Portable 24-hr sampling units were used to collect air samples from eight biofilters on four animal feeding operations. The biofilters were located on a dairy, a swine nursery, and two swine finishing farms. Biofilter media characteristics (age, porosity, density, particle size, water absorption capacity, pressure drop) and ammonia (NH3), hydrogen sulfide (H2S), sulfur dioxide (SO2), methane (CH4), and nitrous oxide (N2O) reduction efficiencies of the biofilters were assessed. The deep bed biofilters at the dairy farm, which were in use for a few months, had the most porous media and lowest unit pressure drops. The average media porosity and density were 75% and 180 kg/m3, respectively. Reduction efficiencies of H2S and NH3 (biofilter 1: 64% NH3, 76% H2S; biofilter 2: 53% NH3, 85% H2S) were close to those reported for pilot-scale biofilters. No N2O production was measured at the dairy farm. The highest H2S, SO2, NH3, and CH4 reduction efficiencies were measured from a flat-bed biofilter at the swine nursery farm. However, the highest N2O generation (29.2%) was also measured from this biofilter. This flat-bed biofilter media was dense and had the lowest porosity. A garden sprinkler was used to add water to this biofilter, which may have filled media pores and caused N2O production under anaerobic conditions. Concentrations of H2S and NH3 were determined using the portable 24-hr sampling units and compared to ones measured with a semicontinuous gas sampling system at one farm. Flat-bed biofilters at the swine finishing farms also produced low amounts of N2O. The N2O production rate of the newer media (2 years old) with higher porosity was lower than that of older media (3 years old) (P = 0.042). Implications: Media characteristics and gas reduction efficiencies of eight field-scale biofilters were evaluated. The media characteristics measured in this study indicated that media older than 3 years should be tested for high-pressure drops and nitrous oxide (N2O) production. The results also indicated that regular water addition can improve gas reduction efficiencies of biofilters but adding excessive amounts of water can cause N2O production. Uniform water distribution can be a challenge.
|Original language||English (US)|
|Number of pages||13|
|Journal||Journal of the Air and Waste Management Association|
|State||Published - 2012|
Bibliographical noteFunding Information:
This project was funded by Rapid Agricultural Response Fund. The authors acknowledge Ilya Salnikov for his assistance during experiments and Brian Hetchler for providing semicontinuous sampling data for the swine nursery farm. The authors also acknowledge Ken Folie, Lee Johnston, and Minnesota livestock producers for their cooperation and support.