Project Description

A study was done to determine if sulfur contained in the feed and water used in the production of pigs could be correlated to hydrogen sulfide (H₂S) emissions from manure storage systems. This is a concern because of an existing state H₂S ambient air standard which may be exceeded at certain times of the year at some pig production sites.

Research Procedures

The project used the findings from six pig farms representing three different manure storage types (two paired farms per manure storage type) in an ongoing odor monitoring project. Air samples collected at the surface of the manure storage unit showed similar odor levels for each of the three different manure storage types selected. One of the farms in each manure storage type had a much higher concentration of H₂S than the other paired site. The manure storage types studied were: earthen basin, outdoor pit or tank, and indoor deep pit. Geographically, three farms were located in the southwest section of the state while the other three are in the central Minnesota. Samples of drinking water and feed were collected from the selected six farms and chemical analysis for total sulfur were performed on these samples. All air samples used olfactometry to determine the odor threshold and a Jerome^TM meter or sensidyne indicator tubes for hydrogen sulfide.

Results

Figure 1 shows the hydrogen sulfide (H₂S) levels collected directly above the manure surface for all six farms during the spring, summer, and fall seasons. The manure storage systems are designated by "eath-basin" for earthen basin, "out-tank" for outdoor pit or tank, and "indr-pit" for an indoor deep pit. The number designation is "1" for the high H₂S farm and "2" for the low H₂S farm. This figure simply confirms the hydrogen sulfide designations. It also indicates that the fall season has the highest hydrogen sulfide levels among the three seasons for the air directly above the manure storage surface, an observation supported by the larger monitoring odor project. It also shows that no single manure storage type seems to have higher H₂S levels, another trend which is more strongly supported by the larger odor monitoring project.

Figure 1. H₂S concentrations, for air collected directly above the manure surface, for the three paired manure storage units

The variations in odor threshold levels for the same three paired manure storage units over the summer, fall, and spring seasons are shown in Figure 2. As shown by this graph, very little difference in odor level existed between paired farms with similar manure storage systems. This was the case even though H₂S concentrations (Figure 1) varied considerably between the paired the farms. Figure 2 also reveals that odor levels are much higher during the spring (April and May) compared to those measured during the summer and fall. This is logical due to the increasing temperature that accelerates microbial activity in decomposing organic compounds, thereby producing large quantities of odorous gases. Also, there does not seem to be a consistent manure storage system that has higher odor levels. This was also noted in the larger monitoring project of over 40 farms. Finally, comparing Figure 1 with Figure 2, reveals that the odor threshold levels are not proportional to the levels of ambient hydrogen sulfide. According to this study, the highest odor threshold levels occurred in the spring while the highest hydrogen sulfide levels showed up in the fall.

Figure 2. Odor levels, for air collected directly above the manure surface, for the three paired manure storage units

As indicated in the procedures, water and feed samples were collected from the six different farms. Total sulfur analysis was done for both with the results tabulated in Table 1 and also shown in Figure 3. Water samples showed either relatively high levels, from 200 to 300+ ppm total sulfur or levels below 10. The three farms located in the southwestern part of the state all had the high sulfur levels while the central Minnesota farms recorded the low values. Feed was collected from a variety of diet sources (farrowing, gestation, finishing, etc) on several of the farms, so the total sulfur analysis was "weighted" according to the percentage of feed fed to animals which contributed to the manure storage unit. Average H₂S levels (from the 3 measurements in Figure 1) collected above the manure storage units are also listed in Table 1 and graphed in Figure 3 for reference.

Table 1

Farm Average H₂S level, ppm Water - Sulfur, ppm Feed- Total Sulfur x 10^3, ppm

eath-bas-1 22 331 244

eath-bas-2 3 6 278

out-tank-1 37 223 412

out-tank-2 4 195 344

indr-pit-1 25 4 225

indr-pit-2 5 7 186

Figure 3. Average H₂S levels, total sulfur in water and feed concentrations for the three paired manure storage units

Figure 3 shows that the H₂S variations between the two earthen basin farms may be explained by the sulfur contained in the pig’s drinking water. However, this is not the case for the other two paired farms, since both water sulfur levels are high for the two outdoor tanks farms and low for the two indoor pit sites. Although not as dramatic as water, sulfur levels in the feed show higher concentrations in both of the high H₂S farms for the outdoor tank and indoor pits manure storage systems. Both feed and water are factors in determining the level of H₂S produced from the manure storage units but from this preliminary study it is not obvious which one may be the most important, or how much they impact H₂S emissions. The biological and chemical processes which produce hydrogen sulfide are complex involving the reduction of sulfate by the sulfate-reducing bacteria.

It was planned to also collect pharmaceuticals from each of the farms and determine what their contribution was to the production of H₂S. This unfortunately was not done. Although not as significant in quantity of use, pharmaceutical drugs utilized by producers may help explain some of the results and need to be measured for future studies.

Summary

The study revealed that the sulfur content of drinking water and feed may indeed affect the hydrogen sulfide emissions from the manure storage system on a pig farm. There is not a clear correlation between levels of sulfur in these important "inputs" and H₂S levels found directly above the manure surface although it is impacted by them. Further work is needed with more farms included to determine the level of impact from water and feed as well as other inputs like pharmaceuticals. This study does indicated that if high sulfur water is present and levels of sulfur are relatively high in the feed as well, one may monitor H₂S levels to see if some preventative measures need to be taken.