In this dataset, advanced oxidation process (AOP) filings cover Fenton and Fenton-like oxidation, ozonation, and related radical-generating chemistries used to break down recalcitrant pollutants in wastewater. Nearly all of these filings are classified under IPC subclass C02F, the dedicated water and wastewater treatment classification, which covers all 885 tracked families. Smaller but distinct clusters extend the technique into catalysis-heavy reactor designs (B01J), separation and filtration hardware (B01D), and electrolytic production processes (C25B), showing the core chemistry frequently gets paired with mechanical or electrochemical add-ons in a single filing.

Filing volume rose steadily from 30 families in 2017 to a peak of 118 in 2024, but the pace has since flattened; the 2022 midpoint of 71 sits well below the 2024 peak, and 2026's count of 17 is a partial year that will rise as later filings publish. Taken together, the trend looks like a field that grew through the late 2010s and early 2020s and has since plateaued rather than one still accelerating. Because publication lags filing by roughly 18 months, the true 2025-2026 filing rate will not be fully visible for some time.

China's receiving office accounts for 560 of the 885 tracked filings, far ahead of any other jurisdiction. The United States follows with 66, then WIPO's PCT route with 44, South Korea with 42, Europe with 41, and India with 35. This distribution suggests most inventive activity in this space is being protected domestically in China first, with international filers spreading more thinly across the remaining major markets.

The corpus shows a mix of specialist water-treatment corporations, a research university, and a small group of individual co-filing inventors, rather than a single dominant leader. Several named corporate and university assignees recorded zero filings in the most recent tracked year, which may reflect either a genuine slowdown or simply that their newest applications have not yet published. The strongest co-filing relationships in the data are between individual named inventors, pointing to close-knit specialist teams working outside large corporate R&D structures.

The smaller IPC clusters point to the open branches: electrolytic production (C25B, 27 records), alkali-metal compound handling (C01D, 9 records), and fuel-cell-adjacent designs (H01M, 7 records) are all present but thin relative to the dominant C02F and B01J clusters. Recent representative filings, such as a 2026 semiconductor wastewater application combining UV-activated persulfate oxidation with anaerobic biological treatment, suggest hybrid and application-specific combinations remain comparatively under-claimed. Anyone drafting new claims should look at these hybrid combinations before defaulting to standalone Fenton or ozonation claims, which sit on the densest prior art.