Nitrogen Transformations in Aerated Swine Manure Slurries
- T. E. Loynachan,
- W. V. Bartholomew and
- A. G. Wollum
A laboratory study was conducted to evaluate the effect of aeration rate, temperature, and manure loading rate on nitrogen transformations in swine manure slurries. Periodic samples were collected and analyzed for residual organic N, NH4-N, NO2-N, and NO3-N, as well as NH3 volatilized from the aerated slurries. It was found that organic N decreased rapidly leaving a rather constant fraction after the first several weeks. At the end of the 83-day study at 25C, one-fourth of the N remained in solution in organic forms. This represents N that was not mineralized and consequently would not be lost during the denitrification process. From 16 to 26% of the added N was volatilized as NH3-N and from 48 to 87% of the added C was evolved as CO2-C during the study. Increasing temperature, increasing loading rate, and increasing aeration tended to increase volatilization of NH3 and CO2. An N balance at the conclusion of the study showed that 22 to 48% of the N was unaccounted for. While the mechanism responsible for the N losses was not determined, NH3 volatilization apparently predominated. The quantities of lost N increased with an increase in temperature. There appeared to be no relationship between the losses of N and changes in concentration of oxidized forms of N in solution. While nitrification occurred in extensively aerated swine-manure slurries, about 1/4 of the original total N was not mineralized. As this represents a rather stable form and because only 3% of added N occurred in a mineral form at any given time, the extent of denitrification would be limited. Consequently, nitrification-denitrification schemes probably have limited application to N removal from waste substances.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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