comparative efficiency of mesophilic anaerobic digestion and aerated static pile composting in the stabilization of municipal wastewater sludge

Introduction: stabilization of municipal wastewater sludge is a critical requirement for mitigating environmental and public health risks. this study provides a comparative evaluation of mesophilic anaerobic digestion (ad) and aerated static pile (asp) composting for sludge stabilization at iran’s largest municipal wastewater treatment plant, with a focus on process efficiency, hygienic quality, and end-product usability.materials and methods: laboratory-scale experiments were conducted using batch mesophilic anaerobic digestion (35 °c, 24 days) and aerated static pile composting. the composting process employed sludge conditioned with bulking and amendment agents under controlled aeration, including a 6-day thermophilic phase within a 30-day operational period. process performance was assessed based on volatile solids reduction, pathogen inactivation, and biogas production.results: asp composting demonstrated superior stabilization and hygienization performance, achieving more than 50% volatile solids reduction and over 3-log fecal coliform reduction, resulting in compost meeting usepa class a standards. in contrast, anaerobic digestion achieved approximately 40% volatile solids reduction and produced 5405 ml of biogas, yielding biosolids classified as usepa class b.conclusion: while mesophilic anaerobic digestion offers the advantage of renewable energy recovery, aerated static pile composting provides a more hygienically robust pathway for producing stabilized, high-quality compost suitable for agricultural applications. the findings highlight that the selection of sludge treatment technology should be context-driven, balancing priorities between energy generation and the production of sanitized, agriculturally valuable biosolids.