It refers to processes that combine brine minimization or zero liquid discharge treatment — concentrating wastewater to eliminate liquid effluent — with heavy metal recovery or selective precipitation from that brine before final crystallization or disposal. In this dataset the search combines ZLD and brine-minimization terms with heavy-metal-removal, metal-recovery-from-brine, and selective-precipitation terms across 121 patent families. Most records fall under water treatment (C02F), alkali/alkaline-earth compound chemistry (C01D, C01F) and separation processes (B01D), reflecting that the core technical work is chemical precipitation and physical separation rather than metallurgical extraction.

Filing activity rose from 2 families in 2017 to a peak of 11 in 2022, then declined to 8 by 2026, which sits below the 2022 peak rather than above it. That pattern reads as a plateau rather than sustained growth, though the most recent one to two years are always undercounted because publication typically lags filing by around 18 months. A practitioner should treat the 2025-2026 figures as a floor, not a ceiling, but should not assume the field is currently accelerating based on the data available.

The dataset shows a small set of research institutes and water-technology firms as the most active filers, with one research-institute pairing — a national science and industry research organization filing jointly with a technology university — responsible for the largest co-assignee filing volume observed. Beyond that pairing, co-filing is rare across the corpus, with only two co-assignee relationships identified in total. Most other named assignees appear at low volume and show little to no filing activity in the most recent year, suggesting a narrow and somewhat static leader group rather than a broad competitive field.

The four dominant IPC subclasses — water treatment, alkali-metal compounds, separation processes and alkaline-earth/rare-earth compounds — carry the bulk of the 121 families and the densest prior art, including the most-cited records in the corpus. By contrast, metal extraction and refining (C22B) and coating/surface deposition (C23C) each show only single-digit record counts, as does non-metallic inorganic compound chemistry (C01B). That imbalance points toward selective precipitation reagent chemistry and brine-to-metal recovery process integration as comparatively under-claimed branches worth a closer freedom-to-operate check before assuming they are occupied.

US20090045116A1 describes a combined heat-and-power ZLD plant that integrates reverse osmosis or filtering modules with a centrifugal module, dryers, a heating circuit, high-vacuum ejector chambers and an on-site internal combustion engine and alternator for power generation. It is one of the most-cited records in this corpus, indicating it has shaped a meaningful share of later filings in the space, though its 2009 priority date means many of its specific hardware claims may have already been designed around or may be nearing expiry depending on jurisdiction. Anyone building a similarly integrated plant — particularly one combining desalination, waste treatment and on-site power generation in a single system — should review its claim scope directly rather than relying on the abstract alone, since the specific combination of components, not the general ZLD concept, is what a claim of this type typically protects.