Advancing Strategies for the Control and Treatment of Emerging Contaminants in Water Ecosystems

Emerging contaminants (ECs) include pollutants that are not commonly monitored in the environment but have the potential to cause ecological or health impacts. They represent one of the most pressing environmental challenges of the 21st century. These contaminants include pharmaceuticals, personal care products, pesticides, industrial chemicals, antibiotic resistance genes (ARGs), and nanoplastics. They often evade traditional water treatment processes, entering aquatic ecosystems and potentially causing adverse effects on environmental and public health. Addressing these challenges requires innovative and sustainable treatment strategies, which is the focus of the Special Issue Control and Treatment of Emerging Contaminants in Water Ecosystems published in the journal Water. The Special Issue offers a multi-pronged approach to tackling these challenges, including advanced treatment technologies, natural coagulants, and innovative degradative processes. This editorial synthesizes insights from the seven studies featured in the issue, highlighting their contributions to advancing water treatment technologies and improving ecological health.

1. Physiochemical Treatment for ECs

Antibiotics are widely used in our daily life to combat bacterial infections, leading to water contamination and fostering antibiotic resistance. To comprehensively address sustainable water remediation, a study in this Special Issue investigated the degradation of veterinary antibiotics, specifically oxytetracycline and lincomycin, using non-thermal plasma technology. Non-thermal plasma technology achieved near-complete degradation of these antibiotics at initial concentrations of 1 mg/L, with mineralization rates of 21% and 31%, respectively. Beyond mere degradation, the study demonstrated that the treated solutions exhibited reduced biotoxicity, indicating a safer environmental footprint. This research underscores the potential of non-thermal plasma as a sustainable and effective treatment method. Plasma-based systems can target a wide range of organic pollutants with minimal secondary waste, aligning with global goals for green technology.

Meanwhile, the study by Jojoa-Sierra et al. explored an innovative approach to mitigate these challenges using an Ag/TiO₂ catalyst to activate persulfate (PDS) under simulated sunlight. The authors demonstrated that the Ag/TiO₂-PDS system effectively degraded levofloxacin, achieving significant reductions in its concentration and antibacterial activity. The system leveraged the photocatalytic properties of Ag/TiO₂, enhanced by the activation of PDS, to produce reactive species capable of breaking down the antibiotic into less harmful by-products. Notably, this approach also showcased water disinfection potential, broadening its applicability for real-world scenarios. A key strength of the study lies in its dual focus on contaminant degradation and antibacterial activity reduction, addressing both chemical and biological risks. The integration of simulated sunlight makes this method energy-efficient and environmentally friendly, aligning with the principles of green chemistry. However, challenges such as scalability, long-term stability of the catalyst, and the potential formation of secondary pollutants warrant further investigation. Future research should explore the application of this system in diverse water matrices, including industrial effluents and natural water bodies, to assess its broader impact.

Similarly, the study by Karami et al. also investigated a green alternative photocatalyst approach using a biopolymer-based Gellan gum-supported TiO₂ for the removal of pollutants from water. The authors highlight the enhanced photocatalytic activity of the composite material, demonstrating its efficiency in degrading organic contaminants under visible light. The study emphasizes the eco-friendly, sustainable nature of this approach, offering a promising solution for wastewater treatment. This innovative photocatalyst showcases the potential of biopolymer-based composites in addressing environmental pollution challenges and advancing water purification technologies.

2. Biological Treatment for ECs

Nature-based solutions have gained traction as cost-effective and environmentally friendly alternatives to synthetic chemicals. A significant contribution in this Special Issue examined the use of Moringa oleifera seeds as a natural coagulant for industrial wastewater treatment, focusing on tequila vinasses. These vinasses, a byproduct of tequila production, are known for their high organic load and dark coloration, making them challenging to treat. The study found that an optimal dose of 1 g/L of Moringa oleifera seeds at pH 8 resulted in significant reductions in the apparent color, turbidity, true color, and total suspended solids. This method not only offers an eco-friendly alternative for treating industrial wastewater but also promotes the utilization of natural, locally available materials. Such approaches are particularly valuable for small and medium enterprises in developing countries, where resources for advanced technologies may be limited.

The rise in antibiotic resistance is one of the most alarming consequences of emerging contaminants. ARGs, often present in sewage sludge, can propagate through water systems and pose risks to human and animal health. One review in the Special Issue explored the removal of ARGs through composting. The study identified critical mechanisms, such as the high-temperature denaturation of proteins and DNA, adsorption of antibiotics and heavy metals by biochar, and microbial community shifts. While composting shows promise, its effectiveness can vary depending on operational conditions, such as temperature, duration, and the composition of additives. The review emphasizes the need for integrated approaches, combining composting with advanced treatments, to ensure comprehensive ARG removal.

3. Future Challenges: A Call for Collaborative Innovation

The studies featured in this Special Issue illustrated the complexity and urgency of addressing emerging contaminants in water ecosystems. From advanced technologies like non-thermal plasma to nature-based solutions like Moringa oleifera seeds, the research demonstrated a wide array of strategies for mitigating these pollutants. However, no single solution is sufficient to address the multifaceted challenges posed by emerging contaminants. A collaborative approach, integrating advanced technologies, nature-based solutions, and robust policy frameworks, is essential for achieving sustainable water management.

Emerging contaminants are a global problem, transcending geographical and political boundaries. As such, international cooperation in research, technology development, and regulatory standards is crucial. By building on the insights presented in this Special Issue, we can pave the way for cleaner water ecosystems and a healthier future for all.