Bacteria involved in an anaerobic digestion include acetic acid-forming bacteria (acetogens) and methane-forming bacteria (methanogens). Different species of bacteria survive at different temperatures. Optimal temperatures for mesophilic bacteria are 35–40 °C, while thermophilic bacteria can survive at temperatures between 55–60 °C. There are more species of mesophiles than thermophiles. These bacteria are more tolerant to environmental changes than thermophiles. Mesophilic systems are more stable than thermophilic digestion systems.
Anaerobic digestion kills pathogens such as E. coli and S. Aureus. Likewise P. multocida and S. enteritidis serovars typhimurium and anatum are killed within 48 h at 20–30 C, while Salmonella choleraesuis is eliminated after 72 h of digestion [95]. Russell et al. [96] fermented ground broiler offal with 6% sucrose, commercial silage culture and lactic acid bacteria (106 cfu/g offal) for 120 h at 37 C and found that Salmonella levels decreased from 3.7 to