Background Some 20-25% of the municipal solid waste produced in the EU15 around 2008 was treated by incineration, in over 400 installations. One of the important by-products of this process is fly ash. Recent projects have looked at ways of treating and re-using this ash. At the University of Brescia, a new fly ash treatment process, based on colloidal silica medium, has been developed and optimised. The obtained inert product - called COSMOS - shows good mechanical properties for use as a filler in products such as cement, plastics and rubber. Objectives The overall objective of the COSMOS project was to transfer laboratory know-how on the treatment of fly ash from solid-waste incineration to practical application on an industrial scale. The project aimed to demonstrate a nearly-complete re-use of all stabilised material, and to transfer the COSMOS protocol to industrial partners for the construction of a prototype system capable of generating 100 kg/day of the COSMOS filler from fly ash. Associated partner the University of Brescia aimed to optimise this protocol to ensure that the practical application achieves at least the same performance as the laboratory system. The project team will carry out a lifecycle assessment (LCA) of the process to inform the evaluation of the best applications for the COSMOS filler from both the financial and environmental points of view. Results The COSMOS project demonstrated at industrial scale the technical viability of the fly ash inertisation process, which had previously been tested at the laboratory scale. It also showed that the output of the process (the COSMOS product) is safe and that it can be used in several industrial production processes. The project generated new knowledge about the fly ash inertisation process and its applications, with the partners collaborating and providing complementary specialist skills in order to transfer this know-how into industrial applications. The project team demonstrated the viability and applicability of the COSMOS inertisation process in a mid-scale industrial plant treating around 100 kg of fly ash per day. The pilot plant was constructed and tested, and after a period of optimisation the production of COSMOS was started. The project carried out toxicity tests in the pilot plant, in compliance with the ISO EU legislation, which demonstrated the effectiveness of the inertisation process. The tests assessed the level of toxicity both in the fly ash and the COSMOS product. The results clearly showed that the treatment carried out is able to totally eliminate the original toxicity of the fly ash, so that it is no longer harmful, while the COSMOS material was technically classified as inert. The project identified around ten feasible applications of the COSMOS product, for example, as a filler for a range of plastics and bitumen, and as a binder for cement. The impact on the environment due to the fly ash generated by municipal solid waste incineration was reduced, with the recycling of fly ash meaning that it is not disposed of in landfill (or underground in abandoned German salt mines). Landfill disposal risks contaminants being dispersed into the air both during the transport and storage of untreated fly ash. An environmentally-friendly filler was produced from the COSMOS product, which can be used in several industrial processes, such as the production of plastics (e.g. PVC, polyethylene), plaster, asphalt and concrete. In most cases, the use of the COSMOS product can increase the performance of the composites compared to standard production. However, the LCA could not confirm the environmental sustainability or economic viability of the process to make the COSMOS product. The main constraint to a widespread uptake of the inertisation process is linked to the costs required for COSMOS production. A high energy cost is linked to the production of colloidal silica, which is the main COSMOS component. According to the LCA the pilot process is not competitive mainly because of the economic costs of colloidal silica, which represent 90% of the total production costs. In order to overcome this issue, the beneficiaries have started a follow-on LIFE project COSMOS-rice (LIFE11 ENV/IT/000256), which aims to find an alternative to colloidal silica to make the whole process cheaper and more eco-friendly, and therefore more competitive compared to the current practise of fly ash disposal. Considering the vast amount of fly ash produced in the EU each year, a cost-effective and sustainable process for recycling fly ash could generate significant environmental benefits. The project produced a website, videos, brochures, an e-learning course, school gadgets, and a series of scientific papers, to disseminate its findings and raise awareness of the potential of fly ash as a resource. From the legislative point of view, the project supports the implantation of the Waste Framework Directive (2008/98/EC), with particular reference to Article 6 on establishing procedures to change the status of waste to products when recovered with reliable transformation processes (like COSMOS). The project demonstrated an innovative methodology that had a high demonstration value, because it showed that the COSMOS process could be up-scaled from laboratory to industrial scale. Furthermore, the beneficiaries demonstrated that the product from the pilot plant can be re-used in several industrial processes with a significant reduction of raw material consumption. Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).