Abstract:The differences between the composting, stabilization and drying processes were discussed. The law criteria for mechanical-biological treatment plant were presented. The purpose of the article was to assess the effectiveness of biodrying MSW (municipal solid waste) in a full scale reactor taking into account the degree of biological decomposition of organic matter and its suitability for RDF (refuse derived fuel). Therefore the microbial activity was measured as the O 2 /96 h uptake. CO 2 /96 h production and the respiration activity AT4 for untreated and biodried waste were compared. The decomposition of organic matter was measured by loss on ignition (LOI) and total organic carbon (TOC). The product after the biodrying process was assessed according to the EURITS and PN-EN 15359 criteria for the quality of RDF (residual derived fuel). The result 8.48 MJ/kg of calorific value shows that bio-dried waste is ranked below the EURITS minimum level and can be classified as fifth class by PN-EN 15359 requirements. The amount of chlorine, mercury and lead fulfil the EURITS criteria. The microbial activity after processing in the biodrying reactor expressed as oxygen uptake exceeded the permissible level of 10 mg O 2 /g d.m. in the time range ten months. The regulatory parameters TOC < 20% d.m. and LOI < 35% d.m. criteria were not met.