摘要
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.
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.
