(37e) Ammonia Generation Rates for Hydrothermal Pretreatment of Chicken Manure

Hydrothermal pretreatment of chicken manure allows nitrogen in the manure released as ammonia, which can then be removed easily from the liquid phase by heating. This process is useful for removing nitrogen from chicken manure so that following methane fermentation is not inhibited by ammonia that is gradually released during biomethanation process. However, actual ammonia generation rate in hot compressed water has not been clarified yet. Because chicken manure contains nitrogen in various forms such as uric acid, deoxyribonucleic acid, ribonucleic acid, protein, adenosine triphosphate, etc., ammonia generation rate should show rather complicated behavior. Thus, experimental determination of the rate for ammonia generation from chicken manure is required. The purpose of this study is to quantitatively obtain ammonia generation rate during hydrothermal treatment of chicken manure.

Experimental

An autoclave equipped as shown in Fig. 1 was employed in this study. The volume of the autoclave was 300 mL and 200 mL of chicken manure suspended in water (10 wt% solid content) was placed in it. After closing the lid, the reactor was heated to the target temperature, and after holding the temperature for desired time, it was cooled down. After the temperature got lower than 60 °C, the content of the reactor was taken out, and analyzed for ammonium ion concentration. The target reaction temperature ranged from 150 °C to 350 °C, and holding time ranged from 0 to 240 min.

Results and discussion

Fig. 1 shows the ammonia release rate at 350 C. Ammonia yield increased with holding time, and reached 80% after 240 min. This result indicates that hydrothermal treatment is effective for ammonia generation and nitrogen removal from chicken manure. When ammonia yield was extrapolated to the negative time, however, the time to get zero ammonia generation was much longer than the heating time. This fact indicates that chicken manure at least includes two kinds of nitrogen. Thus, by using much lower temperature and shorter holding time, we also determined the reaction rate for the ammonia production from easily decomposed components.

Conclusion

We successfully determined the ammonia generation rate from chicken manure in hot compressed water. There are at least two types of nitrogen with different ammonia generation characteristics. The experimental reaction rates were determined for both of them. These reaction rates can be used to design the hydrothermal reactor to remove ammonia from chicken manure for effective use of the manure for feedstock of methane fermentation and other purposes where nitrogen is inhibiting easy conversion of the chicken manure.

Acknowledgment

This research was performed by the Environment Research and Technology Development Fund (JPMEERF20203001) of the Environmental Restoration and Conservation Agency of Japan. We would like to express our sincere thanks to Japan Chicken Resource Development Project Research Center for providing us with the raw materials.