Background The EU’s economy uses 16 tonnes of materials per person per year, of which six tonnes becomes waste, half of it going to landfill. Overall, the EU produces up to three billion tonnes of waste every year, with a huge negative impact on the environment, as well as significant losses of materials. Municipal solid waste (MSW) generation continues to grow both in per capita and overall terms. Although disposal of this waste in landfills has decreased in the last decade, it is still the most common option for waste management in most EU countries. Landfills cause a major negative impact on the environment, with one of the main problems being generation of leachate. Leachate is highly polluted water generated by the decomposition of organic matter and rainwater percolating through the waste layers at a landfill site. Leachate usually contains large amounts of organic matter, ammonia, heavy metals, chlorinated organic compounds, inorganic salts and other pollutants. Landfill leachate is a heavily polluted liquid, the release of which into the environment must be avoided and is, in fact, forbidden by many regulations. Unless appropriately managed or treated, leachate will have harmful effects on the groundwater and surface water surrounding a landfill site, and will also pose a serious risk to public health. An average municipal landfill site can produce up to 150 cubic metres of leachate per day, which equates to the amount of fresh water that an average household consumes in a year. Therefore, management and treatment of landfill leachate is one of the most important environmental issues related to waste management. Conventional treatment of landfill leachate is based on biological processes and chemical and physical methods. Although these are usually suitable for young to intermediate leachate, with the continuous hardening and aging of landfill sites, such methods are no longer sufficient to treat leachate from old landfill sites. Objectives The main objective of the LIFE RELEACH project is to demonstrate the technical and economic feasibility new landfill leachate treatment strategies based on different existing technologies, primarily membrane separation processes. In particular, the project will: Thoroughly evaluate the different policies and legislation on landfill leachate; Prepare a detailed characterisation of leachate from representative landfills at two demonstration sites (Manresa and Oris); Using bench-scale equipment, reproduce and optimise the different steps in the new process, and define the best operational conditions for treating a specific leachate; Design and build an innovative landfill leachate treatment based on the membrane process, including pre-treatment, desalination and concentrate treatment. The plant will be built and tested at the Manresa and Oris landfills; and Conduct an environmental and economic assessment of the methodology. Expected results: A database with the composition of several leachates from different landfills in Catalonia and other European regions; A versatile leachate treatment plant based on membrane processes to treat old landfill leachate; Treatment of at least 2 000 m3 of landfill leachate at the Manresa and Oris sites; Assessment of the different steps of the new process. The recoveries expected for each step are: ultrafiltration >95%; nanofiltration 90-95%; reverse osmosis 90-95% and electrodyalisis reversal 85-90%; Obtaining of a final effluent that can be discharged into water bodies without any risk; A reduction in the negative environmental impact of the landfill leachate treatment compared to the currently used technologies, by reducing the reagents used and energy consumption. Energy consumption of less than 25 KWh/m3 is expected compared to more than 50 KWh/m3 currently; and A reduction of more than 50% of the total operational costs of treating landfill leachate.