TITLE:
Ammonium Dissociation for Swine and Dairy Cattle Manures
AUTHORS:
Min Liu, David Giard, Suzelle Barrington
KEYWORDS:
Ammonium Dissociation; Manure; pH; Temperature
JOURNAL NAME:
Journal of Environmental Protection,
Vol.4 No.5A,
May
27,
2013
ABSTRACT: The dissociation of ammonium (NH4+) into ammonia (NH3) in wastewaters is a key factor governing atmospheric nitrogen volatilization. Relatively rich in total ammoniacal nitrogen (TAN or NH4+ plus NH3), livestock manures are most susceptible to NH3 volatilization, although indirect measurements report 5 times less NH4+ dissociation as compared to theoretical values. The objective of this study was therefore to directly measure NH4+ dissociation of two standard NH4Cl solutions (1750 and 3500 mg TAN/L), and of swine and dairy cattle manures at various dilutions and temperatures using a ammonia selective electrode (hydrogen and silver-silver chloride electrode couple) at various pH and temperatures. All solutions demonstrated NH4+ dissociation varying from theory, especially because of dissolved compounds such as atmospheric CO2. At a neutral pH, ratios of theoretical to measured [NH3-N] ranged from 1.5 to 3.5, with higher ratios corresponding to higher TAN levels. At a pH below 6, NH3 volatilization was enhanced by the shift of HCO3- to H2CO3 and CO2. With previous research projects reporting 5 times less NH3 volatilization as compared to theory, the present indicates that dissociation activity account for half of this drop with gas diffusion accounting for the other half.