Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2001
Publication Date: 1/1/2002
Citation: Varel, V.H. 2002. Carvacrol and thymol reduce swine waste odor and pathogens; stability of oils. Current Microbiology. 44:38-43.
Interpretive Summary: Stored manure from swine production facilities contain pathogenic micro- organisms and produce offensive odors as a result of microorganisms fer- menting these wastes. In laboratory studies we have identified two chemicals, carvacrol and thymol, which can be added to the waste to stop the fermentation and kill the fecal coliforms or the predominant pathogenic cbacteria in the waste. These two chemicals are oils that can be extracted from plants; thus, they are natural products which we assume would not be harmful to the environment. These chemicals inhibited the production of the primary source of odor from swine waste, short-chain volatile fatty acids, for 62 days. The fecal coliforms were killed within 2 days. We conclude that these chemicals may be useful as antimicrobial agents to control pathogens and odor in stored swine waste. Field tests are needed to determine the economics and usefulness of these agents in production facilities.
Technical Abstract: An incomplete anoxic fermentation of livestock waste results in offensive odor emissions. Antimicrobial additives may be useful in controlling odor emissions and pathogens. Natural antimicrobial compounds, carvacrol or thymol at 16.75 mM (2.5 g/l) completely inhibited the production of the offensive odor compounds, isobutyrate, valerate, isovalerate, and cresol, and significantly reduced other short-chain volatile fatty acids and gas emissions from swine waste. Fecal coliforms were reduced from 6.3 * 10**6 to 1.0 * 10**3 cells per ml 2 days after treatment with carvacrol (13.3 mM) and were not detectable within 14 days. Total culturable anaerobic bacteria were reduced from 12.4 * 10**10 to 7.2 * 10**8 cells per ml after 2 days and were suppressed below this level for 28 days. Lactate product- ion was not prevalent in untreated swine waste indicating that the micro- bial populations differ from cattle waste. Carvacrol and thymol were stable in swine waste under anoxic conditions for 62 days with 90 to 95% of the additive being recovered in the waste solids. In conclusion, carvacrol and thymol are not metabolized in anoxic swine waste and they are potentially useful in controlling odor emissions and pathogens in swine waste.