Ammonia, hydrogen sulphide and carbon dioxide release from pig manure in under-floor deep pits

Releases of ammonia (NH3), hydrogen sulphide (H2S) and carbon dioxide (CO2) from deep manure pits were investigated in two overnight tests to minimize the influence of solar radiation and sudden outdoor temperature changes using two pig fattening buildings. The rooms of the buildings had been emptied and cleaned between groups of pigs. The identical buildings had tunnel and pit Ventilation fans and 2.4 m deep under-floor pits with a surface area of 800 m(2) each. The first test was conducted in Building 3A. A new manure additive was applied in the pit to reduce gas and odour emission. The pit ventilation mode was used and the building was heated for about I h with one direct-fired propane space heater. The second test was conducted in Building 3B, in which the pit did not receive the additive application. The tunnel ventilation mode was used and the building was heated for about 2 h with two space heaters. Gas concentrations, ventilation, temperatures and differential pressure were continuously measured overnight. Gas release rates in the tests were compared with the gas release rates in the same buildings when they were fully occupied. Ammonia release rates during heating were 167 +/- 11 g/h (mean +/- 95% confidence interval) in the first test and 46 +/- 2 g/h in the second test, equivalent to 65.5 and 24.9% of the rates from fully occupied buildings, respectively. The maximum H2S release rates measured after Ih of heating were 9.6 g/h in the first test and 3.1 g/h in the second test, equivalent to 80 and 41% of the full buildings, respectively. The maximum CO2 release rates after heating were 3.4 kg/h in the first test and 7.0 kg/h in the second test. Heating immediately increased NH3, H2S and CO2 concentrations and release rates in the under-floor pits in both tests. Ventilation modes and rates affected the indoor gas concentrations at different locations. Higher ventilation rate was related to higher gas release rate in the first test. A peculiar behaviour of H2S characterized by burst releases was found in the two tests. It was a new phenomenon not yet reported in the literature and might be related to some unexpected incidents involving acute H2S concentrations in animal facilities. (C) 2000 Silsoe Research Institute.