Utilization of co-substrates in municipal sewage sludge co-pyrolysis: Yields and characterization of biochar, bio-oil, and syngas, with economic feasibility analysis

Abstract

Co-pyrolysis has emerged as a pivotal method for processing municipal sewage sludge (MSS), offering the dual benefit of reducing waste volume and generating valuable clean energy products. As the production of MSS continues to rise globally, and the demand for sustainable waste management solutions intensifies, co-pyrolysis represents a promising avenue for the recovery of resources and energy generation. This review presents a comprehensive investigation of the co-pyrolysis of municipal sewage sludge (MSS) with various co-substrates, with a particular focus on the yield and characterization of biochar, bio-oil, and syngas. This study examines the impact of diverse co-substrates, including lignocellulosic biomass (e.g., wood chips, agricultural residues) and non-biomass materials (e.g., plastics, excavated waste), on the quality and quantity of pyrolysis products. The role of co-substrate properties, such as proximate and elemental composition, in optimizing energy recovery and improving product quality is a key focus of this study. Furthermore, this review presents an economic analysis of the co-pyrolysis process, demonstrating the substantial influence of co-substrate selection on the profitability of the operation. The integration of specific co-substrates not only enhances product yields but also improves the economic feasibility of the process, as evidenced by a favourable net present value (NPV). By optimizing feedstock combinations and pyrolysis conditions, the process becomes more marketable and economically viable, offering a competitive alternative to traditional waste disposal methods.