Effect of the co-substrate ratio on the anaerobic co-digestion of sewage sludge and the organic fraction of municipal solid waste at pilot scale

Abstract

The anaerobic co-digestion (ACoD) of sewage sludge (SS) and the organic fraction of municipal solid waste (OFMSW) has become a viable strategy for waste management, contributing to renewable energy production in the form of biogas and reducing environmental impact. This study aimed to evaluate the co-digestion process of these wastes at pilot scale, assessing three co-substrate ratios of 75/25 (R1-1), 50/50 (R2-1), and 25/75 (R3-1) of OFMSW and SS, respectively. The results indicated that the 75/25 ratio generated the highest methane gas yield, reaching 992.5 mL CH₄/gVS, and showed a greater rate of organic matter degradation, volatile solids removal reached 53.75%. The degradation of pathogenic microorganisms was effective in all reactors, meeting the requirements for producing digestate with potential use as fertilizer. The applied kinetic models allowed for high precision fitting of experimental data, with determination coefficients (R²) exceeding 0.99, confirming their ability to predict biogas production across different configurations. This study demonstrates that the ACoD of OFMSW and SS is an efficient solution for waste management and bioenergy production, generating a digestate suitable for agricultural use. The data provided at pilot scale are closer to real conditions and offer a better understanding for its implementation at full scale.