Location: Bioenergy Research Unit
Title: Effects of condensed tannins on hydrogen sulfide production and the sulfate-reducing bacterial population of swine manure Authors
Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: March 19, 2008
Publication Date: N/A
Technical Abstract: Condensed tannins are natural plant compounds that have antibacterial properties and have been used in studies to reduce methane emissions and frothy bloat in cattle. The objective of this study was to test the effects of condensed tannins on swine manure to target bacterial groups responsible for odor production. Odorous compounds and emissions produced from stored swine manure create a nuisance and can influence zoning decisions about the proposed sites of new swine facilities. These nuisance odors largely result from sulfides, volatile fatty acids, and phenols, which are produced as a result of anaerobic digestion of materials present in the manure. Hydrogen sulfide (H2S) is an offensive odorant from swine manure and is being considered as a regulatory standard to monitor emissions from swine production facilities. Production of H2S involves sulfate reduction largely by anaerobic sulfate-reducing bacteria (SRB). A quantitative real-time PCR approach was used to target and quantify the SRB population in manure, in response to treatment with condensed tannins. This assay specifically targeted the conserved dsrA gene of SRB, which encodes a key enzyme involved in sulfate respiration and production of H2S. Swine manure was collected from a local swine facility and diluted in an anaerobic buffer to a 10% final solution. One hundred ml samples of 10% manure were treated with 0.5% w/v condensed tannins and together with control solutions were incubated anaerobically at room temperature for 28 days. All experiments were performed in triplicate. H2S production was measured with a gas analyzer, and 1 ml aliquots of manure were removed periodically for enumeration of the different populations of SRB. Addition of condensed tannins to swine manure in vitro reduced the numbers of Desulfobulbus-like Group 1 SRB by 96% after 7 days. This reduction in SRB correlated with a 98% reduction in H2S production over the course of the study. This research demonstrates that condensed tannins can suppress H2S production and reduce levels of SRB in swine manure.