Nitrogen potential recovery and concentration of ammonia from swine manure using electrodialysis coupled with air stripping

The practice of intensive animal production in certain areas has resulted in excessive manure production for the available regional land base. Consequently, there is a need to develop treatment technologies to recover the valuable nutrients that manure contains so that the resulting product can be transported and used as fertilizer on agricultural land. The project presented here used electrodialysis in a dilution/concentration configuration to transfer the manure ammonia in the diluate solution by electromigration to an adjacent solution separated by an ion-exchange membrane under the driving force of an electrical potential. Then, air stripping from the electrodialysis-obtained concentrate solution without pH modification was used to isolate the ammonia in an acidic solution. An optimal process operating voltage of 17.5 V was first determined on the basis of current efficiency and total energy consumption. During the process, the swine manure pH varied from 8.5 to 8.2, values favourable for NH4+ electromigration. Total ammonia nitrogen reached 21 352 mg/L in the concentrate solution, representing approximately seven times the concentration in the swine manure. Further increases in concentration were limited by water transfer from the diluate solution due to electroosmosis and osmosis. Applying vacuum to the concentrate reservoir was found to be more efficient than direct concentrate solution aeration for NH3 recuperation in the acid trap, given that the ammonia recuperated under vacuum represented 14.5% of the theoretical value of the NH3 present in the concentrate solution as compared to 6.2% for aeration. However, an excessively low concentrate solution pH (8.6–8.3) limited NH3volatilization toward the acid trap. These results suggest that the concentrate solution pH needs to be raised to promote the volatile NH3 form of total ammonia nitrogen.

► Maximum NH3 concentration of about 21 000 ppm is reached in the concentrate. ► Osmosis and electroosmosis limited the maximum NH3 concentration in concentrate. ► Concentrate low pH limited NH3 volatilization to the acid traps.