Production rates of toxic gases from liquid swine manure: Health implications for workers and animals in swine confinement buildings

Abstract

Gas production rates from three liquid swine manure storage structures (SS) were monitored over a 12-month period. All three SS were under slatted-floor buildings. Rates of gas production were monitored relative to various chemical and physical parameters of the manure, such as pH, temperature and manure removal. A gas collection device was constructed which captured gas over a known surface area of the manure. This gas was quantified, and the proportions of hydrogen sulfide, methane and carbon dioxide were determined. Manure in SS under the farrowing building produced 8–20 times more gas per cubic meter of manure than manure from nursery and finishing buildings. This apparently was due to the high ammonia and volatile acids in the latter two SS inhibiting biological activity. Gas production per cubic meter of manure decreased following emptying, especially when done in a cool season. It was felt this reduced gas production was due both to reduced critical biomass and a loss of heat in the biomass. When the manure temperature fell below 18°C, there was a significant decrease in gas production. Therefore, gas production was significantly less in the winter than in the summer. This phenomenon was especially pronounced in a modified open-front building. Winter manure temperatures and gas production were thus affected by building design. Ambient pit off-gassing does not appear to be a problem, in terms of build-up of toxic gases in the environment, as long as buildings are ventilated in accordance with the Midwest Plan Service guidelines. Winter ventilation rates were more than adequate to handle ambient gas generation from these SS. However, excess atmospheric ammoni is a common problem, indicating that there are other sources of ammonia (i.e. feces and urine on top of floors or slats). Spike release of hydrogen sulfide during manure agitation is a problem that may overload the ventilation system, resulting in acutely toxic environments.