Hydrogen Sulfide Detector Warns of Dangerous Gas Levels

A research team at Iowa State University (ISU) has developed a wireless hydrogen sulfide (H2S) detector that successfully detects the potentially fatal gas released from manure in deep-pit barns during slurry agitation and pumping events. This project was funded by the National Pork Board.

Lethal concentrations of H2S can develop rapidly and vary spatially in a swine barn during manure agitation and removal.

It is estimated the lost market value of 20 or more hogs to H2S poisoning during slurry agitation would pay for the new detection system in one year.

Personnel should never enter a swine barn during slurry agitation. The Occupational Safety and Health Administration's (OSHA) limit for immediate threat to life is 100 ppm of H2S. Field studies have shown that H2S concentrations can exceed this level quickly during slurry agitation with concentrations recorded as high as 1,300 ppm.

Researchers at ISU have the following objectives for this project to reduce the risk of human or animal fatalities from H2S gas:

  1. Develop and test a wireless hydrogen sulfide detection system for use during hog manure agitation and removal;

  2. Better establish building ventilation management strategies to increase human safety and maintain animal health during the manure agitation and removal process; and

  3. Add to the knowledge base about the development of hazardous conditions due to H2S from manure.

Initially, six commercially available H2S sensors were tested in ISU's Agricultural Waste Management Laboratory.

The prototype consists of a sensor/transmitter and a handheld receiver. The sensor/transmitter is equipped with the H2S sensor, a wireless communication system and battery power. The unit is placed inside the swine barn before agitation begins. The receiver remains outside so the operator can safely monitor H2S gas levels inside the barn. Both an audible and visual alarm are activated when a predetermined H2S concentration is detected.

The prototype matched performance of a research grade H2S analyzer.

To better understand H2S burst formation and distribution in swine facilities, the prototype system was used to detect concentrations at various locations in a swine finishing facility. While using surface agitation with splashing (agitation that disturbs the slurry surface), measurements were collected simultaneously from the pit below the slats and just above the slats in the same location. The use of stir fans equalized H2S concentrations above and below the slotted floor. By using stir fans, the operator can obtain a representative sample of room gas levels using a single point detection system.

H2S gas levels from above and below the slats in the same location can be collected during subsurface agitation (no disturbance of the slurry surface). While H2S concentrations were detected below the slats, no measurable H2S concentrations were detected above the slats. These results suggest that subsurface agitation should be used whenever possible to minimize H2S burst releases.

In a third test, H2S gas data was collected simultaneously from different areas within the barn just above the slats. In less than 10 minutes after vigorous surface agitation, the H2S gas concentration had exceeded the maximum range of the gas detector (500 ppm), demonstrating the dangers of H2S gas emissions during slurry agitation.

Researchers: Ross Muhlbauer, Randy Swestka, Robert Burns, Hongwei Xin, Steve Hoff and Hong Li, all of Iowa State University. Contact Burns by phone (515) 294-4203, fax (515) 294-4250 or e-mail rburns@iastate.edu.

Electrostatic Collection System Reduces Barn Dust

Test results in a hog finishing barn demonstrate that the Electrostatic Space Discharge System (ESDS) maintained a significant level of dust reduction compared to the control group.

The ESDS reduced 63% of total particle sizes (expressed as “total spatial particulates” or TSP) of dust and 47% of smaller particles less than 10 microns in size (PM-10). The 10-micron and smaller dust particles are the size inhaled by workers in hog barns.

Dust is a mixture of very small particles and liquid droplets that can cause or worsen health conditions in people and pigs. The PM-10 and smaller particles are of most concern because they can settle in the bronchia and lungs.

The ESDS reduces dust by negatively charging particles and causing them to attach to walls and equipment in the barn. This reduces the dust concentration in the room air as well as the air exhausted through the ventilation fans.

The ESDS has been shown to reduce dust levels in poultry buildings with great success — but little is known about the advantages in swine confinement facilities, the main goal of this research project.

To evaluate ESDS, a 1,000-head, two-room finishing barn was tested. Each room contained 24 pens, 12 per side. One room was equipped with an ESDS unit and the other served as a control.

The ventilation in each room included four pit fans and six wall fans. The ventilation controller was set to run through six stages. Fresh air entered the room through quad ceiling inlets for stages 1-3, and entered through wall inlets near the ceiling during stages 4-6.

Ventilation air flow ranged from 8 to 22% less than fan manufacturers' published data, probably due to the dirtiness of the fans.

The ESDS consists of an electrical multiple wire design, which maximizes the ions created by the 30,000 volts in the ESDS.

Air samples in each room were collected using MiniVol portable air samplers suspended 6 ft. above the slotted floor. The system samples air at 1.3 gal./minute, collecting in three different particulate categories: total spatial particulates (TSP), particles less than 10 microns (PM-10) and particles under 2.5 microns (PM-2.5). Particle size separation is achieved through impaction and collection on 2-in. filters.

Dust samples were collected over 24-hour periods. The collection process was repeated three times at about six-week intervals: first for 29- to 48-lb. pigs, then for 150- to 169-lb. pigs and finally for 240- to 260-lb. pigs. Each filter was weighed before and after sampling to get the mass of the dust particles on the filter.

In all three dust removal particle size test groups shown in Figures 1-3, the ESDS room reflected a significant advantage in total dust removal over the control room.

The greatest amount of TSP removal occurred in all three finisher weight groups (Figure 3).

Also, the first group of finishing pigs weighing 29-48 lb. showed a greater percentage reduction of dust particles.

Concentrations of dust removed were less in general for the middle weight group (150-169 lb.) because outside temperatures were warmer, increasing fan operation and decreasing dust concentration because of greater air exchange.

The application of the ESDS technology needs further study to determine the impact on other hog barn issues, such as odor, pathogens and gases, researchers note.

Dust will continue to be an issue in swine barns. Efficient and effective ways of removal will be key to maintaining a healthy working environment for the workers and for swine.

Researchers: R.E. Nicolai and B.J. Hofer, both of South Dakota State University. Contact Nicolai by phone (605) 688-5663, fax (605) 688-6764 or e-mail nicolaid@sdstate.edu.

Gas-Phase Biofilters Reduce Odor, Emissions

Alternative media are being tested for use in gas-phase biofilters in an effort to minimize pressure drop, lower operating costs and reduce the biofilter footprint. Improved biofilters will also be more resistant to rodents and extend the useful life through reduced maintenance costs.

Gas-phase biofilters are a proven method for reducing odor and other gaseous emissions from swine facilities. However, widespread adoption of biofiltration has stalled due to four issues:

  • The relatively large footprint needed to manage the media pressure drop;

  • The concerns about the biofilter media harboring rats;

  • The potential problem of long-term biofilter media compaction; and

  • The concerns about potential nitrate leaching from the biofilter media into the soil.

This project at the University of Minnesota, funded by Pork Checkoff, was designed to identify and evaluate alternative biofilter media that would solve some of these issues.

Six media were evaluated in Phase 1: bag mulch, lava rock, cedar chips, pine bark nuggets, western pine bark and wood shreds. Media sieve analysis (filtration process), porosity and unit pressure drop vs. unit airflow relations were determined.

Phase 1 testing was conducted in a biofilter media testing unit with six columns, including individually controlled airflow rates and moisture control (pictured above).

Phase 1 testing involved the air-cleaning performance and pressure drop characteristics of each media evaluated on the basis of hydrogen sulfide (H2S), and ammonia (NH3) removal.

In Phase 2, three media — wood shreds, pine bark nuggets and lava rock — were placed in similar columns and evaluated for pressure drop and reductions of H2S and NH3.

In Phase 3, pine bark nuggets were used in all six columns and H2S, NH3 and odor removal were analyzed.

Overall, pine bark nuggets and lava rock scored the highest by recording the lowest unit pressure drops vs. unit airflow rates.

Results from Phase 1 indicate that all six media supported microbial growth if seeded, and were effective, reducing H2S concentrations between 21-75% and NH3 concentrations between 43-80%.

All three media in Phase 2 performed well in the study.

Some biofilter media in Phase 3 had lower percent H2S, NH3 and odor removal than others.

Researcher: Kevin A. Janni, University of Minnesota. Contact Janni by phone (612) 625-3108, fax (612) 624-3005 or e-mail kjanni@umn.edu.

Crop Residues + Swine Manure Enhance Methane Generation

Co-digesting swine manure with crop residues shows great promise in boosting methane generation in anaerobic digesters.

The problem with using swine manure only for anaerobic digestion is its low carbon/nitrogen (C:N) ratio (6:1 to 8:1, normal range), while good digestion re-quires a C:N ratio between 16:1 and 25:1.

University of Minnesota agricultural engineer Jun Zhu says the use of crop residues can be an effective way to enhance methane production, and at the same time reduce the volume of crop residue materials for disposal.

In his research, the addition of the crop residues at all C:N ratios increased the total daily gas volume produced (Figure 1). Wheat straw didn't achieve the same increase in gas production compared to corn stalks and oat straw during the first two weeks of production, but surpassed corn stalks later for the C:N ratio of 25.

Corn stalks and oat straw performed equally well in increasing gas production when compared to the control group (Figure 1).

When the C:N ratio was increased from 16:1 to 20:1, there was a clear increase in gas volume produced for all of the materials tested (Figure 1). However, continuing to increase the C:N ratio to 25:1 didn't produce the same increase in gas production seen in the increase in the C:N ratio to 20:1.

Figure 2 shows the methane (CH4) content in the gas from reactors using different crop residues and C:N ratios. Not much difference was observed in methane production between wheat straw and the control. However, the difference was quite significant for the other two crop products tested. Oat straw showed quick success, achieving a 44.4% digestion rate on Day 1 for a C:N ratio of 20:1, and a 58.8% digestion rate and C:N ratio of 16:1 by Day 3.

Corn stalks also reached 45% methane content on Day 5 for C:N ratios of 16:1 and 20:1.

The increase in C:N ratio doesn't seem to correlate with an increase in methane production for wheat straw treatment as compared to the control when the digester enters into a steady state.

But methane content mushrooms for both oat straw and corn stalks during the same period at a C:N ratio of 20:1 with 57% for oat straw, 68.2% for corn stalks and just 46.5% methane digestion rate for wheat straw.

“Since the quantity of pure methane is a product of total gas volume and the methane concentration in the off-gas, the higher the methane content and gas volume, the more methane is produced,” Zhu explains.

“Therefore, it appears that oat straw and corn stalks perform better than wheat straw when co-digested with swine manure, from the perspective of pure methane productivity,” he concludes.

Researcher: Jun Zhu, University of Minnesota Southern Research and Outreach Center at Waseca. Contact Zhu by phone (507) 837-5625, fax (507) 835-3622 or e-mail Zhuxx034@umn.edu.