Semi-continuous air sampling versus 24-hour bag samples to evaluate biofilters on a swine nursery in warm weather

Economical and effective methods are needed to assess practices that reduce gas emissions. This project compared gas concentrations measured using semi-continuous sampling with dedicated gas analyzers versus concentrations obtained using 50 L FlexFoil bags filled over 24 h. Sampling was done over four months in summer and early fall of 2010 and 2011 from four biofilters (flat-bed with old media, A-frame, and two flat beds with either 10 cm or 5 cm screen birch mulch) treating air from deep manure pits below swine nurseries. Concentration ratios and percent reductions were calculated and compared using both sampling methods. The NH₃, H₂S, CO₂, CH₄, and N₂O concentration data indicated that the 24 h bag sampling concentrations and percent reductions tracked the semi-continuous sampling concentrations and percent reductions well. Most (77%) of the NH₃ concentrations differences (24 h bag sample minus semi-continuous) were within ±2 ppm of the semi-continuous concentrations, 78% of the H₂S concentration differences were within ±200 ppb, 87% of the CH₄ concentration differences were within ±10 ppm, and 88% of the N₂O concentration differences were within ±75 ppb. Ratio means for NH₃, CO₂, and N₂O were close to one (between 0.95 and 1.09). H₂S ratio means varied from 0.61 in 2010 to 1.68 in 2011. Semi-continuous percent reduction results indicated that the four biofilters reduced NH₃, H₂S, and CH₄ emissions. For three of the four biofilters, mean percent NH3 reductions ranged from 53% to 86%, mean percent H₂S reductions ranged from 41% to 74%, and mean percent CH₄ reductions ranged from 8% to 39%. One biofilter reduced N₂O concentrations by 17% to 22%, while three biofilters generated N₂O by 8% to 81%. The 24 h bag sampling system tested was an effective method for measuring gas concentrations and percent reductions of an air treatment system in the field based on NH₃, CH₄, and N₂O.