Comparing semi-continuous air sampling versus 24-hour bag samples to monitor gas emissions and treatment from a swine nursery with biofilters

There is a need for economical and effective methods to assess practices that reduce gas emissions. The purpose of this project was to compare gas concentrations measured using semi-continuous sampling with dedicated gas analyzers versus concentrations obtained using 50 L bags filled over 24-h. Sampling was done in 2010 and 2011 from four biofilters (flat-bed with old media, A-frame, two flat beds with either 10 cm or 5 cm birch mulch) treating air from swine nurseries. Concentration ratios and percent reductions were calculated and compared using both sampling methods. The NH₃, H ₂S, CO₂, CH₄ and N₂O concentration data indicated that the 24-h bag sampling concentrations and percent reductions tracked semi-continuous sampling concentrations and percent reductions well. Most NH₃ concentrations differences (24-h bag sample minus semi-continuous) were within ±2 ppm of the semi-continuous concentrations, H₂S concentration differences within ±200 ppb, CH₄ concentration differences within ±10 ppm and N ₂O concentration differences within ± 75 ppb. Ratio medians for NH₃, CO₂ and N₂O were close to one, between 0.95 and 1.09. H₂S ratio medians varied from 0.61 in 2010 to 1.68 in 2011. Semi-continuous percent reduction results indicate that the four biofilters were able to reduce NH₃, H₂S and CH₄ emissions. Mean percent NH₃ reductions of three out of four biofilters ranged from 53 to 86%, percent H₂S reductions ranged from 41 to 74%, percent CH₄ reductions of three out of four biofilters ranged from 8 to 39%. One biofilter reduced N₂O concentrations 17 to 22% while three biofilters generated N₂O by 8 to 81%.