Impact of Bacillus subtilis on manure solids, odor, and microbiome

Authors: HWANG, OKHWA - National Institute Of Animal Science; YUN, YEO-MYEONG - Chungbuk National University; Trabue, Steven - Steve

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2023
Publication Date: 2/7/2023
Citation: Hwang, O., Yun, Y., Trabue, S.L. 2023. Impact of Bacillus subtilis on manure solids, odor, and microbiome. Journal of Environmental Management. 333. Article 117390. https://doi.org/10.1016/j.jenvman.2023.117390.
DOI: https://doi.org/10.1016/j.jenvman.2023.117390

Interpretive Summary: Odor from swine production is a major air quality issue for swine producers. These odors originate from microbial breakdown of undigested feed material in the manure. Manure additives containing microorganisms are inexpensive and easy to use and provide a sustainable solution to odor problems. However, little is known on the effectiveness of these additives. A study was conducted to determine the effect manure microbial additives have on manure properties, odor, and the microbial community and if pouring or spraying additives on manure surfaces improved performance of the additives. The microorganisms added to manure did not survive nor did they alter the manure's microbial community. However, the manure organic solids and odor were lower as a result of the following: 1) treating manures multiple times with the microbial additives; and 2) the physical action of spray droplets on manure surfaces removing crust layer. This research is important to growers and engineers who are interested in reducing odors from swine production.

Technical Abstract: Bioaugmentation by microbial additives is a management strategy that supplements the existing microbial community with cultured microorganisms to biodegrade containments. A study was conducted to determine the effectiveness of supplementing swine manure with Bacillus subtilis (BS) to improve digestion of manure solids and lower odor emission. Large bioreactors (400 L) with manure (100 L) were treated with commercially available BS and compared to bioreactors without treatment. The microbial inoculums were applied at a rate of 1% manure volume by either directly pouring into the bioreactor or surface application through spray technology. Manure physicochemical properties, odor emissions, and microbiome were monitored following treatment. Manures treated multiple times with BS or treated using spray technology had lower electrical conductivity, volatile solids, chemical oxygen demand, and total kjeldahl nitrogen values compared to non-treated control manure. Total ammonia nitrogen and volatile fatty acids were the only class of odorants in manure affected by different manure treatments and in general were lower than non-treated manure. Total odor was lowered in manure by either the physical mixing of spay droplets with manure or after multiple microbial treatments. However, the BS was not detected even after one day of multiple microbial treatments showing limitations of manure bioaugmentation. The decreases in manure organic strength and odor were a result of physical mixing of manure and chemical constituents of the microbial inoculum.