This dataset identifies 447 patent families published between 2015 and mid-2026 that combine anaerobic digestion or biogas digestion terms with sludge stabilisation, sludge digestion, biosolids treatment or volatile solids reduction claims, classified under core wastewater treatment IPC codes. That count is a filtered view built around a specific search string, so a broader query on biogas or sludge processing generally would return a larger number. Patent families, not raw document counts, are the more reliable unit here because they neutralise duplicate filings of the same invention across jurisdictions.

Filing activity concentrates among Japanese engineering groups, with the strongest co-assignee relationships found within Fujita-affiliated entities and between Ebara and Toray Engineering, alongside specialist digestion technology firms such as Anaergia. However, every one of the most-active assignees tracked shows zero filings in the most recent year, so current leadership by cumulative volume does not necessarily indicate who is filing now. A momentum check alongside the cumulative ranking is the more useful read for competitive tracking.

The data shows filings peaked at 26 in 2020 and fell to a midpoint of 6 by 2022, a decline that predates and is therefore not explained away by publication lag. This pattern is typical of a field where the core process claims — digester configuration, gas collection, thickening and dewatering steps — were substantially staked out earlier in the decade. A slowdown in filing volume does not mean the underlying technology has stopped being deployed commercially; it more often means the easy claim space has been filled and remaining filings require more specific, narrower claims to clear prior art.

US20220259088A1, filed by Anaergia Inc. and published August 2022, covers a system combining high-solids anaerobic digestion with a post-digestion thermal hydrolysis step, where hydrolysed digestate can be processed into Class A biosolids and its liquid fraction recycled back into the digester alongside a separate returned portion of dewatered digestate. The specific value of the claim is the recycle architecture — returning both hydrolysed liquid fraction and untreated dewatered digestate to the digester — which the abstract states allows a smaller digester tank than comparable systems. Anyone designing a similar high-solids-plus-hydrolysis process should review this recycle loop structure closely before finalising a process flow.

The IPC composition points to several thinner branches relative to the 447-record core: fertiliser-directed use of digestate (C05F, 19 records), separation and filtration integration (B01D, 16), mechanical pre-treatment such as grinding (B02C, 12), and inorganic chemical additions (C01B, 9). These are not necessarily untouched, but filing density there is a fraction of the core wastewater treatment class, meaning a well-drafted claim on, for example, digestate-to-fertiliser conversion methods or mechanical pre-treatment integration faces less crowded prior art than a claim on the digestion process itself.