Background Sewage sludge from water treatment plants is identified as a hazardous waste in the European Union, and its management is a major undertaking. The main environmental problems related to sewage sludge are: Its disposal in controlled landfills, which involves an ever-growing demand for capacity, and which generates emissions; Treatment using environmentally harmful methods, such as incineration; The increasing trend in the EU to directly apply it to agricultural land. Because of the physical-chemical processes involved in the treatment of sewage sludge, it tends to include concentrations of heavy metals, trace organic compounds and potentially pathogenic organisms (viruses, bacteria, etc.) that are present in wastewater. However, sewage sludge is also an alternative source of phosphorous and other nutrients and contains valuable organic matter that is useful when soils are depleted or subject to erosion. The organic matter and nutrients are the two main elements that make this kind of waste suitable for spreading on land as a fertiliser or an organic soil improver. Sludge used on agricultural land must meet certain requirements. The environmental quality limits for the sludge, especially relating to heavy metal content, have been much debated, with many EU member states establishing more stringent national limits than those in the EU Sewage Sludge Directive (86/278/CEE). For this reason, it is necessary to identify policies and practices that enable the use of sludge on agricultural land under more stringent conditions, and that will harmonise the EU-level restrictions and reduce impacts on soil and water. Objectives The LIFE iCirBus-4Industries project will demonstrate the use of fly ash from forest biomass power plants as an adsorbent agent for heavy metals and other organic materials in sewage sludge. This will make the sludge suitable for the production of low-impact fertiliser. In a second stage, the project will also demonstrate the viability of a further use in recyclable construction materials of the used biomass that contains heavy metals and organic pollutants from sewage sludge. The project will first characterise the sewage sludge and the forest biomass fly ash. Then, the two-phase sludge treatment to reduce the presence of heavy metals and other contaminants will be validated at laboratory scale. The project will then scale up the process in a prototype sewage treatment plant with a capacity of 100 kg/hour of clean sludge. Overall, the project expects to produce: 500 kg of low impact fertiliser; and 17 000 kg of recyclable construction materials. The project will demonstrate an innovative collaborative inter-industrial structure or 'industrial symbiosis' that reduces the amount of local waste while increasing the competitiveness of the regional economy in a sustainable way. Expected results: 100% of fly ash produced in biomass power plants will be suitable for use as an adsorbent agent for heavy metals, leading to a 100% reduction of fly ash disposed in landfill sites; 90% of fly ash after the adsorbent process will be suitable for use as an inertising agent for recyclable construction material; 100% of treated sewage sludge will be suitable for use as fertiliser, leading to a 15% reduction of hazardous pathogens in soil compared to current practices of direct disposal of sewage sludge onto agricultural land; Use of fly ash in recyclable construction materials will lead to a replacement of 35% of cement weight; 15% reduction in emissions from transport of wastes and from landfill sites; and 10% energy, water and other resource saving in the production of construction materials and compost fertilisers compared to current practices, and a replacement rate of 25% of currently employed chemical fertilisers.