Comparative Efficiency of Mesophilic Anaerobic Digestion and Aerated Static Pile Composting in the Stabilization of Municipal Wastewater Sludge

Mohammad Hasan  Kowsari; Mojtaba  Yeganeh; Mohsen  Ansari; Behnaz Abdolahi  Nejad; Masoumeh  Hasham Firooz; Mahdi  Farzadkia

doi:10.18502/jehsd.v10i4.20657

Mohammad Hasan Kowsari Research Center for Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran.
Mojtaba Yeganeh Research Center for Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran.
Mohsen Ansari Department of Environmental Health Engineering, School of Public Health, Qazvin University of Medical Sciences, Qazvin, Iran.
Behnaz Abdolahi Nejad Research Center for Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran.
Masoumeh Hasham Firooz Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
Mahdi Farzadkia Research Center for Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran.

DOI: https://doi.org/10.18502/jehsd.v10i4.20657

Keywords: Wastewater, Sewage Sludge, Anaerobic Digestion, Composting, Aeration, Biogas.

Abstract

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.