Degradation of swine manure and a computer model for predicting the desorption rate of ammonia from an under-floor pit
Zhang, Ruihong
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https://hdl.handle.net/2142/20580
Description
Title
Degradation of swine manure and a computer model for predicting the desorption rate of ammonia from an under-floor pit
Author(s)
Zhang, Ruihong
Issue Date
1992
Doctoral Committee Chair(s)
Day, Donald L.
Department of Study
Agricultural and Biological Engineering
Discipline
Agricultural Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Agricultural
Language
eng
Abstract
Manure degradation and ammonia desorption rates from under-floor pits in swine buildings were investigated in this research. Manure degradation was experimentally determined under simulated pit operational conditions (1.8% and 3.3% initial manure TS, 20$\sp\circ$C and 30$\sp\circ$C manure temperature). The chemical components of the manure were characterized into different layers. It was found that solids and organic matter accumulated, and pH dropped in the bottom layers of manure. Ammonia generation rate within the manure varied in an inverse proportion with storage time.
A mathematical model was formulated, which coupled diffusion and generation of ammonia in the manure with convective transfer of ammonia at the manure surface. The dissociation reaction of ammonia in the manure was also included in the model.
The dissociation constant of ammonia in 1% TS swine manure was determined to be about one fifth of the constant in water by conducting the ammonia desorption tests. The mass transfer coefficient was correlated as a second order polynomial function of the velocity and a first order function of the temperature.
Computer simulations were conducted for specified pit operational conditions, which included two levels of liquid temperature (20$\sp\circ$C and 30$\sp\circ$C), four levels of air flow velocity (0 m/s, 0.203 m/s, 0.406 m/s and 0.508 m/s), and one level of ambient ammonia concentration (2.4 ppm). The simulation results showed significant effects of air flow velocity and liquid temperature on ammonia desorption rates. For a given surface concentration of ammonia in the manure, higher temperature and higher velocity all resulted in higher desorption rates of ammonia. Throughout the pit operation, higher temperature always enhanced ammonia desorption, but, influence of the velocity on the desorption rate depended more on the variation of surface ammonia concentration in the manure.
Significant accumulation of NH$\sb3$-N concentration occurred in the bottom layers of manure along the storage period. Higher ammonia concentrations and lower pH levels in the bottom layers of manure suggested a feasible practice of separating the bottom layers from the surface layers to improve fertilizer values of the manure for land application and to reduce ammonia loss by desorption.
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