Mechanism of Gas Release from Liquid Swine Wastes

Releases of ammonia (NH3), hydrogen sulfide (H2S), carbon dioxide (CO2), and sulfur dioxide (SO2) from swine manure in 138-L laboratory reactors at 20° C were studied with high frequency sampling (one sample per min) for 260 d. Release behaviors of these gases were investigated under transient conditions with sudden disturbance of the manure by manure addition or mixing, and reactor shaking, and under steady state conditions with different ventilation rates. Different mechanisms were discovered in the releases of various gases. Convective mass transfer, controlled by profiles of concentration, velocity, and temperature, governed NH3 release and influenced H2S release. A new model of “bubble release” is proposed to explain release behavior characteristics. Bubble release controlled releases of H2S, CO2, and SO2 when manure was disturbed. Bubble release is believed to be responsible for previously discovered “H2S burst releases” that were defined as sudden increases of release by more than 100% as compared with previous release in less than one hour. Solubility of gases probably played an important role in the releases. Moreover, there was a dynamic interaction among different gases via their effect on the pH of surface manure.