Aeration's effect on ammonia volatilization depends on the type of system employed. Some aeration systems are specifically designed to accomplish nitrogen removal by providing enough oxygen to allow microbial reactions to convert ammonia-N to nitrate or nitrite (which can subsequently be converted to dinitrogen gas (N2) and be released harmlessly). If these systems are properly designed and operated, ammonia concentrations will be small in the treatment system, and ammonia emissions will be greatly reduced.

For low- to medium-level aeration systems, where the objective is primarily odor control, the answer is not so clear. Tendency for ammonia volatilization increases with increasing temperature and with increasing surface area between the liquid and the air (provided by increasing aeration rate). So, for a constant ammonia concentration in the liquid, ammonia volatilization would be expected to increase with increased aeration rate, although at low temperatures this effect might be small. However, volatilization rates decrease with decreasing ammonia concentration in the liquid, so if the aeration system causes a decrease in the ammonia concentration, the overall effect could be a decrease in ammonia emissions. These interactions are fairly complicated, and more work is needed before reliable predictions can be made.

Author: Sarah Liehr, North Carolina State University