Sludge Thermal Utilization, and the Circular Economy

In 2015, the European Commission has adopted an ambitious Circular Economy Action Plan (CEAP), which includes measures that would help stimulate Europe’s transition towards a circular economy. In general four key action areas have been defined: production, consumption, waste management and secondary raw materials. Actions will lead to the resource-efficient and environmentally friendly outcomes. Biological materials should be returned to the natural metabolic cycles after necessary pre-treatment while waste that can not be prevented or recycled is to be used for the energy recovery. Sewage sludge is a large-tonnage waste produced at wastewater treatments plants (WWTPs). Its utilization causes some problems. High water content in sludge, hazardous substances as heavy metals, organic toxins and pathogens limit some potential methods of sludge utilization. Thermal treatment methods offer a solution, some hazardous substances can be destroyed or removed, energy can be recovered and some nutrients can be obtained from ash or other by-products.