Sludge Digesters Filtration Sludge ADI-Hybrid reactor: A high-rate system that combines elements of two anaerobic processes—the UASB (upflow anaerobic sludge blanket) on bottom and UFF (upflow fixed film) on top—and retains process advantages of each. In addition, minimum land space is required. Other advantages include: Granular sludge bed. Minimal space requirements.