Table 1.
The chemical and physical properties of feces, urine, and manure samples (Mean±SD; n = 3).
Figure 1.
The rates of formed TAN as catalyzed by fresh pig and cattle feces.
The rate of TAN formed (R. of formed TAN; panels A and B) and specific rate of TAN formed (S.R. of formed TAN; panels C and D) as catalyzed by pig feces (panels A and C) and cattle feces (panels B and D) in reaction mixtures containing fresh feces and different concentrations of urea.
Figure 2.
The Michaelis-Menten kinetics of the urease activity in fresh pig and cattle feces.
Michaelis-Menten curves (panels A and B) and Lineweaver-Burk plots (panels C and D) for the specific reaction velocities of hydrolyzed urea (V0) as catalyzed by pig feces (panels A and C) and cattle feces (panels B and D). The curves are generated from Figure 1 data. The maximum specific Vmax and K'm values of the urease activity in fresh feces from pigs and cattle were determined from the graphic presentations. The goodness of fit values (R2) were 0.84 (panel A) and 0.91 (panel C) for the pig feces and 0.82 (panel B) and 0.81 (panel D) for the cattle feces.
Figure 3.
Urease activity in fresh manure from pigs and cattle.
The formed TAN and changes in pH over time in fresh pig manure (panel A) and fresh cattle manure (panel B). During the first hours after mixing urine and feces, the concentration of formed TAN (open squares) and pH (filled triangles) increase rapidly in both pig and cattle manures. However, the rate of TAN formation in pig manure is significantly faster than it is in cattle manure and the TAN concentration reaches a higher plateau in pig manure than in cattle manure. In both manures, the pH decrease continuously after reaching a maximum.
Table 2.
Kinetic parameters of the urease activity in fresh feces.
Figure 4.
The effect of the pH on fecal urease activity.
Urease activity at different pH values are presented as the rate of TAN formation (R. of formed TAN; panels A) and the relative R. of formed TAN compared with that of pig feces at pH 7 (panel B). The optimal pH for urea hydrolysis catalyzed by fecal urease is approximately pH 7 for pig feces and between pH 7 and 8 for cattle feces.