Influence of sludge dehydration strategies on biological stability and hygienization in extended aeration activated sludge systems

The quality and stability of sewage sludge generated in municipal wastewater treatment plants are strongly influenced by treatment technology and post-treatment processes. Extended aeration activated sludge (EAAS) systems operate at long solids retention times, which may promote partial aerobic stabilization of the biomass; however, additional treatment is often required to ensure adequate biological stability and hygienization. This study evaluated, at pilot scale, the influence of three sludge dehydration strategies, namely, conventional drying beds (ConDry), solar drying (SolDry), and solar drying combined with ultraviolet radiation (SolDry + UV), on moisture reduction, biological stability, and fecal coliform removal. Sludge samples were obtained from two EAAS systems operating under contrasting climatic and operational conditions. The SolDry + UV strategy exhibited the highest drying efficiency, achieving moisture contents below 60% within 19 days for EAAS1 and 26 days for EAAS2. Solar-based strategies significantly enhanced volatile solids reduction, reduced specific oxygen uptake rates, and promoted greater pathogen removal compared to conventional drying. Overall, the results demonstrate that solar drying, particularly when combined with UV irradiation, substantially improves sludge stabilization and hygienization, enabling the attainment of Class A biosolid quality and supporting its safe agricultural reuse.