Occurrence, Distribution, and Potential Role of Bacteria and Human Pathogens in Livestock Manure and Digestate: Insights from the Guangxi, China

Livestock manure and digestate (biogas slurry [BS] and biogas residue [BR]) contain bacteria that can potentially destroy the environment microecology and affect human health. This is a problem in China since it is a big producer of livestock and poultry. Thus, herein we have analyzed the bacterial content of both manure and digestate in 18 pig farms located in the Guangxi Zhuang Autonomous region. Specifically, we show that mid-temperature anaerobic fermentation affects both bacterial colony structure of swine manure (SM) and the relative abundance of bacteria and human pathogens. Indeed, the bacterial composition of SM changed after manure was fermented into BR and BS. These changes were dependent on bacterial adaptability; although some bacteria were reduced after fermentation, we observed an increase in Novosphingobium, Acidovorax, Longilinea, and Mycobacterium. The first three can potentially degrade polycyclic aromatic hydrocarbons and other harmful substances and may have a beneficial effect on the control of soil environmental pollution. However, the increased abundance of Mycobacterium poses a greater threat to human health. Thus, the transition from SM to digestate in the current condition for mid-temperature anaerobic fermentation needs to be optimized to reduce the entry of potential human pathogens in the soil after anaerobic fermentation.