Proceedings

India is currently in the early stages of defining and establishing a circular economy for biosolids derived from sewage treatment plants. Historically, sludge has undergone partial stabilisation and dewatering in inadequately operated anaerobic digestion plants or dried in drying beds. With the upcoming expansion and new sewage treatment plants (STPs), there is a recognized need for national regulations and management guidelines pertaining to biosolids. This study focuses on calculating the life cycle costs for three anaerobic digestion technologies, all producing class A biosolids: pasteurisation, temperature-phased anaerobic digestion (TPAD), and Thermal Hydrolysis Process (THP). A comparative analysis assesses different sludge treatment options and their associated costs, involving two types of sludge—waste activated sludge (WAS) and a 50% primary sludge and 50% WAS mixture. The cost components considered in the value chain encompass capital costs (capex), operational costs (opex), dewatering, solar drying, pyrolysis, temporary storage, transport, and the final utilisation of biosolids. The transportation distance to the end-use location is standardised at 50 km. The analysis is based on three scenarios: a) land application of dewatered biosolids, b) solar drying before land application, and c) solar drying before pyrolysis and landfilling. These scenarios incorporate three advanced anaerobic digestion technologies and two types of sludge. The findings indicate that the Thermal Hydrolysis Process (THP) emerges as the most cost-effective technology for waste activated sludge (WAS) across all scenarios, while TPAD is favoured for mixed sludge when considering land application after dewatering, with pasteurisation not considered an economically viable option.