Comprehensive assessment of frass as a biogas resource: Insights from the European insect farming industry

Insect farming represents a sustainable alternative to conventional livestock production. However, its nutrient-rich byproduct, frass, remains underutilized beyond fertilization. Although suitable for anaerobic digestion, its methane production potential has not been comprehensively assessed. This study systematically evaluated the physicochemical characteristics and biochemical methane potential (BMP) of frass from ten European insect farms to determine its suitability as a biogas substrate. Samples from Hermetia illucens and Tenebrio molitor were analyzed for total and volatile solids, elemental composition, and C/N ratio. BMP assays were performed under mesophilic conditions. Significant interspecies differences were observed in pH, solids content, and elemental composition. Methane yields ranged from 0.3196 to 0.372 m³ CH₄/kg VS, with methane concentrations between 61.9% and 65.0%, comparable to manure and crop residues. T. molitor frass showed rapid but less stable methane release, whereas H. illucens demonstrated slower yet more stable degradation. Survey data indicated that 75% of insect farms use frass solely as fertilizer, and only 12.5% utilize it for energy recovery. This first large-scale assessment highlights frass as a promising substrate for anaerobic digestion, supporting resource valorization and promoting circular economy approaches within the insect production sector. • Carbon, hydrogen, and sulfur content in frass is species-dependent. • Frass addition significantly increases methane yield, regardless of species. • Methane content in biogas from frass averaged between 61.9-65.0%. • Biogas from Hermetia frass contains more H2S due to its higher sulfur content. • Only 12.5% of insect farms use frass for biogas, while most utilize it as fertilizer.