Principal Investigators:

Chuck Clanton, Associate Professor
R. Vance Morey, Professor and Department Head
Department of Biosystems and Agricultural Engineering
University of Minnesota

Cooperator:
David R. Schmidt
Department of Biosystems and Agricultural Engineering
University of Minnesota, St. Paul, MN 55108

Date: August 1999

INTRODUCTION

Odor emissions from manure storages and animal housing facilities can be a nuisance for both farmers and the nearby residents or surrounding communities. Most of these odorous emissions are the result of specific gasses generated and released during the anaerobic decomposition of manure. This study was designed to identify the individual sulfur gases released from both swine and dairy manure. These sulfur gases are known to be odorous and some have a very low detection threshold, meaning that they can be detected by the human nose at very low concentrations.

PROJECT DESCRIPTION

A total of 53 air and liquid sulfur compounds were collected and analyzed from three separate studies: a batch study, a semi-batch study and a field study. The objective and descriptions of the individual studies are outlined below. All liquid and air samples were sent to a commercial analytical laboratory in California for analysis of sulfur compounds using gas chromatography. Air samples were also analyzed for total reduced sulfur using a Jerome Meter, at the time of sample collection, and odor using dynamic olfactometry.

Batch Study

A batch study was conducted to determine the changes in sulfur gas species formation over time. In this study, fresh swine and dairy manure were placed in 30 cm diameter PVC columns at a depth of 87 cm. No additional manure was added to the columns&endash;allowing the manure to degrade anaerobically without disruptions. Air and liquid samples were collected weekly for nine weeks beginning April 29, 1999.

Semi-batch Study

A semi-batch study was conducted to simulate the development of gas emissions over time in a typical manure storage where manure is added on a regular basis. In this study, swine and dairy manure was placed in PVC columns similar to those used in the batch study. Manure was added on a bi-weekly (Monday and Thursday) basis using 3.8 L per addition, increasing the manure depth by 2.5 cm with each addition. The first data was collected three weeks from initial manure addition. Air and liquid samples were collected weekly over the next eight weeks. The final samples were collected on May 12, 1999.

Field Study

A field study was conducted to verify that the compounds formed in the laboratory are also formed in actual manure storages. In this study, liquid and air samples were collected from five Minnesota livestock operations.

RESULTS AND DISCUSSION:

A total of 53 paired (air and liquid) samples were collected. Of the 20 sulfur-containing compounds able to be detected by the analytical laboratory, only hydrogen sulfide, carbonyl sulfide, methyl mercaptan, dimethyl sulfide, carbon disulfide, and dimethyl disulfide were detected in the air samples. These same compounds were also detected in the liquid manure samples along with isopropyl mercaptan. Table 1 lists these compounds and the range of concentrations found. All of the compounds detected in the air samples, except methyl mercaptan, were found in at least one sample taken from the field. All air samples contained hydrogen sulfide.

Of these compounds detected, only hydrogen sulfide showed any correlation to odor. This may be because of the limited number of samples taken that contained other reduced sulfur compounds. Compounds such as dimethyl sulfide and dimethyl disulfide have extremely low odor detection thresholds, possibly below the detection threshold of the equipment used to detect the compounds.

Two of the compounds detected, hydrogen sulfide and carbon disulfide, are listed in Minnesota’s Proposed Inhalation Health Risk Values (HRV). Emissions of hydrogen sulfide are currently being studied in depth at the Department of Biosystems and Agricultural Engineering. Emissions of carbon disulfide may need to be investigated further, however, from the concentrations detected in this study, it is unlikely that concentrations in or around livestock facilities will exceed the proposed HRV of 700 mg/m³.

CONCLUSIONS:

This study confirmed the literature findings that several reduced sulfur compounds are formed and emitted from anaerobically stored manure. However, only six of the twenty-three previously reported compounds were detected in this study. The compounds detected in the air samples were at fairly low levels. It is possible that concentrations of these compounds in air samples collected during the agitation and pumping of the manure could be much greater than indicated in this study.

Table 1. Number of times detected, average concentrations and minimum and maximum concentrations of air and liquid manure samples.

	Number of times detected	Mean	Minimum	Maximum
Odor Units	52	982	55	4591
Air Sample (GC1/) (ppb)
-Carbonyl sulfide	36	10.9	2.9	35.1
-Methyl mercaptan	13	8.5	1.9	26.9
-Dimethyl sulfide	8	8.6	2.2	44.4
-Carbon disulfide	49	32.3	1.9	405
-Dimethyl disulfide	7	2.7	1.2	6.5
-Hydrogen sulfide (Jerome)	51	568	7	2400
-Hydrogen sulfide (GC)	48	445	4	2820
Liquid sample (GC) (mg/kg)
-Carbonyl sulfide	32	47.2	4.8	351.0
-Methyl mercaptan	41	52.5	3.2	317.0
-Dimethyl sulfide	11	16.4	5.0	41.1
-Carbon disulfide	30	23.4	4.5	75.8
-Isopropyl mercaptan	2	9.8	7.7	11.9
-Dimethyl disulfide	4	7.1	5.1	9.2
-Hydrogen sulfide	45	5212	8	48,600

^1/CG&endash;Gas chromatograph