MONITORING SULFUR PROCESSES IN SWINE MANURE WITH ISOTOPE LABELLING AND PTR-MS

DALBY, F.¹, HANSEN, M.J.², FEILBERG, A.³

Department of Engineering, Aarhus University, Denmark

ABSTRACT: The Biological processes that cause emission of reduced sulfur compounds from livestock production are problematic due to odour nuisance. A better understanding of the microbial processes influencing reduced sulfur compounds emissions may lead to strategic abatement technologies. In this study, we developed a method to monitor sulfur processes in swine manure using ³³S isotope labelling and Proton-Transfer-Reaction Mass Spectrometry (PTR-MS). We validated our method in biological triplicates in batch reactors and successfully traced the reduction of ³³SO4-2 to H233

S and its further methylation to CH333

SH with PTR-MS. Addition of methionine and cysteine affected the ratio of emitted H233S: H232S and it was possible to calculate the origin of H₂S based on the isotope pattern. H₂S methylation was responsible for 30% of the CH3SH formed and the remaining CH3SH came from methionine degradation. Sulfate reduction inhibitors reduced the H2S emissions with 96% indicating that most of the H2S comes from sulfate reduction. This study provides a high time resolution method for determining the contributing sources to- and production rate of sulfurs from swine manure and is applicable in other substrates.

Keywords: Sulfur, emission processes, method, PTR-MS, isotope labelling

INTRODUCTION: Livestock production is responsible for gas emissions of ammonia, methane, volatile organic compounds and reduced sulfur compounds (Amon, Kryvoruchko et al. 2006). These compounds evaporate from animal manure in the barn and when land spreading and have environmental impact in the form of eutrophication, particle formation and odor nuisance. The major contributor to odor nuisance is reduced sulfur compounds (Feilberg, Liu et al. 2010), which constitute mainly hydrogen sulfide, methanethiol and to a lesser extent dimethyl sulfide. The microbial processes involved in the production of reduced sulfur compounds have been elucidated in earlier studies on bio solids and marine sediments (Jørgensen 1977, Higgins, Chen et al. 2006), which found that sulfur originates from sulfate reduction, cysteine degradation and methionine degradation. However, a proper method for monitoring these processes and determining the dominant pathways has been absent. In this study we provide a novel method for monitoring the sulfur processes in swine manure with a high time resolution Proton-Transfer-Reaction Mass Spectrometer and isotope labelled sulfate. By adding quantitative amounts of ³³SO4-2 to the swine manure, the reduction of sulfate to hydrogen sulfide can be distinguished from the degradation of cysteine and methionine to hydrogen sulfide and methanethiol respectively. In this study the isotope pattern of hydrogen sulfide and methanethiol was monitored with the novel method combined with inhibitors to assess sulfate reduction, cysteine degradation and methionine degradation.

Measurement methods

1. MATERIALS AND METHODS. Swine manure was collected from a storage tank from finishing growing pigs at Aarhus University, Foulum. It was sewed through a 6 mm metal grid to remove straw and large particles, then split into 10L aliquots and stored at 5 °C until experiment initiation. Before experiment initiation the manure was analyzed with respect to sulfate-, ammonium- and volatile fatty acids concentration by ion chromatography, turbidity kit and gas chromatography respectively. Dry matter content and pH was also measured.

The experimental setup consisted of three reactors with 200 mL sewed swine manure, which had a nitrogen headspace exchange rate of 200mL/min through the reactor lid.

The flowrate was controlled with mass flow controllers (Broncks) and the manure was stirred quietly with magnet stirrers to avoid pH gradients building up. The outlet flow was diluted with nitrogen before being detected with a High Sensitivity Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) (Ionicon Analtik, Innsburg). The PTR-MS switched between reactors through a five-way valve and measured 4 min at each reactor and a background signal yielding a total cycle time of 16 min. During the experiments the manure was chemically altered by injection through the headspace with dissolved Na³³SO4-2 (Sigma Aldrich, Copenhagen, Denmark), L-Cysteine (Sigma Aldrich, Copenhagen, Denmark) or L-methionine (Sigma Aldrich, Copenhagen, Denmark).

2. RESULTS AND DISCUSSION. The swine manure had a dry matter content of 4.6 % w.

Sulfate and ammonium was present in 3.9 mM and 4 g/L respectively. The swine manure contained mostly acetic acid (6 g acetic acid/L) and to a lesser extent propionic - and butyric acid (2-and 1.7g/L).

The method relied on isotope labelled sulfate (³³SO4-2) reduction to take place. In Figure 1, isotope labelled sulfate was added in different concentrations after 18 h, which gave rise to increased isotope labelled hydrogen sulfide (m/z 36) emissions.

Emissions of Gas and Dust from Livestock – Saint-Malo, France – May 21-24, 2017 122

Figure 2, cysteine and methionine was added after 41 h influencing the ratio between H233

S and H2S differently.

Figure 8. The ratio of H2

33S and H2

32S in the effluent gas. Methionine (○) and cysteine (○) was added to separate reactors after 41 h.

When cysteine was added the ratio declined quickly, whereas methionine affected the ratio less but over a longer period of time. This was most likely due to methionine being degraded to methanethiol prior to demethylation to hydrogen sulfide.

Figure 3 presents the methanethiol emission rate after BES addition. From the isotope pattern of methanethiol the contribution to methanethiol from hydrogen sulfide methylation was also determined.

Figure 9. The total methanethiol effluent concentration (□) and the methanethiol originating from hydrogen sulfide methylation (○). BES was added a–er 25 h to increase methanethiol concentra—on and

decrease the uncertainty.

The contribution from hydrogen sulfide methylation was approximately 30% of total methanethiol production 15 h after BES addition. The hydrogen sulfide methylation declined after 42 h due to sulfate depletion.

Measurement methods

In Figure 4, the effect of molybdate on hydrogen sulfide emissions and the isotope ratio is presented.

Figure 10. The effect of molybdate on the concentration of H2S in the effluent gas (○) and the corresponding ratio between H2

33S and H2

32S (○). Molybdate was added after 18 h.

Figure 4. shows the hydrogen sulfide concentration was reduced 96.5% upon molybdate addition after 18 h. A corresponding decline in the isotope ratio between H233S and H232

S indicated that the remaining H2S emissions after molybdate was relatively less sulfate reduction than other sources, such as cysteine degradation.

CONCLUSION: This study demonstrated how the isotope labelling and PTR-MS could be combined to trace the sulfur processes in swine manure. Furthermore, we elucidated the relative activity of sulfide methylation vs methionine degradation, the effect of cysteine and methionine addition and finally the proportion of hydrogen sulfide originating from sulfate reduction.

Acknowledgements. This study was part of the ManUREA project funded by GUDP under the Danish AgriFish Agency, ministry of environment and food Denmark (Grant 34009-15-0934).

REFERENCES:

Amon, B., V. Kryvoruchko, T. AmonS. Zechmeister-Boltenstern.2006. Methane, nitrous oxide and ammonia emissions during storage and after application of dairy cattle slurry and influence of slurry treatment. Agriculture, Ecosystems & Environment. 112,

Emissions of Gas and Dust from Livestock – Saint-Malo, France – May 21-24, 2017 124

REDUCED DIRECT MEASURING METHODS IN THE RIDGE VENT OF A DAIRY BARN DE VOGELEER, G.¹, PIETERS, J.G.², VAN OVERBEKE, P.¹, DEMEYER, P.¹

1 Technology & Food Unit, Flemish insitute for Fisheries, Agricultural and Food Research (ILVO), Burgemeester Van Gansberghelaan 115, 9820 Merelbeke, Belgium;

2 Department of Biosystems Engineering, Ghent University, Coupure links 653, 9000 Ghent, Belgium;

INTRODUCTION

Accurate measurement of livestock housing emissions is necessary to assess their environmental impact of the performance of applied mitigation techniques. These emission measurements can be conducted by combining local air velocity and pollutant concentration measurements. However, unsteady wind conditions challenge measuring the air velocities at naturally ventilated buildings. Spatially dense measurements, however, are rarely feasible due to economic and practical constraints. Simplification of measurement methods with limited loss of accuracy is therefore necessary.

The objective of this research was to reduce the amount of air velocity sampling places in order to measure the airflow rate through the ridge vent without exceeding an accuracy loss of ± 20% with respect to detailed measurements.

Keywords: Measuring method, reduced method, accuracy, ridge vent, ultrasonic anemometer