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What are the advantages and disadvantages of aerobic treatment of liquid manure instead of anaerobic treatment?

Aerobic treatment requires supplying enough oxygen to support aerobic bacteria. The amount of aeration needed (in increasing order) depends on whether it is desired to just reduce odor, or completely remove the oxygen demand of the organic matter, or to supply enough oxygen for nitrification of ammonia to nitrate.

Advantages of aeration can be reduced odor, nitrification of ammonia to nitrate (thus potentially reducing ammonia emissions and also having a nitrogen form that is readily crop-available but also more prone to leaching), and reduction of greenhouse gases (especially methane) compared to anaerobic treatment.

Disadvantages include higher capital cost for aeration equipment, higher operating cost (particularly energy for pumps or aerators), higher maintenance requirements, and possibly monitoring requirements for checking the dissolved oxygen level in the liquid. There are various methods and types of equipment for aeration, and selecting the most efficient equipment and methods may be difficult. Consultation with knowledgeable professionals is advisable. Aeration has not been used much in treatment of liquid manure primarily because of the increased expense.

For more information on aerobic treatment and other treatment options, see:
LPES Lesson on Biological Processes for Controlling Emissions

Author: Phil Westerman, North Carolina State University

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Does aeration tend to increase ammonia volatilization?

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