A circular approach for the management of biogas flows from sewage sludge

Sewage sludge is considered one of the most critical resources to be managed in the urban context for the transition toward a circular economy. If the one hand, the sewage sludge includes potentially dangerous components to human health and ecosystems; on the other hand, it is rich in nutrients and valuable materials (e.g., phosphorus, nitrogen, etc.), allowing to ensure an energetic production comparable with traditional fuels. Therefore, it is recommended to adopt treatments to reduce the hazardous contaminants recovering energy and matter from sewage sludge. For this scope, the anaerobic digestion treatment is one of the most adopted processes. It allows the biological stabilisation of the treated sludge mass and, at the same time, the recovery of matter (i.e., digestate production) and energy (i.e., biogas production), in total compliance with a circular economy perspective. The biogas produced can be used for various purposes (e.g., electricity production, grid connection, refilling of vehicles, etc.). To identify the best environmental alternative, it is necessary to analyse the chemical and physical characteristics of the biogas, strictly related to features of the sewage sludge adopted as input on anaerobic digestion treatment. To this concern, the objective of the present work was to develop an analytical model that, starting from the physic-chemical characteristics of the sewage sludge to be treated, allows predicting the composition of the biogas and then identifies the most effective utilisation under an environmental perspective. The model developed was applied to the case of sewage sludge produced in the metropolitan city of Bari, southern Italy. The results show the model's effectiveness in suggesting the most eco-friendly utilisation of the biogas produced starting from the physic-chemical characteristics of the sewage sludge. © 2022, AIDI - Italian Association of Industrial Operations Professors. All rights reserved.