Anaerobic digestion of chicken manure coupled with ammonia recovery by vacuum-assisted gas-permeable membrane process

Abstract

To overcome the ammonia inhibition problem during anaerobic digestion of chicken manure, this study used a novel vacuum-assisted gas-permeable membrane (V-GPM) process for ammonia removal from liquid digestate prior to the liquid digestate backflow to the digester. Compared with the typical gas stripping process for ammonia removal, the V-GPM process could avoid several process problems, such as pH and dissolved oxygen increase, which harmed the anaerobic digestion process. Results show that more than 80% of the ammonia can be removed from the liquid digestate within 6 h under the conditions of 70 °C and 30 kPa. The low-ammonia-contained liquid digestate can be recycled to dilute the anaerobic feedstock. During the anaerobic digestion treatment of chicken manure, 75% of the feed solution can be replaced by this low-ammonia-contained liquid digestate. Compared with the case of liquid digestate recycling without ammonia removal, a higher biogas yield is obtained for the ammonia removal case, in which the specific methane production increases from 1.0 L/g-VS to 2.4 L/g-VS. Finally, the economic evaluation indicates that the ammonia recovery process could bring an extra benefit of $ 0.51/kg-N.