Background In Spain, there is a generally low level of treatment of wastewater in conglomerations with populations of fewer than 2 000 inhabitants (treatment rate of less than 40-50%). According to EUROSTAT, about 35% of Europeans live in towns with a population of more than 100 000, while 40% live in small urban agglomerations. In the smaller municipalities, there is a problem of a lack of facilities with effective systems for the treatment of wastewater, mainly because of lack of funding for more effective treatment systems. Objectives The project aims to increase the sustainability of membrane-based water treatment processes by improving their durability and reducing their environmental cost. The processed water obtained as a result of the treatment will contribute to European Union efforts to become a “recycling society,” as laid down in the Waste Framework Directive (2008/98/CE). The improved treatment will also demonstrate an alternative to the disposal in landfills of exhausted reverse-osmosis filtration membranes used in wastewater treatment. At national level in Spain, the project will comply with Royal Decree 1620/2007 on reuse of wastewater, while enabling the use of recycled membranes. Membranes from reverse osmosis desalination plants will be recycled and used in lower-pressure filtration processes (ultra-nanofiltration). The membrane recycling process is based on chemical treatment. The proposed methodology will include the development of three pilot plants: two membrane recycling plants (one with active treatment, and another for passive treatment), and a monitoring plant for checking membrane quality before and after wastewater treatment (capacity 1 000 m3 /day). The recycled membranes will be tested in a pre-treatment process before the reverse osmosis step in the Cuevas de Almanzora desalination plant, and in wastewater tertiary treatment in the Guadalajara wastewater treatment plant. Expected results: Transformation of old reverse-osmosis membranes for their reuse in low pressure ultra-nanofiltration processes; Demonstration of the reverse-osmosis membrane modification process, enabling membrane reuse in pilot-scale low pressure (ultra-nanofiltration) filtration processes. Identification of the optimal operating conditions; Pilot and demonstration measures: one membrane monitoring pilot, two regeneration pilots and three demonstrators of reuse of the recycled membranes;,/li> An economic and financial feasibility study; Creation of a new database of every fluid treatment plant in Spain that uses reverse-osmosis membranes; A proposal for a new Best Available Technologies document for recycling of reverse-osmosis filtration membranes; Production of guidelines for recycling and reuse of old reverse-osmosis membranes; and Inclusion of information and knowledge gained about membrane recycling and reuse in academic programmes at Rey Juan Carlos and Alcalá universities.