Graduate Thesis Or Dissertation
 

An ammonia stripping and recovery system for animal wastewaters

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  • Traditionally, livestock operations were small and combined with cropping operations. This allowed farms to be self-sustaining because nutrients were constantly recycled on the farm. Since the Haber-Bosch chemical process was patented, crop farmers turn to industrial fertilizers when soils nutrients are depleted. Animal and plant operations diverged, functionally separated, and specialized, leaving the traditional nutrient cycle open. Animal operations continued to grow in size, while the total number of livestock operations has consistently decreased over time, creating great amounts of animal wastes with insufficient crop and utilization area for land application of the manure. Any time fertilizers are over applied, there is a risk of environmental pollution and contamination. Of primary concern to this project is the concentration and loss of nutrients, particularly nitrogen in the form of ammonia. Ammonia readily volatilizes, so containment and storage in wastewater is not guaranteed. Ammonia discharged to the atmosphere will oxidize to nitric acids, contributing to acid rain and greenhouse effects. Even as farmers lose a valuable nutrient resource, ammonia volatilization is a concern because it is a major odor nuisance. Litigation between neighbors has brought odor control to the forefront of animal waste management issues. This project seeks to close the circle of the nutrient cycle by allowing crop farmers convenient access to animal based fertilizers, Mass transfer techniques were employed to separate the ammonia from a prepared wastewater and then convert that ammonia into a usable fertilizer. Ammonia stripping is a chemical treatment specifically designed to remove ammonia from a liquid. An absorption tower was then used to convert the pure ammonia back into an ammonium crystal solution. The solution is a fertilizer of known quality and quantity that is easier to handle than the original wastewater. Several components of the apparatuses were varied to determine the most efficient method of stripping ammonia from wastewater. Calculations were made to determine the efficiency of each apparatus and compared. Simply agitating the wastewater produced high rates of ammonia removal (70.7 and 75.0 mg/L/h). A stripping tower performed well with advantages including effective dispersal droplets with high surface area to volume ratios and slower volumetric flow rates. The stripping tower with an irrigation nozzle runs produced the highest percentages of ammonia removal (9.2 - 34.9%). Using an aerator produced variable rates of ammonia removal (12.9- 129.3 mg/L/h), depending on initial ammonia concentration and absorption tower configuration. A small mass transfer tower is capable of acid absorption (44.6 and 74.6% recovery), and further improvements to the recovery tower such as increasing tower height, intentionally causing an acid backup or improving acid recirculation will probably increase the efficiency. The benefit of using the described technology is the targeted removal of ammonia from wastewater. This decreases the nitrogen load in the wastewater, while concentrating the nutrient into a manageable form. The mass transfer technology discussed in this paper has potential applicability to livestock operations when regulations enforce controls on ammonia emissions from livestock wastewater.
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