University of Illinois Extension

Reducing Fatality Risks From Manure Pit Storages

Background

In spite of growing efforts to create more awareness in health and safety in the farming community, fatalities due to manure pit accidents are still reported. The causes seem to be a combination of: needs to enter manure storage; highly varied toxicity levels from manure pits; lack of information on why and when dangerous conditions exist; the need for more effective education; and safety procedures, and practical reliable sensors to detect toxic gas conditions. Manure in storage pits can release gases which can be toxic - hydrogen sulfide, cause irritation - ammonia, or cause oxygen deficient conditions. These gases especially the toxic ones can cause human and swine deaths. Ammonia and hydrogen sulfide are some of the gases we are interested in studying. Trace release of hydrogen sulfide is common, while rapid release have been reported when manure pits are being emptied. Hydrogen sulfide is also very corrosive, therefore, its production may result in equipment and building corrosion problems.

Objectives

  1. To investigate how air velocity, air temperature above the manure surface, manure temperature and manure solids content interact to influence the production and release of manure pit gases.
  2. Develop control and management methods to reduce manure pit gases.
  3. Develop safety procedures and safety educational training materials for people working in and around manure pits.

Laboratory Studies

Factor Interaction Tests

The emission of manure pit gases has been found to be a function of both environmental (air temperature and velocity) and manure (manure temperature and solids content) factors. The influence of these factors on ammonia and hydrogen sulfide emission from liquid manure were studied in a Convective Emission Chamber (CEC), where the air temperature, air velocity, relative humidity, turbulence intensity and liquid temperature were precisely controlled. The overall mass transfer coefficients of ammonia and hydrogen sulfide at the liquid manure surface were determined experimentally and used to indicate their emission rates in a range of environmental and manure conditions. For ammonia, the emission rate increased as the liquid temperature and air velocity increased but decreased with increasing air temperature. While for hydrogen sulfide, the mass transfer coefficient increased with increasing liquid temperature and decreased with increasing air temperature. Increase in air velocity slightly decreased the mass transfer coefficient of hydrogen sulfide.

Ventilation Tests

The purpose of these tests was to evaluate the effect of airflow through the headspace of manure storage pits on the generation and release of ammonia and hydrogen sulfide gases. The manure storage pits were simulated using 0.4m diameter by 1.2m high barrels fitted with ventilation boxes. The ventilation air was passed at 0.15 and 0.5 m/s through the ventilation boxes. The concentrations of ammonia and hydrogen sulfide gases were measured everyday in the manure pit head space. The manure samples were taken at regular intervals and analyzed for ammonia-N., total sulfide, pH and solids content. The results showed higher ammonia concentrations in the head space of the control treatment compared to the ventilated treatments. Very little hydrogen sulfide was detected in the effluent streams in all the barrels. The ammonia-N in the manure increased with time of storage for all the treatments. Generally, the concentration of ammonia-N in the control was higher than in the other treatments. The sulfide concentration in the control was always higher compared to the other treatments. At the end of the storage period, the manure in the storage barrels was stirred and the concentration of the gases in the effluent stream measured. Ammonia concentrations were 1234, 1000 and 881 mg/L for the control, 0.15 and 0.5m/s treatments, respectively. While for hydrogen sulfide, the gas concentrations were >502, 352 and 379 mg/L for the control, 0.15 and 0.5 m/s treatments respectively.

Chemical control tests

The chemical treatments were intended to suppress the release of one gas while providing conditions suitable for the release of the other. Two approaches were used in these tests. The first approach involved fixing ammonia while providing conditions suitable for hydrogen sulfide release. The second approach involved providing conditions suitable for ammonia release while fixing hydrogen sulfide in solution. Ammonia was fixed by lowering the pH to 5.0 while hydrogen sulfide was fixed by adjusting the pH to 9.0. The manure that had the pH adjusted to 5.0 produced lower concentration of hydrogen sulfide gas compared to the control. The results showed poor or no solids reduction in the treated manure. The solids quickly settled after the pH of the manure was adjusted. When the pH was adjusted to 9.0 to fix hydrogen sulfide and provide favorable conditions for ammonia release, the tests showed that there was more ammonia-N present in the treated manure compared to the control. The manure that was treated for pH changes in both cases was slimy at the end of the test periods. This indicated that there was not enough stabilization of the manure going on when the manure was in storage.

Impact/Significance of the results

Researchers and scientists are still seeking solutions to problems associated with liquid manure storage. These problems are related to occupational health, safety and welfare of workers and animals in environmentally controlled livestock buildings. Generation rates of gases such as ammonia and hydrogen sulfide in the manure provides useful information on how much gas can potentially be released from the manure. Along with the generation rates, it is important to know the rate at which the gases are emitted from the surface of the liquid manure into the environment above the liquid. The emission rate is useful in designing for adequate ventilation for the pit or manure storage facility. The results from the emission chamber tests (factor interaction) indicate that higher liquid manure temperatures increases the potential for both ammonia and hydrogen sulfide release. Emission rate of both the gases reduces with increase in air temperature. Increasing air velocity potentially increases the release of ammonia while the release of hydrogen sulfide is slightly reduced. A combination of these results especially those involving air can be used with ventilation to control the amount of gases emitted. The results from the head space ventilation tests showed that ammonia and sulfide concentrations were lower in the ventilated treatments compared with the control. Whether the reduction was due to dilution effects still need further investigation. This result shows the positive effect of ventilation the storage pit headspace.