Kinetic Determination of Urease Activity in Fresh Pig Feces and Slurry and the Effect on Ammonia Production at Different Conditions

Abstract

Ammonia (NH3) emissions have become a serious environmental pollution problem, and livestock production is an important source of NH3 emissions, especially pig farming. The origin of NH3 release is the hydrolysis of urea in urine that is catalyzed by urease present in feces. This research determined the urease activity in fresh feces by Michaelis–Menten kinetics and then compared the process of urea hydrolysis and ammonia production in fresh slurry. For feces, the kinetic parameters Vmax and K’m were calculated by determining the concentration of ammonium in initial 5 minutes in closed vessels, and the resulting Vmax and K’m were 26.9 ± 1.2 mmol·[urea]·kg−1·min−1 and 99.7 ± 3.5 mmol·[urea]·l−1, respectively. In fresh slurry, the rate of urea hydrolysis determined directly was higher than the ammonium formation rate in the early stage (0–8 h) and was accompanied by a rapid rise in pH. In addition, we further explored the effects of temperature, pH, and mixing rate on urease activity within different periods (0–5 min, 5 min–2 h and 2 h–8 h). Our observations show that the optimal urease activity occurred at 35 °C, pH 6.71, and 821.83 rpm of stirring, indicating that microbial species and communities associated with urease production are affected by environmental conditions.

Pig slurry organic matter transformation and methanogenesis at ambient storage temperatures

“…This is equivalent to 2.95 g urea kg urine −1 . This is low compared to concentrations reported in other studies, and carbon-rich metabolites are normally not reported in pig urine (Canh et al, 1997;Dai & Karring, 2014;Figuero et al, 2000;Hao et al, 2019). Approximately 6% of COD originated from the urine, even though ∼10% of VS was from urine.…”

“…Ureolysis increases pH by ammonia production (Dai & Karring, 2014; Sigurdarson et al., 2018), and the pH increases at 10–15°C suggest that ureolysis was still incomplete, whereas the reaction was complete for 20–25°C by day 2. At room temperature, ureolysis is usually complete within 1 day (Béline et al., 1998; Dai & Karring, 2014; Hao et al., 2019). The pH drop after day 4 was concurrent with the increase in VFA and this trend accelerated with temperature.…”

Measurement of Ammonia and Hydrogen Sulfide Emission from Three Typical Dairy Barns and Estimation of Total Ammonia Emission for the Chinese Dairy Industry

“…The temperature effect can be explained by the activities of enzymes involved in the chemical reactions. The urease activity is optimum at 35 • C and declines with decreasing temperature, as shown by Hao [22]. Thus, low temperature during the winter would reduce NH 3 production.…”

Potential application of urease and nitrification inhibitors to mitigate emissions from the livestock sector: a review

“…The mixing of feces and urine promotes hydrolysis [20] and occurs rapidly within 1 to 2 days of excretion [21].…”