A critical review of conventional and emerging methods for improving process stability in thermophilic anaerobic digestion

Anaerobic digestion has received significant attention in recent years due to dual benefits of waste diversion from landfill and bioenergy recovery. Among various temperature regimes, digesters operated under thermophilic (50–70 °C) condition has potential to provide several advantages over mesophilic (30–45 °C) and psychrophilic (<20 °C) conditions, which include faster degradation of organics and higher energy recovery. However, the operation of thermophilic digesters requires closer monitoring and control due to an additional risk of ammonia inhibition and irreversible acidification through the accumulation of volatile fatty acids. Conventional strategies to alleviate instabilities in thermophilic anaerobic digestion process have been focused primarily on the development of robust microbiome and co-digestion of complementary substrates. On the other hand, emerging strategies include the integration of digesters with microbial electrochemical systems and amendment of conductive additives. This review provides a critical overview of these strategies and summarizes research gaps to guide researchers and practitioners in the future research.