Generation of High Concentration Free Volatile Fatty Acids from Continuous Anaerobic Digestion of Chicken Manure by Suppressing the Decomposition of Nitrogenous Components.

Free volatile fatty acids (free VFA) play a crucial role in the inactivation of pathogens during the anaerobic digestion of animal manure. However, the decomposition of nitrogenous components can release alkaline ammonium-N, which might increase the pH and reduce the concentration of free VFA. In this study, continuous anaerobic digestion of high-solid chicken manure was conducted for 150 days. The results indicated the process stabilized at a pH of approximately 6.0, with total ammonia nitrogen (TAN) of around 7.0 g/L. The resulting concentration of free VFA was only about 3.1 g/L, which might not sufficiently effective for pathogen inactivation. On the 70th day, hydrogen chloride was added into the reactor to adjust the pH to 5.5. This led to a further decrease in pH to 4.3 and TAN to 2.3 g/L. As a result, the concentration of free VFA significantly increased, reaching up to 12.6 g/L. These findings support the potential for generating high levels of free VFA even for nitrogen-rich manure by implementing an appropriate process regulation.