Background Wastewater treatment plants (WWTPs) in the EU generate ever-increasing amounts of sludge waste. The use of sludge from WWTPs for the fertilisation of farming soils has become relatively widespread because of the richness of its organic components. However, the European Sewage Sludge Directive (86/278/EEC) has set limits on this form of valorisation, because the sludge also has a high content of heavy metals, which contaminate the natural environment. The mining industries also generate large amounts of sludge waste from the process of washing extracted aggregates. This contains particles of such small size that the sludge is largely liquid, which significantly limits its potential applications. This mud is usually stored in basins, affecting large areas of land and generating stability problems and other risks to the environment. The European Directive on the Management of Waste from Extractive Industries (2006/21/EC) states that a management plans must take into account the recovery and/or reuse of the mud. Since current methodologies for the management and treatment of these forms of sludge waste are inadequate and expensive, new solutions are needed. It is important to avoid landfill and incineration as much as possible and attempt to find alternative means of valorising these waste streams that address their contaminating components. Objectives The LIFE Sludge4Aggregates project aims to demonstrate the viability of the valorisation of sludge from both WWTPs and the aggregate extraction process. It specifically hopes to develop a new artificial, lightweight aggregate from the sludge that can have industrial applications. The project will apply a new technology based on the treatment of different mixtures of the mining and WWTP sludge wastes to obtain new and inert low density ceramic products. The project will design and develop a pilot plant for the production of these new artificial lightweight aggregates, including defining the necessary technological and environmental parameters for the process. The project will then work to achieve technological and environmental validation of both the process and the final product through product application and lifecycle analysis. This will include demonstration of conformity with required quality and environmental parameters to meet national and European legislation – notably around resistance to physical and chemical degradation and the avoidance of dangerous emissions during manipulation. It hopes to show potential uses of the new product in sectors including construction, infrastructure and horticulture, both valorising a current waste stream and reducing the need for ‘new’ lightweight aggregates in these sectors. The project thus hopes to reduce the amount of contaminated sludge waste requiring expensive or environmentally-damaging management solutions, extending the lifecycle of existing aggregate material and reducing the need to extract raw materials, particularly clays. Expected results: The project expects to achieve the following results: Demonstration of an innovative process for producing lightweight aggregates using sludge from WWTPs and the extractive industries; Confirmation that the high metals content of the sludge is rendered inert inside the new lightweight aggregate; Valorisation of the new lightweight aggregate in different sectors of activity; Reduction of the volume of WWTP and mining sludge going to landfill; Less extraction of new raw materials – clay – for lightweight aggregate production; and A reduction in the costs and an increase in the competitiveness of companies valorising the sludge waste streams.