Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 8, 2000
Publication Date: March 1, 2001
Citation: Varel, V.H., Miller, D.N. 2001. Plant-derived oils reduce pathogens and gaseous emissions from stored cattle waste. Applied and Environmental Microbiology. 67:1366-1370. Interpretive Summary: Stored manure from livestock production facilities contain pathogenic microorganisms and produce offensive odors as a result of microorganisms fermenting 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 cattle waste, short-chain volatile fatty acids, for 23 days. The fecal coliforms were killed within 4 days. We conclude that these chemicals may be useful as antimicrobial agents to control pathogens and odor in stored livestock waste. Field tests are needed to determine the economics and usefulness of these agents in production facilities.
Technical Abstract: Production of livestock in confinement facilities generates a large amount of waste in a small area. This has the potential to create environmental pollution such as nutrients and pathogens in drinking water and on food sources, odor, and global warming gases. In practice, complete anaerobic or aerobic digestion of the waste has not been technically or economically effective. Another approach is to treat the waste chemically to inhibit any fermentation. This would prevent emissions, retain nutrients, and potentially destroy pathogens in the waste. Our objective was to evaluate plant essential oils, in particular carvacrol and thymol, as chemical agents to control microbial fermentation in stored cattle waste. Anaerobic 2-liter Erlenmeyer flasks (working volume 0.5-liters) and open jars (working volume 1.4-liters) were used to evaluate the effect of carvacrol and thymol on production of gas, short-chain volatile fatty acids, lactate, ,and the abundance of total anaerobic bacteria and fecal coliforms in store cattle waste. Carvacrol and thymol in combination at 6.7 mM each, but not at 5.0 mM, completely inhibited the production of short-chain volatile fatty acids and lactate in the anaerobic flasks over 23 d. The fecal coliforms were reduced from 4.6 * 10**6 to 2.0 * 10**3 cells per ml 2 d after treatment, and to nondetectable within 4 d. Total anaerobic bacteria were reduced from 8.4 * 10**10 to 1.5 * 10**7 cells per ml after 2 d and continued to be suppressed to that level after 14 d. If the concentration of carvacrol or thymol were doubled (13.3 mM) they could be used individually to obtain the same inhibitory fermentation effect. We conclude that carvacrol or thymol may be useful as antimicrobial chemicals to control pathogens and odor in stored livestock waste.