Enhancing pathogen inactivation in pig manure by introducing thermophilic and hyperthermophilic hygienization in a two-stage anaerobic digestion process.

Conventional mesophilic anaerobic digestion (AD) is widely used to treat animal manure, but pathogen inactivation remains a significant challenge. Thermophilic and hyperthermophilic hydrolysis pretreatment was thus introduced as a hygienization step in a two-stage anaerobic digestion process. Results from 100-day experiments showed culturable Escherichia coli (E. coli) reduction was up to 6.9 log through a hygienization step, but RT-qPCR tests showed much less reduction in viable E. coli. The difference between viable and culturable cells revealed the complexity in pathogen inactivation. High-throughput sequencing indicated that the second stage in the two-stage AD further reduced the relative abundance of pathogens, including Enterococcus, Streptococcus, and Acinetobacter, while Clostridium_sensu_stricto still exhibited high relative abundance. Thermophilic hygienization induced a 6.7% increment in methane production, while hyperthermophilic pretreatment showed minimal effect on methane production. Focusing on the energy recovery and environmental safety point of view, the introduction of an integrated system incorporating the thermophilic and two-stage anaerobic process is recommended.