Application of Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) and ³³S Isotope Labeling for Monitoring Sulfur Processes in Livestock Waste

Abstract

Reduced sulfur compounds emitted from livestock production cause odor nuisance for local residents. The microbial processes responsible for this are not well described in swine manure and a method for monitoring the biological processes is necessary to develop strategic abatement technologies. In this study, Proton-Transfer-Reaction Mass Spectrometry and isotope-labeled sulfate were combined and applied to elucidate the sulfur processes in swine manure with high time resolution. We successfully monitored reduction of isotope S labeled sulfate into correspondingS hydrogen sulfide and found that some of the S hydrogen sulfide was further methylated intoS methanethiol. The isotope patterns in reduced sulfur compounds together with usage of inhibitors enabled us to calculate a sulfate reduction rate of 1.03 ± 0.18 mM/day equivalent to 76.9 ± 3.0% of total hydrogen sulfide emissions. Cysteine degradation constituted 20.2 ± 2.7% of the total hydrogen sulfide produced and the remaining hydrogen sulfide came from demethylation of methanethiol and dimethyl sulfide. Another source to methanethiol, besides hydrogen sulfide methylation, was methionine degradation, which contributed with 78.3 ± 2.5% of the methanethiol production, whereas the remaining 21.7 ± 2.5% came from hydrogen sulfide methylation. This study suggests, therefore, that emissions of odorous sulfur compounds from swine manure can be reduced by inhibiting methionine degradation and sulfate reduction.

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

“…The isotope ratio in unlabeled control manure was in close agreement with the theoretical isotope ratio based on a reference R ( 33/32 S) of 0.788% [ 33 ]. The labeled controls indicate that approximately 80% of the hydrogen sulfide was produced by reduction of sulfate ( Fig 5A ), which is consistent with previous estimates of 77 ± 3% in swine manure [ 7 ]. Treatment with TA-NaF yielded a R ex ( 33/32 S) H2S value similar to the R ex ( 33/32 S) SO4 value, suggesting that more than 95% of the emitted hydrogen sulfide was derived from sulfate reduction.…”

“…Though cysteine degradation was almost completely inhibited, it remains unclear exactly how methionine degradation was affected. It has been shown that methanethiol from swine manure originates primarily from methionine degradation [ 7 ], and hence a huge reduction in methanethiol production, as those seen for TA-NaF treatment in this study, is likely to result from inhibition of methionine degradation. The limited production of methanethiol made it challenging to achieve the precision needed to differentiate between the untreated control manure and TA-NaF treated manure.…”

“…A widely deployed technique to study such interactions is the usage of isotope-labeled precursors supported by microbial community analysis. The application of 33 S-sulfate labeling in swine manure to examine sulfur transformations has recently been demonstrated and it was shown that approximately 80% of hydrogen sulfide came from sulfate reduction [ 7 ]. Likewise, the incorporation of 13 C-labeling of the methyl carbon in acetate has been used in numerous studies to trace methanogenic pathway activity [ 19 – 21 ].…”

Reducing greenhouse gas emissions from pig slurry by acidification with organic and inorganic acids

“…Common practice is to lower the pH to 5.5 with H 2 SO 4 with reported CH 4 reductions of 63–99% [ 6 ]. Proposed inhibition mechanisms include H 2 S-mediated inhibition [ 7 ], which is mainly derived from sulfate reduction [ 8 ], uncoupling of the cell membrane by protonated fermentative products [ 9 , 10 ], or competitive inhibition of methanogens by microorganisms able to respire more energetic electron acceptors [ 11 ]. The latter may be relevant if acidification is carried out using H 2 SO 4 or HNO 3 , which dissociates to the more preferable electron acceptors, sulfate and nitrate, than CO 2 during methanogenesis [ 11 ].…”

Methanogenic pathways and δ13C values from swine manure with a cavity ring‐down spectrometer: Ammonia cross‐interference and carbon isotope labeling

“…[18][19][20][21][22] Measuring 13 C/ 12 C ratios in CH 4 and CO 2 emitted from manure using CRDS may enhance our understanding of the methanogenic pathways contributing to CH 4 emissions from livestock facilities. 5,23 However, NH 3 and livestock trace gases such as H 2 S are often present at ppm levels [24][25][26] and may exceed the CH 4 concentrations inside buildings where animals are kept. NH 3 cross-interference on 13 C/ 12 C ratios in CH 4 was reported recently, 18 and H 2 S crossinterference on 13 C/ 12 C ratios in CO 2 was thoroughly described by Malowany et al 27 These interferences may disturb 13 C/ 12 C measurements to the detriment of evaluating the relative contribution of methanogenic pathways.…”