Specification and Classification of Pelletised Dried Sewage Sludge: Identifying its Key Properties as a Renewable Material for Enabling Environmentally Non-harmful Energy Utilisation

Renewable active sludge is a smart material for wastewater treatment and the protection of surface water bodies. The generated pellets (dried and pelletised dehydrated anaerobically stabilised excess sludge) are produced in a quantity of 31.4 g ± 5.6 g dry matter (DM) per one Population equivalent calculated to COD (PE_COD) in one day. They are the appropriate tools for reaching sustainable development goals (SDGs) in renewable energy production. The specification and classification of pellets as non-hazardous alternative solid recovered fuel (SRF) create a bridge between »treated sewage sludge as the tool to remove pollutants and nutrients from wastewater« and »preparation of the valuable material as an SRF that meets customer-specific requirements«. In the last eleven years, pellets' net calorific value (NCV) is 13.0 ± 0.7 MJ kg^-1 as received (ar). In 2021, the 80^th percentile of the Hg/NCV ratio was 0.079 mg Hg MJ^-1. The halogen contents of the pellets do not threaten corrosion to the incineration facility. Stable pellets' energy potential, perspective ash composition for critical raw materials recovery, and reduction of the annual amount of Hg transferred to stakeholders by 64.3 % m/m - from 10.1 kg in 2010 to 3.67 kg in 2021 - qualify pellets as a specific waste stream and a renewable material for SRF production.