Effects of combined tannic acid/fluoride on sulfur transformations and methanogenic pathways in swine manure.

Livestock manure emits reduced sulfur compounds and methane, which affect nature and the climate. These gases are efficiently mitigated by addition of a tannic acid-sodium fluoride combination inhibitor (TA-NaF), and to some extent by acidification. In this paper, TA-NaF treatment was performed on swine manure to study the treatment influence on methanogenic pathways and sulfur transformation pathways in various laboratory experiments. Stable carbon isotope labeling revealed that both untreated and TA-NaF treated swine manures were dominated by hydrogenotrophic methanogenesis. However, in supplementary experiments in wastewater sludge, TA-NaF clearly inhibited acetoclastic methanogenesis, whereas acidification inhibited hydrogenotrophic methanogenesis. In swine manure, TA-NaF inhibited s-amino acid catabolism to a larger extent than sulfate reduction. Conversely, acidification reduced sulfate reduction activity more than s-amino acid degradation. TA-NaF treatment had no significant effect on methanogenic community structure, which was surprising considering clear effects on isotope ratios of methane and carbon dioxide. Halophile sulfate reducers adapted well to TA-NaF treatment, but the community change also depended on temperature. The combined experimental work resulted in a proposed inhibition scheme for sulfur transformations and methanogenic pathways as affected by TA-NaF and acidification in swine manure and in other inocula.
Competing Interests: A patent application, "Mitigation of ammonia, odor and greenhouse gases", was filed by University of Southern Denmark on 12th of June 2019 to the European Patent Office under Application No/Patent No 19179648.1 – 1105. The patent inventors who are also authors of this paper are: Frederik R. Dalby, Michael J. Hansen, and Anders Feilberg. The patent covers the application of tannic acid and sodium fluoride for abatement of gaseous emission from manure slurry. This does not alter our adherence to PLOS ONE policies on sharing data and materials.