Robust Performance of Sub‐Thermophilic Anaerobic Digestion Enabled by Microbial Functional Redundancy

Global demand for renewable energy continues to rise, highlighting the importance of renewable natural gas asa sustainable alternative to fossil fuels. Anaerobic digestion (AD) is a proven, scalable technology for producing biogas, yet its efficiency depends on stable microbial communities operating under suitable temperature regimes. This study evaluates the effect of lowering operating temperatures in pilot‐scale digesters on gas yields, digestate chemistry, and microbial dynamics. Six continuously stirred tank reactors are acclimated at 55°C before three are gradually reduced to 48°C, while three remain at 55°C. Over a 60‐day period, methane yields do not significantly differ between the two treatments, averaging 140 l CH 4 kg −1 VS at 48°C and 125 l CH 4 kg −1 VS at 55°C, with biomethane composition stable at 54%. Metagenomic analyses reveal higher microbial diversity and functional redundancy at 48°C, with greater representation of methanogenic taxa such as Methanocelleus . In contrast, communities at 55°C show reduced diversity and dominance by thermophilic taxa. These results suggest that lowering AD operating temperatures may enhance microbial resilience without compromising methane production. Reduced energy input for heating at 48°C also offers potential operational and environmental benefits, which may improve commercial viability, subject to site‐specific factors and further validation of large‐scale AD facilities.