Membrane bioreactors for sustainable, fit-for-purpose greywater treatment: a critical review

Water scarcity, increasing demand, and new paradigms in water management are gradually switching public perception and attitude toward wastewater. The actual term “waste” water is nowadays being gradually replaced by “used” water, and this is further declined in an array of sub-components, including greywater, depending on provenance. Greywater is increasingly seen as a resource to be recovered. Treated greywater can be used on site for different purposes: toilet flushing, non-food irrigation, fire protection, and others. For this, greywater needs to be treated to remove organic matter, surfactants, micropollutants, and microbial activity. Membrane bioreactors have proven able to provide a high-quality effluent, ensuring also an efficient removal of microorganisms; the technology can be applied in decentralized treatment due to its small footprint, but some issues about the economic investment and fouling phenomenon are still present. Applications and possible solutions to undetermined issues are herein discussed, with a particular stress on the fit-for-purpose approach for greywater treatment and reuse.