Impact of Seasonal Variability of Source-Separated Organics in Cold-Climate Regions on Energy Recovery from High-Solids Anaerobic Digestion with Percolate Recirculation

High-solids anaerobic digestion (HSAD) of source-separated organics (SSO) enables cities to sustainably valorize organic waste, enhance waste diversion from landfills, and promote a circular bioeconomy within urban infrastructure. In cold-climate regions, seasonal variations in SSO composition and their implications for HSAD performance remain poorly understood. Here, we investigated the effects of seasonal changes in SSO characteristics on the performance of percolate-recirculated HSAD systems operated with SSO collected from a green bin program in Edmonton, Canada. Winter/spring SSO was more energy-dense due to the presence of mainly food waste, whereas summer/fall SSO had a significant portion of yard waste with relatively lower energy content. Correspondingly, winter SSO showed the highest methane yield among the samples, while energy efficiency exhibited the opposite trend, peaking in spring and reaching minimum values in winter. Winter SSO favored Methanoculleus dominance, whereas summer and fall shifted toward Methanosarcina and Firmicutes-enriched communities, enabling metabolic diversity and resilience under complex substrates. Across all seasons, the 50% digestate recycling consistently outperformed the 40% recycling, achieving higher-quality biogas (higher methane and lower H2S), better process stability, and higher energy recovery efficiency. Overall, these results provide practical guidance for the seasonally adaptive operational strategy for HSAD facilities in cold-climate regions.