Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 26, 2006
Publication Date: April 5, 2007
Citation: Varel, V.H., Wells, J. 2007. Influence of thymol and a urease inhibitor on coliform bacteria, odor, urea, and methane from a swine production manure pit. Journal of Environmental Quality 36(3):773-779. Interpretive Summary: Pathogens, ammonia, odor, and greenhouse gas emissions are serious environmental concerns associated with swine production. In the laboratory, we have shown that these parameters can be controlled with plant oils such as thymol, carvacrol, and eugenol. However, in the present study conducted in a swine production facility with two 33,000 liter pits, we have demonstrated that thymol can be used to control these parameters in a field-scale environment. Compared to the control pit, odor (volatile fatty acid production) was reduced 64 and 100% when thymol was added to the pits at 1.5 and 3.0 grams per liter. These same thymol concentrations reduced methane production from the pits 78 and 93%, respectively. Pathogenic microorganisms such as coliform bacteria including Escherichia coli, were reduced greater than 99%. Further studies are needed to determine the economic cost of thymol as a potential treatment for swine waste. If the cost is excessive, other plant oils derived from waste byproduct streams may be useful.
Technical Abstract: Pathogens, ammonia, odor, and greenhouse gas emissions are serious environmental concerns associated with swine production. This study was conducted in two manure pits (33,000 l each) to determine the influence of 1.5 or 3.0 g thymol/l and 80 mg/l urease inhibitor amendments on urea accumulation, coliform bacteria, odor, and methane emission. Each experiment lasted 18 or 19 days, during which time 30 to 36 250-ml samples (six per day) were withdrawn from underneath each pit and analyzed for urea, thymol, VFA, coliform bacteria, and Campylobacter. At the end of each experiment, six 50 g samples from each pit were placed in serum bottles, and gas volume and composition were determined periodically for 28 d. Compared to the control pit, VFA production was reduced 64 and 100% for the thymol amendments of 1.5 and 3.0 g/l, respectively. Viable coliform cells were reduced 1.68 and 2.88 log10 CFU/g of slurry for the 1.5 and 3.0 g thymol/l, respectively; and Escherichia coli were reduced 1.67 and 3.01 log10 CFU/g of slurry, respectively. Campylobacter was not detected in the pits treated with thymol, in contrast to 63% of the samples being positive for the untreated pit. Urea accumulated in the treated pits from day 3 to 6. Total gas production from the serum bottles was reduced 65 and 76% for thymol amendments of 1.5 and 3.0 g/l, respectively; and methane was reduced 78 and 93%, respectively. These results suggest that thymol markedly reduces pathogens, odor, and green house gas emissions from a swine production facility. The urease inhibitor produced a temporary response in conserving urea.