The ranked assignee list covers 100 companies at the family level, with the leader holding 890 records and the fifth-ranked holding 406. The field is not dominated by a single filer: the top five combined reach only 4.2% of all 73,901 records in scope, and the top ten reach 6.6%. That spread means the leading names set direction in specific sub-areas like separation hardware or catalysis rather than controlling the field as a whole, so a competitive scan needs to look beyond just the top few names.

Filing volume peaked at 966 records in 2018 and has since eased, running at 814 in 2021 and down to 586 by 2024 — a documented 28% decline over that three-year span. The years after 2024 show much lower counts, but that is largely an artefact of publication lag, since patent publication typically trails filing by around 18 months. The honest reading is a cooling from a 2018 peak rather than a collapse, and the most recent two years should not be treated as reliable evidence either way.

C02F, covering water and wastewater treatment, is the largest single class at 15.8% of all 73,901 records, followed by B01D, separation processes including filtration, at 8.2%. Every other class in the dataset — catalysis, material testing, mixing equipment, inorganic compounds, microorganism-based methods and control systems — sits at or below 2.3% of records. Because a record can carry multiple IPC codes, these shares add up to more than 100%, which reflects genuine overlap in claim scope rather than double-counting error.

The thinnest classes relative to the field's core — control and regulating systems (G05B), microorganism-based remediation (C12N), mixing/dosing equipment (B01F) and inorganic sorbent materials (C01B) — each sit under 1.5% of all records, compared with 15.8% for core treatment chemistry. That gap suggests the sensing, dosing and biological-remediation layers around treatment infrastructure carry meaningfully less claim density than the treatment chemistry itself, making them a more promising area to search before drafting a new application.

US20110262331A1, filed by Mitsubishi Heavy Industries, describes an air pollution control system that chains a boiler, NOx removal equipment, a desulfurizer using an absorbent, and a downstream waste-water treatment device with a solid-liquid separating unit. It is a useful reference point for the specific architecture of linking flue-gas desulfurization to waste-water solid-liquid separation, but it does not cover water treatment methods generally. Anyone filing in adjacent air-pollution or desulfurization waste-stream handling should review its claims specifically, rather than assume it blocks unrelated treatment approaches.