Membrane bioreactors (MBRs) are used for treating blackwater and greywater through a combination of suspended growth activated sludge with immersed membrane equipment separating solids and liquids. MBRs provide secondary and tertiary treatment for organic waste, phosphorus, and nitrogen and can be enhanced to increase removal efficiency. Pretreatment for MBRs includes screening and primary treatment (settling and clarification). MBRs yield very good effluent quality due to their very high solids removal efficiency, require only a compact area, are scalable to accommodate community growth, and can be combined with other technologies. The primary uses for MBRs have been for facilities requiring water quality for wastewater reuse or very low outflow nutrient concentrations and facilities with significant land area restrictions. They are relatively high-tech systems used in moderate to high density communities to provide treatment for satellite systems (including resorts, buildings) or centralized systems and have been sized to treat small to large communities.