From Oxidation Chemistry to Intelligent Water Systems: Emerging Directions in Process Optimization and Environmental Engineering

Advanced oxidation processes (AOPs) are treatment technologies designed to generate highly reactive oxidizing species, mainly hydroxyl radicals and, in some systems, sulfate radicals, for the degradation of refractory organic pollutants that are difficult to remove by conventional biological or physicochemical treatment. Globally, AOPs are now recognized as an important part of advanced water and wastewater treatment, particularly for the removal of micropollutants, toxic organics, color, odor, and residual toxicity. However, the field shows a clear gap between commercially mature technologies and emerging research-stage technologies [1,2].

The current global situation of AOPs can be described as scientifically mature but industrially selective. Established systems such as ozonation, UV/H₂O₂, and Fenton-based processes are already used in real treatment practice, while many other variants remain largely confined to laboratory and pilot scales. Recent reviews emphasize that AOP research has expanded rapidly, but full-scale implementation is still limited by operating cost, oxidant consumption, energy demand, water-matrix effects, by-product control, and scale-up difficulties [1,2].

The papers gathered in this Topic entitled “Advanced Oxidation Processes: Applications and Prospects, 2nd Volume” illustrate the breadth of process engineering while revealing a shared scientific direction: the move toward more selective, efficient, and operationally relevant technologies for environmental protection, resource recovery, and product-quality enhancement. Although the studies cover distinct application domains, namely, tannery wastewater, landfill leachate, municipal effluents, natural water, aquaculture, gold tailings, soybean oil processing, and dissolved oxygen forecasting, they are united by a common commitment to process intensification, optimization, and decision support under realistic conditions.

A dominant theme across the collection is the central role of oxidation-based technologies in water and wastewater treatment. Urbina-Suarez et al. [3] examined an enhanced UV/H₂O₂ system for tannery effluents and showed that a carefully optimized combination of acidic pH, elevated temperature, ultraviolet power, and hydrogen peroxide can simultaneously reduce multiple pollution indicators, including ammonium, chromium, BOD, COD, and color. Their study is notable because it addresses a complex real industrial effluent rather than a simplified laboratory matrix, thereby reinforcing the practical value of statistically optimized advanced oxidation processes.

A complementary perspective is offered by Becerra-Moreno et al. [4], who evaluated catalytic ozonation with magnetite for landfill leachates. Their results showed substantial COD removal and, importantly, improved biodegradability, evidenced by increases in the BOD₅/COD ratio. This contribution underscores a key strength of catalytic ozonation: it can function not only as a polishing technology but also as a transformation step that renders recalcitrant mixtures more amenable to downstream biological treatment. At the same time, the gradual decrease in catalyst efficiency after repeated cycles reminds us that catalyst stability and regeneration remain decisive issues for scale-up.

Dominguez et al. [5] extended the oxidation discussion into the electrochemical domain through boron-doped diamond anodic oxidation of wastewater treatment plant effluents. Their work demonstrated the strong capacity of EO-BDD to eliminate neonicotinoid pesticides and other emerging contaminants from real effluents intended for reuse. Particularly relevant is the authors’ simultaneous consideration of degradation efficiency, kinetics, mineralization, and specific energy consumption. Such multidimensional evaluation is essential if advanced treatment technologies are to move beyond proof-of-concept and become credible tools for water regeneration.

Shen et al. [6] addressed another pressing water-quality issue by comparing several UV-activated advanced oxidation systems for humic acid removal from natural water. Their identification of UV/peroxymonosulfate (UV/PMS) as the most effective option highlights how oxidant selection can decisively alter process performance. Beyond the high mineralization achieved, this study is significant because humic substances are closely linked to color, heavy-metal transport, and disinfection by-product formation. In this respect, the paper contributes not only to oxidation science but also to safer drinking-water treatment strategies.

The broader conceptual and technological framework for many of these studies is supplied by Zhang et al. [7] in their review of ozone technology. By surveying ozone generation methods and applications in water treatment, air pollution control, soil remediation, food preservation, medicine, and the power industry, the review demonstrates the continuing versatility of ozone as a platform technology. It also highlights a persistent tension in ozone research and deployment: ozone is simultaneously mature in many industrial uses and still evolving through innovations in generation efficiency, reactor design, coupling with other processes, and application-specific integration.

The coupling of oxidation chemistry with aquaculture management appears in the paper by Afif et al. [8], who proposed a lime-based composite integrating calcium peroxide, titanium dioxide, and peracetic acid encapsulated in Fe-alginate granules. Their system was designed to provide in situ oxygenation while promoting advanced oxidation at the sediment–water interface in shrimp ponds. The reported maintenance of dissolved oxygen and the removal of ammonia, sulfide, and turbidity suggest that this strategy may offer a practical route for improving pond-bottom conditions in traditional aquaculture systems. The work is especially timely because it frames advanced treatment not as an isolated laboratory exercise but as a farmer-oriented technology requiring safety, simplicity, and operational resilience.

If Afif et al. [8] focused on intervention, Wang et al. [9] focused on anticipation. Their deep learning-based rolling forecasting of dissolved oxygen in coastal waters demonstrates the growing role of artificial intelligence in water-quality management. By comparing several forecasting architectures and building an ensemble-based early-warning system, the authors moved beyond model benchmarking to deployment-oriented decision support. This is an important signal for the field: future environmental engineering will increasingly combine treatment technologies with predictive analytics, enabling a shift from reactive management to proactive control.

The Topic collection also broadens the notion of process optimization beyond water treatment. Kenzhaliyev et al. [10] investigated the use of trichloroisocyanuric acid as an oxidizer in the leaching of gold-containing concentrate derived from tailings. By showing improved gold recovery following oxidative pretreatment, the paper contributes to the sustainable valorization of technogenic raw materials and reminds us that oxidation processes can serve both environmental remediation and resource recovery objectives. In a different industrial context, Mohammadi-Moghaddam et al. [11] optimized stripping and drying parameters in soybean oil extraction, demonstrating how relatively targeted adjustments in temperature and pressure can substantially influence quality indicators such as acidity, color, peroxide value, moisture, and oxidative stability. This paper underscores that process engineering advances are not confined to pollutant destruction; they also include the refinement of manufacturing conditions for better product quality and improved industrial efficiency.

Taken together, these papers suggest several directions for future work. First, optimization remains indispensable, but it must increasingly be linked to realistic matrices, lifecycle performance, and techno-economic constraints. Second, hybridization—whether between ozone and catalysts, oxygen release and AOPs, electrochemical oxidation and water reuse, or forecasting and early warning—has emerged as a defining strategy for improving robustness and applicability. Third, future progress will depend on connecting chemistry with systems thinking: treatment performance, energy use, catalyst durability, digital monitoring, and end-use requirements must be considered together rather than in isolation.

In summary, this Topic collection captures a field in productive transition. Advanced oxidation processes continue to evolve from single-process laboratory studies into integrated solutions for complex environmental and industrial challenges. Meanwhile, process optimization, materials design, and machine learning are expanding the disciplinary boundaries of process engineering. The papers assembled here, therefore, do more than report individual results; collectively, they show how modern process research is becoming more interdisciplinary, more application-driven, and more closely aligned with the demands of sustainability.

The scientific contributions to this Topic have shed light on the state of the art of emerging advanced oxidation technologies, which show promise for being incorporated into the industrial sector in the not-too-distant future.