Sludge Treatment Patents: Who Leads, Where the Gaps Are 2026
- Filing has plateaued, not grown. Annual filings ran from 48 in 2017 to a peak of 55 in 2024, with a flat midpoint of 53 in 2022 — this is a mature, densely claimed field rather than an emerging one.
- China dominates the receiving-office split. 485 of the tracked filings came through China, versus 140 in Japan and 65 in the United States, meaning defensibility and freedom-to-operate analysis has to start with Chinese filings.
- Co-filing is rare and clustered. Only 10 co-assignee pairs appear across 863 families, with the strongest ties sitting between the same small group of individual inventors rather than institutional partners.
A settled field built on dewatering and digestion, not a new one
Sludge treatment patenting sits almost entirely inside C02F, the water and wastewater treatment subclass, with 859 of 863 tracked records touching it. Secondary claim activity spreads thinly across separation processes, solid waste disposal, fuels, fertilisers and incineration — evidence of a core technology (dewatering, anaerobic digestion, thermal hydrolysis) surrounded by narrower downstream applications rather than several competing technical paradigms.
The most-cited prior art in this corpus dates back to the 1980s and 1990s activated-sludge and dewatering patents, which still anchor citation chains today. That is a citation-count artefact of an older, well-searched corpus more than a sign those methods remain the state of the art — recent filings build on thermal hydrolysis and co-digestion approaches that have not yet accumulated comparable citation counts.
Filing trend and technology composition
Annual filing counts and IPC subclass distribution across the 863 families tracked in this dataset, drawn from the C02F11, C05F7 and B09B3 classification set.
Filings plateaued after a mid-2020s peak
Filings ran from 48 in 2017 to a peak of 55 in 2024 with 2022 sitting at 53 — a flat trajectory rather than sustained growth. The 2026 figure of 2 reflects the publication lag of roughly 18 months rather than an actual collapse in filing activity; the most recent 12–18 months are always undercounted at the point of publication.
Claim activity concentrates in wastewater treatment
C02F covers 859 of 863 records, meaning nearly every filing frames its claims around wastewater or sludge treatment specifically. Filtration (B01D), solid waste disposal (B09B), fuel conversion (C10L), fertiliser production (C05F), mixing equipment (B01F), inorganic chemistry (C01B) and incineration (F23G) each appear in a minority of records, marking them as secondary or downstream claim territory rather than independent filing centres.
Shares are the percentage of the 863 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Sludge Treatment and Resource Recovery with Eureka
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Try EurekaThe most-cited prior art and a recent representative filing
Sludge and kitchen waste collaborative digestion process coupled with intermediate thermal hydrolysis
The filing describes a two-stage process: kitchen waste is slurried and mixed with desanded primary sludge for a first-stage anaerobic co-digestion, the digestate is then blended with residual activated sludge and centrifugally dewatered, and the resulting cake undergoes thermal hydrolysis before further desanding of the hydrolysed material.Filed by Beijing Drainage Group, dated 2024-11-14 — one of the more recent substantive filings in this dataset, illustrating current interest in coupling co-digestion with intermediate thermal hydrolysis rather than treating either step in isolation.
| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US5906750A | Method for dewatering of sludge | 99 |
| 2 | US5514277A | Treatment of wastewater and sludges | 91 |
| 3 | US20060249448A1 | Process for biological treatment of organic wastewater and apparatus therefor | 72 |
| 4 | CN102381820A | 基于水热改性技术的污泥处理工艺 | 70 |
| 5 | US4749494A | Treatment of waste water by the activated sludge process | 64 |
| 6 | CN101708937A | 一种臭氧促进污泥减量化的方法 | 53 |
| 7 | US5976375A | Process for reducing production of biomass during activated sludge treatment of pulp and paper mill effluents | 52 |
| 8 | US4818405A | Sludge treatment | 51 |
| 9 | US20070241041A1 | Waste water and sludge treatment apparatus | 48 |
| 10 | JP2003200198A | Method and apparatus for treating sludge | 40 |
Citation counts favour older, longer-indexed documents; treat this table as a map of influential prior art, not of current filing activity.
Patent titles are shown in the language they were filed in, not translated, so that each record stays verifiable against the original filing — a translated title will not match in Eureka or in any national register. Each row carries its publication number; clicking a row searches Eureka by that number.
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Three patterns from the dataset matter more than any single ranking: where claim density sits, who is still active, and how filings connect to each other.
Chinese filings set the prior-art baseline
With 485 of 863 records filed through China against 140 in Japan and 65 in the United States, any freedom-to-operate check in this space has to clear Chinese prior art first, not treat it as a secondary jurisdiction.
A plateaued field, not a growing one
Filings peaked at 55 in 2024 after sitting near 53 at the 2022 midpoint. That flat trajectory signals occupied claim space in the core process routes rather than headroom for broad new filings.
Co-filing is thin and personal, not institutional
Only 10 co-assignee pairs exist across the corpus, and the strongest ties link the same three individual names to each other repeatedly rather than connecting universities, utilities and equipment makers.
Influential prior art predates current filing activity
The most-cited record in this corpus is a 1990s dewatering patent; heavy citation weight sits with older activated-sludge and dewatering art, which shapes how examiners read novelty in newer thermal hydrolysis and co-digestion claims.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to sludge treatment and resource recovery, with the prior art for and against each one.
Assignee activity has gone quiet at the top
Momentum data shows the named institutional assignees in this dataset — universities, municipal utilities and established equipment makers — recording zero filings in the latest tracked year, several down 100% year-on-year. That does not mean the field is abandoned; it means recent activity is dispersed across smaller or individual filers rather than concentrated in the historically dominant names.
Prior leaders have gone quiet
Named assignees including Mitsubishi Electric, Tongji University, Beijing Drainage Group, Ebara Corporation, Kurita Water Industries and Shanghai Municipal Engineering Design Institute all show zero filings in the most recent tracked year.
Sharp year-on-year drop-offs
Tongji University and Beijing Drainage Group both show a full year-on-year decline to zero, a pattern consistent with publication lag but also with a genuine pause in new filing after a period of activity.
Individual inventors, not institutions, cluster tightest
The strongest co-filing relationship in the dataset links two individual named inventors on 13 shared families, with a third individual tied to both at 11 each — a tighter cluster than any institutional pairing in the corpus.
| Assignee | Recent year | YoY |
|---|---|---|
| Mitsubishi Electric Corporation | 0 | — |
| Tongji University | 0 | -100% |
| Beijing Drainage Group Co., Ltd. | 0 | -100% |
| Ebara Corporation | 0 | — |
| Kurita Water Industries Ltd. | 0 | — |
| Shanghai Municipal Engineering Design Institute (Group) Co., Ltd. | 0 | — |
| LI JINMIN | 0 | — |
| LI DAYONG | 0 | — |
Where to take this analysis
The dataset points to a mature core with specific gaps rather than a field wide open for broad claims. These are reasonable next steps for teams deciding where to file or where to challenge.
Map claim scope against the China baseline
Before drafting new claims in thermal hydrolysis or co-digestion, run a targeted search against the Chinese filings that make up the majority of this corpus rather than relying on US or EP prior art alone.
Explore assignee filings in EurekaTest the under-claimed branches
Struvite crystallization control and sludge-derived biochar show thinner coverage than the core dewatering and digestion routes; a narrow, well-drafted claim there faces less prior art density.
Run a white space search in EurekaWatch for renewed institutional filing
Several previously active university and utility assignees dropped to zero in the latest year; monitor whether this reflects publication lag or an actual shift in R&D priority before assuming the space is open.
Set up assignee monitoring in EurekaCommon questions about sludge treatment patents
Momentum data in this corpus shows the historically active assignees — including Mitsubishi Electric, Tongji University, Beijing Drainage Group, Ebara Corporation and Kurita Water Industries — all recording zero filings in the latest tracked year. This suggests leadership in raw filing counts sits with names built up over 2017-2024 rather than with a currently accelerating filer. Anyone assessing competitive position should look at cumulative family counts alongside recent momentum, since the two tell different stories in this field.
The dataset does not break out these two routes as separate IPC subclasses, but the representative recent filing from Beijing Drainage Group shows the two being combined rather than treated as competitors: co-digestion feeds into intermediate thermal hydrolysis in a coupled process. That pattern suggests the more heavily contested claim space now sits around how these steps are sequenced and coupled, not around either technique alone.
Based on this corpus, secondary IPC subclasses like C05F (organic fertilisers) and C01B (inorganic compounds) carry far fewer records than the core C02F wastewater treatment class, pointing to thinner coverage around resource-recovery outputs such as struvite-based phosphorus recovery and sludge-derived biochar. A first claim in these areas should focus on the specific recovery mechanism or downstream product rather than the general dewatering or digestion step, which is already densely claimed.
China represents 485 of the 863 tracked filings, more than three times the next-largest jurisdiction, Japan at 140. This concentration reflects both the scale of municipal wastewater infrastructure investment in China over the tracked period and a filing culture that favours domestic patent protection for process and equipment improvements. For freedom-to-operate purposes, this means Chinese-language prior art needs to be searched directly rather than assumed to mirror English-language filings.
The 2026 figure of 2 filings should not be read as a collapse in activity. Patent publication typically lags actual filing by around 18 months, so the most recent one to two years in any trend chart are structurally undercounted at the point of data collection. The more reliable read on recent trajectory comes from 2023-2024 figures, which show a peak of 55 filings in 2024 following a flat period around 53 in 2022.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.