A semi full-scale (15-m(3)) one-stage thermophilic anaerobic digester (TAnD) was started-up and studied over a 18-months period. The aim of this work was to evaluate the stabilization process of wastewater sludge and assess the pathogen standards included in the "Proposal for a Directive of the European Parliament and of the Council on spreading of sludge on land". The conversion strategy from mesophilic to thermophilic conditions was performed by a rapid and single temperature increase. Parameters such as volatile solids destruction (VSD), total volatile fatty acids (VFA), biogas production, macronutrients and heavy metals were measured. Salmonella spp., Escherichia coil, and C perfringens spores were cultivated, and pathogenity genes invA and cpa PCR-amplified. The reactor was operated over a range of sludge retention times (SRT) of 28, 20, 18, and 16 days and organic loading rates (OLR) ranging from 1.5 to 2.5 kg VS m(-3) d(-1). Adequate process performance was obtained in all the stable periods reaching VSD values over 40% and an average biogas production of 0.64 Nm(3) kg(-1) VSfed-1. Thermophilic anaerobic digestion successfully reduced Salmonella spp., and Escherichia coil below detection limits but not Clostridium perfringens spores (4.63 log(10) spores mL(-1)). Thus, the final product met Class A biosolids final disposal regulations, but further investigation is needed in order to satisfy the future European legislation. (C) 2013 Elsevier B.V. All rights reserved.