metals, and organic pollutants, while advanced adsorbents like layered double hydroxides [5] and plant-derived activated carbons [6] target persistent contaminants, including phosphates and phenols. Advanced oxidation processes, UV and ozone disinfection [7], nanotechnology, and ozone nanobubbles [8] enhance the breakdown of complex organics and microplastics, often without harmful chemical residues. Biological strategies, such as alternating anaerobic–aerobic regeneration of polymer beads [9], further extend sorbent life and reduce operational costs. Together, these approaches point toward hybrid systems that integrate natural, chemical, and biological methods [10,11] to deliver efficient, sustainable, and resilient water treatments. While challenges remain in terms of scalability, long-term performance, and multi-contaminant removal, investing in these advanced technologies is crucial to ensuring safe water for communities and protecting ecosystems for future generations.

This Special Issue “Advanced Technologies of Water and Wastewater Treatment (2nd Edition)” highlights the wide range of studies that examine advanced water and wastewater treatment technologies, serving as a continuation of the already published first edition [12]. It features eight articles and one review, which I briefly outline in the following paragraphs. I would like to clarify that the aim of this Editorial is not to provide an in-depth analysis of each piece, but rather to encourage readers to explore them further.

The review by Coleman et al., 2024 (contribution 1), highlights the use of chitosan, a natural biopolymer, as a coagulant for removing health-related microorganisms from water and wastewater. Chitosan is biodegradable and non-toxic and offers an eco-friendly alternative to traditional chemical coagulants like alum. The paper emphasizes its effectiveness in aggregating bacteria, viruses, and protozoa, as well as its potential for integration into low-cost water treatment systems. The review also addresses challenges such as its variable removal efficiency depending on water chemistry, suggesting that further optimization and field-scale studies are necessary for widespread adoption.

The study by Orbuleţ et al., 2025 (contribution 2), explores the adsorption of phosphates from wastewater using MgAlFe-layered double hydroxides (LDHs). LDHs are promising due to their high surface area, tunable composition, and strong anion exchange properties. The authors demonstrate significant phosphate removal efficiency, highlighting LDHs as a sustainable approach for preventing eutrophication in natural water bodies. The paper also considers the regeneration and reusability of the adsorbent, indicating practical feasibility for large-scale applications.

In the research by Teweldebrihan et al., 2025 (contribution 3), the use of activated carbon derived from Catha edulis stems for phenol removal from aqueous solutions is investigated. The study demonstrates that agricultural waste can be converted into high-performance adsorbents, supporting circular economy principles. The results indicate strong adsorption capacity and rapid kinetics, making it a cost-effective and environmentally friendly solution for industrial wastewater treatment, particularly in regions with abundant Catha edulis residues.

Furthermore, the paper by Macena et al., 2025 (contribution 4), presents the valorization of pinecones as biosorbents for Zn-contaminated wastewater. Pinecones, being abundant and renewable, offer a low-cost solution for heavy metal remediation. The study highlights significant zinc uptake capacity and the influence of factors such as the pH and contact time. This approach not only addresses metal contamination but also promotes waste valorization, aligning with sustainable environmental management practices.

Ozone nanobubbles were utilized by Aber et al., 2025 (contribution 5), to enhance water treatment in constructed floating wetlands. Ozone nanobubbles improve disinfection and degradation of organic pollutants due to increased mass transfer and reactive oxygen species generation. The research underscores the potential for integrating advanced oxidation processes into natural treatment systems, enhancing efficiency without large-scale infrastructure, and contributing to more resilient water treatment strategies.

In addition, the contribution by Béalu et al., 2024 (contribution 6), to this Special Issue evaluates the combined use of ozonation and granular activated carbon (GAC) filtration to remove organic micropollutants and microplastics. Ozonation breaks down complex pollutants, while GAC adsorbs residual organics, offering a complementary treatment approach. The study demonstrates high removal efficiencies and provides insights into the operational parameters that are necessary to optimize combined treatment systems, showcasing an effective solution for emerging contaminants in municipal wastewater.

Mosca Angelucci et al., 2024 (contribution 7), investigated the feasibility of regenerating polymer beads that have been used to adsorb reactive dyes under alternating anaerobic–aerobic conditions. The study addresses a key challenge in adsorbent reuse and wastewater treatment sustainability. By demonstrating efficient bio-regeneration, the research suggests that cyclic biological treatment can extend sorbent life, reduce operational costs, and mitigate the environmental footprint of dye-laden industrial effluents.

Last but not list, in the study by Kalaronis et al., 2024 (contribution 8), the authors examined the adsorption behavior of common pharmaceuticals onto pristine and aged polypropylene microplastics. Their findings reveal that microplastics can act as vectors for pharmaceuticals in aquatic environments, with adsorption being influenced by polymer aging and surface properties. The research highlights the complex interactions between micropollutants and plastics, underlining environmental risks and the need for advanced treatment or remediation strategies to address pharmaceutical contamination in water bodies.

We would like to thank the authors for their contributions and their willingness to share innovative ideas and methods in this Special Issue. In addition, we would like to express our appreciation to the reviewers for the considerable amount of time that they in-vested to provide accurate and fair manuscript evaluations. Finally, we would like to express our pleasure in working with staff in the Environments Editorial Office for this fruitful and excellent cooperation.