Evaluating different insect frass’ biomethane potentials under varying substrate dose scenarios

• Insect frass shows high biodegradability and suitability for anaerobic digestion • Methane yields from frass equal or exceed those of common agricultural substrates • Z. morio frass achieved the highest cumulative methane yield and digestibility index • Insect species affected cumulative methane yield more strongly than substrate dose This research is motivated by the need to effectively utilize by-products from insect breeding, which often remain underutilised. The study examines the potential of frass for biogas production through mesophilic anaerobic digestion. Three types of frass were examined: Tenebrio molitor, Alphitobius diaperinus , and Zophobas morio . The main objective was to assess the methane production capacity of these substrates at different substrate doses. The results show that the highest cumulative methane yields were obtained at substrate doses of 10-14 g VS /L, ranging from 0.300 to 0.351 m³/kg VS . Notably, the maximum yield was achieved for Zophobas morio frass, with methane production of 0.351 m³/kg VS at a substrate dose of 14 g VS /L. These findings indicate that substrate dose had a secondary influence on cumulative methane yield compared to insect species, as optimal or near optimal yields were achieved across a broad range of substrate doses. Overall, the study expands current knowledge on the use of relatively unexplored insect frass for biomethane production and highlights its potential as a valuable resource. Overall, this study expands current knowledge by providing new insights into species-specific variability and the role of substrate loading in anaerobic digestion of insect frass, supporting its more efficient integration into biogas production systems.