Hydrogen Sulfide Detection System for Slurry Applicators
By Ross Muhlbauer, Research Associate and Randy Swestka, Graduate Research Assistant, Department of Agricultural and Biosystems Engineering, Iowa State University
Each year swine are lost to hydrogen sulfide (H2S) poisoning from unexpected burst releases during slurry removal from deep pit swine housing. Commercial slurry applicators, producers and previous research agree that increased ventilation can be required to dissipate dangerous H2S bursts that occur during pump-out events. However, continuous increased ventilation during cold weather can lead to increased heating costs and stressful conditions impacting swine health. Previous research has also shown that H2S concentrations can change from harmless to dangerous in a matter of minutes. It is this burst characteristic of H2S gas releases within the pit that create the danger.
The ability for applicators and producers to monitor H2S levels during slurry removal would be beneficial. Instead of utilizing high ventilation at precautionary levels or low ventilation to reduce costs and to reduce animal stress, ventilation could be adjusted accordingly to disperse H2S gas and decrease the chance of swine loss. Although it is never recommended a person enter a swine house during slurry agitation, monitoring H2S levels and managing ventilation and agitation techniques to prevent hazardous conditions could also increase human safety in the event of inadvertent entry. Previously, no system had been developed for manure applicators and producers to safely and remotely detect H2S gases in swine housing.
The Agricultural Waste Management Laboratory in the Agricultural and Biosystems Engineering Department at Iowa State University developed a portable, wireless H2S detection system for use in swine production systems during manure agitation and removal from under-floor swine slurry storage pits. Initially, multiple commercially available H2S sensors were tested in a controlled laboratory environment. From those results a prototype wireless H2S detection system was developed for testing in swine housing by commercial slurry applicators.
A two-piece prototype consisting of a battery operated sensor/transmitter and receiver was constructed.
- The sensor/transmitter is placed in the swine housing area before agitation/removal begins; the operator can then monitor H2S concentrations from outside the building.
- An operator-programmed visual/audio alarm can be set to activate at a desired concentration to alert the operator of dangerous H2S conditions.
- Once alerted, the operator can take action to dissipate the H2S gas. Research has shown H2S gas can be dispersed by stopping agitation and increasing ventilation.
The prototype detection system was field tested in swine confinements where it was used to detect H2S gas bursts during agitation of sub-floor slurry pits. Besides a quick reaction time, it showed good accuracy when tested against laboratory H2S measurement equipment. Testing confirmed that if monitored, dangerous levels of H2S gas can be dissipated by adjusting ventilation during slurry agitation and removal. This testing also showed that eliminating above surface slurry agitation greatly reduces H2S burst releases.
Portable H2S detection system prototypes are currently being used by two commercial slurry applicators during slurry application events from swine housing with sub-floor slurry storage. A data recorder within each prototype collects information on sensor run-time and H2S exposure. The units are being evaluated for durability, effectiveness, accuracy drift, and user-friendliness. So far the units have performed well but limitations have been identified. The system is limited by its single point monitoring scheme. While the system monitors H2S concentration at one point, dangerous levels could be present elsewhere in the swine house. During testing, methods were devised to minimize this problem. Use of interior circulation fans equalized H2S concentrations in the building, thus increasing the effectiveness of the single point monitoring scheme.
The portable H2S detection system is intended for use by custom manure applicators and producers that handle their own slurry. The portable system is battery powered so it can be easily transported and it requires minimal setup. The battery lasts 14 hours which would be compatible with most slurry removal events. The sensor/transmitter is placed inside the swine house before slurry removal. The H2S concentration can then be monitored by the operator from outside the building via the receiver. With the sensor/transmitter in the swine house the signal can be received via the receiver unit up to approximately 400 feet from the building. The range increases to approximately 2 miles line-of-site with long range antennas. The receiver unit can be configured for internal battery or connection to a vehicle accessory DC power outlet making it ideal for use in a vehicle or carried around a site.
Additional information about the wireless H2S detection system will be provided during an educational session at the 2009 Upper Midwest Manure Handling Expo in Boone, Iowa. Results from field testing and H2S mitigation techniques will also be discussed by the development team.
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This article originally appeared in the May/June 2009 Manure Manager Magazine and is reprinted with permission.