"Membrane Bioreactors" are often discussed in the context of:

Membrane Bioreactors (MBRs) are advanced wastewater treatment technologies that combine conventional biological treatment (activated sludge) with membrane filtration (microfiltration or ultrafiltration). MBRs produce high-quality treated effluent suitable for water reuse, occupy a smaller footprint than conventional treatment plants, and effectively remove suspended solids, pathogens, and many organic contaminants. They are increasingly used in municipal and industrial wastewater treatment globally, including for water recycling in water-scarce regions.