Some authors (Amon et al., 2006; Clemens et al., 2006) have already shown that anaerobic digestion is an effective means to reduce GHG emissions. In contrast, slurries which have been codigested anaerobically in biogas production plants have a higher NH3 volatilization potential than untreated slurries because pH and TAN (NH3 + NH4 +) concentrations are higher (Sommer, 1996).